Breeding hotset indeterminate tomato (Solanumlycopersicum L.) resistant to bacterial wilt suitable for protected cultivation

Abstract

The present investigation was undertaken to develop an indeterminate hotset tomato with bacterial wilt resistance through line × tester analysis. The experiment was conducted at the Department of Vegetable Science, College of Agriculture, Vellanikkara, Kerala Agricultural University, during the year 2018- 2020. The first experiment was the performance evaluation of 35 tomato genotypes for two seasons in the year 2018, summer evaluation from January 2018 and rainy season evaluation from July 2018, in two protected structures viz., polyhouse and rainshelter. Genotypes exhibited significant variation for vegetative, flowering, fruit, yield and biochemical traits under both growing structures across season. Under polyhouse during summer the genotypes EC- 164263, EC-620387, EC-620401, EC-620406, EC-620410, and EC-620417 performed better for hotset traits (flowers with exerted stigma, pollen viability and fruit set per cent) and yield traits (average fruit weight, number of fruits per plant and yield). In rainshelter, the genotypes EC-165395, EC-165690, EC- 538153, EC-620401, EC-620406, EC-620410 were superior. During rainy season, EC-164263, EC-538153, EC-620401, EC-620406, EC-620410, EC-631369 were superior under polyhouse, and EC-620395, EC-620401, EC-620406, EC-620410, EC-631369 and EC-631379 inside rainshelter, for hotset traits and yield traits. The pooled data of flowers with exerted stigma, pollen viability, fruit set per cent, number of fruits per cluster, days to first fruit set, average fruit weight, pericarp thickness, number of fruits per plant and yield per plant were subjected to multivariate analysis for discrimination of genotypes into clusters. Under polyhouse seven clusters and inside rainshelter five clusters were observed. The selection index was also applied for ranking of genotypes based on the hotset distinctions and yield attributes. The hotset genotypes with high yield potential, identified suitable for protected cultivation were EC-164263, EC-538153, EC- 620387, EC-620389, EC-620401, EC-620406, EC-620410, EC-620417 and EC-631369. The genotypes EC-620401 (1), EC-620406 (2) and EC-620410 (3) were selected as hotset line for the line × tester analysis. In the second experiment the genotypes were tested for bacterial wilt resistance. The 35 tomato genotypes were sown in 98 well pro-trays holding sterilised soil medium. Another set of pro-trays holding the same medium were drenched with bacterial suspension with OD adjusted 0.8 to 1.3 at 600 nm and kept as the sick pro-trays. The twenty-one days old seedlings were used for inoculation through root dip method. With the help of sterilized scissors the tertiary roots of the seedlings were sectioned. The root clipped seedlings were dipped in bacterial suspension for thirty minutes. The inoculated seedlings were transplanted in the sick pro-trays. The entire experiment was conducted inside rainshelter with three replications. Each replication had five plants per genotype. Periodical observation on bacterial wilt symptom expression was taken from third day onwards. The disease index has revealed EC-620382 (0.20) and Arka Abha (0.20) as highly resistant. Nine genotypes viz: EC-165395 (0.24), EC-165700 (0.25), EC-521067 B (0.25), EC-620376 (0.30), EC-620378 (0.28), EC-620427 (0.21), EC-620429 (0.23), Akshay (0.21), Anagha (0.28) were resistant. From these EC-620382 (4), EC-620427 (5), EC-620429 (6) and Arka Abha (7) were selected as testers. In the third experiment, the identified lines and testers were crossed and seeds were collected for twelve cross combinations. The fourth experiment was the evaluation of F 1 hybrids from third experiment during summer in two protected structures viz., polyhouse and rainshelter. The cross combinations were laid along with the parents and two checks viz., one check hybrid (Abhilash) and one check variety (Akshaya). The mean performance, relative heterosis (RH), heterobeltosis (HB), standard heterosis (SH) and combining ability studies were conducted. For vegetative traits, the cross combination 3 × 7 exhibited superiority in the mean performance with significant positive sca effects in both the structures. For flowering traits, the cross 2 × 5 exhibited significant positive sca effects for pollen viability and significant negative sca effects for flowers withexerted stigma with significant RH, HB and SH in both the structures. In the case of fruit and yield traits, the cross combination 2 × 5 exhibited negative significant sca effects for days to first fruit set and positive significant sca effects for pericarp thickness, average fruit weight and yield per plant with significant RH, HB and SH. Inside rainshelter, 3 × 5 and 3 × 7 noted significant sca effects and positive significant heterosis for fruit and yield traits. For biochemical traits, the cross combination 2 × 5 exhibited positive significant sca effects and positive significant RH, HB and SH for TSS, ascorbic acid and acidity under polyhouse. In the seedling stage, all cross combinations exhibited resistance reaction to bacterial wilt in the challenge inoculation. Depending on the mean performance, heterosis and sca effects, the cross combination 2 × 5 was recommended for polyhouse and the crosses 3 × 5 and 3 × 7 were recommended for rainshelter. None of the parents revealed significant and desirable gca effect for all traits studied. The comprehensive assessment of the parents by considering gca estimates revealed that among lines EC-620406 is a good general combiner for vegetative, fruit and yield characters under polyhouse, and EC-620406 and EC- 620410 could be regarded as good general combiners for vegetative, reproductive, fruit and yield, quality characters and shelf life inside rainshelter. In the case of testers EC-620427 and Arka Abha were good combiners for vegetative, reproductive, fruit characters and shelf life in both the growing structures. Dominant gene action was observed predominantly for characters studied under both the structures. Plant height at harvest, days to 50% flowering, days to first fruit set, days to first fruit harvest, number of fruits per plant, average fruit weight, yield per plant, yield per plot, lycopene, ascorbic acid, shelf life, flowers with exerted stigma, pollen viability, number of flowers per cluster, number of fruits per cluster and fruit set per cent exhibited dominant gene action under both the structures. Pericarp thickness exhibited complete dominance inside rainshelter.In the fifth experiment, available SSR markers were validated for bacterial wilt resistance. Two SSR markers, SLM6124 and SLM6-110, produced polymorphism between resistant and susceptible genotypes, two distinct bands for resistant genotypes and four bands (two distinct and two fainted) for susceptible genotypes. In conclusion, the work indicates the change in the behaviour of genotypes under different protected structures in different seasons. Hence the selection of genotype and structure depending on the season is important. The heterosis breeding is effective in improving hotset traits in tomato. The hybridisation involving one resistant parent can generate bacterial wilt resistant off-springs. The application of molecular markers can effectively reduce the time and labour intensive field evaluation.