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

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 cost-effective, 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

Mapping and genetic dissection of QTL influencing bitter pit symptoms in apple (Malus ×domestica)

Bitter pit is the most economically important physiological disorder affecting apple fruit production. Brown pits develop in the cortical apple flesh – due to the breakdown of the cell plasma membranes – especially during storage, rendering the fruit unmarketable. Environmental conditions and cultural practices play a role in symptom expression, and there is a link between the severity of symptoms and relative concentrations of calcium in the fruit, leading to the application of calcium sprays and dips; however, these are not completely effective. Cultivars vary in susceptibility and thus there is scope for breeding for resistance. In this investigation, we have identified two major QTL controlling bitter pit symptom expression in four large apple mapping populations. The QTL intervals were defined using SSR and SNP markers, and candidate genes from both intervals were characterised. The markers identified will be useful for marker assisted selection in programmes for the genetic improvement of cultivated apple

Estimating soil moisture by electrical resistance measurements

On perpendicular to the row transects in eight Trentino vineyards, we measured electrical resistance in the soil in three 70 cm wide strips and at three depths (0-20 cm, 20-40 cm, 40-60 cm). A custom-made instrument, based on an Arduino single-board microcontroller, transmitted resistance measurements every 15 minutes to the Meteo Centre of San Michele. By using a Richard's pressure plate at 10 kPa (field capacity) and at 1400 kPa (wilting point) we estimated the water available at the three depths. With fixed 50 cm TDR probes inserted vertically near the transects, we measured soil moisture at field capacity and at wilting point. We then perfected an algorithm that, when receiving values of electrical resistance from each layer, gives an output corresponding to soil moistur