Responses of Two-, Three-, and Four-Component Barley Mixtures to a Variable Pathogen Population
- B. A. McDonald ,
- R. W. Allard and
- R. K. Webster
Cultivar mixtures have been suggested as a means to control foliar diseases in small grains, but little information is available on how to choose component lines for use in cultivar mixtures. This 3-yr study tested the ability of two-, three-, and four-component barley (Hordeum vulgare L.) mixtures to control scald disease caused by the fungus Rhynchosporium secalis (Oud) Davis. The mixtures were composed of lines from the parents of Composite Cross II (CCII), a naturally evolving barley population, and from the 45th generation of CCII. The lines differed in resistance or susceptibility to four diagnostic pathotypes of the scald fungus. The results indicate that some barley lines, when grown in mixture, interact to reduce or increase incidence of scald. Lines from the 45th generation of CCII interacted to reduce incidence of scald more often than parental lines of CCII. The largest reductions in sca.ld were observed in mixtures containing lines that were susceptible when grown in pure stand. Genes for resistance to R. secalis were deployed singly in mixtures and also pyramided into single lines. Differences between these methods of gene deployment were nonsignificant statistically. Some two-component mixtures made up of one resistant and one susceptible line and some three-component mixtures made up of two susceptible components and one resistant component had no more disease than the resistant component of the mixture grown alone. The results were interpreted as indicating that cultivar mixtures offer an effective strategy for controlling damage due to R. secalis.
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