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Sel’skokhozyaistvennaya Biologiya [Agricultural Biology], 2011, № 1, p. 85-91
UDK 632.3:[582.683.2+579.841.112]
RESISTANCE OF Brassica rapa L. AND B. napus L. TO BLACK ROT AND LEAF SPOT PATHOGENS
A.N. Ignatov1, A.M. Artemyeva2, Yu. V. Chesnokov2, V.A Polityko3, E. V. Matveeva3,
A.A. Oraevskiy4, N. W. Schaad5
1 Center "Bioengineering" of RAS, Moscow 117312, Russia e-mail: [email protected]
2 N.I. Vavilov All-Russia Research and Development Institute of Plant Growing, RAAS, St.Petersburg 190000, Russia 3 All-Russia Research and Development Institute of Phytopathology, RAAS, Moscow province, Odintsovo region,
Bol’shye Vyazemy settlement 143050, Russia
4State Agrarian University -MTAA named after K.A. Timiryazev, Moscow 127550, Russia 5 Foreign Disease - Weed Science Research Unit of the United States Department ofAgriculture, 21702-5023 MD, Fort Detrick, USA
Received June 24, 2010 S u m m a r y
The authors estimated the apple varieties and hybrid gene pool created during 1970-2009 years in All-Russian Scientific Research Institute of Orchard Culture the content of sugars, organic acids, ascorbic acid and P-active substances. The peculiarities of varying and inheriting of these substances have been investigated. The prospect of apple varieties selection with improved biochemical composition of fruit was shown.
Keywords: race-specific resistance, model «gene-for-gene», interaction plant—pathogen.
Cruciferous plants (the family Brassicaceae) are susceptible to many phytopathogens, the most harmful of which is the bacteriumXanthomonas campestris Pam. (Dow.). X. campestris variants cause diseases with different symptoms - vascular bacteriosis (X. campestris pv. campestris - Xcc) and leaf blotch (X. campestris pv. raphani - Xcr). Physiological races are detected by reaction of cultivars possessing race-specific resistance genes (1, 2). Three genetically close diploid species of the genus Brassica (B. rapa, B. nigra and B. oleracea) are distinct in type of resistance to bacterioses caused by X. campestris. In forms carrying B-genome, this feature is determined by the gene Rxa1 (previously designated as Rb) (1), in A-genome - Rxa4, and in C-genome - Rxa3 encoding the most common type of resistance (2). Along with it, there are allelic variants of three major loci and other types of resistance to X. campestris (3, 4). Breeding for pathogen resistance is limited by a small number of available donors (especially in B. rapa and B. napus), while the existence of more than 9 pathogen races (4) complicates interpretation of literature data on resistance of these species. Resistance to vascular bacteriosis was also found in several cultivars of B. rapa (5).
The purpose of study - to assess geographical distribution and rate of occurrence of race-specific resistance upon the analysis of Brassica rapa and B. napus collection samples by their response to strains of five pathogen races that cause vascular bacteriosis and one race of the leaf blotch pathogen.
Technique. B. rapa and B. napus samples were obtained from collections of the N.I. Vavilov All-Russia Research and Development Institute of Plant Growing (VIR), National Research Institute of Vegetables, Ornamental Plants and Tea (NIVOT, Japan), the All-Russia Research and Development Technology Institute of Rape (Lipetsk) and several breeding companies. The object of study were 134 samples of eight cultivated subspecies of B. rapa representing different geographic regions of Western Europe, Russia, Central Asia, China, Korea and Japan, and 10 wild populations from Russia and Western Europe (Great Britain and Germany). Some of these samples had been previously analyzed by molecular methods to determine the level of genetic diversity, phylogenetic relations of subspecies and taxonomic status of certain forms of a species (6, 7). Along with it, there were tested 56 samples of oilseed rape (B. napus var. oleifera L.) originated from the area Western Europe - Japan.
