VIEW ARTICLE

Resistance

Histology of the Relation Between Minor and Major Genes for Resistance of Barley to Leaf Rust. R. E. Niks, Institute of Plant Breeding, Agricultural University, Lawickse Allee 166, 6709 DB Wageningen, the Netherlands, Present address of senior author: ICARDA, P.O. Box 5466, Aleppo, Syria; H. J. Kuiper, Institute of Plant Breeding, Agricultural University, Lawickse Allee 166, 6709 DB Wageningen, the Netherlands. Phytopathology 73:55-59. Accepted for publication 21 May 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-55.

Pa7 and Pa3, two major genes that confer hypersensitive resistance to leaf rust (caused by Puccinia hordei) in barley were introduced into three genetic backgrounds with different levels of partial resistance (PR) (the genetic complement controlling PR will be referred to collectively as “PR genes”) to study the interaction between both types of resistance. The growth rate and the degree of abortion of the colonies in the genotypes were determined by fluorescence microscopy. The degree of host cell necrosis was recorded. The PR genes affected the success of colony establishment in the host and reduced the growth and development rate of colonies after establishment. This effect was also apparent in the presence of Pa7, the effects of which were seen relatively late in the infection process. Apparently, PR genes and Pa7 acted independently and consecutively. Pa3 acted shortly after the establishment of the colonies and largely obscured the effect of the PR genes. Nevertheless, the level of PR can be assessed in the presence of Pa3 by determining the proportion of early aborted colonies not associated with host cell necrosis.