Type text ] NEW AND EMERGING ROOTSTOCKS The Ernie Christ Memorial Lecture

Introduction New rootstocks for peaches have been recently introduced into the United States through commercial nurseries. Most all of these rootstocks are complex Prunus L. hybrids that are propagated asexually. Past experience with newly introduced Prunus rootstocks has shown that extensive testing is critical to avoid potential problems in commercial situations due to nonadaptation of some rootstocks to North American climatic and edaphic conditions. In addition, putative resistance of introduced rootstocks to common soil diseases and other pathogens has not always carried over to orchard sites in the United States. To ensure widespread horticultural testing of new rootstocks, the NC-140 regional research group (www.nc140.org) continues to serve as an unbiased tester in many geographic and production areas of the United States, Canada and Mexico. Economic viability of a fruit production enterprise is linked directly to orchard productivity and management efficiency. To increase productivity and efficiency requires tree survival, managed vigor, and increased marketable yields over the expected life span of the orchard. The growers’ choice of rootstock is often as important if not more so than the scion variety whenever peaches are grown on soils having high bulk density, nematodes, root rot pathogens, or other edaphic or replant problems. If one or more of these conditions are present, tree survival and growth can be improved by selecting the appropriate rootstock for each soil or site situation. Peach production has been limited in the past by the absence of rootstocks that moderate vigor or are tolerant to undesirable soil properties, site characteristics, and soil-borne pathogens. As good orchard sites become scarce and chemical control practices become cost-prohibitive or unavailable, new rootstocks will be needed to overcome many soil and site problems that had been corrected previously by orchard relocation or chemical fumigation. Many new peach rootstocks have been developed in the past 20 years (Loreti, 1994; Loreti, 1997; Reighard, 2000; Moreno, 2004) since those listed by Layne (1987) and Okie (1987). Moreover, many of these are now available to growers in the U.S. This paper discusses some of the recent rootstock releases and their potential for solving some of the specific soil and site problems that stone fruit growers currently face.