Components of quantitative resistance to yellow rust in ten spring bread wheat cultivars and their relations with field assessments

Latency period, infection frequency, lesion length, lesion growth, disease severity and percentage of infected leaf parts were assessed on 10-day-old seedling leaves and flag leaves of ten bread wheat (Triticum aestivum L.) cultivars after inoculation with urediospores of Puccinia striiformis Westend. f. sp. tritici. For all components significant genotypic differences were detected. Components of resistance tended to be associated. A long latency period was associated with a low infection frequency, small lesions, a low disease severity and a low percentage of infected leaf parts. The latency period, measured as time period until first pustule appearance (LP1), was highly correlated with the latency period measured as time period until 50% of the pustules appeared (LP50). Assessment of latency period of large numbers of cultivars could therefore be reliably done by measuring LP1 which is less time consuming than measuring LP50. Latency period, infection frequency and disease severity were highly correlated with disease development data from field experiments. These results suggest that selection in the greenhouse for one of these components should result in cultivars with high levels of quantitative resistance. Disease severity after uniform inoculation in the greenhouse can be used for monocyclic evaluations because it is the easiest to assess.