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28Russian Journal of Nematology, 2015, 23(1), 41 - 52
Host range characterisation, in vivo reproduction and damage potential of Pratylenchus coffeae populations from Vietnam
Nguyen Thi Tuyet1, Annemie Elsen2, Ho Huu Nhi3 and Dirk De Waele4' 5
1 Post Graduate Training Department, Vietnam Academy of Agricultural Sciences (VAAS), Vinh Quynh, Thanh Tri,
Hanoi, Vietnam
2 Bodemkundige Dienst van Belgie, Herentsesteenweg 42, B-3012, Wilsele, Belgium
3 Laboratory of Basic Research, Hybrid Rice Research and Development Centre, Food Crops Research Institute, Vietnam
Academy of Agricultural Sciences (VAAS), Van Dien, Thanh Tri, Hanoi, Vietnam
4 Laboratory of Tropical Crop Improvement, Department of Biosystems, Faculty of Bioscience Engineering, University of
Leuven (KU Leuven), B-3001, Leuven, Belgium 5 Unit for Environmental Sciences and Management, North-West University, Private Bag X6001, 2520,
Potchefstroom, South Africa e-mail: dirkdewaele@pandora.be
Accepted for publication 31 March 2015
Summary. The in vivo reproduction of ten Pratylenchus coffeae populations, collected in different agro-ecological regions in Vietnam, on 13 agricultural crops was very similar. Of the 13 varieties of the 13 crops included in our study (one variety per crop), the varieties of banana, sugarcane, maize and upland rice were good hosts of P. coffeae. The soybean variety was a poor host and the varieties of groundnut, tomato, sweet potato, ginger, sesame, pineapple and citrus were very poor hosts or nonhosts of P. coffeae. The in vivo damage potential on the banana, coffee, sugarcane and maize varieties was very similar for all ten P. coffeae populations. All the P. coffeae populations were able to cause considerable damage to the vegetative growth of banana and coffee but not to sugarcane and maize. In view of the low reproduction on coffee, the extensive damage the P. coffeae populations caused on this agricultural crop is surprising and illustrates the high damage potential of P. coffeae on coffee. In general, there was similar in vivo reproduction on the 13 agricultural crops examined and in general, similar in vivo damage potential on banana, coffee, sugarcane and maize, indicating that the ten P. coffeae populations from Vietnam examined belong to the same pathotype.
Key words: biodiversity, damage, host range, plant growth, reproduction factor, root-lesion nematode, root necrosis.
Pratylenchus coffeae is one of the root-lesion nematodes that are considered important plant pathogens. This migratory endoparasite has a pantropical distribution and a wide host plant range (Siddiqi, 1972; Castillo & Vovlas, 2007). Over the years, when more and more P. coffeae populations were studied, differences in host range, in vivo reproduction and damage potential on agricultural crops among some of these populations were observed.
Populations of this species were found as an important pathogen of yams in Uganda and the Pacific but did not invade the surrounding banana plants. By contrast, in Ghana, a population of P. coffeae was found that damaged both yams and plantains (Bridge et al., 1997). Edwards & Wehunt
(1973) demonstrated that P. coffeae populations from Panama can infect maize but those from Honduras did not. Silva & Inomoto (2002) reported that different populations of P. coffeae can have different host ranges and suggested the existence of biotypes of P. coffeae based on differences in in vivo reproduction on coffee and citrus between two P. coffeae populations. Other studies on bananas (Bridge et al, 1997), on sweet potato (Mizukubo, 1995; Mizukubo & Sano, 1997) and on coffee (Kubo et al, 2003; Villain et al, 2002 cited by Campos & Villain, 2005; Inomoto et al., 2007) showed differences in damage potential among P. coffeae populations originating from different geographical regions. Inoculation of seven different
host plants with a P. coffeae population originally isolated from coffee revealed differences in in vivo reproduction and damage potential (Kumar & Viswanathan, 1972). Based on the in vivo reproduction of P. coffeae populations on different agricultural crops and on susceptible and resistant sweet potato cultivars, Mizukubo (1995) suggested the presence of physiological races among Japanese P. coffeae populations.
In Vietnam, P. coffeae has been reported as the most common and widespread Pratylenchus species (Chau & Thanh, 2000). In this country, it is found on many crops including banana, coffee, ginger, sugarcane, pineapple, etc. (Chau et al, 1997). Although it is known that P. coffeae can cause considerable damage to several agricultural crops worldwide (Bridge et al, 1997), its impact on agricultural crops in Vietnam is largely unknown. In fact, only damage caused by P. coffeae on bananas (van den Bergh et al, 2006) and coffee, in relation to yellow-leaf disease (Nghi et al., 1996; Trung et al, 2000; Sung et al, 2001), has been studied.
The characterisation of intraspecific differences with respect to the host range, in vivo reproduction and damage potential on agricultural crops among populations of the same nematode species is very important for the development of efficient and sustainable nematode management strategies such as crop rotation (Bakker et al., 1993). In addition, this characterisation provides additional information on the biodiversity of this nematode species. Therefore, the objectives of our study were: i) to establish the host range of ten P. coffeae populations collected from different agro-ecological regions in Vietnam; and ii) to compare the in vivo reproduction and damage potential of these P. coffeae populations on selected agricultural crops. The description of these agro-ecological regions (Tuyet et al., 2008), the morphological, morphometrical and molecular characterisation of the P. coffeae populations (Tuyet et al, 2012, 2014), and the effect of temperature on their in vitro reproduction (Tuyet et al., 2013) have been reported previously.
