Assessment of adult plant resistance to stripe rust in wheat

[摘要] English: The objective of this study was to develop and optimise methods to detectadult-plant resistance (APR) in wheat to stripe rust caused by Puccinia striiformisf.sp. tritici. A collection of spring wheats was tested at the seedling stage withdifferent temperature and light regimes to test the hypothesis thatenvironmental variation can induce APR expression in primary leaves.Treatments included pre-inoculation conditioning of seedlings at either 18° or25°C, followed by post-inoculation temperature and light treatments. In sometreatments intermittent low and high temperatures (18° or 25°C) were used aswell as a treatment with continuous low temperature (10°C). The highestinfection types were encountered with a pre-inoculation treatment of 18°Ccombined with a 24 h light cycle, and a post-inoculation treatment of 18°Ccombined with a 18 h light and 6h darkness cycle. Day length influencedinfection types more than temperature. All treatments subjected to less than14 h light per day showed a reduction in infection levels. Dark periodsexperienced prior to inoculation were not conducive to infection typedevelopment. Clear banding of infection zones and reduced sporulationoccurred. Based on the lack of correlation between seedling infection typesand adult responses observed in the field, no environment was conducive toexpression of APR to stripe rust in seedlings.Rating of adult plants for stripe rust resistance has traditionally beenproblematic in terms of infection levels and repeatability. Furthermore, severalattempts to investigate the reaction of normally grown adult plants in the glasshouse failed due to leaf damage. To improve these methods, anaccelerated system of producing adult wheat plants in a controlled environmentwas tested. By manipulating plant density, pot size, light and temperature,wheat plants reached maturity quicker than normally grown adult plants andwere referred to as mini-adult plants. In terms of leaf damage the mini-adultswere better suited for flag (terminal) leaf evaluation. For optimum results, themini-adult plants should be grown in a glasshouse rather than growth chamberand inoculated between heading and flowering.According to flag leaf infection type and whole plant reactions observed,the mini-adults provided an acceptable system for comparing adult plants todifferent isolates of P. striiformis. This system accurately detected APR inmost winter wheats tested and was reliable for a collection of CIMMYT springtype wheats. Disease ratings of 98 CIMMYT lines tested with this acceleratedsystem showed a correlation of 88% with field ratings.The mini-adult plant system was also tested with populations segregatingfor APR. Because of the likely application of genetic studies to resistancebreeding, it is essential to correlate glasshouse tests with field assessments.The approach followed in the present study conformed to guidelines in terms ofselecting cultivars with high levels of APR not previously analysed, as well ascomparing glasshouse and field data. Segregation ratios indicated thepresence of two resistance genes in the F3 of a Baviaans x Avocet S cross (χ²7:8:1= 0.1029), but were inconclusive for a Sunmist x Avocet S cross whereMendelian ratios could not be confirmed. The accelerated screening systemwas less successful than the screening of pure lines. Based on the fact thatthe reaction of Avocet S was not completely susceptible in the glasshouse, andmost likely influenced ratios, the lower success rate appeared to be a functionof the parental genotypes rather than in the system in general.Compared to the normal glasshouse procedure, the improved APR system took significantly less time and physical resources to achieve ratings.

[发布机构] University of the Free State