Failure of haustorial development as a factor in slow growth and development of Puccinia hordei in partially resistant barley seedlings

Abstract

Observations on six barley lines differing for partial resistance, at 44 h and 6·5 days after inoculation with Puccinia hordei, indicated that a proportion of colonies fail to form haustoria, the proportion failing being related to the level of partial resistance. Following the formation of the first hauslorium, the rate of formation of further haustoria was reduced for some time in lines with high levels of partial resistance. Failed haustorium formation was quantified by determining the number of induced papillae. When colonies reach a certain size, the host-colony interaction appears to change abruptly towards high compatibility, since the hyphae formed from then on induce fewer papillae than before. Indications were found for differences in resistance levels between epidermal and mesophyll cells. Differences in size and phase of development of colonies at 6·5 days after inoculation both within and between barley lines were connected with differences in the degree of formation of wall appositions (papillae formation) around the point of entry into the leaf. The results are likely to have importance for understanding the mechanisms that determine basic compatibility.