Screening of tomato (Solanum lycopersicum L.) genotypes for high temperature tolerance

Abstract

Tomato (Solanum lycopersicum L., 2n=24) cultivation is prevalent in both tropical and sub-tropical climates. For optimum yield and quality, the crop needs a climate that is dry and fairly cold, and are sensitive to hot and humid climate. In the current context of global warming, high temperature is considered as a major threat to agriculture with profound consequences on yield and quality. Plant morphology, physiology, biochemistry, and molecular pathways are disrupted by heat stress. The optimum temperature range for fruiting in tomato is narrow viz., 15 to 21 °C at night and 30 to 35 °C during the day. Depending on the stage of growth, a daily mean temperature between 21 and 24 °C is ideal for tomato. The current study, ‘Screening of tomato (Solanum lycopersicum L.) genotypes for high temperature tolerance’ was conducted during 2021–2023 at the Department of Plant Breeding and Genetics, College of Agriculture, Vellanikkara. Thirteen NBPGR accessions, four hybrids from IIHR, Bengaluru, eight improved lines from the World Vegetable Centre, Taiwan, and five KAU varieties made up the 30 tomato genotypes used in the study. Genotypes were subjected to laboratory screening for thermotolerant traits, and selected genotypes were taken for polyhouse screening. Field screening was done during summer for evaluating the performance of all the genotypes for thermotolerance and yield traits. All experiments were laid out in completely randomized design with three replications for laboratory and polyhouse screening, and two replications for field screening. Physiological traits (electrolyte leakage and membrane stability) and morphological traits (pollen viability, pollen germination, style length and style protrusion) were evaluated under laboratory and polyhouse screening. Plant height and yield characters (days to 50 per cent flowering, fruit set per cent, deformed fruits per cent, number of fruits per plant, average fruit weight and fruit yield per plant) were recorded under field screening along with morphological traits. Arka Samrat, EC 538153, AVTO 1314, and Manuprabha were superior genotypes for electrolyte leakage and membrane thermostability under laboratory screening. EC 528368, EC 620486, Akshaya, and Vellayani Vijay outperformed other varieties in terms of pollen viability and germination at 40 ℃. Superior genotypes based on pollen viability and style protrusion were EC 315489, EC 523851, EC 528368, EC 538153, EC 567305, EC 620486, EC 620488, EC 636872, AVTO 0922, AVTO 1725 and Vellayani Vijay. Based on style protrusion and pollen germination at 40 ℃, and their combination with other traits, 14 genotypes (AVTO 1702, AVTO 1706, AVTO 1725, AVTO 1726, EC 315489, EC 538153, EC 549819, EC 620428, EC 620486, EC 620488, EC 620494, EC 636872, Manulakshmi, and Vellayani Vijay) were selected for polyhouse evaluation. Polyhouse screening was done inside a non-ventilated structure to ensure temperature build up, and an increase of 4-5℃ was found inside the structure compared to ambient condition. All genotypes showed a decrease in pollen viability and germination under polyhouse compared to the open condition. All the genotypes, except Vellayani Vijay showed an increase in style protrusion. Superior genotypes with respect to electrolyte leakage were AVTO 1725, AVTO 1702, AVTO 1706, EC 620428, EC 538153, and Manulakshmi. EC 549819, EC 620428, and EC 636872 were considered as superior genotypes based on style protrusion and pollen germination, as they are important thermotolerant traits. Field screening was carried out to assess the yield traits along with thermotolerant traits in summer season. EC 528360 was found to be superior in pollen viability and style length. Style protrusion increased in all breeding lines and hybrids, except EC accessions. Genotypes like Akshaya, Arka Rakshak, AVTO 1314, and EC 636872 were significantly superior for fruit set percentage compared to Vellayani Vijay. Deformed fruits percentage showed no significant variation between genotypes, and was more than 80 per cent for every genotype examined. Vellayani Vijay and EC 636872 exhibited higher fruit number per plant. Arka Rakshak had a significantly higher average fruit weight than all other genotypes. Pollen viability, style protrusion, number of fruits per plant, fruit set, average fruit weight, and fruit yield per plant all demonstrated high GCV and PCV. The GAM and high heritability of the remaining characters suggested that they had additive gene effects and can be used for selection. Correlation analysis of observations recorded for field screening showed that style length and style protrusion had a significant positive correlation with fruit set per cent, average fruit weight and fruit yield per plant. Molecular markers did not reveal polymorphism in the present study and needs further investigation to identify reliable markers. AVTO 0922, EC 523851, EC 528368, EC 549819, EC 620494, EC 636872, and Vellayani Vijay were identified as heat-tolerant genotypes based on laboratory, polyhouse, and open field evaluations. Akshaya, Anagha, Arka Rakshak, AVTO 0301, AVTO 1314, AVTO 1707, Manuprabha, and Vellayani Vijay had higher yields and, with the exception of AVTO 0301, all had high fruit set percentage in the summer season. In general, thermotolerant genotypes performed moderate to poor in terms of yield traits. Hence, the study demonstrated that specific donors for thermotolerance traits and yield traits needs to be included in crop improvement programmes for heat tolerance in tomato. Vellayani Vijay had heat tolerance traits as well as superior yield traits indicating its suitability for incorporation in crop improvement programmes.