The plants were grown in pots of 10 cm diameter in a greenhouse at 20/16 °C (day/night) and 16-hour daylight before inoculation performed when the stage of 3-4 true leaves. The plants were inoculated with strains of five races Xcc (2): B-32 (race 6), Cal54-3 (race 5), HRI1279a (race 4), NCPPB528T (race 3), PHW231 (race 1) and the strain 5001a of race Xcr 1 (8). Bacteria were stored at -84 °C; the 2-days culture grown on the modified King B medium was used to prepare the inoculum by dilution to the titer 106 cells/ml. In the variant with Xcc races, plants were infected by pinching 3-4 leaves, in the variant of Xcr, plants were sprayed with bacterial suspension (107 cells/ml). Inoculated plants were kept in a moist chamber for 24 h, then grown in a greenhouse during 2 weeks at 24 °C. For plants infected by pinching, the results were recorded in 2 weeks using the 3-point scale: 0 - no reaction recorded or necrosis only around the point of inoculation (hypersensitivity reaction - HSR), 1 - necrosis around the point of inoculation and chlorosis of areas 0,5 cm diameter, 2 - the development of V-shaped necroses. The lesion of plants infected by spraying was assessed in 1 week by the 3-point scale: 0 - no reaction or HSR (necroses of less than 0,1 mm diameter ), 1 - necroses occupy up to 5% leaf area, necrotic spots of 1-2 mm diameter; 2 - necroses greater than 2 mm diameter cover more than 10% leaf area. Three independent tests were performed on 50 plants of each sample; resistant plants were re-inoculated to confirm the result. The obtained data on three tests were used to determine average rate of resistant individuals (pathogen lesion - 0 or 1 point) as a percentage from the total number of plants in each sample. The number of tested plants was sufficient for detection of 99% resistant individuals whose frequency exceeded 3%.
The significance of differences between samples in share of plants resistant to certain pathogen races were determined by analysis of variance (9). Correlations between samples’ responses to different races were estimated by the Pearson’s method of correlation analysis (10) using the program STATISTICA 6.0 (StatSoft, USA)
Results. It was revealed a diversity of plant reactions in different samples, subspecies and geographic groups. Most of the samples exhibited test-reproducible responses. The response of B. rapa varied depending on pathogen race, subspecies and region of plant origin (Tables 1, 2 and 3). On average, 47,3% individuals of the sample manifested resistance to race Xcr 1, 11,1% - to Xcc 1, 18,7% - to Xcc 3, 49,1% - to Xcc 4, 17,0% - to Xcc 5 and 2,0% were resistant to Xcc 6. Only two samples of B. rapa (rosette cabbage
Ta-gu-tsai VIR-129 and Chinese cabbage Local VIR-108 originated from Southern China) were resistant to all pathogen races including Xcc 6. B. napus samples showed more uniform response - about 92,7% plants were resistant to race Xcr 1, 37,2% - to Xcc 1, 30,8% - to Xcc 3, 95,5% - to Xcc 4,30,0% - to Xcc 5, and no plants resistant to Xcc 6.
Plant responses to infection with races Xcr 1 and Xcc 4 were found to be highly correlated (r = 0,96 for B. rapa and r = 0,915 for B. napus), as well as responses to Xcc 3 and Xcc 5 (r = 0,98 for B. rapa and r = 0,99 for B. napus). Along with it, there was a statistically significant correlation (r = 0,53) between responses of B. rapa to races Xcc 1 and Xcc 5.
1. Geographical origin and resistance of Brassica rapa and B. napus samples to several races of the pathogen Xanthomonas campestris Pam. (Dow.)
Share of resistant plants, %
Sample Source Subspecies Region Xcr 1 Xcc 1 Xcc 3 Xcc 4 Xcc 5 Xcc 6
Just Right F1а Takii Seeds rapifera J 100 0 0 100 0 0
Tokyo Cross F13 Takii Seeds rapifera J 100 0 0 100 0 0
Seven Top Green3 Sakata Seeds rapifera 100 0 0 100 0 0
Suwan NIVOT rapifera J 70 2 10 62 12 0
Hijiore NIVOT rapifera J 66 0 12 70 10 0
Shogoin oomaru NIVOT rapifera J 90 0 10 100 12 4
Local 3091 NIVOT dichotoma A 60 0 30 64 24 0
Local 3096 NIVOT dichotoma A 52 0 34 50 30 0
Local 3124 NIVOT dichotoma A 44 0 36 50 40 0
