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  • Author or Editor: Kim S. Lewers x
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Raspberries are a delicate, high-value crop with an extremely short shelf life exacerbated by postharvest decay caused by Botrytis cinerea Pers. European red raspberry (Rubus idaeus L.) is the most widely grown variety. Yellow (R. idaeus L.), black (R. occidentalis L.), and purple raspberries (R. ×neglectus Peck. or R. occidentalis ×idaeus hybrids) are available mainly at local markets and U-pick farms. To compare the postharvest quality of the raspberry color groups, pesticide-free fruit from cultivars and breeding selections of red, yellow, purple, and black raspberries were examined for oxygen radical absorbance capacity (ORAC), phenolics, anthocyanins, soluble solids, titratable acids, pH, color, firmness, decay and juice leakage rates, ethylene evolution, and respiration. There were significant correlations between decay rate and physiochemical properties. Both decay and leakage rates were correlated with weather conditions before harvest, but each color group responded differently to different weather factors. There were no correlations among changes in color, firmness, decay, or juice leakage rates. All the other color groups were less acidic than the familiar red raspberry. Yellow raspberries had the worst decay rates but the best leakage rates. Black and purple raspberries, with the highest phenolics and anthocyanins and the lowest ethylene evolution rates, resisted decay the longest but bled soonest.

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Diseases affecting strawberries have been of major concern in recent years because of their widespread occurrence and potential for yield loss. Anthracnose caused by the fungus Colletotrichum acutatum is one of the most serious disases of strawberry worldwide. Although chemical controls are being used to treat anthracnose, generating disease resistant plants is a more attractive solution to the problem because chemicals can pose a health hazard, have a negative impact on the environment and may only be moderately effective. Tissue culture-induced (somaclonal) variation provides us with one strategy for generating disease-resistant genotypes. An in vitro screening system was used to evaluate several commercially important cultivars, Chandler, Delmarvel, Honeoye, Latestar, Pelican and Sweet Charlie, and shoots regenerated from leaf explants of these cultivars for resistance to C. acutatum isolate Goff (highly virulent). Somaclones with increased levels of anthracnose resistance were identified for all the cultivars. The greatest increases in disease resistance were observed for somaclones of cultivars Chandler, Pelican and Sweet Charlie that exhibited 6.8-, 12-, and 4.2-fold increases in resistance, respectively. These studies provide evidence that: 1) in vitro screening can be used to evaluate strawberry germplasm for anthracnose resistance, 2) soma-clonal variation is influenced by stawberry genotype, and 3) generating somaclonal variants may be a feasible approach to obtaining strawberry plants with increased levels of anthracnose resistance.

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