MATERIALS AND METHODS
Host range experimental set-up. To study the host range of the ten P. coffeae populations from Vietnam (Table 1), 13 agricultural crops commonly grown in Vietnam were included in four glasshouse experiments: soybean (Glycine max (L.) Merr. var. VX93), groundnut (Arachis hypogea L. var. V79), tomato (Solanum lycopersicum L.), banana (Musa cv. Ngop Dui Duc BBB), sweet potato (Ipomoea batatas (L.) Poir. cv. Hoang Long), coffee (Coffea
arabica L. var. Catimor), ginger (Zingiber officinali Rose. cv. Rose), pinapple (Ananas comosus (L.) Merr. cv. Cayen), sesame (Sesamum orientale L. var. V67), upland rice (Oryza sativa L. var. CIRAD141), sugarcane (Saccharum oficinarum L. var. ROC20), maize (Zea mays L. var. LVN10) and citrus (Citrus nobilis Lour. var. nobilis).
Seedlings were grown in plastic pots, each of which contained 2,000 ml of a sterilised compost mixture of a sandy alluvial soil: composted manure: rice chaff (6:1:2). For coffee and citrus, seeds were first sown in trays containing sterilised sand and seedlings with two fully expanded cotyledons were individually transplanted to the plastic pots. For banana, sugarcane and pineapple, in vitro produced plantlets were first transplanted to trays containing sterilised sand. After 4 weeks (for banana and sugarcane) and 8 weeks (for pineapple), the plantlets were individually transplanted to the plastic pots. For ginger, ginger tubers were first planted into trays containing sterilised sand. After 1 month, uniformly sized plantlets were individually transplanted to the plastic pots. For sweet potato, three-node stem cuttings were individually planted in the plastic pots. For maize, sesame, tomato, upland rice, groundnut and soybean, seeds were directly sown in plastic pots: one seed for maize, tomato, groundnut and soybean, two seeds for sesame and five seeds for upland rice. The plants were watered as needed.
The banana, pineapple and sugarcane plantlets were inoculated 4 weeks after transplanting. The sweet potato plantlets were inoculated 10 days after planting of the nodal cuttings. Maize, sesame, tomato and rice seedlings were inoculated 2 weeks after emergence of the seeds. The groundnut and soybean seedlings were inoculated 10 days after the emergence of the seeds. The coffee plants were inoculated 8 months after sowing when the seedlings had 8-10 leaves (1st experiment) and 2 months after sowing when two leaves were expanded (2nd experiment). The citrus plantlets were inoculated 6 weeks after emergence of the seeds.
During the duration of the experiments, the soil temperature was measured. A thermometer was put 8 cm deep in the soil in the pots and the temperature recorded at the hottest time of the day, i.e., between 14:00 and 16:00. The monthly minimum and maximum soil temperature in the glasshouse ranged from 20.0 to 32.5°C.
The experiments were designed as completely randomised blocks with nine replicates for experiment 1 and six replicates for the experiments 2, 3 and 4. Each pot was considered a replicate. In the experiments 2 and 3, the banana plants were
used as the reference (control) host plant to confirm the viability of the inoculum and the effectiveness of the inoculation.
Damage potential experimental set-up. To study the damage potential of the P. coffeae populations from Vietnam, four agricultural crops commonly grown in Vietnam were included in four experiments: banana (Musa cv. Ngop Dui Duc BBB), coffee (C. arabica var. Catimor), sugarcane (S. officinarum var. ROC20) and maize (Z. mays var. LVN10). The preparation of the seedlings as well as the time of inoculation and the experimental conditions were similar to those described for the host range experiments.
The experiments were designed as completely randomised blocks with seven replicates for banana, five replicates for coffee and six replicates for sugarcane and maize.
Preparation of nematode inoculum and inoculation. The nematode inoculum was obtained from in vitro carrot disc cultures (Moody et al, 1973; Speijer & De Waele, 1997; Tuyet et al, 2012) with vigorous developing nematode populations (many active nematodes in the Petri dish). Nematodes were extracted from the carrot discs by the maceration-sieving technique as described by Speijer & De Waele (1997). Suspensions of all vermiform developmental stages were used as inoculum for the experiments. Each pot was inoculated with 1,000 vermiforms. Three holes were made in the soil around every plant, 5 ml of the nematode suspension was added with a pipette and the holes were recovered with soil.
Assessment of the nematode reproduction. Fourteen weeks after inoculation, the plants were removed from the pots, and the entire root systems and 200 ml of soil sampled. The nematode population densities were assessed both in the soil and roots. For the extraction of the nematodes from the plant roots, roots were cut into 1-cm-long pieces and macerated in a kitchen blender for 30 s (10-s periods separated by 5-s intervals). The suspension was passed through 260, 106 and 40 ^m-pore sieves, rinsed with tap water and the nematodes from the 40 ^m-pore sieve collected and counted using a stereomicroscope. For the extraction of the nematodes from the soil, the modified Baermann dish method was used (Hooper et al, 2005). Two hundred ml of soil was placed on a sieve in a dish containing 300 ml of distilled water and left at room temperature for 48 h. Then the suspension in the dish was collected and the nematodes counted using a stereomicroscope. The number of nematodes in the soil in the pots was determined based on the number of nematodes in 200 ml of soil.
Assessment of the host plant range. The final nematode population density (Pf) was calculated as the number of vermiform nematodes in both root and soil. The reproduction factor (RF = Pf/Pi) was used to determine the host plant response to P. coffeae. When RF > 1 the host plant was considered a good host. When RF < 1 but > 0.5 the host plant was considered a poor host. When RF < 0.5 the host plant was considered a nonhost (Pinochet & Duarte, 1986; Robinson & Percival, 1997; Bell & Watson, 2001).
