Issue link: http://read.dmtmag.com/i/63050
THE RIGHT ROOTSTOCK boosts fireblight resistance D o fireblight-resistant rootstocks make the scion variety growing on them more resistant to fireblight as well? Growers have noticed some vari- eties seem more resistant to fireblight when grown on certain rootstocks, but a new study confirms it. Not only can a fireblight-resistant rootstock live on while the scion is severely damaged or even killed, it can reduce the damage the scion variety suffers. Eleven authors, including Drs. Philip Jensen, Robert Crassweller, Henry Nguygi, Naomi Halbrendt and several others at Pennsylvania State University and Dr. Gennaro Fazio at the USDA-ARS Plant Genetic Resources Unit in Geneva, New York, recently published a paper in the journal BMC Genomics. "In this study, we found that root- stock genotype influenced Gala scion fireblight susceptibility in grafted apple trees," they wrote. "This indicates that at least some level of resistance possessed by the rootstock can be con- ferred upon the scion variety that is grafted to it." They measured the extent of shoot death on Gala scions grafted to several different rootstocks in a three-year-old orchard that was planted at the Penn State University Fruit Research and Extension Center at Biglerville, Penn- sylvania. Trees on G.30 and MM.111 showed the lowest rate of necrosis while trees on M.27 and B.9 showed the highest rates. They found a relationship between fireblight susceptibility and several genes. "A major objective of this study was to identify candidate genes in apple that are potentially involved in deter- mining fireblight resistance prior to an infection event," they wrote. "The identification of these genes will con- tribute to the understanding of host- pathogen interactions as well as provide plant breeders with valuable new markers for improved disease resistance breeding." —R. Lehnert The decision to look deeper came a few years ago when Michael Grusak, a sci- entist at USDA-ARS's Children's Nutrition Research Center at Baylor College of Med- icine in Houston, Texas, wanted to know whether rootstocks affected uptake and nutritional level of zinc in apples. Grusak contacted the Geneva researchers, where Fazio is in charge of one of the largest col- lections of apple rootstocks in the world. At Geneva, Darius Kviklys, a visiting scientist from the Lithuanian Research Center for Agriculture and Forestry, was 28 MAY 1, 2012 GOOD FRUIT GROWER Darius Kviklys, a visiting scientist from the Lithuanian Research Center for Agriculture and Forestry in Babtai, Lithuania, spent a year at Geneva collecting data on 38 rootstocks and their ability to take up a dozen different nutrients. Calcium uptake How different rootstocks affected the leaf calcium concentration in Golden Delicious trees. 10 12 14 16 18 0 2 4 6 8 4.5 SOURCE: G. Darius Kviklys proposing to spend his sabbatical year at Geneva doing research on root- stock effects on the uptake of a dozen elemental nutrients—phosphorus, potassium, magnesium, calcium, sodium, iron, manganese, copper, sulfur, molybdenum, nickel, and zinc. So the three—Fazio, Kviklys, and Grusak—joined by Cornell University horticulturist Terence Robinson, designed experiments aimed at answer- ing four questions: • How well do different rootstocks absorb and transmit macro- and micronutrients? • Is this capacity influenced by soil type? • Is this capacity influenced by replant disease? • Is this capacity influenced by soil pH? The experiments used 38 rootstocks, two scion varieties, and pots filled with trees growing in pasteurized and unpasteurized (replant dis- ease susceptible) soil of various textures and pH levels. All were fertilized weekly. Then the researchers measured tree sizes and weights and the mineral contents of leaves. The experiments used three well-known Malling rootstocks (M.26 EMLA, M.9 T337, and MM.111), Budagovsky 9 and three other less well- known Budagovsky rootstocks, a Japanese rootstock, and 30 Geneva rootstocks, nine of them released for commercial use (G.11, G.16, G.30, G.41, G.202, G.214, G.890, G.935, and G.969) and 21 of them still www.goodfruit.com 5.5 6.5 pH G.41 MM.111 CG.6969 7.5 8.5 CALCIUM (milligrams per gram dry weight) photo by gennaro fazio