Thursday, May 19, 2011

Breeding New Pest Resistant Rootstocks for Grapes

With bloom well underway, grapevine breeders and geneticists, such as Peter Cousins, with the USDA’s Grape Genetics Research Unit, in Geneva, NY, are busy making crosses between pairs of vines having favorable traits.  Cousins is a rootstock breeder, so traits that interest him include resistance to root-knot nematodes, soil-borne pests whose feeding activities can cause extensive damage to grapevine roots, thereby weakening the vines and reducing yields.  Though Cousins, is based in NY, he is cultivating some advanced selections from his rootstock breeding program in a vineyard at the Kearney Agricultural Research and Extension Center in Parlier, California.  By growing the vines at Kearney, Cousins can assess their performance in the San Joaquin Valley, one of the most important grape-growing regions in the world.  Vines that maintain their nematode resistance, grow well, and are easily propagated, may eventually be released as commercial rootstocks, and serve as a genetic resource for future crosses aimed at further strengthening their nematode resistance by incorporating as many resistance mechanisms for resistance as possible.
Some wild grapevine species have unique nematode resistance mechanisms, and are thus used as parents in rootstock breeding.  Cousin’s goal is to incorporate as many different forms of resistance as possible into new rootstocks, so some advanced selections are complex hybrids of several species.  Wild grapevines, and their hybrids, are dioecious; invididual vines bear clusters of either male or female flowers.  Dioecious vines are relatively easy to cross as the flowers do not have to be emasculated; to prevent unwanted crosses, he simply encloses female flower clusters in paper bags prior to bloom. 
As bloom approaches, he periodically he taps on the bags, listening for the rattle of detached petals that signals the blossoms are ready to be pollinated.  Properly prepared, pollen, which Cousins prepares by grinding flowers in a coffee mill, can be stored for a relatively long time, facilitating crosses between vines that might not flower at the same time.  To pollinate, the bags are removed, the appropriate pollen is slathered on with paint brush, and the cluster is labeled, and recovered with the bag.  Cousins will return in the summer, to extract the seeds from the fruit.  Seedlings will then be screened for nematode resistance, and the best selections may eventually end up returning to Parlier, to be evaluated alongside their parents.  To learn more about Dr. Cousin’s research program, and see his rootstock selection vineyard, plan to attend Grape Day at Kearney, August 18, 2011.

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