Host-pathogen interactions in the wheat-Phaeosphaeria nodorum pathosystem
Stagonospora nodorum blotch, causal agent Phaeosphaeria nodorum, is part of the wheat leaf spotting complex and is a major disease in Saskatchewan and other wheat growing regions. Host resistance results from insensitivity to proteinaceous host-selective toxins produced by P. nodorum. Different toxin combinations amongst individuals in the P. nodorum population are expected to contribute to host specificity. Genetic variation in the pathogen populations needs to be well understood in order to develop cultivars with durable resistance. The presence of host specificity was investigated by evaluating the reaction of 49 isolates on 16 wheat lines at the second leaf stage. ANOVA revealed a significant interaction between the isolates and wheat lines indicating host specificity is present in this pathosystem. Based on differences in virulence, the 49 isolates could be placed into 3 clusters that could be further sub-divided into 9 groups. The present data is consistent with a toxin-based, inverse gene-for-gene model. Another aspect of this study looked at the genetics of resistance to Stagonospora nodorum blotch. Breeding resistant varieties is desirable but requires an understanding of the genetic basis of resistance. Resistance to Phaeosphaeria nodorum isolates Kelvington and 06-SN-002 was studied in the wheat population Altar Synthetic/Kenyon. This population consisted of 96 F6-derived recombinant inbred lines. The population was evaluated for disease reaction in a RCBD experiment with 3 replicates inoculated at the second leaf stage. The second leaf was rated on a 1 to 5 scale at 7 days post inoculation. When inoculated with isolate 06-SN-002, Altar Synthetic and Kenyon had intermediate disease reactions of 2.9 and 3.0, respectively. When inoculated with Kelvington, Altar Synthetic was resistant (rating of 1.8) and Kenyon was highly susceptible (rating of 4.6). One major QTL was found, suggesting that a single locus is controlling the resistance reaction. Microsatellite markers were identified that are closely linked to this QTL.
Master of Science (M.Sc.)