Development of barley leaf rust, Puccinia hordei, infections in barley. II. Importance of early events at the site of penetration for partial resistance

Abstract

The investigation involved three barley genotypes that varied from extremely susceptible (‘Akka’) to an extreme level of partial resistance (‘17-6-16’). The barley leaf rust colony size was measured in primary leaves 3, 6, 12 and 18 days after inoculation and in flag leaves 6, 12, 18, 24 and 30 days after inoculation with race 1-2-1. ‘Akka’ always had the largest colonies, ‘17-5-16’ the smallest, with ‘Vada’ at an intermediate position. The genotypic differences were proportionally largest at the second sampling day and smallest at the last sampling day. The rate of colony growth decreased rapidly over time for all genotypes and in both plant stages. Measured at the same time (colony age the same) the rate of colony growth was largest for ‘17-5-16’ and smallest for ‘Akka’ in most periods. The time needed to reach a given colony size showed already large differences in the very early states especially in the flag leaves. ‘Akka’ took 3.9 days to reach a size of 17 × 10-3 mm2 (only 5 to 10% of the colony size at the start of sporulation), ‘Vada’ needed 8.3 days and ‘17-5-16’ even 12.0 days. To reach a size of 320 × 10-3 mm2 the three genotypes needed 12.7, 18.0 and 22.8 days respectively, differences that are only slightly larger than those at the very small colony size.