Histological examination of the interaction between Rhynchosporium secalis and susceptible and resistant cultivars of barley

Abstract

The infection processes of Rhynchosporium secalis were compared in three barley cultivars, Lenka (susceptible), Digger (resistant), and Osiris (highly resistant). Appressorial formation and attempted cuticular penetrations were similar in cvs Lenka and Digger. Penetration attempts were associated with the formation of papillae and haloes in the cell walls around the penetration pegs in all cultivars, but the papilla size increased with time after inoculation and became significantly larger in resistant than in susceptible plants. A correlation, although less pronounced, was found between halo size and plant resistance. After successful penetration of the cuticle in Lenka, first thin hyphae, then later thicker hyphae developed; both developed subcuticularly. The thick hyphae proceeded into the outer periclinal epidermal cell walls, through the anticlinal walls and into the inner periclinal walls of the epidermis. Very few hyphae grew into the intercellular spaces of the mesophyll. As infection proceeded, the cells collapsed in advance of hyphae, staining affinity of chloroplasts changed, and polyphenolic substances accumulated. Conidia were produced on short conidiophores penetrating the otherwise intact cuticle. In cv Digger, a strong correlation was found between papilla size and inhibition of fungal penetration, indicating papilla formation as a resistance mechanism. Only a few hyphae were established subcuticularly, no cell collapse or accumulation of polyphenolic substances took place, and only restricted sporulation occurred in the leaf margins. The only macroscopic symptom of infection was limited chlorosis.