Susceptibility of Pistachio Male Cultivars to Botrytis Blossom and Shoot Blight Caused by Botrytis cinerea. Themis J. Michailides, Assistant Research Plant Pathologist, Department of Plant Pathology, University of California, Berkeley, Kearney Agricultural Center, Parlier 93648. Plant Dis. 75:410-415. Accepted for publication 18 October 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0410.

The pistachio (Pistacia vera) male cultivars 02-16 and 02-18 showed higher levels of Botrytis blossom and shoot blight caused by Botrytis cinerea, had more inflorescences 1 mo after blooming, and retained more inflorescences 10 mo after blooming than did the cultivar Peters. When shoots were inoculated, more shoots of 02-16 and 02-18 than of Peters became blighted, and significantly larger cankers developed. Inoculation of inflorescences with either a spore suspension or mycelial plugs of B. cinerea caused more shoots on 02-16 than on Peters to become blighted, and cankers that originated from the inoculated inflorescences were significantly larger on 02-16. In both experiments (inoculation of shoots and inflorescences), the cultivar 02-18 was intermediate in susceptibility to infection by B. cinerea. Agar media amended with ground, unwashed or washed inflorescences of 02-16 supported better growth and sporulation of B. cinerea than media amended with unwashed or washed inflorescences of Peters. The inflorescences of 02-16 and 02-18 are significantly larger, contain more pollen grains, retain significantly more water, and dry more slowly than those of Peters. Saturated inflorescences of 02-16 and 02-18 required 4 days to dry to 1–2% moisture, compared with 2 days for inflorescences of Peters. In addition, inflorescences of 02-16 and 02-18 are bulkier and more firmly attached to the supporting shoots than are those of Peters. The greater susceptibility of 02-16 and 02-18 to infections by B. cinerea stems from more extensive colonization of shoots, more available infection sites that are richer in nutrients, and more favorable conditions for infection.

Keyword(s): gray mold, resistance.