38th Annual Meeting of the Society for Invertebrate Pathology

Conidial pigmentation is involved in protection against heat and ultraviolet radiation in several fungi. In this study, we compared the tolerance to wet-heat (45^oC, for 2, 4, and 6 h) and two kinds of ultraviolet radiation (at total dose of 7.14 kJ/m2) of 17 color mutants of wild-type ARSEF 23 and 13 color mutants of wild-type ARSEF 2575 of Metarhizium anisopliae var. anisopliae. The stress tolerance of all mutants were compared with that of their wild-types, and with the most thermo- and ultraviolet-tolerant wild-type we have tested to date, viz. ARSEF 324, an M. anisopliae var. acridum. The color of each isolate or mutant was identified using the PANTONE Color Standard (Eiseman and Herbert, 1990). In addition, the pigments of each mutant or wild-type were extracted and their UV absorbances compared with each strain’s tolerance to both stresses. No correlations were detected. Color mutants of ARSEF 23, in general, were less UV tolerant than their parent wild-type. The conidial pigmentation is important for conidial tolerance to UV radiation for ARSEF 23, but less so for ARSEF 2575. The ARSEF 2575 color mutants demonstrated less variability in UV tolerance than those of ARSEF 23, even though very similar colors were presented in the two groups of mutants. Color mutants when reverted to wild-type color conidia recovered wild-type UV tolerance. For thermotolerance, however, mutants in several instances were more tolerant than their wild-types parents. Accordingly, the darker pigmentation of wild-types did not provide protection against heat.