Development of barley leaf rust, Puccinia hordei, infections in barley. I. Effect of partial resistance and plant stage

Abstract

The fate of Puccinia hordei, race 1-2-1, infection units in seedlings and adult plants was followed from the moment appressoria were formed over the stomata. This was done in six spring barley cultivars, ranging from absolutely no partial resistance against barley leaf rust (‘L94’) to good partial resistance (‘Vada’). Infection units can abort anywhere between appressorium formation and sporulation. The abortions were classified into three groups: The cultivars differed significantly for Ap in the adult plant phase, not in the seedling phase. For EA cultivars varied significantly in both plant phases. With LA the cultivar effects were more pronounced in the adult plant phase. In seedlings the proportions AP, EA and LA among cultivars ranged from 0.03 to 0.05, from 0.04 to 0.39 and from 0.04 to 0.11 respectively. In the adult plants the respective ranges were from 0.04 to 0.20, from 0.07 to 0.26 and from 0.06 to 0.26. The size of the mycelial colonies measured at the same moment (7 to 8 days, depending on the series, after inoculation) varied widely between cultivars, especially in the adult plants. In de adult plant phase the linear correlation coefficients between partial resistance and the four histological parameters Ap, EA, colony size measured at the same moment, and LA were 0.95, 0.62, 0.80 and 0.16 respectively. Seedlings appeared considerably less representative than adult plants for a study of the relation between partial resistance and the histological parameters of fungal growth in the host tissue. It is concluded that the host pathogen interaction evens occurring during stoma penetration and very shortly after that are of decisive importance in the expression of partial resistance; it has the characteristics of a recognition process. The colony size in adult plants remains far behind those in seedlings suggesting another type of resistance, provisionally named mature plant resistance, besides partial and hypersensitive resistance.