Genetic Expression of Wheat Streak Mosaic Virus Resistance in Two Wheat‐Wheatgrass Hybrids1

Abstract

Two intergenic amphiploids wheat (Triticum aestivum) tall wheatgrass (Agropyron elongatum) and wheat ✕ intermediate wheatgrass (A. intermedium) are potential sources of wheat streak mosaic virus (WSMV) resistance. The genetic control of WSMV resistance must be understood before sources can be effectively used in wheat breeding. The amphiploids and the derived disomic addition lines of individual chromosomes in T. aestivum were analyzed to determine chromosome locations, epistatic interactions, and dosage effects of genes for WSMV resistance. The evaluation of resistance was carried out by symptomatology under both growth chamber and glasshouse conditions in conjunction with double antibody sandwich enzyme‐ linked immunosorbent assay (ELISA) and slot‐blot hybridization, which were useful in identifying minor genes for WSMV resistance. The amphiploids were resistant to WSMV infection and remained symptom‐free throughout their growth under both growth chamber and glasshouse conditions. A single chromosome addition line 6E from A. elongatum and L5 from A. intermedium were resistant to WSMV under growth chamber conditions. ELISA and slot‐blot values suggested a minor factor for genetic resistance on another chromosome in both Agropyron species. Apparently, one major factor and at least one minor genetic factor control the resistance observed in these two Agropyron species. Epistatic interaction between chromosomes 5E and 6E in A. elongatum appeared to be involved in genetic expression of WSMV resistance. Moreover, WSMV resistance was hemizygous ineffective as plants with a monosomic addition of 6E were susceptible. The results indicate that resistance in the specific Triticum ✕ A. elongatum amphiploid analyzed here will be difficult to transfer to wheat. The resistance on chromosome L5 of, A. intermedium may be more promising provided one of the ditelosomic lines expresses a level of resistance equal to the L5 chromosome. The hemizygous ineffective nature of WSMV resistance should be taken into account while evaluating breeding lines for resistance. The techniques of ELISA and slot‐blot hybridization proved to be useful in identifying minor genes for WSMV resistance.