After the release of Guardian® in 1993 (Okie et al., 1994a), the USDA-ARS peach rootstock breeding program at Byron, GA, shifted its emphasis to combining resistance to PTSL, ARR, and several species of root-knot nematodes into a single rootstock. To a large degree, this was driven by the recognition of Guardian®’s deficiencies, in particular its susceptibility to ARR (Beckman et al., 1997). This deficiency now looms large. With the suppression of PTSL that Guardian® rootstock provided, ARR, formerly second in importance to PTSL, has moved to the forefront and is now the single most important cause of premature tree death in the southeastern U.S. peach industry (Miller, 1994). Unlike stone-fruit production areas in Europe and California where Armillaria mellea appears to be the predominant species encountered (Adaskaveg et al., 2008), in the southeastern United States, the principal species encountered appears to be A. tabescens and only occasionally A. mellea (T.G. Beckman, unpublished data; Rhoads, 1954; Savage et al., 1953; Schnabel et al., 2005). The search for a rootstock capable of dealing with all these soil-borne disease problems was pursued via the testing of a wide variety of plum and peach species and the creation and testing of plum, peach, and plum × peach interspecific hybrids.
Early work demonstrated that FLA 1-1, a putative native North American plum hybrid, had potential for use on PTSL- and ARR-infested sites. FLA 1-1 was subsequently named and cooperatively released for trial by the USDA-ARS and the University of Florida as ‘Sharpe’ (Beckman et al., 2008). Unfortunately, ongoing testing subsequently demonstrated that ‘Sharpe’ was unable to match the production efficiency and fruit size offered by Guardian® rootstock such that widespread commercial use could not be recommended (Beckman and Chaparro, 2015).
More recently, ‘MP-29’, a clonal plum × peach interspecific hybrid, was cooperatively released for trial by the USDA-ARS and the University of Florida (Beckman et al., 2012). ‘MP-29’ improved considerably on ‘Sharpe’ rootstock by offering not only PTSL resistance, comparable to Guardian®, but also resistance to ARR, significantly better than that provided by Guardian® or even ‘Sharpe’ (Beckman et al., 2012). Additionally, ‘MP-29’ offered resistance to several root-knot nematode species of interest in the Southeast, i.e., Meloidogyne incognita and M. floridensis. Horticulturally, ‘MP-29’ also offered a significant reduction in tree vigor, similar to that of ‘Sharpe’. However, unlike ‘Sharpe’, ‘MP-29’ displayed excellent productivity and fruit size comparable to, if not better than, that provided by Guardian® rootstock (Beckman et al., 2012). Since its release, ‘MP-29’ has moved into commercial production and is now being offered by several nurseries in Tennessee, Florida, and California. The testing of the disease resistance and other attributes of ‘MP-29’ has continued in researcher and grower trials. The purpose of this report is to describe the disease resistance of ‘MP-29’ in these trials.
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