Local 3159 NIVOT dichotoma A 50 0 56 70 60 0
Local 3161 NIVOT dichotoma A 68 0 80 100 70 0
Local 3166/1 NIVOT dichotoma A 44 0 50 84 50 0
Local 3166/2 NIVOT dichotoma A 80 0 70 100 70 0
Local 3167 NIVOT dichotoma A 70 0 44 100 34 0
Local 3170 NIVOT dichotoma A 100 0 54 50 40 0
Local 3171 NIVOT dichotoma A 100 0 56 50 50 0
Local 3172 NIVOT dichotoma A 80 0 40 80 30 0
Local 3177 NIVOT dichotoma A 30 0 70 42 46 0
Local 3181 NIVOT dichotoma A 44 0 74 84 48 0
Local 3188 NIVOT dichotoma A 100 0 50 100 40 0
Local 3103 NIVOT dichotoma A 100 100 100 100 100 0
Naeshubaekno
baechu VIR-308 NIVOT pekinensis K 84 76 0 90 0 0
Ta-gu-tsai VIR-- NIVOT rosularis Ch 100 100 100 100 100 100
129
Local VIR--108 NIVOT pekinensis Ch 100 100 100 100 100 100
Len-sin-dzon VIR- NIVOT pekinensis Ch 78 0 68 80 74 0
-122
Ducre VIR--312 NIVOT pekinensis K 76 100 0 100 0 0
Kasin VIR--132 NIVOT pekinensis J 68 0 80 76 80 0
Siao-bai-kou VIR-- NIVOT pekinensis Ch 100 100 100 100 100 0
74
Okuta Osaka pekinensis V
shirona VIR--217 NIVOT chinensis J 70 0 62 72 56 0
Bansei mana VIR-- NIVOT pekinensis V
372 chinensis J 56 0 68 60 60 0
Local VIR--53 NIVOT dichotoma A 64 0 50 58 50 0
Hikoshima spring NIVOT pekinensis V narinosa J 45 70 75 68 50 0
VIR--100
Bansei Nagasaki NIVOT pekinensis V narinosa J 69 100 100 100 100 0
VIR-- 212
Nagoya Market VIR- NIVOT pekinensis V narinosa
-238 J 0 46 60 0 54 0
Dou early VIR--89 NIVOT pekinensis Ch 60 54 53 45 48 0
Osaka Market VIR-- NIVOT pekinensis V chinensis J 80 85 75 90 100 0
98 Dunganskaya VIR- NIVOT pekinensis A 100 100 100 100 100 0
-139
Hiroshimana VIR-- NIVOT pekinensis V chinensis J 100 78 60 100 62 0
335
Bi ce VIR--58 NIVOT pekinensis J 52 0 50 52 48 0
Piorbai VIR--75 NIVOT chinensis Ch 24 0 10 30 8 0
Tai na VIR--46 NIVOT chinensis R 30 0 10 34 0 0
Nicanme Juki Jiro NIVOT
Taisai VIR--214 chinensis J 65 45 0 70 0 0
Ching Pang Ju Tsai NIVOT
VIR--203 chinensis Ch 75 0 100 80 60 0
Hae Yu Tatsai VIR- NIVOT rosularis Ch 100 0 23 100 10 0
-84 Mibuna VIR--115 NIVOT nipposinica J 100 100 0 100 0 0
Local VIR--163 NIVOT rapifera Ch 80 20 25 90 20 0
Goseki Late VIR-- NIVOT rapifera pervidis J 80 50 50 60 50 0
242
Gurin Debyu VIR-- NIVOT chinensis V narinosa
302 J 40 0 10 40 10 0
Shelgam VIR B. napus A 100 0 94 100 85 0
t-161 VIR B. napus A 70 0 100 100 80 0
Murasaki natane VIR B. napus J 100 0 100 100 100 0
Ergly VIR B. napus E 100 0 70 100 75 0
Jiho VIR B. napus E 100 100 100 100 100 0
Bronowski VIR B. napus E 100 0 82 100 70 0
Haplona VIR B. napus E 95 0 70 90 74 0
Galaksi VIR B. napus E 100 0 100 100 100 0
Starleit VIR B. napus E 100 0 100 100 100 0
Zolotosevski VIR B. napus E 100 0 100 100 100 0
Galant VIR B. napus E 100 0 100 100 100 0
Vesreo VIR B. napus E 100 0 100 100 100 0
417 VNIPTIR B. napus R 80 100 0 100 0 0
Continuation of Table 1
419 VNIPTIR B. napus R 100 100 0 100 0 0
420 VNIPTIR B. napus R 80 100 0 100 0 0
422 VNIPTIR B. napus R 75 100 0 100 0 0
423 VNIPTIR B. napus R 82 100 0 100 0 0
425 VNIPTIR B. napus R 90 100 0 100 0 0
428 VNIPTIR B. napus R 100 100 0 100 0 0
430 VNIPTIR B. napus R 100 100 0 100 0 0
431 VNIPTIR B. napus R 73 100 0 100 0 0
433 VNIPTIR B. napus R 86 100 0 100 0 0
434 VNIPTIR B. napus R 100 100 0 100 0 0
437 VNIPTIR B. napus R 93 100 0 100 0 0
441 VNIPTIR B. napus R 100 100 0 100 0 0
443 VNIPTIR B. napus R 100 100 0 100 0 0
Masora VIR B. napus E 100 100 100 100 100 0
424 VNIPTIR B. napus R 100 100 100 100 100 0
426 VNIPTIR B. napus R 100 100 100 100 100 0
438 VNIPTIR B. napus R 100 100 100 100 100 0
439 VNIPTIR B. napus R 100 100 100 100 100 0
440 VNIPTIR B. napus R 100 100 100 100 100 0
Note. a - differentiating varieties according to J.G. Vicente et al., 2002; A — Central Asia, including Middle Asia, India and Pakistan, E — Western or Eastern Europe, Ch — China, J — Japan, K — Korea, R — Russia; NIVOT, VIR, VNIPTIR — respectively, National Research Institute of Vegetables, Ornamental Plants and Tea (Japan), N.I.Vavilov All-Russia Research and Development Institute of Plant Growing (St.Petersburg), All-Russia Research and Development Technology Institute of Rape (Lipetsk).
