The ability of two Metarhizium species, M. acridum (IMI 330189) and M. anisopliae (IMI 385045), to germinate at five water activities ranging from 0.998 to 0.944, was examined for conidia harvested from cultures of different ages. The culture ages ranged from 4 to 22 days old. All of the conidia on each plate were harvested 4 days after inoculation, then again after 11, 18 and 22 days. Therefore, the conidia were never greater than 7 days old. The data suggested that conidia of M. anisopliae were generally fitter, as defined by higher viability at all water activities, when harvested from the 4 day-old culture compared to those from the 22 day-old culture. At the lowest water activity (0.944) germination of M. anisopliae conidia was 71.5% from the 4 day-old culture compared to 0% from the 22 day-old culture. In contrast, conidia of M. acridum were generally fitter when they were obtained from 11, 18 and 22 day-old cultures than the conidia obtained from the 4 day-old culture. However, at the lowest water activity, germination for all treatments of M. acridum was less than 8%. The culture growth phase and media age may affect conidia fitness. The capacity of conidia to withstand water stress and possible reasons for interspecific variation, including susceptibility to imbibitional damage, are discussed.
Smith, K.; Edgington, S. Germination at different water activities of similarly aged Metarhizium conidia harvested from ageing cultures. Journal of Stored Products Research (2011) 47 (3) 157-160. [DOI: 10.1016/j.jspr.2011.01.007]