Identification and validation of a QTL influencing bitter pit symptoms in apple (Malus × domestica)

Abstract

Bitter pit is one of the most economically-important physiological disorders affecting apple fruit production, causing soft discrete pitting of the cortical flesh of the apple fruits, which renders them unmarketable. The disorder is heritable, however the environment and cultural practices play a major role in expression of symptoms. Bitter pit has been shown to be controllable to a certain extent using calcium sprays and dips, however, their use does not entirely prevent the incidence of the disorder.Previously, bitter pit has been shown to be controlled by two dominant genes, and markers on linkage group 16 of the apple genome were identified that were significantly associated with the expression of bitter pit symptoms in a genome wide association study. In this investigation, we identified a major QTL for bitter pit defined by two microsatellite (SSR) markers. The association of the SSRs with the bitter pit locus, and their ability to predict severe symptom expression, was confirmed through screening of individuals with stable phenotypic expression from an additional mapping progeny. The data generated in this current study suggest a two gene model could account for the control of bitter pit symptom expression, however, only one of the loci was detectable, most likely due to dominance of alleles carried by both parents of the mapping progeny used. The SSR markers identified are costeffective, robust and multi-allelic and thus should prove useful for the identification of seedlings with resistance to bitter pit using marker assisted selection in apple breeding programs.

Control efficacy of Ca‐containing foliar fertilizers on bitter pit in bagged ‘Fuji’ apple and effects on the Ca and N contents of apple fruits and leaves

“…Bitter pit is a major problem in the apple-growing industry worldwide and can result in severe economic losses. 1,2,15,16 The universally acknowledged hypothesis associated with BP formation in fruits during production is a deficiency in Ca 2+ due to the improper uptake of nutrients by plants as well as high N content and N/Ca ratios in fruits. 4,7,17 The Ca content, N content, and N/Ca ratio in different parts of pitted apple fruits may be different.…”

“…Bitter pit (BP) is a Ca 2+ deficiency physiological disorder that affects apple fruit production worldwide, especially for bagged apples, and often causes significant economic losses. 1,2 In addition to Ca 2+ , other nutrients, including magnesium (Mg 2+ ), potassium (K + ), boron (B) and nitrogen (N), may play an important role in the development of BP in apple fruits, and commercial apple growers frequently rely on the (K + + Mg 2+ )/Ca 2+ and N/Ca 2+ ratios as guides both for predicting fruit's susceptibility to BP and for deciding the application time of Ca fertilizers. [3][4][5] In general, high Ca and B content is related to a low incidence of BP, especially for moderate and severe BP, whereas high incidence of BP is positively associated with N, K and Mg content.…”

Pale green lethal disorder in apple (Malus) is caused by a mutation in the PHYLLO gene which is essential for phylloquinone (vitamin K1) biosynthesis

“…This area of LG 16 is also a QTL hotspot for phenolic content and diversity (Khan et al 2012). Finally, a major QTL conferring bitter pit resistance is located in an interval surrounding SSR CH05c06 (Buti et al 2015).…”

“…We investigated a possible relationship between the bitter pit resistance QTL and the PGL locus using progeny from a cross between 'Cameo' and 'Jonathan,' which are both PGL carriers. Buti et al (2015) reported that 'Cameo' is not susceptible and demonstrated that the CH05c06 101 bp allele (104 bp in the GDR) segregates with bitter pit resistance. This is the same allele of CH05c06 that segregates with PGL in our mapping population.…”

“…The CH05c06 SSR was mapped to the top of apple Linkage Group (LG) 16 in several independent populations (Celton et al 2009;Fernández-Fernández et al 2008;Patocchi et al 2009). Genes controlling three major economically important traits: fruit acidity (malic acid), phenolic content/diversity, and bitter pit resistance (a calcium-related postharvest disorder) also reside in this region of LG 16 (Bai et al 2012;Khan et al 2012;Buti et al 2015).…”