There were found reliable differences in distribution of resistance in B. rapa subspecies (Table 2) and samples of different geographical origin (Table 3). The highest resistance to races Xcc 4 and Xcr 1 was shown by the samples B. rapa nipposinica, B. rapa dichotoma and, respectively, by samples originated from Central Asia and Japan. Some individuals of this group exhibited resistance to races Xcc 1, Xcc 3 and Xcc 5. Several samples originated from India and Middle Asia were resistant to all races except Xcc 6.
2. Resistance of Brassica rapa subspecies to different races of the pathogen Xanthomo-nas campestris Pam. (Dow.)
Subspecies Pathovar, race Number of samples
Xcr 1 | Xcc 1 | Xcc 3 | Xcc 4 | Xcc 5 | Xcc 6
campestris 2,7 C 2,0 B 0,7 B 1,7 B 1,0 B 0,25 A 8
narinosa + rosularis 10,3 BC 0 B 0 B 9,3 B 0 B 0 A 6
pekinensis 25,4 B 19,8 AB 20,4 A 26,0 AB 20,0 AB 3,2 A 31
chinensis 26,2 B 4,6 B 20,5 A 27,6 AB 14,4 AB 0 A 14
parachinensis 35,0 B 0 B 0 B 43,2 AB 0 B 0 A 8
rapifera + perviridis 67,8 A 3,3 B 4,2 B 66,4 A 4,0 B 0,2 A 32
dichotoma 74,1 A 7,7 B 44,0 A 79,5 A 37,8 A 0 A 22
nipposinica 76,3 A 23,9 A 24,8 A 81,1 A 25,2 A 0 A 11
Total 132а
Note. a — the rest of samples had unclear taxonomic status or their number was insufficient for statistical analysis; A, B, C -
groups of means whose differences are reliable at 95 % according to Duncan’s criterion (11).
Resistance to race Xcc 1 was most frequently observed in samples of B. rapa nipposinica and B. rapa pekinensis, to Xcc 3 and Xcc 5 - in B. rapa dichotoma. On the contrary, majority of plants the subspecies campestris, narinosa, chinensis originated from Russia, Western Europe and China were susceptible to the pathogen.
Over 90% rape varieties manifested resistance to Xcc 4 and Xcr 1, but all plants of this species were susceptible to Xcc 6 and more susceptible to Xcc 1, Xcc 3 and Xcc 5 than B. rapa. The oilseed rape varieties of different geographical origin were not suitable for comparison owing to the widespread use in breeding work of genetic material from Western Europe. In general, rape samples showed higher uniformity of response than B. rapa; only two cultivars (Hanna and Capricorn) were susceptible to all strains of the pathogen. Only 7 samples of B. napus (mainly spring rape) manifested a complex resistance to races Xcc 1, Xcc 3 and Xcc 5.
