Multi-year analyses on three populations reveal the first stable QTLs for tolerance to rain-induced fruit cracking in sweet cherry (Prunus avium L.)

José Quero-García,Camille Branchereau,Teresa Barreneche,Philippe Letourmy,José Antonio Campoy,Svetoslav Malchev,Elisabeth Dirlewanger

doi:10.1038/s41438-021-00571-6

Abstract

Rain-induced fruit cracking is a major problem in sweet cherry cultivation. Basic research has been conducted to disentangle the physiological and mechanistic bases of this complex phenomenon, whereas genetic studies have lagged behind. The objective of this work was to disentangle the genetic determinism of rain-induced fruit cracking. We hypothesized that a large genetic variation would be revealed, by visual field observations conducted on mapping populations derived from well-contrasted cultivars for cracking tolerance. Three populations were evaluated over 7–8 years by estimating the proportion of cracked fruits for each genotype at maturity, at three different areas of the sweet cherry fruit: pistillar end, stem end, and fruit side. An original approach was adopted to integrate, within simple linear models, covariates potentially related to cracking, such as rainfall accumulation before harvest, fruit weight, and firmness. We found the first stable quantitative trait loci (QTLs) for cherry fruit cracking, explaining percentages of phenotypic variance above 20%, for each of these three types of cracking tolerance, in different linkage groups, confirming the high complexity of this trait. For these and other QTLs, further analyses suggested the existence of at least two-linked QTLs in each linkage group, some of which showed confidence intervals close to 5 cM. These promising results open the possibility of developing marker-assisted selection strategies to select cracking-tolerant sweet cherry cultivars. Further studies are needed to confirm the stability of the reported QTLs over different genetic backgrounds and environments and to narrow down the QTL confidence intervals, allowing the exploration of underlying candidate genes.

Highlights

Rain-induced fruit cracking has been traditionally considered as one of the most important agronomic problems in sweet cherry cultivation
For the first time, cracking was decomposed into three main regions of the sweet cherry surface: Pistillar end (PE), Stem end (SE), and Fruit side (FS). The usefulness of this strategy was further confirmed by the identification of different Quantitative trait locus (QTL) underlying the variation of each of these three types of cracking, several QTL colocalizations for different traits were hypothesized
By working with three different mapping populations, at least one stable region was identified for each type of cracking, in three different linkage group (LG) (2, 4, and 5), and explaining each a minimum of 20% of the phenotypic variance during 1 year of the study

Summary

Introduction

Rain-induced fruit cracking has been traditionally considered as one of the most important agronomic problems in sweet cherry cultivation. Quero-García et al Horticulture Research (2021)8:136 hypothesis, referred to as the ‘critical turgor’ hypothesis These conclusions were further supported by a study which proved that a sweet cherry fruit was far from behaving as an ideal osmometer[11]. A different model was proposed in which cracking would be the result of a local defect, which in turn would provoke a zipper-type propagation in order to form a crack[8] In line with this new ‘Zipper’ hypothesis/ model, it was demonstrated that cell wall swelling, which favors fracture of epidermal cell walls, appears to be an early, critical, and essential step in a reaction of events, leading to cracking[14]. This finding was consistent with the Zipper model since the development of microcracks into macrocracks requires continuity of surface wetness on the fruit area[19]

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