Masoud Ahmadi-Afzadi

European pome fruit genetic resources evaluated for disease resistance

Pome fruit genetic resources collections constitute a highly valuable resource not only for fruit breeding but also for direct use by nurseries, growers, and home gardeners. In order to use these resources efficiently and sustainably, reliable evaluation data on fruit and tree characteristics must be generated. Here we focus on pome fruit genetic resources evaluated phenotypically and genotypically for susceptibility to apple scab (Venturiainaequalis), powdery mildew (Podosphaeraleucotricha), fire blight (Erwiniaamylovora), pear rust (Gymnosporangiumsabinae) and storage diseases (e.g., Penicilliumexpansum). Examples are presented of several ongoing projects throughout Europe, with the aim to evaluate fruit genetic resources for disease susceptibility and potential use in breeding and for commercial use. The COST action 864 has fostered international cooperation in the evaluation of pome fruit genetic resources, and some of these evaluations therefore involve research groups from several of the participating countries.

DNA marker-assisted evaluation of fruit firmness at harvest and post-harvest fruit softening in a diverse apple germplasm

Several different genes have been proposed as responsible for fruit texture variability at harvest and/or after storage. We have analysed 127 apple cultivars for allelic composition in two key genes that are directly involved in the ethylene biosynthesis pathway, Md-ACS1 and Md-ACO1, and two other genes that are involved in cell wall degradation, Md-Exp7 and Md-PG1. Firmness was measured with a penetrometer at harvest and after 6 or 12xa0weeks (early- and late-maturing cultivars, respectively) of cold storage. Maturation time was positively correlated with firmness at harvest and negatively correlated with fruit softening rate (difference between firmness at harvest and after storage, divided by number of weeks in storage). Polyploid cultivars showed significantly higher firmness at harvest compared to diploids. Alleles previously described as responsible for good texture were associated with significantly lower softening for Md-ACS1 and Md-PG1, but the opposite was noted for Md-EXP7. Results were nonsignificant for Md-ACO1. Allele frequencies were very uneven in all four loci, with the three most common multi-locus configurations accounting for 64xa0% of the entire material. The predictive power of these genes was calculated with a partial least squares discriminant analysis, and these accounted for 15xa0% of the observed variation in initial firmness and 18xa0% for softening rate. Inclusion of maturation time, storage time (i.e. 6 or 12xa0weeks) and initial firmness into the model however increased the predictability of softening rate to 38xa0%. Dividing the material in modern (released after 1960) and old cultivars did not change the outcome of our analyses.

Alkylresorcinols isolated from rye bran by supercritical fluid of carbon dioxide and suspended in a food-grade emulsion show activity against Penicillium expansum on apples

Apple cultivars are attacked by many fungal diseases, both on the tree and during storage. One of the most serious is blue mould, caused by Penicillium expansum. In this study, 5-(n)-alkylresorcinols (AR) were isolated from rye bran by the supercritical fluid of carbon dioxide and were used for the preparation of bioactive emulsions. These emulsions were applied to harvested fruit of five apple varieties to determine the levels of antifungal activity. A significant inhibition of disease symptoms was obtained after spraying some of the prepared AR emulsions on fruits that had been experimentally infected with Penicillium expansum. The most effective emulsions consisted of 0.025% (m/v) ARs, 0.1% (m/v) xanthan gum, 0.5% (m/v) Synperonic 91/6 or PDMs-copolymer, 0.2% (m/v) Tween 20, 1% (m/v) Trioleate, 2% (m/v) oleylalcohol, 2% (m/v) PEG 400, 5% (m/v) CaCl2 or NaCl suspended in water.

Genome-wide expression analysis suggests a role for jasmonates in the resistance to blue mold in apple

Blue mold, caused by the necrotrophic fungal pathogen Penicillium expansum, causes serious postharvest losses in apple, and threatens human health through production of the potent mycotoxin patulin. Recent studies indicate a quantitative control of resistance against this disease in apple cultivars. A whole genome apple microarray covering 60k transcripts was used to identify gene(s) that appear to be differentially regulated between resistant and susceptible cultivars in P. expansum-infected fruits. A number of potential candidates was encountered among defense- and oxidative stress-related genes, cell wall modification and lignification genes, and genes related to localization and transport. Induction of one cell wall-related gene and three genes involved in the ‘down-stream’ flavonoid biosynthesis pathway, demonstrates the fundamental role of the cell wall as an important barrier, and suggests that fruit flavonoids are involved in the resistance to blue mold. Moreover, exogenous application of the plant hormone methyl jasmonate (MeJA) reduced the symptoms resulting from inoculating apples with P. expansum. This is the first report linking MeJA and activation of cell wall and flavonoid pathway genes to resistance against blue mold in a study comparing different cultivars of domesticated apple. Our results provide an initial categorization of genes that are potentially involved in the resistance mechanism, and should be useful for developing tools for gene marker-assisted breeding of apple cultivars with an improved resistance to blue mold.