3. Geographical distribution of resistance to the pathogen Xanthomonas campestris Pam. (Dow.) races in Brassica rapa
Region Pathovar, race Number of samples
Xcr 1 | Xcc 1 Xcc 3 | Xcc 4 Xcc 5 Xcc 6
Central Asiaa 73,40 A 8,00 A 40,00 A 77,52 A 35,36 A 12,00 A 25
China 25,30 B 7,40 A 14,90 AB 26,30 B 13,03 AB 3,57 A 56
Western Europe 0,25 B 2,70 A 0 B 0,25 B 0 B 0,25 A 10
Japan and Korea 74,70 A 15,90 A 17,40 AB 76,30 A 16,80 AB 0,09 A 46
Russia 6,50 B 2,00 A 2,50 B 6,00 B 1,50 B 0,25 A 8
Total 145
Note. a - including India and Pakistan; A, B, C - groups of means whose differences are reliable at 95 % according to Dun-
can’s criterion (11).
Races Xcc 1, Xcc 3, Xcc 4, Xcc 5 and Xcc 6 used in this study are known to be represented by 3 of 4 avirulence genes described in studies of “gene-for-gene” relationship between differentiating cultivars and pathogen (1-3).
Differentiating varieties B. rapa Just Right Fi and Tokyo Cross Fi - descendants of a common ancestor (cv Shogoin oomaru) resistant to the race Xcc 4 - showed the similar reaction to inoculation with many Xcc isolates collected in different regions (1, 2, 12, 13). The role of a single dominant gene providing resistance to Xcc 4 has been confirmed by results of assessment of populations obtained by crosses between Seven Top Green (heterozygous plant) Vi Just Right F1, Just Right F1 V> Just Right S4 (susceptible line S4) and the sample 3177 V Just Right S4. All of these plants most likely carry homologous resistance genes (14). The presence of different alleles of one resistance locus Rxa4 has been recently established in these differentiators and in the cultivar Seven Top Green (3). Though, it’s still an open question about the homology of dominant genes for resistance to race Xcc 4 in B. rapa and B. napus .
Significant correlation between plant responses to races Xcr 1 and Xcc 4 confirms the data about identical racial structure of these two pathovars (8, 15). The correlation between resistance to races Xcc 3 and Xcc 5 possibly indicates the presence of a homologous Rxa3 gene in A-genomes of plants.
Highest rates of resistance to vascular bacteriosis were established in B. rapa subpopulation from Central Asia known to be of the largest genetic diversity among the gene pool of this species (16) and in the genetically close subpopulation from Japan (17). These samples effectively combated the race Xcc 4 widespread in Japan, Russia, Great Britain and Portugal (1, 2).
The population of B. rapa includes genetically isolated groups of vegetable crops of Chinese origin, oilseeds from Central Asia and turnip from Europe and Russia resulting the selection in contrast climate and soil conditions (16, 18). Recent studies based on molecular analysis showed the trend to classify samples by geographical origin - European, Indian (or united Eurasian) and East Asian groups (19, 20). Distribution of resistance to the race Xcc 4 sharply contrasts in groups separated by a small distance (Japan and China , or Central Asia and China). The studied samples of Chinese rosette cabbage and leaf cabbage resistant to all six pathogen races can be close relatives (6). Resistance to Xcc 4 in B. napus can be inherited from B. rapa (possibly, a diploid ancestor). However, it’s not clear whether the resistance genes for particular races are homologous in all studied samples.
Thus, highest rates of Brassica rapa subspecies resistant to Xanthomonas campestris Pam. (Dow.) race Xcc 4 were established in samples originated from Central Asia and Japan. For the first time the authors have detected samples-donors of complex resistance to six pathogen races and sources of resistance to races Xcc 1 and Xcc 3. These findings will help the creation of B. rapa and B. napus cultivars and hybrids resistant to vascular bacteriosis and leaf blotch caused by phytopathogenic Xanthomonas.
REFERENCES
1. Ignatov A.N., Kuginuki Y. and Hida K., Creation of Plants the Family Brassicaceae Resistant to Stem Bacterioses Caused by Xanthomonas campestris, S.-kh. biol., 2002, no. 5, pp. 75-84.
2. Vicente J., Conway S., Roberts J. et al., Identification and Origin of Xanthomonas campestris pv. campestris Races and Related Pathovars, Phytopathology, 2001, vol. 91, no. 5, pp. 492-499.
3. Ignatov A.N., Mazurin E.S. and Dzhalilov F.S., Rases of Xanthomonas campestris pv. campestris, in Tr. I nauch.-prakt. conf. “Sovremennye tendentsii v selektsii i semenovodstve ovoschnykh kul’tur. Traditsii iperspectivy ” (Proc. 1st Sci.-Pract. Congress “Modern Trends in Selection and Seed-Growing of Vegetable Crops. Traditions and Prospects”), Moscow, 2008, p. 45.