Assessment of the damage potential. To assess the damage potential of the P. coffeae populations from Vietnam on banana, coffee, sugarcane and maize, plant height, shoot and root fresh weights of plants inoculated with the P. coffeae populations and uninoculated plants were recorded at 14 weeks after inoculation. For banana, the root necrosis was determined by following the methodology of Speijer & De Waele (1997). Five 10 cm-long pieces of roots were collected randomly and cut lengthwise. The percentage of necrosis was scored for one half of each of the five roots. The maximum root necrosis per root half was 20% giving a maximum root necrosis of 100% for the five root halves together. For sugarcane, ten roots were collected randomly to assess the damage caused by P. coffeae. The percentage of necrosis on the surface of each root was scored. The maximum root necrosis per root was 10% giving a maximum root necrosis of 100% for the ten roots together.
Data analysis. For the statistical analysis of the results, the STATISTICA® package (Anonymous, 1997) was used. The Shapiro-Wilk's test was applied to evaluate whether the dependent variable was normally distributed within groups. The homogeneity of the variances of the groups was tested with the Levene's test. The nematode population densities were logi0(x+1) and the root necrosis data were arcsin(x/100) transformed before analysis. When less than ten replicates per group were available, the outliers were determined by calculating the standardised residuals. Outliers were defined as data with a standardised residual falling outside the range from -2 to 2. One-way ANOVA was used to analyse the data. The means were separated using Tukey's Honestly Significant Difference test (P < 0.05).
RESULTS
Host range of Pratylenchus coffeae populations from Vietnam. The results of the four host range experiments are presented in Table 2. In the three experiments in which banana was included as one of the host plants, all the P. coffeae populations
Table 1. Origin and population codes of the ten Pratylenchus coffeae populations from Vietnam used in our study
Host plant Province Agro-ecological region Population code
Banana Dien Bien Northwest NW
Coffee Yen Bai Northeast NE1
Banana Yen Bai Northeast NE2
Banana Phu Tho Northeast NE3
Banana Bac Kan Northeast NE4
Banana Ha Tay Red River Delta RRD1
Ornamental tree Hung Yen Red River Delta RRD2
Banana Thanh Hoa North Central Coast NCC1
Coffee Nghe An North Central Coast NCC2
Coffee Dak Lak Central Highlands CH
examined reproduced very well on banana: in the 1st experiment, the reproduction factor (RF) on banana ranged on average from 16.0 to 27.2, in the 2nd experiment from 28.9 to 37.7 and in the 3rd experiment from 29.4 to 42.5. The RF on banana among the P. coffeae populations examined was similar. All P. coffeae populations examined reproduced on rice (with the exception of the Red River Delta 1 population), sugarcane and maize. On these three crops, RF between 2 and 5 were observed. On soybean, the RF of all the P. coffeae populations examined fluctuated on average around
1 (0.7 to 2.5) while on the other eight crops included in the experiments the RF was < 1. No nematodes were extracted from the roots of groundnut, ginger and pineapple.
In vivo reproduction and damage potential on banana. The results of the in vivo reproduction experiment on banana cv. Ngop Dui Duc are presented in Table 3. Differences were observed in in vivo reproduction on this banana cultivar among the ten P. coffeae populations from Vietnam examined. The highest average nematode population density observed per root system (32,209, North Central Coast 1 population, originally isolated from banana) was seven times higher (P < 0.05) than the lowest average nematode population density observed per root system (4,457, North Central Coast 2 population, originally isolated from coffee). The RF of the Northwest, Northeast 4 and North Central Coast 1 populations were on average significantly (P < 0.05) higher than the RF of the Northeast 2, Red River Delta 2, North Central Coast
2 and Central Highlands populations. The highest average nematode population density observed per 10 g fresh roots (13,793, North Central Coast 1 population) was 15.4 times higher (P < 0.05) than the lowest average nematode population density observed per 10 g fresh roots (893, North Central
Coast 2 population). The average nematode population densities of the population originally isolated from the roots of an ornamental tree (Red River Delta 2) per root system and per 10 g fresh roots were 7,520 and 1,512, respectively, which was not significantly different from the Northeast 2, Red River Delta 1, North Central Coast 2 and Central Highlands populations which were originally isolated from banana and coffee.
The relationship between the average nematode population densities per 10 g fresh roots and the percentage root necrosis is illustrated in Fig. 1. In general, the nematode populations with the highest root population densities also caused the highest percentage of root necrosis. The North Central Coast 2 population, which had the lowest nematode population densities per root system and per 10 g fresh roots, still caused about 10% root necrosis, a percentage that was not significantly different from the root necrosis caused by several other populations such as the Northeast 2, Northeast 3 and Red River Delta 2 populations.
The plant height, shoot and root fresh weights of this banana cultivar were reduced by all the ten P. coffeae populations from Vietnam examined with 13.4-38.7%, 7.4-50.7% and 3.4-42.4%, respectively, compared with the uninoculated control plants (Table 3). Significant (P < 0.05) differences were observed in reduction in plant height and shoot fresh weight among the populations examined. For instance, the Northwest and Northeast 4 populations decreased these two plant growth variables significantly (P < 0.05) more than the Northeast 3, North Central Coast 2 and Central Highlands populations. No differences were observed in damage potential among the populations originally isolated from banana and coffee. Also the Red River Delta 2 population originally isolated from the roots of an ornamental tree caused a reduction in plant
Fig. 1. Nematode population density per 10 g fresh roots and percentage root necrosis caused by ten Pratylenchus coffeae populations from Vietnam on banana cv. Ngop Dui Duc, 14 weeks after inoculation with 1,000 vermiforms per plant. ■: number of nematodes per 10 g fresh roots; ♦: percentage root necrosis. Each point and bar is the mean ± standard error of seven replicates. For the list with the nematode population codes see Table 1.
