The mechanism of differential susceptibility to alternaria black spot, caused by Alternaria alternata, of stem- and bottom-end tissues of persimmon fruit

• Susceptibility to Alternaria alternata was characterized by increased colonization of stem-end persimmon fruit tissue.
• The stem-end part of the fruit had greater production of ethylene and CO2.
• The stem-end part of the fruit had increased cracked areas and A. alternata development.
• The stem-end part of the fruit had reduced chlorophyll values suggesting early maturation.

In Israel, alternaria black spot (ABS), caused by Alternaria alternata, is the main postharvest factor that reduces quality and impairs storability of persimmon fruit Diospyros kaki cv. Triumph. The fungus infects the fruit in the orchard and remains quiescent until harvest, or starts development just before harvest, following rain or high humidity. During 2–3 months of storage at 0 °C, the pathogen colonizes the fruit, eliciting ABS symptoms. Susceptibility of the fruit to A. alternata attack is characterized by colonization in the upper, stem-end tissue, in contrast to lack of development at the bottom end. Comparison between the physiology of the stem-end and the bottom-end tissues showed greater production of ethylene and CO2 in the former during early stages of fruit growth, and greater cracked areas and reduced chlorophyll levels in the later stages of growth, before harvest. Increasing fruit weight by increasing irrigation in the orchard enhanced the cracked area and susceptibility to ABS during growth and at harvest. Wound inoculation enhanced ABS colonization in both ends of the fruit, but more significantly in the upper stem end. The present results suggest that the differential susceptibility to ABS during storage is caused by a differential ripening process, and possibly, by increased maturity at the stem end, leading to cracking and increased ABS development.