Histological, genetical and epidemiological studies on partial resistance in wheat to wheat leaf rust

Partial resistance (PR) of wheat to wheat leaf rust acted in two steps. The first step led to a reduced infection frequency (IF), the second step to a longer latency period (LP).The genes for a prolonged LP inherited in a recessive way and showed additive gene action. The PR-genotype Akabozu carried two and Westphal 12A three LP-prolonging genes. BH 1146 contained one HR gene and two or three LP genes. Transgression was observed in the progenies.PR, measured as LP, was best expressed in the young flag leaf stage, at low temperatures. LP is a good estimator for PR.Three epidemiological parameters were used to assess PR in the field., 1) disease severity at the time that susceptible controls are severely rusted, 2) AUDPC, 3) the logistic growth rate. 1) and 2) are reliable estimators for PR, 3) appeared unsuitable. Long LP and low IF were correlated.Conclusive evidence for or against race specificity of PR has not been obtained. PR was expressed in a wide range of environments, indicating that PR is stable. The ranking orders were similar at all locations and years. The PR studied might be durable. The PR in BH 1146 is effective since 1955