|Berg C C|
|Sherwood R T|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/1993
Publication Date: N/A
Interpretive Summary: Genetic resistance to disease is the only practical method to reduce and control the losses caused by diseases in forage grasses. Orchardgrass and bromegrass germplasm has been developed with high levels of resistance to purple leaf spot and brown leaf spot, respectively. However, it is not known if this resistance will persist through several generations of seed increase as would happen when populations are increased from breeders seed to certified seed. This study demonstrated that this germplasm was stable (disease resistance was not diminished) over two generations of seed increase without artificial selection. Therefore, it would be reasonable to expect that cultivars could be developed from these populations, or sub-populations could be selected from these populations without losing the disease resistance that has been developed.
Technical Abstract: Genetic resistance is the only practical method to control foliar diseases on forage grasses. Recurrent phenotypic selection was used to develop orchardgrass (Dactylis glomerata L.) germplasm PL-OGDR1 with resistance to purple leaf spot (caused by Stagonospora arenaria Sac.), and smooth bromegrass (Bromus inermis Leyss.) germplasm PL-BDR1 with resistance to brown leaf spot (caused by Pyrenophora bromi (Died.) Drechs.). This study was conducted to determine whether resistance would be maintained when the germplasms were advanced two generations without conscious selection for disease resistance. The germplasm releases and the two unselected generations and three cultivars of each species were rated for disease reaction in two greenhouse inoculations. Disease scores, based on spot size and coverage, were low for all generations of resistant germplasm, and there were no differences among generations. The frequency distribution of fdisease scores remained relatively constant over generations. Cultivars were much more susceptible, with disease scores that averaged two- to three-fold higher than the resistant germplasms. Apparently, a large number of additive genes were accumulated in the resistant populations and nonadditive loci were homozygous for recessive (resistance) genes. The Apparently a large number of additive genes were accumulated in the results indicate that in the absence of selection pressure, the population can be advanced for two successive generations without a shift in resistance to orchardgrass purple leaf spot or bromegrass brown leaf spot.