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Title: Progress in developing Armillaria resistant rootstocks for use with peach

item Beckman, Thomas - Tom

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2011
Publication Date: 10/3/2011
Citation: Beckman, T.G. 2011. Progress in developing Armillaria resistant rootstocks for use with peach. Acta Horticulturae. 903:215-220.

Interpretive Summary: Since its release in 1993, Guardian peach rootstock has provided outstanding resistance to peach tree short life (PTSL). Guardian is now the dominant rootstock utilized in the southeastern US peach production area. Unfortunately, Guardian, like all other available peach seedling rootstocks, is highly susceptible to Armillaria root rot (ARR). Not surprisingly, Armillaria root rot (ARR) has now emerged as the primary cause of peach tree mortality. Anticipating this, the USDA stonefruit rootstock development program at Byron, Georgia has been breeding and evaluating potential replacements for Guardian since its release. Sharpe rootstock was jointly released by the USDA and the University of Florida in 2007 as part of the effort to develop rootstocks with improved resistance to ARR. Now the first group of plum and plum x peach interspecific hybrid selections from the Byron breeding program are nearing completion of their testing. Several items stand out, displaying superior resistance to ARR, PTSL and species of root-knot nematodes common to this production area. Additionally, these materials display a useful range of tree vigor in combination with good overall productivity. The release of one or more from this group will provide growers with new rootstocks that will provide not only a significant improvement in tree life but also improved productivity and adaptability to different management regimes and growing sites.

Technical Abstract: GuardianTM (BY520-9) peach seedling rootstock was released in 1993 to provide a rootstock with superior resistance to peach tree short life (PTSL) which at the time was the number one cause of premature death of peach (Prunus persica L. [Batsch]) trees in the southeastern US. Since that time Guardian has become the dominant rootstock in this production area principally due to its exceptional resistance to PTSL. However, Guardian, like most peach seedling rootstocks, is highly susceptible to Armillaria Root Rot (ARR). Since Guardian’s release, ARR has replaced PTSL as the leading cause of tree death in the southeastern US. Accordingly, the rootstock development program at Byron has shifted its focus to the development of peach, plum and plum-peach interspecific hybrid materials with resistance to ARR, incited principally by A. tabescens in this production area. In 2007, the USDA, in cooperation with the Univ. of Florida, released ‘Sharpe’ rootstock for grower trial on Armillaria infested sites. ‘Sharpe’ is a clonal plum hybrid rootstock with resistance to PTSL, ARR and root-knot nematodes (Meloidogyne spp). ‘Sharpe’ is semi-dwarf; producing trees ca. 60% the size of those budded on Guardian. A number of plum hybrid, and plum x peach interspecific hybrids are nearing release in the Byron program that not only provide superior resistance to PTSL, ARR and root-knot nematodes but also offer a range of vigor from 60% to 105% that of seedling peach rootstocks with comparable, if not superior, horticultural productivity.