New Mexican-type chile peppers are susceptible to a fruit rot caused by Alternaria alternata. Experiments were conducted to determine the relationship between the rate of decay from A. alternata and chile pepper maturity. Flowers were tagged at anthesis, and peppers were harvested on a weekly basis, wounded, and inoculated with a conidial suspension of A. alternata. Alternaria disease severity increased as peppers matured and ripened, with the largest lesions occurring on fruits harvested 61 days after flowering. This harvest date corresponded to the period when peppers were turning red, total sugar content peaked (13.0 mg/ml), and reducing sugar content increased fourfold. The seasonal data were confirmed by the differential reaction of peppers from four maturity stages to A. alternata decay. Ten days after inoculation, green peppers had small lesions averaging 6.7 mm in diameter. Peppers that were 10% red, 50% red, or 100% red had mean lesion diameters of 17.5, 23.2, and 22.3 mm, respectively. When A. alternata was cultured on fruit extracts from chile peppers at different maturity stages, mycelial dry weights were greatest on extracts from 100% red and 50% red fruit, in which the total and reducing sugar contents were highest. A. alternata showed little preferential growth among media amended with cell walls extracted from chile peppers at the four maturity stages.
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