Crown rust affects plant performance and interference ability of Italian ryegrass in the post‐epidemic generation

Abstract

SummaryThis study investigated the effects of crown rust (caused by Puccinia coronata f.sp. lolii) in Italian ryegrass (Lolium multiflorum) on plant growth and interference ability in the post‐epidemic generation. Rust‐infected Italian ryegrass plants produced seeds with lower weights than healthy plants (on average proportionately 0·36 lower). Furthermore, the early seedling vigour of plants from rust‐infected parents was reduced by 0·50 compared with seed from healthy parents. Under disease‐free conditions in the post‐epidemic generation, mature plants from rust‐infected parents produced 0·13 less shoot dry weight, 0·15 fewer tillers, 0·11 fewer leaves and 0·25 less leaf area than plants from healthy parents. As such, the effects of crown rust in Italian ryegrass persisted for at least one post‐epidemic generation. Under rust‐infected conditions in the post‐epidemic generation, however, the difference in performance between plants from healthy and rust‐infected parents was minimal. This suggests that any advantage plants gain from having healthy parents, compared with rust‐infected parents, might be lost when the post‐epidemic generation is grown under conditions of rust infection. Irrespective of rust infection in the post‐epidemic generation, the magnitude of intra‐specific interference was greater in monocultures of Italian ryegrass from healthy parents than in those from rust‐infected parents. However, the magnitude of inter‐specific interference and the relative interference ability of plants of rust‐infected and healthy parents did not differ. The implications of these results to plant ecology are discussed.