The ascospore production season ofVenturia inaequalis(Cke.) Wint., the apple black spot fungus

Abstract

Ascospore production by Vel1ll/ria illa('qllalis (Cke.) Wint. on overwintered apple leaves was tested through spring and early summer in Nelson. Test leaves were wetted in a wind tunnel and the released ascospores were trapped and counted.

Discharge ofVenturia inaequalisascospores during daytime and nighttime wetting periods in Ontario and Nova Scotia

“…While this study agrees with previous reports (Brook 1966, 1969a, MacHardy & Gadoury 1986) that light stimulates ascospore release of V. inaequalis, it disagrees with MacHardy and Gadoury's observation that no spores are captured until morning when rainfall begins after 1800 h (MacHardy & Gadoury 1986). The numbers and density of ascospores trapped in the S.E.F.…”

“…The primary factors affecting ascospore release were considered to be leaf wetness and temperature. Brook (1966Brook ( , 1969a and MacHardy and Gadoury (1986) reported that light also affects ascospore discharge. Red light with wavelengths between 710 and 730 nm was responsible for stimulating ascospore release (Brook 1969b).…”

Seasonal pattern of maturation ofVenturia inaequalisascospores in New Zealand

“…Generally, leaf-wetness periods would have been longer than the rain periods, allowing greater ascospore discharge than was calculated. Rain periods between sunset and sunrise were ignored because ascospore discharge by V. inaequalis is negligible in darkness (Brook 1969a(Brook , 1969b. Times of sunrise and sunset were obtained from N.Z.…”

“…The apparatus for testing ascospore discharge (Brook 1966) comprised wind tunnel; impactor; and microscope slide coated with petroleum jelly; and vacuum pump which drew 15 l/rnin, giving an airspeed of 11 cmls over the leaves. At each locality the apparatus was set up indoors in natural light.…”

“…Maximum activity in all four districts occurred during the last week of September and the first 2 weeks of October. In Nelson Brook (1966) found mature ascospores from early September 1965 until January 1966, maximum numbers occurring during October.…”