Blue mold, caused by the fungus Penicillium expansum, is the scourge of apple breeders and producers throughout the world, causing extensive losses to stored apples. As the familiar saying goes, one bad apple really can spoil the whole bunch—good fruit stored in containers with decaying fruit often absorbs a moldy odor and flavor.
In a survey of the New York market from 1972 to 1984, blue mold caused by Penicillium expansum was the most damaging parasitic postharvest disease of apples. Documented losses from blue mold and other postharvest diseases have focused on the fate of apples in storage, in transit, and in markets, but little information is available on the significant losses that can occur in apples sold to restaurants and in groceries. Despite the severity of this problem, apple breeders have not been able to evaluate new fruit varieties for blue mold resistance because of the apple's gene pool.
A theory called "geography of genes" posits that breeders looking to create mold-resistant apples should obtain breeding seeds, or germplasm, from the fruit's geographic area of origin. The geography of genes theory has assumed particular significance as fruits' natural habitats are quickly being eliminated.
Based on this gene theory and looking for answers to the blue mold problem, Wojciech J. Janisiewicz, a researcher at the U.S. Department of Agriculture's Agricultural Research Service, undertook a study of a new apple germplasm collection from the center of origin in Kazakhstan. The germplasm represents a much broader gene pool and was evaluated for resistance to blue mold. Apples were harvested from trees that were 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.
The objective of the study was to determine disease resistance to postharvest blue mold decay among apples from the Kazakhstan germplasm (Kazak) collection. According to Janisiewicz, "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. This may lead to the utilization of any identified high-resistance germplasm in apple breeding programs using traditional or genetic engineering approaches."
- Janisiewicz, Wojciech J., Saftner, Robert A., Conway, William S., Forsline, Philip L. Preliminary Evaluation of Apple Germplasm from Kazakhstan for Resistance to Postharvest Blue Mold in Fruit Caused by Penicillium expansum. HortScience, 2008; 43: 420-426
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