Diversity and fertility of Fusarium sacchari from wild rice (Oryza australiensis) in Northern Australia, and pathogenicity tests with wild rice, rice, sorghum and maize

Research was undertaken to identify Fusarium spp. associated with an endemic wild rice (Oryza australiensis) community in northern Australia and determine the incidence of species reported as pathogens of tropical grain crops. A total of 92 isolates representing six Fusarium species were recovered from O. australiensis. Taxa were delimited based on morphological and phylogenetic (TEF-1α sequence) characters and identified as F. incarnatum-equiseti species complex (55 %), Gibberella fujikuroi species complex (GFSC, 27 %), F. longipes (14 %) and an unidentified Fusarium sp. (3 %). F. sacchari was dominant in the GFSC, a reported mycotoxin (beauvericin, fumonisin) producer and pathogen of sugarcane and sorghum. No isolates were identified as F. fujikuroi, the cause of Bakanae disease of rice in south-east Asia and other rice growing regions. Morphological, phylogenetic and phenetic (AFLP) analyses were in accordance, differentiating all F. sacchari isolates from other Fusarium taxa. The ratio of F. sacchari mating types (15 MAT-1:9 MAT-2) in the O. australiensis population was not significantly different from that expected under random mating (1:1). The effective population number (Ne) based on mating type (Ne(mt)) was 94 % of the count (total population). In contrast, that based on female-fertile isolates (Ne(f)) was 15 %, implying low frequencies of sexual reproduction among F. sacchari isolates. Pathogenicities of three F. sacchari genotypes were assessed against O. australiensis and commercial cultivars of rice, sorghum and maize. All F. sacchari isolates significantly (P < 0.001) reduced emergence of O. australiensis and rice, but not sorghum or maize. Isolation frequencies of all genotypes from sorghum and maize and one isolate from O. australiensis were significantly (P < 0.001) greater than the controls. There were no significant differences in F. sacchari re-isolation among rice treatments. Thus, F. sacchari is presumed to be a pre-emergent ‘damping off’ pathogen, endophyte or weak parasite of O. australiensis and rice and a root and crown pathogen of sorghum and maize.