Issue link: http://read.dmtmag.com/i/71703
Peach tree short life can dramatically shorten the life of a peach orchard, as this orchard, only in its fourth leaf, demonstrates. rootstock It is challenging to get enough rootstock material to plant to provide multiple trees of multiple varieties at multiple sites, all in the same year. Poor anchorage can be a problem revealed in rootstock trials. This is Redhaven on Pumiselect. Nemared in 1983, and Guardian in 1994. University of Florida developed a rootstock, Flordaguard, which resists a new root-knot nematode species that occurs in Florida. Because peaches are self-fertile and mostly self-pollinated, planting peach pits of an inbred variety will produce a row of very uniform plants that can be used as rootstocks, Reighard said. The rootstock Guardian, for example, which was developed by USDA and Clemson University, is grown from seeds produced in a seed orchard at Clemson. In apples, all the modern rootstocks are clonal and rated mostly for their dwarfing ability, but more and more of them are being chosen for resistance to diseases like fireblight and the complex called replant disease. Some peach rootstocks are grown from clones, and more of them have been evaluated and are becoming available, especially those from Europe. There are some conditions under which peach roots ROOTSTOCK performance "There are few funding sources, and research funding is often bootlegged on are not capable of producing a good tree, Reighard said. In Colorado and Utah, for example, the high pH soils create iron deficiency in all peaches. For these conditions, interspecific crosses of peach with plum or almond make better rootstocks. These tend to be clonal rootstocks, mostly from Europe and California. In the United States currently, growers have seven seedling rootstocks available— other grants." —Greg Reighard D Lovell, Halford, Bailey, Tennessee Natural, Guardian, Nemaguard, and Nemared. Clonal rootstocks developed in the United States include the Controller series, Viking, Atlas, Cornerstone, Brights Hybrids, Sharpe, and MP-29. Trends Reighard says that peach rootstock testing work is somewhat frustrating. It is not well supported, either by public funding or by private industry. The government provides some funding through Hatch Act funds. "There are few funding sources," he said, "and research funding is often bootlegged on other grants." In peaches, both variety and rootstock breeding is primarily done by private breeders and commercial nurseries, with only a few public breeders. "Most new rootstocks will be proprietary and protected by patents and licenses," he said. Many times, new rootstocks will not be entered into the NC-140 testing program because of concerns over proprietary rights, and if they are entered, they come with legal paperwork and nondisclosure agreements. It is often difficult to get enough rootstocks propagated so that eight to ten trees can be planted at all the locations for good comparison trials. "The work is resource intensive (i.e., field plantings) and long term (5-10 years), thus expensive to undertake and main- tain," he said. "It is very hard to get the trees, the land, and the funds to replicate the trials under all the grower scenarios of spacing, variety, and training systems." Asexual propagation (cloning rather than production from seed) techniques continue to improve, Reighard said, which means more efficient and economical production of complex hybrid rootstocks. And the use of biotechnology, with marker-assisted selection, continues to shorten the time required to find rootstocks with desirable traits. • r. Greg Reighard summarizes what the NC-140 trials have shown about the performance of rootstocks in the face of various problems: Root-knot nematodes: Several rootstocks are immune or tolerant to these nematodes. They include Guardian, Flordaguard, Adesoto 101, Penta, Krymsk 1, Sharpe, MP- 29, Barrier 1, Cadaman, Pumiselect, Felinem, Garnem, Monegro, Replantpac, and Densipac. Root lesion nematodes: Guardian, Viking, and Atlas have some tolerance to root lesion nematodes. Krymsk 1 and 86 have shown tolerance in the greenhouse, as has Replantpac. Brights Hybrid #5 and Cornerstone seem less susceptible, and Densipac has been reported as resistant. Peach tree short life (bacterial canker complex): Guardian, Viking, and MP-29 have excellent resistance, and Sharpe is moderately resistant. Armillaria: Sharpe and MP-29 (both peach/plum hybrids) have shown resistance or tolerance in limited tri- als in Georgia, as have SAM 1 and SAM 2 in California, which are almond hybrids. Waterlogging: Peach roots are not tolerant to wet con- ditions. Viking and Cadaman are better than peach. Plum hybrids such as Penta, Tetra, Mr. S. 2/5, Adesoto 101 and Krymsk 1 and 86 are tolerant. Densipac and Replantpac are also tolerant. Cold hardiness: Krymsk 1 and 86, Fortuna, Evrica, and P. americana are interspecific hybrids that are cold hardy, though compatibility may be an issue with Fortuna and Evrica. Calcareous soils: Cadaman, Barrier 1, Adesoto 101, Felinem, Garnem, Monegro, Penta, Mr.S 2/5, Julior, and ReplantPac, all European clonal rootstocks, show toler- ance to the iron chlorosis problem that come with high pH soils. Semidwarfing rootstocks: Several rootstocks will reduce peach tree size to 70 to 95 percent of their Lovell counterparts. The Controller series 9.5, 9, 8, 7, 6, and 5 as an interstem, Penta, Imperial California, Pumiselect, and Nanopac produce trees in this size range. For still smaller trees, Krymsk 1, Controller 5, Sharpe, Julior, and MP-29 produce trees 60 percent of Lovell size, and Densipac gives a 50-percent-size tree. —R. Lehnert GOOD FRUIT GROWER JULY 2012 23 photos courtesy of greg reighard photo courtesy of greg reighard