Infection of sunflower leaves by ascospores of Sclerotinia sclerotiomm

Abstract

SUMMARY Ascospores of Sclerotinia sclerotiorum infected fully expanded sunflower leaves in the absence of added nutrients, wounds or senescent tissue. The site of infection was confined to a specific region around the junction of the leaf blade and the petiole and was associated with sites of sucrose secretion by the host. In these areas ascospores germinated and formed extensive colonies on the leaf surface. Simple appressoria were visible at 24 h, and complex appressoria at 48 h, after inoculation. Ascospores that germinated in areas where sucrose was not secreted produced germtubes that were shorter (less than 50 μm at 48 h after inoculation) than those produced at sites where sucrose was secreted (greater than 5 mm in length). Infections also developed on severely wounded main leaf veins. Leaf wetness was required for infection, with maximal infection occurring after a 72 h dew period.

New sources of resistance to Sclerotinia sclerotiorum for crucifer crops

“…That study confirmed the earlier studies demonstrating that the presence of nutrients is essential for hyphal development, penetration and for subsequent establishment of a successful invasion of a susceptible host by this pathogen (Abawi and Grogan, 1975;Jamaux et al, 1995). Sedun and Brown (1987) showed that S. sclerotiorum infections in sunflower are associated with specific sites of sucrose secretion at the junction of the leaf blade and petiole. Infections starting at the junction of petiole and stem in our study may have been associated with similar secretions.…”

A Model for Sclerotinia sclerotiorum Infection and Disease Development in Lettuce, Based on the Effects of Temperature, Relative Humidity and Ascospore Density

“…Nutrients can also be supplied by other means, such as through tissue damage, wounds or senescing leaves, which explains plant infection in the absence of flowering [21], [25], [34]. However, Sedun and Brown [26] also observed infection of sunflower leaves in the absence of flowers, wounds or senescent tissue and this infection was found to be associated with specific sites of sucrose secretion around the junction of the leaf blade and petiole. Given this information from other crops, it is still unclear how the necessary nutrients are provided for infection of young lettuce plants as used in this study.…”

Resistance of sunflower (Helianthus annuus L.) to terminal bud attack bySclerotinia sclerotiorum (Lib.) de Bary

“…In contrast, when Correlation parent values/hybrid means r = 0.51 NS r = 0.99** r = 0.84* LSD (5%) 11.4 8.2 11.1 **: P < 0.01; *: P < 0.05; NS: not significant ascospore suspensions in water were applied, they did not adhere; such a suspension may dilute substances necessary for adhesion, as reported by Azmeh (1976) for Puccinia spp. On older leaves, infection generally starts at the base, near the main vein, where a leaf exudate is produced (Sedun and Brown, 1987). The presence of an exudate secreted by spores was observed, a phenomenon which may be necessary for recognition between the fungus and its host (Achbani, 1993).…”