CORRELATION OF RESISTANCE AND SUSCEPTIBILITY OF CITRUS TO ALTERNARIA-ALTERNATA WITH SENSITIVITY TO HOST-SPECIFIC TOXINS

The host ranges of the rough lemon pathotype and the tangerine pathotype of Alternaria alternata, cause of brown spot disease of citrus, were determined by use of inoculations and by reaction to their host-specific toxins (ACR-toxin I, ACT-toxin Ib). Of 67 species, cultivars, and hybrids examined, only two (rough lemon, Citrus jambhiri, and Rangpur lime, Citrus limonia) were susceptible to the rough lemon pathotype and sensitive to its toxin. In contrast, 28 citrus species and cultivars were susceptible to the tangerine pathotype and sensitive to its toxin; these included susceptible genotypes of grapefruit, tangerine (mandarin), tangelo, tangelolo, tangerine-tangelo, and tangor.