Prunus rootstock testing for peach tolerance to Pseudomonas and Armillaria diseases in South Carolina

Abstract

New commercial rootstocks for peach include P. persica seedlings as well as many Prunus interspecific hybrids and plum species. However, no rootstock has been successful in replant infected soils that have the Peach Tree Short Life Syndrome (PTSL) that includes both Pseudomonas syringae canker disease and Armillaria spp. root rot. Four rootstock trials consisting anywhere from 5 to 16 out of 18 total rootstocks were budded with 4 scion cultivars, ‘Flameprince’, ‘Crimson Lady’, ‘Julyprince’ and ‘Fireprince’ and planted in 2012, 2013, 2013, 2015, respectively, in either Edgefield or Oconee Counties in South Carolina, USA. Tree death from bacterial canker (P. syringae) occurred in all sites planted before 2015. Trees on the hybrid or plum species rootstocks except MP-29 had the highest mortality. P. munsoniana selections “1, 2, 3, and 4” had tree death of (24-63%) from either incompatibility or bacterial canker in the 2012 test. Trees on these rootstocks were also ~40 to 50% smaller than the controls after 4 years. Hybrid rootstocks Replantpac, Tempropac, Densipac and Purplepac had PTSL-related mortality of 50, 63, 67, and 33%, respectively for the 2013 ‘Crimson Lady’ planting. Several ‘Julyprince’ trees on Densipac and Tempropac rootstocks have also died from PTSL. The plum hybrid MP-29 had a high survival and semi-dwarfing effect (~50% standard) on the “2” test sites in which it was planted in 2013. Lovell and Guardian® have had minimal PTSL death from bacterial canker but Armillaria has started to kill trees in the 2012 planting site. Another 3-5 years will be necessary to determine Armillaria tolerance, but the new rootstocks appear to have less resistance to bacterial canker than their commercial standard counterparts.