Alfalfa Germplasm Enhancement for Blue Aphid and Stem Nematode Resistance
Vegetable and Forage Crops Production Research
2012 Annual Report
1a.Objectives (from AD-416):
Screen dormant alfalfa germplasm for resistance to blue alfalfa aphid (Acyrthosiphon kondoi) and stem nematode (Ditylenchus dipsaci) and release germplasm.
1b.Approach (from AD-416):
Plant selected dormant germplasm in greenhouse for determination of resistance to blue aphid. At the same time, screen large numbers of plants from Columbia Basin College germplasm for selection purposes. Score resistance reaction according to standard tests using known non-dormant resistant varieties as resistant checks. If dormant resistant plants are identified, cross in greenhouse, test and reselect. If no resistance is identified in dormant germplasm, cross with resistant non-dormant germplasm in the greenhouse. Screen seed from dormant germplasm for resistance and plant in the field to select for class four dormant plants. Recombine in greenhouse for germplasm release.
Standard tests developed for screening and testing for stem nematode have failed to produce resistant varieties that will perform well in the field. Recurrent field selection is a good indication that field selection may be better suited than standard screening procedures that have been in use for over 30 years with little or no progress. Columbia Basin College (CBC) will plant experimental varieties selected from infested fields for stem nematode to evaluate progress for resistance. Additional selections will be made from the field for seed increase and testing. Germplasm will be released based on test results. At the same time a greenhouse screening procedure will be developed that will allow more time for infection of all plants. More precision is necessary for progress toward higher levels of resistance.
Three new isolation alfalfa seed increase blocks for Stem Nematode selected plants were transplanted to the field. Thirteen additional cages are established to produce seeds on potential stem nematode and pea aphid resistant lines. This falls under objective 1 of the related in-house project, "Identify molecular markers to screen alfalfa for resistance to environmental and biotic stresses including problems caused by nematodes and diseases". Bees were placed on cages. Biomass experimentals were screened for pea aphid in the greenhouse and about 24,000 plants were transplanted in the field to be selected for lodging and productivity. Seed for potential pea aphid germplasm release has been produced and is ready for characterization for other pests. The greenhouse stem nematode bench is being maintained for fall seeding of variety test. Progress for stem nematode resistance will be estimated with this test. Pea aphid selected germplasm will be seeded into yield test plots in August.