VIEW ARTICLE

Resistance

Role of the Hypodermis and Secondary Cell Wall Thickening in Basal Stem Internodes in Resistance to Strawbreaker Foot Rot in Winter Wheat. T. D. Murray, Graduate research assistant, Department of Plant Pathology, Washington State University, Pullman 99164-6430; G. W. Bruehl, professor, Department of Plant Pathology, Washington State University, Pullman 99164-6430. Phytopathology 73:261-268. Accepted for publication 19 August 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-261.

Anatomical characteristics of the first elongated internode of 11 winter wheats were studied to determine their association with resistance to Pseudocercosporella herpotrichoides. Based on disease indices, cultivar VPM-1 was highly resistant; Cappelle-Desprez, Cerco, Golils, and Rubigus were resistant; Viking was intermediate; and Daws, Nugaines, Sprague, Stephens, and Selection 101 were susceptible to strawbreaker foot rot in the field. Resistance was correlated with hypodermis width and number of hypodermal cell layers, but not with epidermal cell wall thickness, lumen diameter, or stem diameter. Cell wall thickening and lignification occurred earlier in resistant than in susceptible wheats. The fungus invaded all wheats extensively, damaging parenchyma and vascular tissues, particularly phloem. Parenchyma cell walls were more susceptible to damage than lignified cell walls. Epidermal cell walls became thickened and lignified prior to contact with the fungus. Pith parenchyma cell walls became thickened and lignified in diseased tissue. Lignified cell wall appositions (lignitubers) were larger and formed in greater profusion at penetration sites in epidermal cells of stems of resistant than of susceptible wheats. We conclude that resistance to P. herpotrichoides is to a considerable extent correlated with structural attributes of the host and that these differences become more apparent as host maturity approaches.