Fusarium species associated with grain sorghum and mungbean in Queensland

Abstract

Many species within the Fusarium genus are important plant pathogens in Australia and worldwide. A number of important Fusarium diseases occur in grain sorghum and mungbean crops throughout Queensland and northern New South Wales, often resulting in serious losses to crop yields and grain quality. Grain sorghum is typically the largest summer field crop grown in Queensland. Fusarium stalk rot can cause significant losses to growers in Queensland and northern New South Wales, particularly when the disease results in lodged stalks. Historically, F. moniliforme sensu lato was thought to be responsible for Fusarium diseases of grain sorghum worldwide, however recent changes in taxonomy have split the species into a number of different species. This study identifies the Fusarium species associated with Fusarium stalk rot and head blight in eastern Australia. A total of 523 Fusarium isolates were collected from northern New South Wales, southern Queensland and central Queensland during the 2009-2011 cropping seasons from diseased sorghum plants. Nine Fusarium species were isolated from diseased sorghum tissues and pathogenicity tests confirmed that F. andiyazi and F. thapsinum were the dominant stalk pathogens, whilst F. thapsinum and species within the Fusarium incarnatum-F. equiseti species complex were most frequently associated with head blight. Fusarium thapsinum was the dominant stalk rot pathogen across all three major sorghum growing regions in eastern Australia during the 2009-2011 seasons, and was the most widespread and frequently isolated species obtained from diseased stalks, seedlings and stubble, accounting for 40% of the total isolates recovered. The recovery of F. andiyazi and F. thapsinum from all regions sampled suggests that these pathogens are widespread throughout the major sorghum-growing regions in eastern Australia. This study is the first to report the pathogenicity of F. andiyazi and F. thapsinum on stalks and peduncles of grain sorghum in eastern Australia. This study also demonstrated that Fusarium species originally obtained from diseased stalks can successfully infect peduncles, and vice versa. The second part of this study focused on identifying the causal agent and developing a reliable screening technique for the emerging disease, Fusarium wilt of mungbean in southern Queensland. A total of 114 Fusarium isolates were collected from diseased mungbean plants throughout Queensland during the 2011-16 cropping 4 seasons. Eight Fusarium species were recovered from diseased tissues, although F. oxysporum and F. solani were most frequently recovered. Phylogenetic analysis confirmed variability in the DNA profiles of both F. oxysporum and F. solani isolates collected during this study. This was the first study to report the pathogenicity of species within the F. oxysporum and F. solani species complexes on mungbean in Australia. Several pathogenicity tests were trialled during the study, although further research is required to develop a robust screening technique that differentiates relative levels of resistance in different genotypes. The findings in this study provide valuable insight into the diversity and abundance of Fusarium species associated with two important summer field crops in eastern Australia.