Breeding of ToLCV resistant high yielding tomato (Solanum lycopersicum L.) genotypes

Abstract

Tomato (Solanum lycopersicum L.) is a warm season vegetable crop of solanaceae family, which is widely grown in India for use as vegetable as well as fruit. But, its production is hampered by disease incidence leading to severe crop loss. Among the diseases affecting tomato, whitefly transmitted tomato leaf curl virus disease (ToLCD) is very severe, and it can cause upto 100 per cent yield loss depending on stage of infection. As vector management using insecticides leads to environmental pollution and creates vulnerability, exploitation of host plant resistance is the best sustainable strategy to manage ToLCD. Hence, identified resistance sources can be utilised for the development of high yielding ToLCV resistant genotypes through hybridization programmes. In this context, the present study entitled “Breeding of ToLCV resistant high yielding tomato (Solanum lycopersicum L.) genotypes” was carried out during 2021 2023. Ten previously identified genotypes showing field resistance or carrying Ty genes (AVTO 0301, AVTO 0922, AVTO 1314, AVTO 1702, AVTO 1706, AVTO 1707, AVTO 1725, AVTO 1726, EC 519806 and Local Collection (Idukki)) were selected as source of resistance and were crossed with three agronomically superior released varieties viz., Akshaya, Manuprabha and Vellayani Vijay in Line x Tester mating design. Seventeen successful crosses along with parents and check variety, Anagha, were screened for ToLCV resistance in RBD design with two replications during March- June 2022. The disease incidence was assessed at 15, 30, 60 and 90 days after transplanting as per the score given by Banerjee and Kalloo (1987). Among the hybrids screened, Vellayani Vijay × EC 519806, Akshaya × AVTO 1726 and Akshaya × AVTO 1707 showed least Coefficient of Infection (CI) and were highly resistant under field condition. In the present study, the morphological characters affecting growth and yield such as growth habit, plant height, spread of the plant, number of primary branches per plant, days to flowering, fruit colour, fruit size, number of fruits per plant, number of locules per fruit, lycopene content, fruit weight and fruit yield per plant differed significantly among the hybrids. The crosses of EC 519806 followed by Akshaya × AVTO 1726 recorded the highest yield per plant. Moreover, the whitefly population assessment in the field also showed less whitefly infestation on Akshaya × AVTO 1726. Hybrids with significant positive Relative heterosis (RH), Heterobeltiosis (HB) and Standard heterosis (SH) for all growth and yield characters were obtained in the present study. Most of the hybrids exhibited significant SH for all the characters under study. And all the traits exhibited high heritability coupled with high genetic advance. Line x Tester analysis of nine F1’s, developed from three lines (Akshaya, Manuprabha and Vellayani Vijay) and three testers (AVTO 1707, EC 519806 and Local Collection (Idukki)), revealed significant sca effect for hybrids and significant gca effect for parents for days to flowering (Vellayani Vijay x EC 519806, Manuprabha x AVTO 1707); equatorial diameter and fruit size (Manuprabha × AVTO 1707); polar diameter (Vellayani Vijay × AVTO 1707); fruit weight (Akshaya × AVTO 1707); spread of the plant (Akshaya × Local Collection (Idukki), Manuprabha × EC 519806); number of fruits per plant and yield per plant (Vellayani Vijay × EC 519806). Significant sca effect was recorded for plant height (Manuprabha × AVTO 1707); equatorial diameter (Akshaya × EC 519806, Vellayani Vijay × Local Collection (Idukki)); polar diameter and fruit size (Akshaya × EC 519806, Akshaya × Local Collection (Idukki), Manuprabha × AVTO 1707); number of fruits per plant (Akshaya x Local Collection (Idukki), Manuprabha x AVTO 1707); number of primary branches per plant (Akshaya x EC 519806); spread of the plant (Manuprabha × AVTO 1707, Vellayani Vijay × Local Collection (Idukki)); yield per plant (Akshaya × AVTO 1707, Akshaya × Local Collection (Idukki), Manuprabha × AVTO 1707, Manuprabha × Local Collection (Idukki)). Although, significant gca for number of primary branches per plant (Manuprabha; Local Collection (Idukki)); number of fruits per plant (Vellayani Vijay; Local Collection (Idukki)) and spread of the plant (Akshaya; EC 519806, Manuprabha; Local Collection (Idukki)) was observed, their crosses did not have significant sca. Therefore, selection in segregating generations will be effective for these characters. Glandular and non glandular trichome density on both abaxial and adaxial leaf surfaces demonstrated that glandular abaxial trichome density is more effective for ToLCV resistance than adaxial trichomes. Among the hybrids, Akshaya × AVTO 1726 and Akshaya × AVTO 1707 had above average glandular and below average non glandular trichome density. To confirm ToLCV resistance, whitefly mediated artificial inoculation was done on the selected hybrids and observed that Akshaya × AVTO 1726 was highly resistant under artificial screening as well. All crosses of EC 519806 (except Akshaya × EC 519806) and Local Collection (Idukki) were susceptible under artificial screening. Screening for six reported Ty genes using the primers 562 JB/830 JB, SCAR2, P6-25, TY-1/3_K, C2_AT5g51110, AVRDC-TM273 and SLM 10-46 linked to ToLCV resistance genes Ty 1, Ty 2, Ty 3, Ty 1/3, Ty 4, ty 5 and Ty 6 respectively, revealed presence of Ty 1, Ty 2, Ty 3 and Ty 1/3 in all the crosses of AVTO 1726 and AVTO 1707. Whereas, AVTO 0922, AVTO 0301 and AVTO 1314 contributed Ty 1 and Ty 2; Ty 1, Ty 2 and Ty 3; Ty 1 and Ty 3 genes respectively in their crosses. None of the markers showed resistant amplicon in EC 519806. In the present study, none of the genotypes exhibited presence of resistant amplicon for Ty 4. AVRDC-TM273 linked to ty 5 failed to detect polymorphism in the genotypes. Whereas, resistant allele of the marker linked to Ty 6 was amplified only in Local Collection (Idukki) and its crosses. The present study revealed that Akshaya × AVTO 1726 is a very promising hybrid with high yield, ToLCV resistance large sized fruits. Akshaya × EC 519806, Akshaya × AVTO 1707 and Manuprabha × AVTO 1707 are high to medium yielding hybrids with moderate resistance to ToLCV. Vellayani Vijay × EC 519806 was the highest yielding genotype. Therefore, these crosses can be forwarded to further generations to identify superior genotypes from segregating generations