Abstract
Global warming has become a worldwide concern due to its adverse effects on agricultural output. In particular, long-term mildly high temperatures interfere with sexual reproduction and thus fruit and seed set. To uncover the genetic basis of observed variation in tolerance against heat, a bi-parental F2 mapping population from two contrasting cultivars, i.e. Nagcarlang and NCHS-1, was generated and phenotyped under continuous mild heat conditions for a number of traits underlying reproductive success, i.e. pollen viability, pollen number, style length, anther length, style protrusion, female fertility and flowering characteristics, i.e. inflorescence number and flowers per inflorescence. Quantitative trait loci (QTLs) were identified for most of these traits, including a single, highly significant one for pollen viability, which accounted for 36% of phenotypic variation in the population and modified pollen viability under high temperature with around 20%. QTLs for some traits colocalised, indicating trait dependency or pleiotropic-effect loci. We conclude that a limited set of major genes determines differences in performance of reproductive traits under continuous mild heat in tomato. The results contribute to our fundamental understanding of pollen thermotolerance and may support development of more heat-tolerant tomato varieties.
Highlights
High temperature is one of the major abiotic stress factors affecting plants, having adverse effects on both growth and reproduction
Plants were grown under standard greenhouse conditions with a 16-h light period and a temperature of around 25 °C in the day and 19 °C in the night
As tomato seed and fruit set under high temperature are complex traits, which reduces the power of QTL mapping, we analysed various subtraits known to contribute to reproductive success under high temperature, i.e. pollen viability (PV), pollen number (PN), anther length (AL), style length (SL), SP from the anther cone and female fertility (FF)
Summary
High temperature is one of the major abiotic stress factors affecting plants, having adverse effects on both growth and reproduction. When considering long-term mildly high temperatures, representative of heat waves, life cycle stages clearly differ from each other regarding their sensitivity, with reproductive processes found to be more vulnerable than vegetative ones (Hall 1992). This vulnerability applies especially to the meiotic to early microspore stages during pollen development, and early embryo development at 1–3 days after fertilisation (Hedhly et al 2009; Giorno et al 2013; Bac-Molenaar et al 2015; Müller and Rieu 2016). The underlying causal genes and their physiological effects have not yet been reported
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