Fig. 2. Nematode population density per 10 g fresh roots and percentage root necrosis caused by ten Pratylenchus coffeae populations from Vietnam on sugarcane var. ROC20, 14 weeks after inoculation with 1,000 vermiforms per plant. ■: number of nematodes per 10 g fresh roots; ♦: percentage root necrosis. Each point and bar is the mean ± standard error of seven replicates. For the list with the nematode population codes see Table 1.
growth similar to most of the other populations examined. Only the North Central Coast 1 population significantly (P < 0.05) reduced root fresh weight compared with the uninoculated control plants. The lowest reduction (3.4%) was observed in the banana plants inoculated with the Red River Delta 2 population. By contrast, this population reduced the plant height and shoot fresh weight with 30.8 and 32.6%, respectively.
In vivo reproduction and damage potential coffee. The results of the in vivo reproduction experiment on coffee var. Catimor are presented in Table 4. The RF of all ten P. coffeae populations examined was on average < 1. The highest average nematode population density observed per root system (212, Northeast 1 population, originally
isolated from coffee) was 5.9 times higher (P < 0.05) than the lowest average nematode population density observed per root system (36, North Central Coast 1 population, originally isolated from banana). The RF of the Northeast 1 and North Central Coast 2 populations were on average significantly (P < 0.05) higher than the RF of the Northwest, Red River Delta 1, and North Central Coast 1 populations. The highest average nematode population density observed per 1 g fresh roots (330, North Central Coast 2 population, originally isolated from coffee) was 7.7 times higher (P < 0.05) than the lowest average nematode population density observed per 1 g fresh roots (43, North Central Coast 1 population, originally isolated from banana). The average nematode population densities of the population originally isolated from
the roots of an ornamental tree per root system and per 1 g fresh roots were 44 and 98, respectively, which was not significantly different from several other populations which were originally isolated from banana and coffee.
At 14 weeks after inoculation, the root fresh weight of the uninoculated control plants was on average 3.1 g while the root fresh weight of the plants inoculated with the P. coffeae populations was on average < 1 g (Table 4). The plant height, shoot and root fresh weights of this coffee variety were reduced by all the ten P. coffeae from Vietnam examined with 31.1-35.4%, 53.8-61.5% and 7190.3%, respectively, compared to the uninoculated control plants. No significant differences were observed in reduction of these three plant growth variables among the populations examined. Also, the Red River Delta 2 population originally isolated from the roots of an ornamental tree caused a reduction in plant growth similar to most of the other populations examined.
In vivo reproduction and damage potential on sugarcane. The results of the in vivo reproduction experiment on sugarcane var. ROC20 are presented in Table 5. Few differences were observed in in vivo reproduction on this sugarcane variety among the ten P. coffeae populations from Vietnam examined. The highest average nematode population density observed per root system (3,513, Red River Delta 2 population, originally isolated from the roots of an ornamental tree) was 2.4 times higher (P < 0.05) than the lowest average nematode population density observed per root system (1,448, Red River Delta 1 population, originally isolated from banana). The RF of the Red River Delta 2 population was significantly (P < 0.05) higher than the RF of the Central Highlands population. The highest average nematode population density observed per 1 g fresh roots (1,552, Red River Delta 2 population) was four times higher (P < 0.05) than the lowest average nematode population density observed per 1 g fresh roots (391, Red River Delta 1 population).
The relationship between the average nematode population densities per 1 g fresh roots and the percentage root necrosis on sugarcane is illustrated in Fig. 2. In general, the nematode populations with the highest root population densities also caused the highest percentage of root necrosis. However, the North Central Coast 1 population, which had one of the lowest nematode population densities per 1 g fresh roots, caused 62.5% root necrosis, similar to the percentage root necrosis caused by the North Central Coast 2 population from which almost twice as many nematodes per 1 g roots were extracted.
All three plant growth variables measured were not significantly decreased by the ten P. coffeae populations from Vietnam examined, compared with the uninoculated control plants (Table 5). A few differences in damage potential were observed among the P. coffeae populations examined. The North Central Coast 2 and Central Highlands populations caused a decrease in plant height of 16 and 18.1%, respectively, while the North Central Coast 1 population caused an increase in plant height of 7.1% (P < 0.05). The Central Highlands population caused a decrease in shoot fresh weight of 22.3% while the Red River Delta 2 population caused an increase in shoot fresh weight of 13.3% (P < 0.05). The Central Highlands population caused a decrease in root fresh weight of 30% while the Northeast 2 and Red River Delta 1 populations caused an increase in root fresh weight of 10% (P < 0.05).
In vivo reproduction and damage potential on maize. The results of the in vivo reproduction experiment on maize var. LVN10 are presented in Table 6. Few differences were observed in in vivo reproduction on this maize cultivar among the ten P. coffeae populations from Vietnam examined. For seven out of the nine P. coffeae populations examined, the average nematode population density per root system ranged from about 1,000 to 1,800 while for eight out of the nine P. coffeae populations examined, the average nematode population density per 10 g fresh roots ranged from about 500 and 1,000. The highest average nematode population density observed per root system (1,806, Red River Delta 2 population, originally isolated from the roots of an ornamental tree) was 5.2 times higher (P < 0.05) than the lowest average nematode population density observed per root system (346, Red River Delta 1 population, originally isolated from banana). There was no significant difference in RF among the populations examined. The highest average nematode population density observed per 10 g fresh roots (1,074, Central Highlands population, originally isolated from coffee) was 5.2 times higher (P < 0.05) than the lowest average nematode population density observed per 10 g fresh roots (205, Red River Delta 1 population).
