Seasonal variation in lucerne foliar diseases and cultivar reaction to leaf spot pathogens in the field in southern Queensland

Abstract

Detailed assessments were made of leaf and stem disease incidence and severity on 16 lucerne cultivars and lines over 10 months in the field near Gatton, Queensland (27°34'S., 152°17'E.). The 4 major pathogens encountered were Leptosphaerulina trifolii, Uromyces striatus, Pseudopeziza medicaginis, and Cercospora medicaginis. The diseases caused by these pathogens showed a seasonality in occurrence. Both U. striatus and P. medicaginis were more severe on older shoots, whereas L. trifolii caused highest disease levels on shoots sampled 2 weeks after cutting. The relative rankings of the lucerne entries changed across pathogens, but breeding line MSA showed the best resistance to rust, L. trifolii, and P. medicaginis. This work has indicated that there is genetic variability in disease reaction to foliar pathogens which could be exploited in the development of cultivars for subtropical Queensland.