Abstract
Heat is a major abiotic stress that seriously affects watermelon (Citrullus lanatus) production. However, its effects may be mitigated through grafting watermelon to heat tolerant bottle gourd (Lagenaria siceraria) rootstocks. Understanding the genetic basis of heat tolerance and development of reliable DNA markers to indirectly select for the trait are necessary in breeding for new varieties with heat tolerance. The objectives of this study were to investigate the inheritance of heat tolerance and identify molecular markers associated with heat tolerance in bottle gourd. A segregating F2 population was developed from a cross between two heat tolerant and sensitive inbred lines. The population was phenotyped for relative electrical conductivity (REC) upon high temperature treatment which was used as an indicator for heat tolerance. QTL-seq was performed to identify regions associated with heat tolerance. We found that REC-based heat tolerance in this population exhibited recessive inheritance. Seven heat-tolerant quantitative trait loci (qHT1.1, qHT2.1, qHT2.2, qHT5.1, qHT6.1, qHT7.1, and qHT8.1) were identified with qHT2.1 being a promising major-effect QTL. In the qHT2.1 region, we identified three non-synonymous SNPs that were potentially associated with heat tolerance. These SNPs were located in the genes that may play roles in pollen sterility, intracellular transport, and signal recognition. Association of the three SNPs with heat tolerance was verified in segregating F2 populations, which could be candidate markers for marker assisted selection for heat tolerance in bottle gourd. The qHT2.1 region is an important finding that may be used for fine mapping and discovery of novel genes associated with heat tolerance in bottle gourd.
Highlights
Heat stress negatively affects physiological processes, reproduction, and adaptation in crop plants, which are exacerbated by global climate change [1,2]
There have been attempts to deconstruct stress tolerance into measurable components for accurate phenotyping, with the aim that quantitative trait loci (QTL) associated with heat tolerance may be identified and suitable alleles may be introgressed into elite genetic backgrounds [6]
Understanding the genetic basis of heat tolerance and development of reliable DNA markers to indirectly select for the trait are important in breeding for new varieties with heat tolerance
Summary
Heat stress negatively affects physiological processes, reproduction, and adaptation in crop plants, which are exacerbated by global climate change [1,2]. Lanatus, is an important vegetable crop worldwide [3]. QTL-Seq identifies QTL for relative electrical conductivity associated with heat tolerance in bottle gourd (> 35 ̊C) during the summer months [4]. There have been attempts to deconstruct stress tolerance into measurable components for accurate phenotyping, with the aim that QTL associated with heat tolerance may be identified and suitable alleles may be introgressed into elite genetic backgrounds [6]. Cell membrane stability as an indicator of heat stress may be quantified by relative electrical conductivity (REC). REC is highly sensitive to abiotic stress [7,8] and has been used in studies of abiotic stress tolerance in a range of crops, including salinity-alkalinity tolerance in muskmelon [9], drought tolerance in Perennial ryegrass [10], and cold tolerance in alfalfa [11]
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