Genetic Relationships of Crown Rust Resistance, Grain Yield, Test Weight, and Seed Weight in Oat

Integrating selection for agronomic performance and quantitative resistance to crown rust, caused by Puccinia coronata Corda var. avenae W.P. Fraser & Ledingham, in oat (Avena sativa L.) requires an understanding of their genetic relationships. This study was conducted to investigate the genetic relationships of crown rust resistance, grain yield, test weight, and seed weight under both inoculated and fungicide-treated conditions. A Design II mating was performed between 10 oat lines with putative partial resistance to crown rust and nine lines with superior grain yield and grain quality potential. Progenies from this mating were evaluated in both crown rust-inoculated and fungicide-treated plots in four Iowa environments to estimate genetic effects and phenotypic correlations between crown rust resistance and grain yield, seed weight, and test weight under either infection or fungicide-treated conditions. Lines from a random-mated population derived from the same parents were evaluated in three Iowa environments to estimate heritabilities of, and genetic correlations between, these traits. Resistance to crown rust, as measured by area under the disease progress curve (AUDPC), was highly heritable (H = 0.89 on an entry-mean basis), and was favorably correlated with grain yield, seed weight, and test weight measured in crown rust-inoculated plots. AUDPC was unfavorably correlated or uncorrelated with grain yield, test weight, and seed weight measured in fungicide-treated plots. To improve simultaneously crown rust resistance, grain yield, and seed weight under both lower and higher levels of crown rust infection, an optimum selection index can be developed with the genetic parameters estimated in this stud

Multi-location testing to identify oat germplasm with partial resistance to crown rust

Partial resistance to cereal rusts is characterized by reduction in pathogen reproduction despite a susceptible infection type (Parlevliet, 1985). In some pathosystems (e.g. blast in tropical lowland rice) such resistance has proved to be durable (Bonman et al., 1992). To identify oat germplasm with partial resistance to crown rust, caused by Puccinia coronata, a multilocation screening trial was initiated in 2002. Eighty-six entries were tested at 3 locations planted in the fall of 2002 in the southern US and at 5 locations planted in the spring of 2003 in the midwestern US and Canada using at least 2 replications per site. The line MN841804 was the resistant check and cultivars Brooks and Otana were susceptible checks. The resistant check showed an average disease level of 7.5% relative to the susceptible checks across locations. One entry, the cultivar CDC Boyer, may have a useful level of partial resistance for areas less prone to the disease. In the present study it averaged 24.5% disease relative to the checks across locations. CDC Boyer and 26 other lines showing relative severity values between 3% and 25% and low variation between locations were selected for further testing in 2004. Also, adult plants of CDC Boyer, OT389 (12.1% across locations) and IA98822-2 (17.6% across locations), are undergoing greenhouse tests with compatible races of P. coronata. Further field and greenhouse experiments are planned with these and other lines to ascertain if the lower disease level in field trials is correlated with partial resistance assessed in controlled inoculations. Bonman, J.M. et al. 1992. Annual Review Phytopathology 30:507-528; Parlevliet, J.E. 1985. In: Roelfs, A.P. and W.R. Bushnell (eds.) The Cereal Rusts vol. II. New York, Academic Press, Inc. p. 501-525.vokMyynti MTT tietopalvelu