Issue link: http://read.dmtmag.com/i/71703
Crosses of rootstock seedlings are first screened in the greenhouse for complete suppression of a virulent nematode popu- lation capable of feeding on Harmony and Freedom rootstocks. Seedlings that show no egg masses on their roots are then eval- uated in the field at the UC Kearney Research and Extension Center in Parlier, California. Rootstock selections that make the field trial at Kearney are grafted with Syrah as the scion variety. Cousins also has some field trials in grower vineyards. Dormant cuttings are also evaluated for rooting ability and ease of propagation so that plant material can be easily propa- gated by commercial nurseries, which helps keep rootstock costs down. Elite selections are tested for virus at "Growers are in a much better position now than they were 20 years ago." —Peter Cousins the Foundation Plant Services so that if they are chosen as a released selection, clean planting material is readily available for nursery propagation. Four years of fruit data and three years of pruning weight data collected from the three new rootstocks showed the following fruit-to-pruning weight ratios: • Matador—9.43 • Minotaur—8.84 • Kingfisher—6.53 • Freedom (check)—6.14 The higher fruit-to-pruning weight ratios of the new rootstocks demonstrate the improved production efficiency when compared to Freedom, the check. Cousins is already focused on the next generation of root-knot–resistant root- stocks, working to combine genetic con- trol of resistance with more efficient and productive rootstocks. Researchers have discovered two genes that confer resist- ance to root-knot nematodes and are working to include both genes in the breeding of new rootstocks. "Growers would like to have vine size (vigor choices) in the nematode-resistant rootstocks available," he said, noting that phylloxera protection comes in rootstocks that offer high, mid-, and low vigor levels. He also wants to find nematode-resistant rootstocks that work in a variety of soil conditions, such as high salinity. Petiole analysis is part of the evalua- tion process. "Now that we have fruiting on the vines, we want to see what the rootstock behavior is when it comes to nutrients and water," he said, adding that petiole samples are being analyzed to learn if there are rootstock differences in vine nutrient and water uptake. "Grower interest in the project is increasing, and we're getting requests to be part of large, grower planting trials," Cousins said. Some 20 selections grafted to Syrah are currently in the advanced evaluation phase in field trials at Kearney. The first year of yield data from the advanced stage was collected last fall. Another round of ten or so potential rootstocks will be planted in 2013. • Our Reputation Is Everything To Us! ® Grape rootstock breeder Peter Cousins inoculates a grape seedling with an aggressive strain of root-knot nematodes. Seedlings that are resistant are candidates for use as rootstocks. 3008, SWING HITCH 3210: 10.5' WIDTH 3210, SEMI MOUNT 290 Series: 5', 6', 7' WIDTHS 3209: 9' WIDTH 3008: 8' WIDTH 290 Series Burrows Has Been a Full Service Bush Hog Dealer for 45-plus Years! When you buy BUSH HOG, you get great performance NOW AND FOR YEARS TO COME. Gearbox Warranty 5 Year Limited www.goodfruit.com local dealer See your GOOD FRUIT GROWER JULY 2012 31 photo by peggy greb, usda