Spore Exudates and other Factors Affecting Germination Type of Cronartium Quercuum F. SP. Fusiforme Basidiospores

ABSTRACT

Basidiospores of Cronartium quercuum f. sp. fusiforme were germinated under different conditions of agar concentration, pH, washing times, and spore exudate concentrations. At agar concentrations of 0.05-3% the percentage of washed spores that germinated directly, i.e., produced germ tubes, was significantly different from the percentage of unwashed spores that germinated directly. Ninety-nine percent of the washed spores germinated directly at all agar concentrations, while only 4–11% of unwashed (directly cast) basidiospores germinated directly. On pH 3 agar, germination of directly cast basidiospores was only 2%, but 98% of germinating spores germinated directly (produced germ tubes). On pH 4–11 agar, spore germination varied from 70–90% and was predominantly indirect (forming secondary basidiospores). When spores were washed in water at pH 2.2 or pH 5.5 for 2 or 5 min, percent direct germination was 10 times greater than those spores not washed with water. More than 95% of spores germinated directly after 30-min washing with water at either pH 2.2 or 5.5. Both spore exudates washed from the spores and those produced during germination were collected and reapplied to the spores. These applications increased the percentage of direct germination in directly cast spores but did not alter germination type in washed spores. The exudates inhibited germ tube length in both directly cast and washed basidiospores.

Key Words:

• basidiospores
• Cronartium quercuum f. sp. fusiforme
• direct germination
• indirect germination
• spore exudates
• Uredinales