Submitted to: Plant Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/27/2007
Publication Date: 10/1/2007
Citation: Montes-Garcia, N., Isakeit, T., Odvody, G., Prom, L.K., Rooney, W. 2007. Effect of storage temperature and sphacellum age on C. africana conidia survival. Plant Pathology Journal. 6(4):312-317. Interpretive Summary: Sorghum ergot, a fungal disease, was first observed in the western hemisphere in Brazil in 1995. Ergot poses a serious threat to sorghum, especially in hybrid seed production fields. The first symptoms of the disease are called a sphacelium and the spores within this structure can be spread to other plants to start the infection process. In this study, the survival of the spores on the surface or the inside of these sphacelia with different ages and stored at different temperatures was determined by plating them on water agar. The study showed that the fungal spores survive more readily at cool temperatures ranging from 0.3ºC to 7ºC. Also, spores from older sphacelia survive longer than on newly formed ones. Knowing how these spores survive in these fungal structures would help in devising better control methods for this disease.
Technical Abstract: Sorghum ergot, caused by Claviceps africana Frederickson, Mantle & de Milliano, is a disease that poses a serious treat to sorghum, especially in hybrid seed production. The initial sign of the disease is called a sphacelium. Sphacelia containing macroconidia 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 x 106 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. Vials containing sphacelia and distilled water were stirred and a portion of the suspension was placed onto water-agar plates. Replications per treatment were made and incubated overnight at room temperature (21oC). The germination observed in this sample was named germination on the “sphacelium surface”. After rinsing the remaining sphacelia, they were macerated, suspended in distilled water, stirred and placed onto water-agar plates. The germination percentage obtained here was named “within the sphacelium”. Data was transformed using the arcsine of the square root of each value. The results indicated that sphacelia stored under cool temperatures (0-3oC to 7oC) maintained conidial viability, and newly-formed sphacelia located on the sphacelia surface had the highest conidial viability. 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.