All three plant growth variables measured were not significantly decreased by the ten P. coffeae populations from Vietnam examined, compared with the uninoculated control plants. A few differences in damage potential were observed among the P. coffeae populations examined. The Red River Delta 2 population caused a decrease in plant height of 16.6% while the Northwest and Northeast 3 populations caused an increase in plant height of 9.7 and 10.2%, respectively (P < 0.05).
DISCUSSION
Soil temperature is an important environmental factor affecting the reproduction of plant-parasitic nematodes including Pratylenchus spp. According to Radewald et al. (1971), Acosta & Malek (1979) and Gowen (2000), the optimum temperature for development and reproduction of P. coffeae is 25 to 30°C. This is precisely the temperature at which our experiments were carried out.
Out of the 13 agricultural crops included in our study, the reproduction factor of all the P. coffeae populations from Vietnam examined was always > 1 on banana, rice (with the exception of the Red River Delta 1 population), sugarcane and maize and these crops can be considered as good hosts of this nematode species. Compared to the latter three crops, banana is a much better host. The host response of rice, sugarcane and maize was similar. No reproduction was observed on the other eight crops.
Table 2. Reproduction factors (RF: final nematode population density/initial nematode population density) of ten Pratylenchus coffeae populations from Vietnam on 13 selected agricultural crops, 14 weeks after inoculation with 1,000 vermiforms per plant
Crop Pratylenchus coffeae population
NW NE1 NE2 NE3 RRD1 RRD2 NCC1 NCC2 CH
Soybean - 0.9 - 1.0 1.1 0.7 - - 2.5
Groundnut - 0 - 0 0 0 0 - 0
Exp. 1 Tomato - 0.1 - < 0.1 < 0.1 0.1 0.1 - < 0.1
Banana - 27.2 - 16.0 20.8 17.9 27.2 - 25.2
Sweet potato - 0.1 - 0.1 0.1 0.3 0.1 - 0.1
Coffee - < 0.1 - < 0.1 0 < 0.1 < 0.1 - < 0.1
Coffee 0.1 < 0.1 0 0.1 0 < 0.1 < 0.1 0.2 < 0.1
Ginger 0 0 0 0 0 0 0 0 0
Exp. 2 Pinapple 0 0 0 0 0 0 0 0 0
Sesame 0.1 < 0.1 < 0.1 < 0.1 0 0.5 0.2 < 0.1 0
Banana 29.7 37.2 30.5 28.9 31.6 36.9 37.7 - 29.6
Rice 3.0 2.9 - 3.2 0.2 5.4 5.3 - 2.3
Sugarcane 4.5 3.5 2.8 3.6 3.3 5.1 3.6 4.7 2.6
Exp. 3 Maize 2.8 3.7 3.3 2.2 2.0 4.1 3.5 3.4 4.5
Banana 33.9 29.4 32.7 33.7 34.2 35.2 38.4 37.7 42.5
Exp. 4 Citrus 0 0 0 0 < 0.1 0 0.4 0.1 0
'-' indicates missing data. For the list with the nematode population codes see Table 1.
Table 3. In vivo reproduction, percentage root lesions and effect on plant growth caused by ten Pratylenchus coffeae populations from Vietnam on banana cv. Ngop Dui Duc, 14 weeks after inoculation with 1,000 vermiforms per plant (n = 7)
P. coffeae population Mean number of nematodes
per 10 g fresh roots per root system in soil
NW 10,280e 31,561c 3,745
NE1 4,547cd 13,731abc 3,782
NE2 3,760bcd 12,000abc 2,837
NE3 3,940cd 17,817bc 3,622
NE4 7,794de 29,894c 8,042
RRD1 3,453bc 9,518ab 14,211
RRD2 1,512ab 7,520ab 702
NCC1 13,793e 32,209c 3,620
NCC2 893a 4,457a 5,140
CH 2,824bc 14,939abc 1,454
RF
Root lesion
(%)
Plant height
(cm)
% change
Shoot weight
(g)
% change
Root weight
(g)
% change
35.3d 17.5bcd 14.8abc 21.4bcd 37.9d 23.8bcd 8.2a 35.8d 9.7ab 16.4ab
36.4d 25.0bc 19.9abc 20.4abc 29.4cd 28.7cd 14.0ab 28.9cd 9.7a 21.3bc
21.9a 24.0ab 24.1ab 29.3bcd 22.7a 23.7ab 24.7abc 26.4abcd 30.9de 30.3cde
(-38.7) (-32.8) (-32.5) (-17.9) (-36.4) (-33.6) (-30.8) (-26.1) (-13.4) (-15.1)
63.7a 81.6abc 73.6ab 112.5bcd 71.6a 62.7a 85.7abc 71.0a 116.7cd 117.7cd
(-49.9) (-35.8) (-42.1) (-11.5) (-43.7) (-50.7) (-32.6) (-44.1) (-8.2) (-7.4)
30.7ab 37.2ab 35.5ab 41.6ab 39.1ab 29.7ab 46.0b 27.4a 41.5ab 41.0ab
(-35.5) (-21.8) (-25.4) (-12.6) (-17.9) (-37.6) (-3.4) (-42.4) (-12.8) (-13.9)
Control
35.7e
(0.0)
127.1d
(0.0)
47.6b
(0.0)
RF: final nematode population density/initial nematode population density (= inoculum).
