Lower temperature during the dark cycle affects disease development on Lygodium microphyllum (Old World climbing fern) by Bipolaris sacchari

Growth chamber experiments were conducted to examine environmental parameters affecting disease development by the indigenous pathogen Bipolaris sacchari isolate LJB-1L on the invasive weed Lygodium microphyllum (Old World climbing fern). An initial experiment examined three different temperature regimes (20/15, 25/20, 30/25 °C; light/dark cycle) and three different periods of leaf wetness (12, 24, 48 h). Disease incidence was significantly reduced by incubation of plants at the highest temperature regime (30/25 °C) and with the shortest period of leaf wetness (12 h). Subsequent experiments concentrated on the effect of temperature, as determination of an optimal temperature for disease development might determine the best time of year for field inoculations with this fungus. When the light cycle temperature was kept constant at 30 °C, a dark cycle temperature of 15 °C was more conducive for disease development than 25 °C based on disease incidence and area under the disease progress curve (AUDPC). A qualitative examination of conidia germination and appressorial formation in vivo indicated that these initial steps toward infection were probably not influenced by the dark cycle temperature. In vitro, temperature (range of 15–35 °C) did not significantly affect conidia germination, but hyphal growth was significantly affected, with optimal growth between 25 and 30 °C.