Effect of temperature and relative humidity on sorghum ergot development in northern Mexico

Abstract

Trials were planted at Rio Bravo, Tamaulipas, Mexico, during 2002 and 2003 with the objective of determining the relationship between sorghum ergot severity and weather factors, and to develop a risk assessment model. Six sorghum hybrids and three male-sterile genotypes were planted every month from January to October. At anthesis initiation, inoculation was conducted using a local isolate of Claviceps africana. Among hybrids, there was a negative relationship between ergot severity and maximum and minimum temperatures, with the highest significant correlation of —0.71 from 7 to 9 days before anthesis. During this period, minimum temperatures above 10°C increased the risk of ergot development, whereas minimum temperatures above 22.5°C prevented ergot development. In male-sterile plants, ergot was negatively related to maximum temperature after anthesis, with ergot being observed at maximum temperatures up to 38°C. Minimum relative humidity showed a positive and significant correlation with ergot severity. Values of minimum relative humidity above 30% during anthesis promoted infection. Surface response regression models were developed for the effects of minimum relative humidity and minimum and maximum temperature during the infection process on ergot severity.