Submitted to: Australasian Plant Pathlogy Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2009
Publication Date: 10/19/2009
Citation: Montes-Garcia, N., Prom, L.K., Isakeit, T. 2009. Effect of temperature and relative humidity on sorghum ergot development in northern Mexico. Australian Journal of Plant Physiology. 38(6):632-637. Interpretive Summary: Sorghum ergot, a fungal disease that was first observed in Mexico in 1997 poses a serious threat to sorghum, especially in hybrid seed production fields. In 2002 and 2003, six sorghum hybrids and 3 male-sterile lines (A-lines) were planted every month from January to October in Rio Bravo, Mexico to determine the effect of temperature and relative humidity on ergot development. The work showed that minimum temperatures above 10°C will increase ergot development in sorghum hybrids from 7 to 9 days before flowering while minimum temperatures above 22.5C will prevent the disease. In A-lines, ergot development was observed at temperatures of up to 38°C. This study showed that planting of sorghum hybrids at certain times of the year that will avoid exposure to low temperatures before flowering will reduce the level of ergot infection.
Technical 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 africnana. 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 10C increased the risk of ergot development, whereas minimum temperatures above 22.5C prevented ergot development. In male-sterile plant, ergot was negatively related to maximum temperature after anthesis, with ergot being observed at maximum temperatures up to 38C. 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 humididty and minimum and maximum temperature during the infection process on ergot severity.