Two wheat genotypes differ in root disease due to Gaeumannomyces graminis without interaction with site

Data were extracted from five trials where wheat had been naturally infected with the root-infecting pathogen Gaeumannomyces graminis var. tritici in three separate years. Three trials were of local and introduced cultivars, and two were of segregate families from crosses, employing a total of three sets of wheat. Of genotypes considered to differ in resistance to G. graminis, only Temu89-72 and cv. Bayonet were grown at each of the five sites. Measurement at four of the sites of the number of diseased seminal and coronal roots at tillering and anthesis showed differences in root disease between Temu89-72 and cv. Bayonet varied with root system and sampling time. Temu89-72 differed from cv. Bayonet only in having less disease of coronal roots at anthesis, and differences were then independent of site. This finding is not consistent with the predominant view that differences in susceptibility to G. graminis in wheat are very small or non-existent, and environmentally labile. To distinguish between the possibilities that either a level of resistance or differences in rooting pattern were responsible for findings, the relationship between the number of coronal roots and the proportion of infected roots at anthesis was considered. Coronal root number was not correlated with the incidence of root disease in the three sets of wheat, or associated with differences in disease between Temu89-72 and cv. Bayonet. This suggested that in this study, differences in rooting pattern were less significant than resistance in influencing the incidence of root disease.