Clonally replicated peach seedlings [Prunus persica (L.) Batsch] of Lovell, Nemaguard, and four F1 selections of Lovell × Nemared were tested for field survival on a peach tree short life site. Rootstock families differed in growth, survival, and longevity. Genetic variation was similar to environmental variation for most families. Based on seedling within rootstock family, estimated broad-sense heritabilities for survival and longevity were high. The use of clonally replicated seedlings allowed the selection of apparently superior individuals from both Lovell and the other more short-lived rootstock families in a single screening.
Seedlings or rooted cuttings of 35 lines of peach [Prunus persica (L.) Batsch] and other Prunus spp. were screened for resistance or tolerance to the ring nematode Criconemella xenoplax (Raski) Luc & Raski (Cx). Host reaction to Cx was evaluated by comparing root and shoot growth of infested plants with that of uninfested checks. Reaction of Cx to the host was reflected in nematode density per gram root dry weight (NPGR). Effects of Cx on root growth were not always correlated with increases in Cx per 100 cm3 of soil or in NPGR. Prunus japonica Thunb. and P. tomentosa Thunb. showed no Cx-related growth reduction and had lower Cx densities than most other lines. ‘Lovell’ peach had a smaller root system and fewer Cx per pot than ‘Nemaguard’ peach, but differences in NPGR were not significant. With high inoculum levels, significant differences in NPGR between lines, and in growth parameters within lines, could be detected after 6 months.
Peach tree short life (PTSL) is associated with the presence of ring nematode, Mesocriconema xenoplax, and poor orchard management practices. Finding a noncommercial field site to evaluate rootstocks for PTSL resistance is increasingly difficult. The time needed to create a PTSL test site was investigated. In 1994, a site not planted in peaches for >80 years was identified in Byron, Ga. Analysis of preplant soil samples revealed that there were no M. xenoplax on the site. One-third of the land was planted to peach and infested with 1600 ring nematodes per tree in Spring 1994 (P2) and another one-third in Spring 1995 (P1). The remaining one-third of the land received no trees or ring nematode and served as the control (F2). In Fall 1995, trees were removed from P1 and P2 plots and all treatments were replanted to peach in 1996. In 1997, tree death resulting from PTSL occurred only in P2 (7%). By 2000, PTSL tree death reached 41% in P2, 16% in P1, and 4% in F2 plots. Nematode populations were higher (P < 0.05) in P1 (649 ring nematode/100 cm3 soil) than in F2 (221 ring nematode/100 cm3 soil) plots, whereas populations in P2 (300 ring nematode/100 cm3 soil) plots did not differ from those in P1 or F2 plots. Establishing a PTSL screening site was possible 3 years after M. xenoplax introduction; PTSL development among treatments in the subsequent planting was dependent upon cumulative population exposure of trees to M. xenoplax.
Rooted cuttings of ‘Nemaguard’ peach were grown for 10 months in soil infested with or without Criconemella xenoplax (Raski) Luc and Clitocybe tabescens (Fr.) Bres. Trees were pruned in early December and placed in an unheated greenhouse subject to large temperature fluctuations during the winter. In March, 8 of 9 trees infested with C. xenoplax and all infested with C. xenoplax + C. tabescens showed severe stem cambial browning typical of cold injury and did not leaf out, although the root systems were still viable. All check trees and 7 of 9 trees infested with C. tabescens grew normally, although budbreak in the check trees occurred 2 weeks earlier than those infested. Symptoms were similar to symptoms of cold injury associated with peach trees short life in orchards.
Lovell rootstock is recommended for Peach Tree Short Life (PTSL) sites in the Southeast because it outlives Nemaguard. No genetic studies of PTSL tolerance have been done. Clonally replicated peach seedlings [Prunus persica (L.) Batsch] of Lovell, Nemaguard and four F1 selections of Lovell × Nemared were tested for field survival in a high density planting on a PTSL site. Rootstock families (12 seedlings × 8 ramets each) differed in growth, survival and longevity. Genetic variation was comparable to environmental variation for most families. Based on seedling within rootstock family, estimated broad-sense heritabilities for survival and longevity were high. The use of clonally replicated seedlings allowed the selection of apparently superior individuals from both Lovell and the other more short-lived rootstock families in a single screening after 6 years. Survival of Lovell at that time was 50% compared to 16-29% for other families. Across all families, all 8 ramets were dead for 21 seedlings, whereas all 8 were alive for only 3 seedlings.
‘Sunprince’ peach [Prunus persica (L.) Batsch] has been released to provide a cultivar adapted to the southeastern United States ripening in ‘Redskin’ and ‘Blake’ season with better external color and shape than ‘Redskin’ and higher bacterial spot resistance than ‘Blake’.
The evergreen (EVG) peach, first described in Mexico, was used as a parent with deciduous (DE) peaches to develop F1 and F2 hybrid populations in Mexico, Florida, Georgia, and West Virginia. F1 trees were DE and F2 plants segregated 3 DE: 1 EVG. In West Virginia, the most temperate location, the heterozygous class could be distinguished in the first few years of growth by late leaf abscission in the fall. Segregation ratios suggest that the EVG trait is controlled by a single gene, evg, the EVG state being homozygous recessive. Evergreen trees were characterized by insensitivity of shoot tips to daylength and failure of terminal growth to cease growth until killed by low temperature. Lateral buds of EVG trees went dormant in the fall. Deep supercooling occurred in both EVG and DE trees, but it appeared later in EVG trees, was of shorter duration, and occurred to a lesser extent. Evergreen germplasm may be useful in developing peach cultivars for frost-free subtropic and tropical areas. It also presents a useful system for studying dormancy and cold hardiness.
Nineteen peach [Prunus persica (L.) Batsch] genotypes and 45 plum (Prunus salicina Erhr. and hybrids) genotypes with different flesh and skin color were analyzed for their antioxidant content and activity. Anthocyanin content, phenolic content, and antioxidant activity were higher in red-flesh than in light-colored flesh peaches. Carotenoid content was higher in yellow-flesh peaches than in light-colored ones. Red-flesh plums generally had higher anthocyanin and phenolic contents than the other plums but not necessarily greater antioxidant capacity. The total phenolic content had the most consistent and highest correlation with antioxidant activity, indicating that it is more important in determining the antioxidant activity of peaches and plums than are the anthocyanin or carotenoid contents. In general, the wide range of phytochemical content and antioxidant activity found indicates that the genetic variability present can be used to develop cultivars with enhanced health benefits.
The purpose of this three-way cooperative project is to develop new fresh-market peach and nectarine varieties in the 400 to 650 chill hour range for the early season shipping market. Since 1990, >3000 seedlings have been evaluated, resulting in 48 selections. Additionally, several hundred selections from other programs have been evaluated. `Sunsplash', an attractive, early season, 400 chill hour nectarine, was released in 1993 as a result of this cooperative effort. A novel aspect of the program has been the use of non-melting flesh parents for the purpose of improving handling characteristics. Selections include both yellow- and white-flesh types, peaches and nectarines. Some may be adapted for use in other production areas and are available for testing under non-propagation agreement. Evaluation summaries of selections and standards will be presented.