Influence of Temperature and Humidity on the Viability of Ophiognomonia clavigignenti-juglandacearum Conidia.

Abstract

Butternut canker, caused by the fungus Ophiognomonia clavigignenti-juglandacearum, primarily kills butternut (Juglans cinerea). Rain splash and local air currents are the primary means of conidia dispersal but that does not explain its long-distance spread and infection of isolated trees. Dispersal by insect or animal vectors or plant material likely necessitates the ability for conidia to tolerate drying for a period of time over variable temperature and humidity conditions. The objective of this study was to determine the influence of temperature and humidity on conidial germination and survival of air-dried conidia. Conidia collected from 1-month-old cultures germinated on water agar over a wide range of temperatures (4 to 32°C) and were viable after brief periods at 36°C when returned to a lower temperature. Viability of air-dried conidia held on nylon membranes at various temperatures and humidities varied from less than a day at 28°C and 90% relative humidity (RH) to a mean of 15 days at 20°C and 80% RH. RH had the least effect on viability at 12°C, with conidia remaining viable for 7 days at most humidity levels tested. Conidia held at 100% RH began germinating on the membranes after 21 days. Conidia in a water suspension remained viable for 168 days at all temperatures tested. These results suggest that O. clavigignenti-juglandacearum conidia may remain viable on the surface of a vector or plant material and seed for over 2 weeks, given the proper conditions, or for much longer if in water or in an environment of saturated humidity. This potential may, in part, explain the frequent presence of the disease on isolated trees.