Screening of mapping population through marker assisted selection for imparting disease resistance in tomato (Solanum lycopersicum L.)
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Date
2014
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College of Horticulture, Vellanikkara
Abstract
Tomato is the second most consumed vegetable, next to potato and it occupies largest number of cultivated varieties than any other vegetable crop. India is the sixth largest producer of tomato in the world with an area of 0.50 million hectares and with a productivity of 17.4 MT per hectare. Despite the efforts taken up all over the world so far, tomato leaf curl virus (ToLCV) disease and bacterial wilt (BW) still continues to be the major limiting factors in tomato cultivation. The leaf curl virus infects the crop in all locations while bacterial wilt is more severe in the humid tropics. Acidic soils, humid climate and high temperature favour bacterial wilt incidence in Kerala and it affects the crop at all stages of growth resulting in total crop loss. Leaf curl virus incidence is also gaining importance in the state recently and hence it is the need of the hour to develop varieties with combined resistance. Conventional breeding has helped to develop location specific varieties and molecular breeding have identified several Resistant Gene Analogues and QTLs mapped on different chromosomes. Considering the importance of bacterial wilt in Kerala, KAU has developed varieties with relatively good tolerance (eg- Mukthi), but are susceptible to ToLCV and fruit qualities are not superior. Genotypes resistant to different strains of ToLCV have been developed at Indian Institute of Horticultural Research (eg- IIHR-2195) and this project is an attempt to incorporate combined resistance to BW and ToLCV through molecular breeding. The markers that will be validated will be of great use in marker assisted selection. An ideal genotype with ToLCV resistance in bacterial wilt resistance background and having desirable horticultural traits is targeted in the programme. The investigation was carried out during 2012 - 2014 for Screening of F3 and F4 population of a cross between Mukthi and IIHR-2195 for imparting combined disease resistance along with better horticultural traits. Total 921 plants in F3 and F4 population were evaluated in a disease prone field of Department of Olericulture, College of Horticulture. Important biometric parameters were recorded, disease reaction scored and selected molecular markers were validated on resistant and susceptible lines. DNA isolated from the parent Mukthi and IIHR-2195 was used to validate eleven primers already reported for BW and ToLCV resistance. Three primers which showed good polymorphism and reproducibility among parents were selected for further validation in F3 and F4 population. Twenty two F3 and 35 F4 plants with combined resistance to BW and ToLCV were screened out based on disease reaction. The three selected primers (Ualty 3a, Ualty 3b and SSR 20) were validated on resistant F4, their corresponding F3 parental lines, along with susceptible checks. The selected markers segregated with the trait in the F3 and F4 resistant plants and were also found expressed in few susceptible checks. The markers found to segregate along with the trait could be recommended for marker assisted selection in tomato. Fourteen promising lines with combined resistance and better yield (>800g) were identified for further evaluation and variety development.
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