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Wind Scab of French Prune: Symptomatology and Predisposition to Preharvest and Postharvest Fungal Decay. Themis J. Michailides, Associate Plant Pathologist, University of California Davis, Kearney Agricultural Center, Parlier 93648. David P. Morgan, Staff Research Associate, Department of Plant Pathology, University of California Davis, Kearney Agricultural Center, Parlier 93648. Plant Dis. 77:90-95. Accepted for publication 21 August 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0090.

Severe scabbing, termed wind scab (WS), of French prune (Prunus domestica 'French') was caused by developing fruit rubbing against other fruit, leaves, and shoots during strong wind gusts prevailing from north to northwest. WS occurred only during years in which north or northwest winds exceeded 20 km/hr for at least 10 days within 3 wk after full bloom. The affected areas developed several layers of cutinized cells, the outer layers showing deep fractures that retained moisture and facilitated germination of fungal spores and penetration by their germ tubes. Both incidence and severity of WS on mature fruit correlated positively (R2 = 0.720.91 and 0.94, respectively) with the incidence and severity of WS on dehydrated fruit. Surfaces of wind-scabbed areas acted as traps in collecting fungal propagules. The incidence of decay caused by Phomopsis cinerascens was significantly higher in fruit with WS. Although germinated spores of P. cinerascens could penetrate directly through the epidermal layers of unwounded ripe and overripe prune fruit, wounds or cracks on wind-scabbed fruit facilitated infection. WS resulted in yearly average percentages of off-graded prunes equivalent to those of russet scab, as determined by commercial inspectors.

Keyword(s): environment, wind bruise.