The USDA-ARS stone fruit rootstock development program at Byron, Georgia

The primary objectives of the USDA rootstock program at Byron, Georgia, are to develop new peach and plum rootstocks with resistance to peach tree short life (PTSL), Armillaria Root Rot (Armillaria spp.) and root-knot nematodes (Meloidogyne spp.). Significant progress has been made in the identification and development of peach rootstocks with improved resistance to PTSL. A major milestone was achieved in 1993 when USDA and Clemson researchers cooperatively released Guardian((TM)) (BY520-9) rootstock. Through seven years in field trials on severe PTSL sites, Guardian has provided significantly improved tree longevity and productivity compared to Lovell, the long-time recommended rootstock for such sites. Progress has also been made in the identification of potential sources of resistance to Armillaria Root Rot, To date, the most promising selections have been derived from germplasm incorporating native North American plum species. The first of these selections were recently advanced to commercial scale trials. Several interspecific hybrids between promising plum lines and PTSL resistant peach lines are currently undergoing testing for graft compatibility with peach scions and field trials on both PTSL and Armillaria test sites.