Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2004
Publication Date: 1/21/2004
Citation: Leonard, K.J., Anikster, Y., Manisterski, J. 2004. Patterns of virulence in natural populations of Puccinia coronata on wild oat in Israel and in agricultural populations on cultivated oat in the United States. Phytopathology. 94:505-514.
Interpretive Summary: Crown rust, the most destructive disease of oat, is difficult to control. Most resistance in oat is race-specific. Extensive use of any single resistance in commercial oat production selects virulent rust races that can overcome the resistance. In Israel wild oats grow in mixed populations with rich diversity of resistance types, and crown rust does not cause severe epidemics. To understand why, we studied the virulence of crown rust on wild oats in Israel by testing the ability of each rust race to infect oat plants with 26 different resistance genes known to occur in wild oat plants in the Mediterranean region. Just one of the resistance types was effective against all crown rust races from Israel, and no resistance type was completely ineffective. On average, races of crown rust from Israel, where the resistance genes occur naturally, were only slightly more virulent than crown rust races from the U.S., where most of the resistance genes have not been not used commercially. Our results confirm that genetically mixed populations of plants with many different resistance types do not promote selection of highly virulent rust races in natural ecosystems. Therefore, mixtures of crop varieties with different resistance types can be used to prevent severe rust epidemics by preserving adequate levels of effectiveness of the resistance indefinitely.
Technical Abstract: Crown rust, Puccinia coronata, in indigenous populations of Avena sterilis has been cited as an example of stability of wild pathosystems that consist of natural mixtures of resistance and virulence. This study confirmed that virulence/avirulence polymorphisms in P. coronata on A. sterilis in Israel are highly diverse and that super races do not dominate. Isolates of P. coronata from Israel in 1991-1996 were polymorphic for virulence to 35 of 36 differential oat lines with resistance genes from A. sterilis. On average, isolates of P. coronata were more highly virulent to differentials with Pc genes from A. sterilis accessions from Israel than to differentials with Pc genes from other countries. Isolates from Israel were also more virulent on average to 10 additional differentials with Pc genes derived from A. sativa than to differentials with Pc genes from A. sterilis. Frequencies of virulence were usually higher in collections of P. coronata from Israel than in collections from cultivated oat in the United States, even though several of the Pc genes in the differentials have been used extensively in American oat cultivars. Mean virulence complexity of P. coronata from eight regions of Israel was not correlated with the distribution of resistance among collections of A. sterilis from previous surveys in the same areas, probably because pathogen migration between regions within Israel is sufficient to obscure effects of selection locally.