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Azimov Abdulaxat Abdujjaborovich, Senior Researcher of the Institute of Genetics and Plant Experimental Biology, Uzbek Academy of Science, doctor of philosophy (PhD.), of biological Sciences, Tashkent, Uzbekistan E-smail: azimov_genetika@mail.ru
VERTICILLIUM WILT RESISTANCE OF COTTON PLANTS ON THE BASIS OF INTERSPECIFIC HYBRIDIZATION
Abstract: It has been shown that fine-fiber cotton varieties and interspecific hybrids (G.hirsutum L.x G.barbadense L.) exhibit high field resistance to the Verticillium wilt. In the interspecific hybrids, dominance and overdominance of economically valuable traits was observed.
Keywords: introgressive hybrids, interspecific hybridization, wilt races, infectious background.
Introduction
In the practical breeding work interspecific and inter-generic hybridizations it is still considered as a general line for obtaining resistant varieties and disrupting, to varying degrees, the biological compatibility between the pathogen and higher plant.
Despite considerable difficulties that the breeder has to overcome during hybridization, this method now is very often used in cases where it is necessary to drastically improve the immunological properties of a particular crop, and within its species there are no such forms that could be used as a stable parent for hybridization. Breeders are often forced to use as a resistant parent an immune or highly resistant variety belonging to another species, often very distant in genetic terms, including from the wild flora.
The richest variety of sustainable plant forms created by nature is widely used today as a starting material in breeding works for the development of wilt-resistant varieties.
Material and methods
The resistance of parental samples and reciprocal F1-F3 plants to verticillium wilt was studied in the naturally strong infectious background. Every year, at the end of the growing season (October 1-10), the susceptibility of plants to verticillium wilt was determined by cutting of the main stem around the cotyledon leaf and assessment of disease severity according to the four-point scoring system: 0 (I) - healthy; II - mildly affected; III - moderately affected; IV - severely affected. The inheritance of resistance trait to verticillium wilt s wilt was analyzed.
Research results
Feasibility and success of distant interspecific hybridization for the transfer of useful genes is evidenced by the results of works concerning involvement of representatives G.barbadense L. species into the hybridization [1-5]. As many authors noted this species is characterized by high resistance to wilt. We conducted a study of the resistance of the hybrids derived by hybridization of the Tashkent-6 variety (G.hirsutum L.) and the C-6037 variety (G.barbadense L.) in several generations on artificial infectious backgrounds infected with the most aggressive races of the fungus V.dahliae Kleb.
As can be seen from the data presented in (Table 1), the parent variety Tashkent-6 in the background of race I showed a considerable high degree of wilt resistance - the percentage of healthy plants was more than 60%, in contrast to the background of race II, where the number of strongly and weakly affected plants was more than 50%. In variety C-6037, on the background of race I, the percentage of healthy plants was more than 60%, and on the background of race II, more than 75%. It should be noted that this variety showed lack of infected plants with high degree of wilt infection on the background of race I and race II and a very low percentage of cases with a moderate degree of wilt lesions on the background of race I. In contrast to a representative of the G.barbadense L species, C-6037 variety, Tashkent-6 (G.hirsutum L) variety was affected with the wilt on 2 backgrounds to a much greater extent.
Table 1.- Wilt resistance of parental forms and their interspecific hybrids (F1-F4)
Parental forms and hybrids Background of Race I Incidence ofwilt disease (according to the wilt disease severity),% Background of Race I Incidence of wilt disease (according to the wilt disease severity),%
0 1 2 3 0 1 2 3
1 2 3 4 5 6 7 8 9
Tashkent-6 63.5 35.7 0.8 - 21.5 23.4 48.3 6.8
VERTICILLIUM WILT RESISTANCE OF COTTON PLANTS ON THE BASIS OF INTERSPECIFIC HYBRIDIZATION
C-6037 61.2 35.8 3.0 - 75.5 24.5 - -
Fx Tashkent-6 x C-6037 47.8 47.8 4.4 - 30.0 45.0 25.0 -
F2 62.0 28.0 10.0 - 55.0 32.5 12.5 -
F3 31.3 56.2 10.4 2.1 50.0 31.6 15.8 2.6
F4 14.3 45.7 40.0 - 53.6 26.2 13.0 7.2
To characterize the investigated interspecific hybrids for the wilt resistance, the studies were conducted on artificially infected wilt background together with the parental varieties. Sowing was performed with single-row 20-hole plots in 3 replicates and randomized blocks. Assessment ofwilt disease intensity was carried out on 15 IX on a 4-point scale, on the background of race I and race II.
In F1 plants of the interspecific hybrid, dominance of wilt resistance was observed - on the background of race I and race II, there were no plants that were severely affected by wilt, wherein a high percentage of plants was not affected, or weakly affected.
In F2, wilt resistance on two backgrounds was inherited as a polygenic trait - the number of unaffected plants ranged from 55 to 63%. In subsequent generations of hybrids, there was a slight decrease in the number of healthy plants in the
background of race I. There were no diseased plants in F2. Under the background of race II, the trait of the wilt resistance of the hybrids was observed up to 4 generations.
From the plants of the third generation of hybrids (Tash-kent-6 (G.hirsutum L.) x C-6037 (G.barbadense L.)), the L-27 line, promising in a number of indicators, was identified. In order to improve the early ripeness and technological qualities of the fiber, the selected line was backcrossed with the Tashkent-6 variety.
The obtained results showed that hybrids retain relative wilt resistance, expressed in the mixed infectious background. Backcrossing of the line L-27 allowed to enrich the gene pool with forms characterized by a number of economically valuable traits. The results of the study of the wilt resistance of introgression lines are shown in (Table 2).
Table 2.- Estimation of severity and incidence of wilt disease in the introgressive hybrids on the mixed background
Incidence of wilt disease (according to the wilt disease
Introgressive hybrids severity),%
0 1 2 3
L-27FB, [(F3 Tashkent-6 x C-6037) x TarnKem-6] 62.0 30.0 8.0 -
FB, 50.5 42.5 7.5 -
FB2 42.0 48.0 10.0 -
0 - healthy plants, 1 - mildly affected, 2 - moderately affected, 3 - severely affected
The high wilt resistance of G.hirsutum L. x G.barbadense L. hybrids makes it possible to cultivate highly heterotic in productivity, early ripeness and fiber quality of hybrids in heavily wilt-infected areas, where medium-fiber varieties give very low yields as a result of massive damage. All actual data show that by appropriate selection of more early ripening varieties of medium-fiber cotton and varieties with zero type of fruit branches of fine-fiber cotton, there is a real opportunity to create highly heterotic American-Egyptian hybrids in terms of ripeness, yield, wilt resistance and fiber quality.
Discussion and conclusion
Fine-fiber cotton varieties and interspecific hybrids
(G.hirsutum L. x G.barbadense L.) exhibit high field resistance
to Verticillium wilt. In total, wilt disease incidence of fine-fiber varieties, depending on the variety, is 3.8-19.3% versus 25.585.9%, in varieties of medium-fiber cotton. In general, wilt disease incidence of the fine-fiber varieties and introgressive hybrids is zero, while for medium-fiber ones it ranges from 10.4 to 40.3%.
Hybrids developed with involvement of fine-fiber varieties were distinguished by a minimum susceptibility to the wilt; therefore, it is advisable to cultivate the early maturing, high-yielding interspecific cotton hybrids on heavily wilt-infected lands.
References:
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