Phenotypic and genotypic diversity of Puccinia sorghi in Eastern Australia: implications for maize breeding programs

Common rust of maize (CR), caused by Puccinia sorghi Schwein., is found in all maize growing regions across the globe. In recent years, an increase in incidence and severity of CR has been observed in Australia. The challenges posed by a diverse population of P. sorghi to maize breeding programs and the strategies required to deploy durable resistance were explored. Preliminary studies of diversity were conducted by phenotyping the five most diverse isolates against maize lines carrying no resistance genes, and from one and up to four resistances genes. The results showed that further genotyping studies were required. Short reads of 17 CR isolates, collected in an array of agro-ecological regions in Eastern Australia, were mapped back against the hybrid assembly of Isolate 1. A hybrid assembly between short (Illumina paired-end) and long (PacBio) reads was conducted in MaSuRCA of the first isolate collected. A draft genome of 145,963,792 bp was obtained after QUAST analysis and total length of 145,815,044 bp (when removing base pair below ≥ 1000). The prediction from the BRAKER pipeline identified 20,438 genes model. All 17 isolates sequenced represented unique genotypes, and no clones were detected. The 17 isolates grouped into three clusters. The diversity observed within the population of P. sorghi in Australia suggests that monogenic resistance may not be durable.