Journal
PHYSIOLOGICAL AND MOLECULAR PLANT PATHOLOGY
Volume 61, Issue 1, Pages 41-51Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1006/pmpp.2002.0415
Keywords
barley; Hordeum vulgare L.; powdery mildew; Blumeria graminis-Erysiphe graminis; phenolic biosynthesis inhibition; powdery mildew resistance genes and alleles (Mla1, Mlal2, Mla13, Mlg, Mlk, Mlp and mlo5); penetration resistance; epidermal cells; phenylalanine ammonia lyase; cinnamyl-alcohol dehydrogenase
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Barley leaf epidermal cells actively resist penetration by germinated conidia of the powdery mildew fungus Blumeria graminis f.sp. hordei (Bgh). Penetration resistance to the appropriate forma specialis (f. sp.) of Bg is sensitive to inhibition of phenylpropanoid biosynthesis but its genetic basis relative to known race-specific powdery mildew resistance genes (R-genes) and alleles is confusing. In this study, the effects of phenylpropanoid inhibition on penetration resistance in near-isogenic barley lines with genetically defined R-genes or alleles were investigated. Seven members of the Pallas (P) near-isogenic barley set were used. Phenylpropanoid biosynthesis inhibition was accomplished using alpha-Aminooxy-beta-phenylpropionic acid (AOPP), an inhibitor of phenylalanine ammonia lyase (PAL), and ([2-hydroxyphenyl amino] sulfinyl) acetic acid, 1,1-dimethyl ester (OH-PAS) an inhibitor of cinnamyl-alcohol dehydrogenase. Phenylpropanoid inhibition decreased localized autofluorescence at Bgh germ tube contact sites and significantly (P < 0.05) increased fungal penetration. This was true of the parent Pallas and the near-isogenic lines containing Mla1 (P01), Mla12 (P10), Mla13 (P11), Mlg (P21), Mlk (P17) and Mlp (P19) R-genes. These R-genes had no apparent effect on phenylpropanoid sensitivity of penetration resistance. However, in P22, with the race non-specific recessive allele mlo5, penetration resistance was unaffected by either AOPP or OH-PAS treatments, even though both inhibitors reduced the frequency and intensity of localized autofluorescence at fungal germ tube contact sites. The sensitivity of penetration resistance to the phenylpropanoid inhibitors was shared by all isolines, except P22, and appeared to be a property of the Pallas genetic background rather than being associated with race-specific R-genes or their alleles. Thus mlo5 penetration resistance shares a physiological phenomena i.e. insensitivity to phenylpropanoid inhibition, with non-host penetration resistance exhibited by barley, wheat and oat when they are attacked by inappropriate formae speciales (ff. spp.) of Bg. (C) 2002 Elsevier Science Ltd. All rights reserved.
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