Analysis of Combining Ability for Ergot Resistance in Grain Sorghum

Abstract

ABSTRACTErgot caused by Claviceps africana Frederickson, Mantle & de Milliano has become an important constraint to F1 hybrid seed production in North and South America. Identification and utilization of sources of host‐plant resistance would contribute to the effective control of this disease. A Design II mating scheme was used to test the combining ability of four reported sources of ergot resistance in sorghum [Sorghum bicolor (L) Moench]—IS8525, IS14131, IS14257, and IS14357. Male‐sterile hybrids of these accessions and a susceptible check, TxARG1, were produced using five cytoplasmic‐genetic male‐sterile seed parents—A3Tx430, A3Tx436, A3Tx7000, A3KS70, and A3Tx2737. Parent lines and hybrids were planted in three replications at three locations and were evaluated for ergot resistance following artificial inoculation at flowering. Differences in ergot severity and ergot breakdown point (EBP) were used to quantify differences in resistance. The combined analysis of variance showed that the expression of ergot resistance was not stable with significant entry × location interaction. The analyses from two locations showed significant differences among hybrids, while the third location showed no differences. Regression analyses were performed to determine the relationship between weather variables at flowering and observed ergot severity. These analyses indicated a strong relationship between maximum daily temperature and ergot severity. Ergot infection was higher in cooler environments regardless of genetic background. IS8525 appeared to have the highest expression of ergot resistance in male‐sterile genetic backgrounds on the basis of EBP and ergot severity ratings; however, the expression of resistance was only effective within a limited temperature range.