Identification of new sources of heat tolerance in cultivated and wild tomatoes

Abstract

Heat stress adversely affects tomato production worldwide. Breeding thermotolerant varieties is critical to adapt to increased heat stress but tomato has a narrow genetic base for heat tolerance. Identification of new sources of heat-tolerant germplasm is important to understand physiological and molecular mechanisms of adaptation to heat stress and to broaden the genetic base of heat tolerance in tomato. Here, we screened a germplasm collection comprised of 42 tomato entries using 19 quantitative (physiological, reproductive, and morphological) and five qualitative traits. The plants were grown under long term mild heat stress with temperatures and relative humidities ranging from 23.3 to 37 °C, and 47 to 100%, respectively. The analysis of variance revealed significant differences among the entries for all the quantitative traits. Biologically significant associations were recorded for many traits. Proportion of viable pollen was not associated with fruit set percentage. The clustering analysis groups the germplasm into five clusters with a clear distinction between Solanum lycopersicum and Solanum pimpinellifolium entries. We also observed differences between the entries based on their origins. Known thermo-tolerant entries were found in Clusters 3 (eg.: LA2662, LA3317, LA3120) and 4 (e.g.: CL5915-93D4-1-0, CLN1621L, LA2661). Lines BJ01, BJ02 from Republic of Benin, and WAC1 and ATS020 from Ghana in Cluster 3 are potential new sources of thermo-tolerance in tomato. Generation of hybrids from parents belonging to the clusters 1 to 4 identified in this study would improve heterosis for heat tolerance traits in tomato. Useful traits like high pollen viability and high inflorescence numbers per plant could be introgressed from S. pimpinellifolium entries into the cultivated tomato. Our study provides important information to improve heat tolerance in tomato.