An in vitro assay for pre-screening resistance to Fusarium head blight in durum wheat

Fusarium head blight (FHB), caused by Fusarium graminearum Schwabe, is a wheat disease that causes yield losses and mycotoxin accumulation in the grain. In germplasm of durum wheat (Triticum turgidum L. ssp. durum), genetic variability for resistance is scarce. To develop an improved assay for FHB resistance in wheat, we evaluated the effect of F. graminearum inoculation on seed germination and seedling growth and relationships of these parameters with disease severity. A genotype set was examined, comprising ten durum wheats as well as two common wheats, including susceptible and introgressed resistant lines. Genotypes were additionally screened using molecular markers linked to known FHB resistance QTLs. Significant differences were detected among inoculated genotypes for germination, coleoptile length, coleoptile weight, root weight and disease severity. Seedling variables were shown to be correlated across experiments validating repeatability of the in vitro assay. Using multiple regression analysis, coleoptile length was correlated with FHB severity (P<0.05) and explained 63% of head disease. Introgressed genotypes carrying resistance alleles/QTLs when inoculated showed nil or slight reductions in seedling growth, in comparison to controls, and lower disease severities than the corresponding original genotypes, suggesting that the seedling test can detect genetic differences in FHB resistance. Three genotypes performed well in the seedling assay and showed moderate severity even though they lacked the targeted QTLs, suggesting they harbor resistance genes not screened herein. Based on relative coleoptile length and Fisher statistical significance, a ranking of genotypes was established, consisting of three groups with best, intermediate and poorest performance in relation to fungal effect. The advantageous features of this method reside in its statistical basis and predictive ability of head disease. The in vitro assay allows rapid and early determination of resistance/susceptibility to F. graminearum, suitable for evaluating germplasm collections or segregating progenies.