Means in the same column followed by the same letter are not significantly different according to Tukey's test (P < 0.05). % change compared with the uninoculated (control) plants. For the list with the nematode population codes see Table 1.
Table 4. In vivo reproduction and effect on plant growth caused by ten Pratylenchus coffeae populations from Vietnam on coffee cv. Catimor, 14 weeks after inoculation with 1,000 vermiforms per plant (n = 5)
P. coffeae population Mean number of nematodes Plant height Shoot weight Root weight
per 10 g fresh roots per root system in soil RF (cm) % change (g) % change (g) % change
NW 65 ab 52 ab 10 0.1 ab 14.0 a (-33.0) 2 a (-61.5) 0.9 a (-71.0)
NE1 307 bc 212 b 80 0.3 c 14.1 a (-32.5) 2.4 a (-53.8) 0.9 a (-71.0)
NE2 109 abc 84 ab 80 0.1 abc 14.4 a (-31.1) 2.3 a (-55.8) 0.8 a (-74.2)
NE3 58 a 40 a 50 0.1 abc 14.3 a (-31.6) 2.1 a (-59.6) 0.8 a (-74.2)
NE4 150 abc 48 ab 50 0.1 abc 13.5 a (-35.4) 2.0 a (-61.5) 0.5 a (-83.9)
RRD1 78 ab 48 a 30 0.1 ab 13.6 a (-34.9) 2.0 a (-61.5) 0.7 a (-77.4)
RRD2 98 abc 44 a 70 0.1 abc 14.2 a (-32.1) 2.2 a (-57.7) 0.6 a (-80.6)
NCC1 43 a 36 a 10 < 0.1 ab 13.9 a (-33.5) 2.1 a (-59.6) 0.9 a (-71.0)
NCC2 330 c 100 ab 130 0.2 c 13.7 a (-34.4) 2.2 a (-57.7) 0.3 a (-90.3)
CH 107 abc 88 ab 70 0.2 bc 14.0 a (-33.0) 2.1 a (-59.6) 0.8 a (-74.2)
Control 20.9 b (0.0) 5.2 b (0.0) 3.1 b (0.0)
RF: final nematode population density/initial nematode population density (= inoculum).
Means in the same column followed by the same letter are not significantly different according to Tukey's test (P < 0.05). % change compared with the uninoculated (control) plants. For the list with the nematode population codes see Table 1.
On soybean, the reproduction factor fluctuated around 1 (0.7 to 2.5) and therefore we consider this crop as a poor host. Groundnut, tomato, sweet potato, coffee, ginger, sesame, pineapple and citrus can be considered as very poor hosts or nonhosts of P. coffeae.
Our results confirm that banana is a good host of P. coffeae (Gowen et al, 2005). The banana variety used in our experiments belongs to the BBB genome
group, which was previously demonstrated as one of the most susceptible banana varieties in Vietnam to P. coffeae (van den Bergh, 2002). The good reproduction of all the P. coffeae populations from Vietnam examined on this crop also confirms the viability of the P. coffeae populations and effectiveness of the inoculation method used in our experiments.
Table 5. In vivo reproduction, percentage root lesions and effect on plant growth caused by ten Pratylenchus coffeae populations from Vietnam on sugarcane var. ROC20, 14 weeks after inoculation with 1,000 vermiforms per plant (n = 6)
Mean number of nematodes Root lesion (%) Plant height Shoot weight Root weight
P. coffeae population per 10 g fresh roots per root system in soil RF (cm) % change (g) % change (g) % change
NW 839 bcd 2,226 b 3,500 4.5 ab 49.2abc 37.3 ab (-14.6) 38.7 ab (-17.1) 2.6 abc (-13.3)
NE1 692 abc 2,166ab 1,393 3.6 ab 39.2 ab 39.7 ab (-9.2) 39.2 ab (-16.1) 3.2 bc (6.7)
NE2 473 ab 1,650 a 1,350 2.8 ab 25.8 a 38.0 ab (-13.0) 38.9 ab (-16.7) 3.3 c (10.0)
NE3 889 bcd 2,326ab 2,960 3.7 ab 35.8 a 37.5 ab (-14.2) 42.2 ab (-9.6) 2.6 abc (-13.3)
NE4 391 a 1,448 a 2,060 3.3 ab 29.2 a 41.2 ab (-5.7) 39.7 ab (-15.0) 3.3 c (10.0)
RRD1 1,552 d 3,513 b 1,915 5.1 b 60.8 bc 38.6 ab (-11.7) 52.9 b (13.3) 2.4 abc (-20.0)
RRD2 695 abc 1,986ab 1,591 3.6 ab 62.5 c 46.8 b (7.1) 47.8 ab (2.4) 2.8 abc (-6.7)
NCC1 1,289 cd 2,873 ab 2,387 4.7 ab 62.5 c 36.7 a (-16.0) 44.3 ab (-5.1) 2.3 ab (-23.3)
NCC2 704 abc 1,530 a 1,086 2.6 a 28.3 a 35.8 a (-18.1) 36.3 a (-22.3) 2.1 a (-30.0)
CH 839 bcd 2,226 ab 3,500 4.5 ab 49.2 abc 43.7 ab (0.0) 46.7 ab (0.0) 3.0 abc (0.0)
Control 37.3 ab (-14.6) 38.7 ab (-17.1) 2.6 abc (-13.3)
RF: final nematode population density/initial nematode population density (= inoculum).
