Graduate Thesis Or Dissertation
 

Assessment of genetic resistance to strawbreaker foot-rot (Pseudocercosporella Herpotrichoides) in selected winter wheat (Triticum aestivum L.) cultivars

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  • Strawbreaker foot-rot is a major limiting factor to cost efficient winter wheat production in the Pacific Northwest. Development of resistant cultivars has been hindered by the lack of adequate levels of genetic resistance and screening techniques which can consistently detect desired genotypes. Studies were conducted to determine if the reported strawbreaker foot-rot resistance of the cultivar "Rendezvous" is effective on isolates of Pseudocercosporella herpotrichoides found in the Pacific Northwest. Protected, naturally infected and artificially inoculated treatments were employed to determine the level of resistance of 10 cultivars including Rendezvous. Different concentrations of inoculum and stages of development were also used to determine if observations on leaf sheath penetration of seedlings obtained in the greenhouse were related to disease severity index readings taken in the field for selected cultivars. In addition, the nature of inheritance of strawbreaker foot-rot was studied in two crosses involving Rendezvous. Experiments were conducted at three locations and over two years at one location. Despite cultivar x treatment interaction, consistent levels of infection were observed in all experiments at each location. Significant differences were found for treatments and cultivars for most attributes. Yield losses, including the components of yield spikes per square meter, 1000 kernel weight, and kernel number per spike were proportional to the severity of the disease. Losses were greater when lodging occurred, which was also associated with disease severity. However, even in the absence of lodging losses were recorded in the naturally and artificially inoculated plots. Traits measured involving Rendezvous and Vpm/Mos 95//*2Hill were only slightly influenced by the treatments. Under greenhouse conditions, it was possible to distinguish the level of resistance of Rendezvous from susceptible cultivars at concentrations of 100 spores/ml, two weeks after inoculation at the seedling stage. Leaf sheath penetration of seedlings was found to be closely associated with the disease severity index obtained under field conditions. Generation means analysis performed in crosses involving Rendezvous indicated that additive and additive x additive gene action were responsible for most of the genetic variability associated with resistance. Narrow-sense heritability estimates also confirmed these fmdings. It would appear that Rendezvous has at least two major genes for resistance to strawbreaker foot-rot.
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