During ripening of grape (Vitis labruscana L. cv Concord) berries, abundance of several proteins increased, coordinately with hexoses, to the extent that these became the predominant proteins in the ovary. These proteins have been identified by N-terminal amino acid-sequence analysis and/or function to be a thaumatin-like protein (grape osmotin), a lipid-transfer protein, and a basic and an acidic chitinase. The basic chitinase and grape osmotin exhibited activities against the principal grape fungal pathogens Guignardia bidwellii and Botrytis cinerea based on in vitro growth assays. The growth-inhibiting activity of the antifungal proteins was substantial at levels comparable to those that accumulate in the ripening fruit, and these activities were enhanced by as much as 70% in the presence of 1 M glucose, a physiological hexose concentration in berries. The simultaneous accumulation of the antifungal proteins and sugars during berry ripening was correlated with the characteristic development of pathogen resistance that occurs in fruits during ripening. Taken together, accumulation of these proteins, in combination with sugars, appears to constitute a novel, developmentally regulated defense mechanism against phytopathogens in the maturing fruit.

Controlled environment experiments were conducted to determine the influence of temperature and leaf wetness duration on infection of perennial ryegrass by Rhizoctonia solani. Infection of grass plants raised in pots and exposed to mycelium of R. solani was evaluated at various combinations of temperature and leaf wetness duration. Temperatures included 15, 18, 21, 24, and 27°C. Leaf wetness periods were 9, 12, 15, 18, and 24 h. Disease was most severe (more than 50 leaves with brown patch lesions per pot) when plants were in contact with the inoculum source for 24 h of leaf wetness at 24°C. The least amount of disease (0 leaves with lesions per pot) occurred at 15°C and a 9-h wet period. The data were subjected to analysis of variance with orthogonal polynomial contrasts. Significant effects were included in a regression model that described the response of infection to temperature and wetness duration. The polynomial model included linear and quadratic terms for temperature and wetness duration. The adjusted coefficient of determination for the fitted model was 0.93, indicating an excellent fit to the data. The model is intended for use in an improved brown patch warning system for perennial ryegrass in the midwestern United States.

No abstract

No abstract