Means in the same column followed by the same letter are not significantly different according to Tukey's test (P < 0.05). % change compared with the uninoculated (control) plants.
Table 6. Reproduction and effect on plant growth caused by ten Pratylenchus coffeae populations from Vietnam on maize var. LVN10, 14 weeks after inoculation with 1,000 vermiforms per plant (n = 6)
P. coffeae Mean number of nematodes Plant height Shoot weight Root weight
per 10 g fresh roots RF
population per root system in soil (cm) % change (g) (g)
NW 535 ab 846 ab 2,000 2.8 117.7 b (9.7) 40.8 19.7
NE1 616 ab 1,093 b 2,430 3.7 106.2 ab (-1.0) 46.0 18.6
NE2 558 ab 1,186 b 2,086 3.3 112.3 ab (4.7) 54.1 22.2
NE3 507 ab 1,150 b 1,312 2.2 118.2 b (10.2) 45.7 21.6
RRD1 205 a 346 a 2,300 2.0 103.2 ab (-3.8) 43.1 18.0
RRD2 970 b 1,806 b 2,313 4.1 89.5 a (-16.6) 37.4 19.3
NCC1 689 ab 1,532 b 2,193 3.5 110.8 ab (3.3) 37.8 21.2
NCC2 848 b 1,410 b 2,392 3.4 105.8 ab (-1.4) 41.9 16.1
CH 1,074 b 1,793 b 2,800 4.5 111.8 ab (4.2) 41.3 16.1
Control 107.3 ab (0.0) 46.3 21.1
n.s. n.s. n.s.
RF: final nematode population density/initial nematode population density (= inoculum).
Means in the same column followed by the same letter do not differ significantly according to Tukey's test (P < 0.05). % change compared with the uninoculated (control) plants.
n.s. indicates no significant diference according to the analysis of variance (ANOVA; P < 0.05). For the list with the nematode population codes see Table 1.
According to our results, rice, sugarcane and maize are good hosts for all the examined P. coffeae populations from Vietnam, while sweet potato, coffee and citrus are very poor hosts. This observation is, in general, in contrast with the nematological literature in which rice, sugarcane and maize are usually not reported as good hosts of P. coffeae in contrast to sweet potato, coffee and citrus which are usually reported as (very) good hosts of P. coffeae (Castillo & Vovlas, 2007). Interestingly, Silva & Inomoto (2002) made a more or less similar observation when they characterised the host range of two P. coffeae populations originally isolated from coffee in Brazil and observed that coffee, citrus (Citrus limonia Osbeck) and also banana were not among the better host plants of these two populations but rather rice and maize. As mentioned in the introduction, also differences in in vivo reproduction on Musa spp. (Bridge et al, 1997), maize (Edwards & Wehunt, 1973; Silva & Inomoto, 2002), rice and sesame (Silva & Inomoto, 2002) among P. coffeae populations have been reported before.
The contradictions among these studies suggest that the host status classification of an agricultural crop based on the study of one cultivar or variety of this crop cannot and should not be generalised. As emphasised by Jacobsen et al. (2009), this classification might be influenced by several factors including host plant response differences among cultivars and varieties, differences in damage potential among nematode populations and methodological differences among studies. As
mentioned in the introduction, differences in damage potential among P. coffeae populations originating from different geographical regions have been reported. In the experiments conducted by Silva & Inomoto (2002), one of the two P. coffeae populations from Brazil used was originally isolated from coffee plants in the field but maintained on alfalfa callus before the host range experiments were carried out. Culturing plant-parasitic nematodes in vitro on monoxenic plant tissue cultures (such as alfalfa callus or carrot discs) might influence the reproduction fitness, virulence and/or damage potential of the cultured nematodes, although we are not aware of any report in this respect. Finally, methodological differences such as the time of sampling and the extraction method used may also have contributed to the observed differences in host status among the published studies.
Although three out of the ten P. coffeae populations from Vietnam used in our experiments were originally isolated from coffee plants in the field, none of the nematode populations examined reproduced well on the coffee variety used in our experiments. This indicates that coffee var. Catimor is a poor host of P. coffeae. In Brazil, Silva & Inomoto (2002) observed low reproduction (RF < 2.5) on coffee 10 weeks after inoculation with 1,000 nematodes of a P. coffeae population originally isolated from coffee roots in the field.
In their experiments with the two P. coffeae populations from Brazil, Silva & Inomoto (2002) also observed that peanut was a poor host (RF < 1) which
is in agreement with our results while soybean was a good host (RF ranging from 2 to 3). In our study, RF of soybean fluctuated around 1 (RF = 0.7 to 2.5).
The in vivo reproduction of all the P. coffeae populations from Vietnam examined on the 13 agricultural crops was, in general, very similar. In some rare cases, differences were observed. On banana, reproduction of the Northwest, Northeast 4 and North Central Coast 1 populations was about 4.5 times higher than reproduction of the Red River Delta 2 population in one experiment but in another experiment no differences in reproduction on banana among these populations were observed. On sugarcane, only the reproduction of two P. coffeae populations (Red River Delta 2 and Central Highlands populations) was significantly different from each other but the difference was small (RF = 5.1 vs 2.6). On rice, the Red River Delta 1 population was the only population out of seven populations included in the experiment that did not reproduce on this crop (RF = 0.2) but the reproduction factor of the other six populations was also not very high ranging from 2.3 to 5.4. On maize, no differences in reproduction were observed among the populations examined.