4. Fargier E. and Manceau C., Pathogenicity Assays Restrict the Species Xanthomonas campestris into Three Pathovars and Reveal Nine Races within X. campestris pv. campestris, Plant Pathol., 2007, vol. 56, no. 5, pp. 805-818.
5. Guo H., Dickson M.H. and Hunter J.E., Brassica napus Sources of Resistance to Black Rot in Crucifers and Inheritance of Resistance, HortScience, 1991, vol. 26, pp. 1545-1547.
6. Artemyeva A.M., Chesnokov Yu.V. and Klocke E., Genetic Diversity and Intraspecific Phylogenetic Relations between Crops of the Species Brassica rapa L. upon Microsatellite Analysis, Inf. vestn. VOGiS, 2008, vol. 12, no. 4, pp. 608-619.
7. Bonnema G., Pino del Carpio D., Zhao J., Artemyeva A. and Paulo J., Genetic Diversity in Brassica rapa, in Proc. 16th Crucifer Genetic Workshop: Brassica 2008, Lillehammer, Norway, 2008, p. 22.
8. Vicente J.G., Everett B. and Roberts S.J., Identification of Isolates that Cause a Leaf Spot Disease of Brassicas as Xanthomonas campestris pv. raphani and Pathogenic and Genetic Comparison with Related Pathovars, Phytopathology, 2006, vol. 96, pp. 735-745.
9. Anscombe F.J., The Validity of Comparative Experiments, J. of the Royal Statistical Society, Ser. A (General), 1948, vol. 111, no. 3, pp. 181-211.
10. Yule G.U., Notes of Karl Pearson's Lectures on the Theory of Statistics, 1884-96, Biometrika, 1938, vol. 30, no. 1/2 (June), pp. 198-203.
11. Duncan D.B., Multiple Range and Multiple F Tests, Biometrics, 1955, no. 11, pp. 1-42.
12. Ignatov A., Kuginuki Y. and Hida K., Pathotypes of Xanthomonas campestris pv. campestris in Japan, Acta Phytopathologica et Entomologica Hungarica, 1999, vol. 34, no. 3, pp. 177-181.
13. Kamoun S., Kadmar H.V., Tola E. and Kado C., Incompatible Interaction between Crucifers and Xanthomonas campestris Involve a Vascular Hypersensitive Response: Role of the hrpX Locus, Molec. PlantMicr. Interact., 1992, no. 5, pp. 2233-2236.
14. Ignatov A., Kuginuki Y. and Hida K., Distribution and Inheritance of Race-Specific Resistance to Xanthomonas campestris pv. campestris in Brassica rapa and B. napus, J. Russian Soc. Plant Pathologists, 2000, no. 1, pp. 83-87.
15. Ignatov A., Hida K. and Kuginuki Y., Race-Specific Resistance in Brassicas to Black Rot and Leaf Spot Caused by Xanthomonas campestris, Beitrage zur Zuchtungsforschung, 1999, vol. 5, no. 1, pp. 37-39.
16. McGrath J.M. and Quiros C.F., Genetic Diversity at Isozyme and RFLP Loci in Brassica campestris as Related to Crop Type and Geographical Origin, Theor. Appl. Genet., 1992, vol. 83, pp. 783-790.
17. Sinskaya E.N., Oil-Yielding and Root Crops of the Family Cruciferae, Tr. po prikl. bot., gen. i sel., 1928, vol. 19, no. 3, pp. 1-648.
18. Song K.M., Osborn T.C. and Williams P.H., Brassica Taxonomy Based on Nuclear Restriction Fragment Length Polymorphisms (RFLPs). 3. Genome Relationships in Brassica and Related Genera and the Origin of B. oleracea and B. rapa syn. campestris, Theor. Appl. Genet., 1990, vol. 79, no. 4, pp. 497-506.
19. Zhao J., Wang X., Deng B., Lou P., Wu J., Sun R., Xu Z., Vromans J., Koornneef M. and Bonnema G., Genetic Relationships within Brassica rapa Inferred from AFLP Fingerprints, Theor. Appl. Genet., 2005, vol. 110, no. 7, pp. 1301-1314.
20. Warwick S.I., James T. and Falk K.C., AFLP-Based Molecular Characterization of Brassica rapa and Diversity in Canadian Spring Turnip Rape Cultivars, Plant Genetic Resources: Characterization and Utilization, 2007, vol. 6, no. 1, pp. 11-21.
