Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2007
Publication Date: 4/1/2008
Citation: Elliott, M.L., Rayamajhi, M.B. Lower temperature during the dark cycle affects disease development on Lygodium microphyllum (Old World climbing fern) by Bipolaris sacchari. Biological Control. 45:56-63. 2008. Interpretive Summary: An invasive vine called lygodium or old-world climbing fern is one of the most serious weeds of Florida’s landscape. Its vines climb over other plants, forms thick layers and smoother underneath vegetation over time. Chemical control alone is not effective for long-term control of the fern-vines since it grows back from the modified stems in the soil after chemical treatment. Therefore, biological control methods that utilize herbivorous insects and microbial pathogens of foreign and local origin are being currently searched and evaluated. In this process we discovered a fungus called Bipolaris sacchari (bipolaris) locally from foliages of climbing fern. This fungus was observed to causes foliar disease at certain environmental conditions. In the process of identifying the factors that make this fungus a better pathogen on climbing fern we conducted experiments at different temperature and light dark combinations. We found out that the disease is more severe when the fern plants are inoculated and maintained at 15oC during the night cycle. This means that the disease caused by bipolaris fungus is more severe during low temperature conditions. However, farther research will be needed to determine if it is the host that becomes more susceptible to this fungus during relatively cold season of the year.
Technical Abstract: Growth chamber studies 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). Initial studies examined three different temperature regimes (20/15 ºC, 25/20 ºC, 30/25 ºC; light/dark) and three different dew periods (12, 24, 48 h). While both temperature and dew period affected disease development, it was observed that lower temperatures significantly increased disease development. Subsequent experiments concentrated on this temperature influence, as temperature is not an environmental parameter that can be easily influenced under field conditions by human intervention. It was confirmed that a dark cycle temperature of 15 ºC was more conducive for disease development than 25 ºC, even when the light cycle temperature was kept constant at 30 ºC. In vitro, conidial germination was not influenced by temperature, whereas hyphal growth decreased at the highest and lowest temperatures examined (15, 20, 25, 30 and 35 ºC). A qualitative examination of conidial germination and appressorial formation in vivo indicated that temperature did not influence these initial infection steps. This suggests that the lower dark cycle temperature is influencing the plant, which has a lower optimal growth temperature of 26 °C, with 12 °C being the limiting lower temperature for this invasive weed.