STAGE 5 - LINER PRODUCTION...
Liner Production: These dormant nursery liners have been harvested from established intermediate stage stoolbeds. The smaller bundles have been trimmed and sorted in preparation for planting, the larger bundles have not yet been trimmed.
Stoolbed Evaluation: Nursery liners in the mounded stoolbed have not yet been harvested. Genotypes with stoolbeds that produce adequate rooting, few spines or branches, and sufficient vigor are retained for evaluation in stress tolerance tests.
Nursery Tree Growth: Promising stage 5 rootstocks are propagated in the nursery for intermediate stage orchard trials around the US. These trees are ready to be dug and shipped.
Extreme Temperature Tests: Early Spring Frost Injury: The first two plants have been subjected to freezing temperatures after two weeks of warmth, simulating a springtime cold snap. The first plant shows severe injury with regrowth from the roots. The second plant shows moderate injury with regrowth from the stem. The third plant is a control that was not subjected to the freezing temperatures. We expect to see clear differences between genotypes for the amount of injury they experience after a springtime cold snap. Additional screens for tolerance of mid-winter low temperatures is conducted on fully dormant plant material by our cooperators from AgCanada: JP Prive, Charlie Embree, and Dale Hebb. This screening work is supported in part by a grant from the International Dwarf Fruit Tree Association.
Replant Soil Tests: Todd Holleran is shown with our 1999 replant soil test. The tables on the left contain potted rootstock liners growing in a pasteurized soil mix collected from sites in New York with severe apple replant disease history. The tables on the right contain the same genotypes in the same soil mix, but without pasteurization. We hope to determine which rootstock genotypes are more tolerant of replant soil conditions by measuring the relative growth of the plants in pasteurized vesus unpasteurized soils. In 2000 this experiment will be repeated with Washington State Replant Soils. This screening is supported in part by a grant from the International Dwarf Fruit Tree Association.
Crown Rot Tests: We conduct tests in the greenhouse to identify rootstock genotypes resistant to crown and root rots (click above photo for closer look). Twenty vigorously growing rootstock liners of each genotype to be tested are planted into the square pots seen above. Ten of the liners are planted into a soil mix that has been inoculated with one of four different species of the Phytophthora fungus, while the other ten are transplanted into an identical sterile soil mix. After the young trees grow into the soil, they are placed in the flooding table pictured above. The tables are repeatedly filled with water.
Crown Rot Tests: Charlie Bennett is shown above draining a flooding table. The tables are flooded for 36 hour periods, once weekly for 5 to 10 weeks, allowing fungal infections to proliferate. Tolerance to the fungus is measured by the differential growth of the trees in the inoculated versus the flooded but uninoculated control trees. These tests are repeated until all elite genotypes have been tested for their resistance to Phytophthora cactorum (North American isolates), Phytophthora cactorum (European isolates), Phytophthora cryptogea, and Phytophthora cambivora. M.9 rootstock is used as the tolerant control, and MM.106 is used as the susceptible control. These methods are an adaptation of those developed by W. Wilcox, J. Am. Soc. Hort. Sci. 118:63-67. This screening is supported in part by a grant from the International Dwarf Fruit Tree Association.