RESISTANCE TO GAEUMANNOMYCES-GRAMINIS IN WHEAT GENOTYPES GROWN IN-FIELD ENVIRONMENTS AND SAND CULTURE

Evidence of resistance to the root pathogen Gaeumannomyces graminis wa s sought by correlating measurements of disease in wheat grown in sand culture and field environments. Three sets of wheat were studied, one set of seven cultivars previously thought to differ in resistance, an d two sets that had segregated from two crosses, AUS1080 x cv. Condor and Temu89-72 x cv. Bayonet. Seedlings grown in sand culture were inoc ulated with infected agar disks, and disease was assessed from symptom s of colonization. Incidences of infected roots and of ''deadheads'' ( wheat heads prematurely dead and empty of grain), and measures of plan t growth, were recorded for sets of wheat at three field sites natural ly infested with the pathogen. At least two characters detected in san d culture were correlated with root disease in the field, browning of root cortical tissue, and more general susceptibility to colonization. Grain weight was recorded at only two sites, and was positively corre lated with cortical browning in sand culture at one, but not at the ot her site where progressive drought influenced grainfill more strongly than did disease. Other correlations were detected, but these were not directly indicative of resistance. Root colonization in sand culture, and both length of the subcoronal internode and number of tillers in field-grown plants, were correlated (in a complex manner) for both set s of segregate families. Many of the correlations that indicated resis tance, and those that appeared not to have a pathogenic origin, were s ignificantly affected by the maturity of wheat genotypes. Further work is required to evaluate characters indicative of resistance that were detected in this study.