Preliminary evaluation of apple germplasm from Kazakhstan for resistance to postharvest blue mold in fruit caused by Penicillium expansum

Blue mold of apples, incited by Penicillium expansum, causes extensive losses on stored apples worldwide. Despite the severity of this problem, apple breeders do not evaluate their crosses for resistance to this disease, because there has been little resistance to blue mold in the gene pool of the germplasm used. A new apple germplasm collection from the center of origin in Kazakhstan, maintained in Geneva, NY, and representing a much broader gene pool, was evaluated for resistance to blue mold. Apples were harvested from the Elite collection trees that were clonally propagated from budwood collected in Kazakhstan and from seedling trees originating from seeds of the same trees as the Elite budwood or from other wild seedling trees in Kazakhstan. Fruit from 83 such accessions were harvested at the preclimacteric to climacteric stage, wound-inoculated with A expansum at 10(3), 10(4), and 10(5) mL(-1) conidial suspension, incubated for 5 d at 24 degrees C, and evaluated for decay incidence and severity. Two accessions were classified as immune (no decay at 10(3) and 10(4) mL(-1)), four as resistant (no decay at 103 mL(-1)), 53 as moderately resistant (lesions less than 10 mm at 103 mL(-1)), and 24 as susceptible. There were positive correlations (r = 0.92, 0.86, and 0.91) between decay severity and all three inoculum levels. Our results indicate a greater genetic diversity among the Kazak apple collection than among cultivated apples as evidenced by their broad range of fruit maturity, quality, and disease resistance patterns. The immune and resistant accessions may serve as a source of resistance in breeding programs and can be useful in explaining the mechanism of resistance to blue mold in apples.