A study of gene expression changes at the Bp-2 locus associated with bitter pit symptom expression in apple (Malus pumila)

Abstract

Bitter pit is a physiological disorder of apples that develops in the latter stages of fruit development and during storage. It is characterized by localized necrotic cells that collapse and form pits in the epidermis and outer cortex of fruit. The disorder has been associated with low calcium concentrations, and poor calcium distribution within fruit. The mechanism that leads to individual cell necrosis, while surrounding cells remain healthy, is not fully understood. In order to ascertain the underlying process of bitter pit incidence in apple fruit, a mapping population of 'Braeburn' (susceptible to bitter pit) × 'Cameo' (resistant to bitter pit) was used to map the trait over two growing seasons. A subset of 96 genotypes from the mapping population representing the full range of phenotypes in the same ratio as the full population were selected for genotyping and functional characterization. RNA-Seq analysis on fruits samples of three resistant and three susceptible lines at seven developmental stages (21, 42, 63, 84, 105, 126 and 147 days post fertilization) identified a number of candidate genes displaying differential gene expression. A subset of candidate genes selected based on their position within the identified QTL interval on chromosome 16 validated by RT-qPCR, and two candidate genes displaying differential gene expression were highlighted as strong candidates for the control of bitter pit symptom expression at the Bp-2 locus.

The molecular–physiological functions of mineral macronutrients and their consequences for deficiency symptoms in plants

“…Lee et al (2016) demonstrated that the relationship between intracellular Ca concentration and tipburn in Brassica oleracea differed between genotypes and were correlated with differential expression of a number of transporter and stress response genes. In apple, Ca deficiency is called bitter bit, reflecting that the fruit skin develop pits and that brown spots appear on the skin and/or in flesh, resulting in a bitter taste (Buti et al, 2018;Yu XM et al, 2018). Calcium deficiency in carrot leads to cavity spot, characterised by oval necrotic spots developing into craters.…”

Is calcium deficiency the real cause of bitter pit? A review

“…Not surprisingly, bitter pit is under some degree of genetic control in fruit. Apple breeders and geneticists have tried to understand the relationship between genetic variability and bitter pit occurrence to generate bitter pit-resistant cultivars (Volz et al, 2006;Buti et al, 2018;Mao et al, 2021). Volz et al (2006) identified a genetic component to bitter pit incidence, and this effect was present irrespective of the use of several cropping factors, average fruit weight, or even fruit mineral concentrations.…”

“…Not surprisingly, bitter pit is under some degree of genetic control in fruit. Apple breeders and geneticists have tried to understand the relationship between genetic variability and bitter pit occurrence to generate bitter pit-resistant cultivars ( Volz et al., 2006 ; Buti et al., 2018 ; Mao et al., 2021 ). Volz et al.…”

“…These results suggest that fruit Ca concentration may be useful as an indirect indicator index for bitter pit within, but not among families ( Volz et al., 2006 ). More recently, Buti et al. (2018) obtained two candidate genes (MDP0000263725 and MDP0000300083) for the control of bitter pit symptom expression between susceptible and non-susceptible genotypes in the population.…”