Relationship between cultivar height and severity of Fusarium ear blight in wheat

A significant negative relationship between tiller height and resistance to Fusarium ear blight (FEB), following inoculation, was observed in 17 culti vars of winter wheat in the 1995/96 growing season. Tall cultivars such as Kraka and Spark showed fewer symptoms of FEB (6 and 4%) than the shorter cu ltivars Brigadier and Virtue (35 and 51%). To determine if this relationshi p was caused by a genetic association or an effect of the microclimate, hei ght and disease were measured in segregating populations derived from tallx short cultivars and humidity was measured in near-isogenic lines with and w ithout the Rht1 and Rht2 dwarfing genes. Among random F-3 populations there was a clear tendency for tall strawed lines to show less severe disease sy mptoms than shorter strawed lines following inoculation. The effect of the individual dwarfing genes Rhr1 and Rht2 on the severity of FEB was also stu died in an inoculation trial using a number of near-isogenic lines of Maris Huntsman and Maris Widgeon. Within isogenic lines of Maris Huntsman, there was a clear tendency for tall straw to be associated with fewer symptoms, but this was not apparent within lines of Maris Widgeon. Monitoring relativ e humidity at ear height in a short and tall isogenic line of Maris Huntsma n revealed no significant differences between these genotypes from GS 65 to GS 85, suggesting that microclimate cannot explain differences in severity of FEB between these lines. It is suggested that there are independent gen es affecting the severity of FEB that may allow plant breeders to select re sistant cultivars of any height.