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Radboud University Nijmegen (2018)

From flower to fruit in the heat - Reproductive thermotolerance in tomato and its wild relatives

Driedonks, N.J.W.

Titre : From flower to fruit in the heat - Reproductive thermotolerance in tomato and its wild relatives

Auteur : Driedonks, N.J.W.

Université de soutenance : Radboud University Nijmegen

Grade : Doctor 2018

Résumé partiel
Ambient temperatures are rising and the frequency and intensity of heat waves have become a serious worldwide problem for agricultural output. The main reason for this is the low reproductive success under elevated temperatures. Current alterations in agricultural management systems are insufficient to sustain yield under these adverse conditions. This is why breeding heat tolerant cultivars is urgent. However, generating thermotolerant crops is a challenging task because heat-wave like long term mild heat (LTMH) affects multiple reproductive related processes and sensitivity to elevated temperature is highly variable across species and developmental stages. In order to obtain a better understanding of what goes wrong under elevated temperature, this study focusses on the genetic architecture and physiological mechanisms underlying reproductive thermotolerance in cultivated and wild tomato species. Chapter 1 provides an overview of the effects of high temperature on plant physiology, fertility and crop yield. Furthermore, it focusses on the negative effects on reproductive tissue of tomato, in particular the male reproductive tissues including the development of viable pollen. Given the narrow genetic diversity in tomato cultivars, exploration of wild relatives and landraces might provide novel resources for thermotolerance. The research in Chapter 2 provides insight in the genetic variation in thermotolerance of various yield contributing traits, to LTMH among wild tomatoes species. Accessions from lower elevations and higher annual temperatures will probably maintain a higher pollen viability (PV) under LTMH, suggesting there has been local adaptation of this reproductive trait. Moreover, several Solanum pimpinellifolium individuals outperformed the best performing cultivar under LTMH in terms of PV. In order to dissect the genetic architecture of reproductive traits, one of these tolerant genotypes from S. pimpinellifolium was crossed with two sensitive genotypes, from S. pimpinellifolium and S. lycopersicum, resulting in two bi-parental F2 mapping populations. Quantitative trait loci (QTL) analyses in these populations revealed multiple QTLs regarding the number of pollen, PV, anther and style length, and style protrusion under LTMH (Chapter 3). Several QTLs of different traits colocalised within the population and mirrored the phenotypic relation. In contrast, none of the QTLs co-localised between the populations, suggesting epistatic interactions or a lack of segregation of QTL alleles in one of the two populations. The complex character of PV under LTMH was further emphasised as verification of the respective interspecific QTLs in F3 and near isogenic lines (NILs) ; each QTL could only be confirmed in either F3 plants or NILs, but not in both. This implies the influence of the genetic background or subtle changes in the environment, in which the trait is studied. As with many quantitative traits, it suggests that breeding for pollen thermotolerance will be challenging. However, the presence of beneficial genetic regions, deriving from the large variation present in wild species, can be detected and might be further exploitable

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Page publiée le 27 octobre 2018