Effect of Storage Temperature and Sphacelium Age on Claviceps africana Conidia Survival

摘要

Sorghum ergot, caused by Claviceps africana Frederickson, Mantle and de Milliano, is a disease that poses a serious threat to sorghum, especially in hybrid seed production. The initial sign of the disease is called sphacelium that contains macroconidia that could play a role in the survival of the pathogen. Sorghum A-line ATx623 was planted in the greenhouse during 2001, 2002 and 2003 at College Station, Texas. Flowering panicles were inoculated until runoff with a suspension of 1.6 CHI 10~6 C. africana conidia ml~(-1). Sphacelia were collected at several stages depending on their maturity. Petri dish plates containing sphacelia were arranged in a factorial experiment with 16 treatments out of the combination of sphacelia maturity and temperature. Every month a conidia germination test was made. Conidia located on the sphacelium surface had greater germination than the conidia located inside the sphacelium. This may be due to the developmental maturity of the conidia located on the outside. Warmerstorage temperatures (21deg C) significantly reduced conidia viability compared with freezing or cool temperatures. Dry and cool temperatures are required to preserve conidia viability and newly-formed sphacelia have the highest conidial viability especially if conidia are located on the sphacelium surface. However, they show a greater viability reduction through time compared with conidia from older sphacelia, showing that conidial maturity can play a role on the survival of the conidia.