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Title: Genetic diversity of Puccinia kuehnii, the causal agent of orange rust of sugarcane, from Brazil

Author
item URASHIMA, ALFREDO - Universidade Federal De Sao Carlos
item MISTURA, T - Universidade Federal De Sao Carlos
item SAKUNO, C.I.R - Universidade Federal De Sao Carlos
item Austin, Paige
item Arias De Ares, Renee

Submitted to: Journal of Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2020
Publication Date: 8/8/2020
Citation: Urashima, A.S., Mistura, T.F., Sakuno, C., Austin, P.D., Arias De Ares, R.S. 2020. Genetic diversity of Puccinia kuehnii, the causal agent of orange rust of sugarcane, from Brazil. Journal of Phytopathology. https://doi.org/10.1111/jph.12937.
DOI: https://doi.org/10.1111/jph.12937

Interpretive Summary: The rust of sugar cane caused by the fungus Puccinia kuehnii results in significant economic loses. In some countries e.g. Australia, the disease has been effectively managed by the use of resistant varieties of sugar cane; but in Brazil this method has shown ineffective as varieties considered resistant were now infected. Given the relative proximity of Brazil to United States, and the fact the rust spores are known to travel long distances by air; it was in our interest to determine the reason for supposedly resistant varieties to get infected. We determined that there are at least five groups of genotypes of the sugar cane pathogen Puccinia kuehnii, and we also identified statistically significant pathogen/sugar cane interactions, where certain genotypes are more virulent than others to each particular variety of sugar cane.

Technical Abstract: Resistant genotypes are the preferred method to control orange rust of sugarcane (Puccinia kuehnii). This approach was also adopted in Brazil; however, recent outbreaks on varieties previously considered resistant show that the efficacy of this method is vulnerable and requires a better understanding of pathogen diversity. This is achieved by applying genetic and phenotypic tools. Therefore, the present work aimed to examine genotypic and phenotypic variability among isolates of P. kuehnii from São Paulo, the most important sugarcane growing state of the Country. Twenty-nine rust isolates were fingerprinted with 18 SSR markers to estimate genotypic diversity by Neighbor-Joining (NJ) and 3D-Principal Coordinates (3D-PCoA) using the software NTSYSpc v.2.0. Phenotypic data were collected from five isolates inoculated on eight sugarcane cultivars and evaluated 21 days later as diseased-leaf area by Assess 2.0. Our genotypic results showed that all isolates were clustered into four main groups, which could be discriminated by three SSR markers, NPRL_PK_108a, NPRL_PK_162_spka, and NPRL_PK_221_spka. Phenotypic data showed statistically significant interactions (p ' 0.05 and p ' 0.01) in some isolate x cultivar associations, indicating existence of different pathotypes.