MSc

Tomato (Solanum lycopersicum L.) is one of the most important and popular vegetable crops grown globally. However, tomato crop is highly vulnerable to several pest and diseases. Tomato leaf curl virus disease (ToLCV), caused by Begomovirus and spread by whitefly, Bemisia tabaci, is one of the most serious diseases affecting tomato causing yield loss even up to 100 per cent. Disease management through vector control is impractical due to high cost, poor efficiency and development of pest resistance. Introgression of resistance genes from wild species into the domesticated tomato, followed by selection of superior resistant lines from the early segregating generations is an important strategy in resistance breeding. In this context, the present study entitled “Selection of superior tomato leaf curl virus (ToLCV) resistance lines from early segregating generations in tomato (Solanum lycopersicum L.)” was carried out during 2022 - 2024. Segregating generations of three hybrids with high yield and ToLCV resistance viz., Akshaya x EC 519806, Vellayani Vijay x EC 519806, and Manuprabha x AVTO 1707 were evaluated along with parents and check varieties.
Segregation with wide variation was observed in the F2 and F3 generations of all the three hybrids. Growth habit in the F2 of Vellayani Vijay x EC 519806 segregated into indeterminate and determinate genotype, F3 of determinate F2 genotypes were determinate type only, whereas F3 plants generated from indeterminate genotypes exhibited segregation for growth habit. F2 and F3 populations of Akshaya x EC 519806 and Manuprabha x AVTO 1707 was indeterminate and determinate respectively.
Range, mean, variance, Genotypic Coefficient of Variation (GCV) (%), Phenotypic Coefficient of Variation (PCV) (%), heritability, Genetic Advance (%), Genetic Advance as percentage of Mean (%), skewness (%), kurtosis (%), and correlation between growth and yield traits was estimated in F2 and F3 segregating generations. PCV was higher than GCV for all the traits in both generations indicating the influence of environment on character expression. Compared to F 2, reduction in range, and magnitude of GCV, PCV, heritability, GAM and skewness, and higher kurtosis suggests the decrease in variability and the number of transgressive segregants and increase in homozygosity in F3 generation.

ToLCV scoring according to Banerjee and Kalloo (1987) at 15 DAT, 30 DAT, 60 DAT, and 90 DAT categorized individual lines into five classes from score zero (highly resistant) to score 4 (highly susceptible). Segregation for resistance response in the F2 of Akshaya x EC 519806 (128 resistant: 51 susceptible) and Vellayani Vijay x EC 519806 (118 resistant:48 susceptible), fitted into monogenic mendelian ratio of 3:1.
Trichomes play a vital role in the host plant resistance to ToLCV. Glandular abaxial trichome density was higher in resistant lines, whereas, number of non- glandular trichomes on the adaxial leaf surface was higher in susceptible lines. Type IV and Type VI were the prominent glandular trichomes found in the selected resistant genotypes, and type II was the most common non-glandular trichome found in all lines. Type III non-glandular trichome was found only in the resistant lines, and type V was only found in the lines with more than zero score for ToLCV.
Superior high yielding lines exhibiting disease resistance in the field was selected from F2 generation which included 16 lines from the cross Akshaya x EC 519806 viz., 15-9, 15-14, 15-27, 15-48, 15-51, 15-118, 15-130, 15-138, 15-147 ,15-154,
15-157, 15-179, 15-180, 15-197 15-201 and 15-204. Five lines, 17-12, 17-24,17-64,
17-80, 17-103, 17-113 were from Vellayani Vijay x EC 519806 and three lines, 5-10, 5- 11 and 5-15 were from the F2 of the hybrid Manuprabha x AVTO 1707. Severe ToLCV infection was observed in F3 generation compared to F2, since the screening was done during the summer season. Fifteen lines were selected for further evaluation from F3 families having low Vulnerability index (VI) viz., 14-49, 48-12, 48 -29, 118-12, 118-17,
118-22, 154-13, 154-15, 154-20, 154-21, 201-23 from Akshaya x EC 519806, 24-29,
103-33, and 131-40 from Vellayani Vijay x EC 519806 and 5-10-3 from the F3 of Manuprabha x AVTO 1707.
Molecular screening with reported Ty gene markers revealed the presence of resistant allele of Ty 2 and Ty 3 in the male parent AVTO 1707 as well as the selected line viz., 5-10-3, from the F3 of the hybrid, Manupraha x AVTO 1707. All the selected lines were screened with ToLCV coat protein (CP) specific primers and the lines 15-14- 49, 15-48-12, 15-48-29, 15-154 -20, with score 0, and 15-118-12, 15-118-17, 17-24-29,
17-103-33 with score 1 showed amplification. Remaining selected F3 lines with score 0

(15-118-22, 15-154-13, 15-154-15, 15 -154-21, 17-131- 40, 5-10- 3) did not amplify CP
gene, indicating absence of detectable ToLCV load in these selected lines.