Quantitative histological studies of compatible and incompatible interactions between accessions of Macroptilium atropurpureum and Uromyces appendiculatus

Quantitative histological studies of pre‐penetration, penetration and post‐penetration events were made for one compatible interaction and five interactions showing varying degrees of incompatibility between Uromyces appendiculatus and Macroptilium atropurpureum. Four histologically different resistant responses to infection were observed, CPI 91348 exhibited a response, characterized by significantly fewer pustules per unit area and a longer generation time than the susceptible cultivar Siratro. Significantly fewer urediniospores produced appressoria on 91348 than on Siratro. Resistance in CPI 84997 was associated with the development of large areas of necrotic tissue; 99.8% of colonies showed an indeterminant hypersensitive response. Colony areas for the above three host genotypes were not significantly different at 144 h after inoculation. The remaining lines developed varying degrees of chlorosis only. Colonies in CQ 1382 and (CPI 92643 grew only slowly, but were still growing 144 h after inoculation and, as with CPI 84997, this growth continued after necrotic tissue appeared (indeterminant hypersensitivity), In CQ 1398, colony growth ceased by 96 144 h after inoculation, coinciding with the appearance of necrotic tissue (determinant hypersensitivity).