Breeding for resistance to leaf blotch in Saskatchewan oat
Isolates of leaf blotch pathogens from commercial oat fields will be collected to evaluate the virulence spectrum of these pathogens. The effect of temperature, moisture/humidity, inoculum concentration and plant growth stage will be studied to develop an indoor screening technique. Oat germplasm will be screened for resistance and genetic mapping of resistance will be undertaken.
Oat leaf blotch diseases are caused by a complex of Pyrenophora avenae, Cochliobolus sativus and Stagonospora (Septoria) avenae. Concern exists as to the potential harm they may pose to oat yield and physical grain quality (i.e. test weight) which can negatively impact production and the potential to meet minimum standards of milling quality. Growing resistant varieties is an effective method of control, but very little is known about sources and effectiveness of resistant oat germplasm. This project was initiated to address these deficiencies through four objectives: 1) to understand the prevalence of these pathogens in commercial oat fields and develop artificial inoculation techniques suitable for evaluating oat germplasm resistance, 2) to study the virulence variability in these pathogens, 3) to identify resistant oat germplasm and understand the genetic inheritance of resistance and, 4) to map resistance quantitative trait loci (QTL) and identify associated genetic markers.
Over 4 field seasons (2014-2017) P. avena was identified in 59% of 160 fields surveyed, Cochliobolus sativus was present in 23% of surveyed fields while S. avenae was only identified in 3% of fields. Methods to culture these pathogens on artificial media and to develop an effective inoculation procedure to screen oat germplasm were successful. Critical factors included inoculation of 14 day old oat seedlings, maintenance of 100% relative humidity and total darkness following inoculation for a period of 24 hours, and scoring disease reaction seven days after inoculation. A set of 15 P. avenae isolates and 17 C. sativus isolates were screened across a panel of nine diverse oat lines which revealed a wide range in pathogenicity for isolates of P. avenae and C. sativus. Several oat lines with effective resistance to both pathogens were identified, the most resistant being 96-21Cn19 (Aberystwyth University, UK), ND061868 (University of North Dakota) and Ave117.02 (INIA, Chile). In general, lines that showed resistance to one pathogen were also more resistant to the other pathogen.
Four bi-parental recombinant inbred line (RIL) populations were used to study the genetic inheritance of resistance against three P. avenae isolates. One or two gene models explained the inheritance of resistance in four cases with one population unable to be fit to any model. Three bi-parental recombinant inbred line (RIL) populations were used to study the genetic inheritance of resistance against one C. sativus isolate. A three gene model explained the inheritance of resistance in two of the populations with one population unable to be fit to any model. QTL mapping using the OT3011 x Iowa N2052 population revealed a single strong QTL (explaining 67% of the variation) on chromosome 5C that was effective against the two P. avenae isolates. A weaker QTL was also located on chromosome 5C, but a different position, in the AC Ass/S42 x CDC Dancer population. A 150 member association mapping panel, composed of elite breeding lines and varieties adapted to Western Canada, was also investigated for loci linked to P. avenae resistance. Four loci, identified using different association methods, linked to resistance were located across four chromosomes, including chromosome 5C.
A number of significant accomplishments and findings were made through this project including, 1) P. avenae is the most relevant leaf blotch pathogen in terms of prevalence, 2) isolates of P. avenae and C. sativus display a range of pathogenicity across oat germplasm, 3) oat germplam resistant to these pathogens exist and inheritance of resistance tends to be controlled by 1-3 genes and 4) QTL linked to P. avenae resistance were identified and will assist in incorporation of resistance into future oat varieties.