Molecular basis of water soaking of strawberry

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Strawberry is a highly perishable fruit crop species of global importance. The quality of field-grown strawberries is often severely compromised by rain. An important disorder arising from rain is ‘water soaking’. The symptomatic fruit surface has a light greyish color and a translucent and deliquescent appearance. Water soaking is associated with microcracking of the cuticle and anthocyanin leakage from the epidermal cells. The incidence of fruit rots pre- and postharvest is also increased causing significant economic loss. As a result, strawberry production is shifting from open-field, to semi- or fully-protected in plastic tunnels or greenhouses. Genotypes differ in susceptibility to water soaking. The physiological, genetic and molecular bases for such differences are not understood. The objective of the project is to determine the bases of the differential susceptibility of genotypes. (1) We will establish a developmental time course of differential gene expression (RNA-seq), water soaking, cuticle deposition, strain development and microcracking for a pair of parental genotypes selected for their contrasting susceptibilities to water soaking. (2) The parental genotypes will be crossed to produce an F1-population (200 individuals) to perform (i) phenotyping of the segregating F1-population for susceptibility to water soaking, (ii) genotyping for developing genetic linkage maps, (iii) QTL analyses and (iv) develop PCR-based molecular markers flanking the QTL regions for marker-assisted breeding. (3) We will select the most promising candidate genes (CGs) and compare the CGs identified by differential gene expression with those located in the QTL regions. This will allow establishment of a first molecular model for tolerance to water soaking. The model including the identified CGs will be verified by further expression studies using qRT-PCR in independent growing seasons. Finally, we will sequence the most promising CGs in parental genotypes, identify structural variations and develop PCR-based markers for the detection of selected structural variations. The structural variations and their association with water soaking will be verified using the F1-population. These results will help identify the genetic and molecular bases of susceptibility to water soaking in strawberry. Furthermore, provided that significant QTLs are found, new strawberry cultivars that are less susceptible to water soaking may be developed. In addition, these cultivars are likely to be less prone to fruit rots. As a consequence, the sustainability of strawberry production in the open field will be improved.