The results of the damage potential experiments carried out in our study indicate that the P. coffeae populations from Vietnam examined were able to cause considerable damage to the vegetative growth of banana and coffee but not of sugarcane and maize. Our results confirm many earlier observations on the percentage root lesion and damage P. coffeae can cause to banana (Gowen et al, 2005), whilst there are, to our knowledge, no reports on damage caused by P. coffeae to sugarcane (Cadet & Spaull, 1985, 2005) and maize (Mc Donald & Nicol, 2005).
Remarkable is the damage caused by all P. coffeae populations included in the experiment on coffee in spite of the very low reproduction of these populations (RF < 1). Compared with the uninoculated plants, infection with P. coffeae caused about 33% (31.1-35.4%) decrease in plant height; about 60% (53.8-61.5%) decrease in shoot fresh weight and about 70 to 90% decrease in root fresh weight. The root fresh weight of the uninoculated plants at the termination of the experiment was only 3.1 g and this suggests that the fragility of the roots may have resulted in a high sensitivity to damage by P. coffeae. Our results are similar to those of Inomoto et al. (2007) who inoculated two coffee cultivars (Mundo Novo and Catuai) with 8,000 vermiform nematodes of a P. coffeae population originally isolated from coffee roots in the field and maintained on alfalfa callus prior to inoculation. About 37 weeks after inoculation and in spite of a low reproduction
(RF < 1.5) they observed a 72 and 61% reduction in plant weight, 95 and 89% reduction in shoot fresh weight and 93 and 86% reduction in root fresh weight, respectively. The average root fresh weight at 37 weeks after inoculation of the uninoculated control plants was around 10 g. Our results thus confirm the highly destructive nature of P. coffeae on coffee, especially coffee seedlings. Pratylenchus coffeae has been reported as a very destructive nematode to coffee in South America and Asia (Campos & Villain, 2005). This nematode species may cause the destruction of the whole root system resulting in production losses up to 80%, decay of coffee seedlings and trees leading to their death and even the abandonment of coffee fields.
The in vivo damage potential of all the P. coffeae populations from Vietnam examined on banana, coffee, sugarcane and maize was, in general, very similar. As was the case for the in vivo reproduction, differences were only observed in some very rare cases. Exceptionally, the effect on vegetative plant growth of one or a few P. coffeae populations were significantly different either compared with the uninoculated control plants or compared with the other P. coffeae populations.
Finally, our results did not indicate any relationship between host plant range, in vivo reproduction and damage potential on the one hand and geographical origin and host plant from which the P. coffeae populations were originally isolated on the other hand. In conclusion, the in vivo reproduction of all the ten P. coffeae populations from Vietnam on the 13 agricultural crops included in our experiments was, in general, very similar. This supports our previous finding based on the in vitro reproductive fitness on carrot discs experiments that the ten P. coffeae populations from Vietnam examined belong to the same biotype (Agrios, 1997). Based on the results of our in vivo glasshouse experiments, we can confirm that banana is a good host of the P. coffeae populations from Vietnam examined. Surprisingly, rice, sugarcane and maize appeared also to be good hosts of P. coffeae while sweet potato, coffee and citrus are very poor hosts. This observation is, in general, in contrast with the nematological literature in which rice, sugarcane and maize are usually not reported as good hosts of P. coffeae in contrast to sweet potato, coffee and citrus which are usually reported as (very) good hosts of this nematode species. Additional experiments should be carried out to clarify these contradictory findings. It is possible that the host plant specificity is (plant) genotype-dependent. In general, the in vivo damage potential on banana, coffee, sugarcane and maize of all the
ten P. coffeae populations from Vietnam examined was very similar. These populations were able to cause considerable damage to the vegetative growth of banana and coffee but not of sugarcane and maize. In view of the low reproduction on coffee, the extensive damage the P. coffeae populations from Vietnam caused on this agricultural crop is surprising and illustrates the high damage potential of P. coffeae on coffee.
ACKNOWLEDGEMENTS
This study was made possible thanks to a Belgian Technical Cooperation (BTC) Ph.D. scholarship for the first author. This financial support is gratefully acknowledged.
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Резюме. Параметры размножения in vivo (на 13 видах растениях-хозяевах) десяти популяций Pratylenchus coffeae, собранных в различных агро-экологических зонах Вьетнама, оказались сходными. Было отобрано по одному сорту от каждого вида сельскохозяйственных культур. Из 13 испытанных культур только бананы, сахарный тростник, кукуруза и суходольный рис являлись подходящими хозяевами для P. coffeae. Соевые бобы плохо поддерживали размножение пратиленхусов, тогда как арахис, томаты, бататы, имбирь, сезам, ананас и цитрусы оказались еще худшими хозяевами для P. coffeae, или не поддерживали их развитие вообще. Степень вызываемых P. coffeae повреждений на бананах, кофе, сахарном тростнике и кукурузе была сходной для всех 10 исследованных популяций. Все популяции P. coffeae вызывали существенное угнетение вегетативного роста у бананов и кофе, но не у сахарного тростника и кукурузы. Учитывая слабое размножение этих нематод на кофе, значительный уровень вреда, причиняемый ими данной культуре, представляется довольно неожиданным. Выявленные сходные темпы размножения in vivo на 13-и сельскохозяйственных культурах, и сходный уровень угнетения при размножении на бананах, кофе, сахарном тростнике и кукурузе, свидетельствуют о принадлежности всех 10 вьетнамских популяций P. coffeae к одному патотипу.
