Breeding for durable resistance to Puccinia sorghi: status and strategies

Breeding for durable resistance to Puccinia sorghi: status and strategies

Australia has experienced an increase in incidence and severity of maize common rust (CR), caused by Puccinia sorghi, which could threaten the maize industry. Over a 120 isolates collected from seven maize growing regions were stored and maintained their viability and infectivity over 24 months at -80°C. The isolates were inoculated on the main commercial maize lines and it was found that they do not carry any resistance to CR and that the main resistance gene to P. sorghi (Rp gene), Rp1_D, is no longer effective. Maize lines carrying single or compound resistance genes were identified as carrying effective resistance to CR, Rp1_G, Rp5, Rp1_E, Rp1_L, RpGDJ, RpGJF, and Rp5GCJ. And other lines were selected as part of a proposed differential set Rp1_B, Rp1_C, Rp1_D, Rp1_F, Rp1_K, Rp3_D and Rp4_A. An hybrid assembly of the first collected isolate was created with assembling short and long reads. The hybrid assembly of Isolate 1 was also mapped against the short read of 17 isolates. The five most diverse isolates, in terms of collection location, year and host, were phenotyped against a set of maize lines carrying no resistance gene, from one and up to four resistances genes. A QUAST analysis revealed a draft genome of 145,963,792 bp and total length of 145,815,044 bp (>= 1000 bp), compared to 99,534,058 bp in Rochi et al. (2018). The prediction from the Braker pipeline identified 20,438 genes model. No clones were detected among the 17 isolates sequenced and they represented unique genotypes grouped into three clusters. No pattern of association of virulence was detected in the phenotyping study based on location of collection. This suggested that the variation in infection level on the differential set was not related to agro-ecological region of origin. This study successfully identified key strategies for maize ii breeding programs to develop durable resistance and meet national production targets.

This article is part of a UniSQ Thesis by publication. See Related Output.