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- Author or Editor: T. G. Beckman x
- HortScience x
Armillaria root rot is the second leading cause of peach tree mortality (after peach tree short life) in the southeastern United States. Currently, there are no commercially available rootstocks for peach with proven resistance to this pathogen in the United States. Since 1983, we have been screening rootstock candidates for resistance to Armillaria utilizing naturally infected field sites. Inoculation of peach [Prunus persica (L.) Batsch], plum (P. cerasifera J.F. Ehrh., P. munsoniana F.W. Wight & Hedr., P. salicina Lindl. or P. angustifolia Marsh.) × peach and plum × plum hybrid rootstocks with infected plant tissue (such as acorns, Quercus sp.) prior to planting has provided a significantly increased infection and mortality of candidate rootstock lines in comparison with sole reliance on natural inoculum on an infested site.
Recently observed hybrid populations of peach [Prunus persica (L.) Batsch] provide evidence for the presence of a single gene controlling full red skin color. The fruit of seedling populations of `UFQueen' × `Springbaby', `UFQueen' × `Springprince, FL93-12C × `Springprince, FL92-22C × BY79P1945, and AP98-18 o.p. were rated for percent red skin color at full maturity. At this stage of development, “full red” phenotypes display red color over the entire surface of the fruit, including the stem cavity and portions of the fruit shaded by leaves or stems. Both crosses with `UFQueen yielded populations displaying a 1:1 segregation ration for partial red: full red. All other crosses produced populations that did not deviate significantly from a 3:1 segregation ratio. These data are consistent with the hypothesis that the “full red” phenotype is a single gene recessive trait. We propose the gene symbols of fr and Fr for the recessive full red and dominant partial red (wild-type) alleles, respectively.
Most peaches in the Southeast are propagated on either Lovell [moderate longevity on peach tree short-life (PTSL) site, but root-knot nematode susceptible] or Nemaguard (short longevity on PTSL site; root-knot resistant) seedling rootstock. Rootstock BY520-9 appears to confer longer scion life than Lovell on PTSL sites and to be as resistant as Nemaguard to root-knot nematode, based on results from 9-year trials in Georgia and South Carolina followed by a 5-year budded trial in South Carolina. Parental line B594520-9 is a relic of USDA root-knot resistance breeding and traces back to a 1955 cross between a seedling of S-37 and Nemaguard. USDA and Clemson are making available bulked seed from superior selections of B594520-9, collectively known as BY510-9, to facilitate broad-scale industry testing. Plant Variety Protection (PVP) for BY520-9 is being applied for. Testing to select a single parental genotype continues at several southeastern test sites.
Large field plantings are often difficult to label and to plant randomly. A DOS computer program was developed in SAS and BASIC to randomize lists of experimental factors and print sorted paper labels to apply to trees or plants. Tagged trees can be resorted readily by block or row to speed planting. The computer lists are useful for plot verification and subsequent data collection, especially if data are collected and inputted directly to a computer. Copies of the programs are available from W.R. Joyner if a formatted diskette and self-addressed mailer are supplied.
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.
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.
Peach tree fungal gummosis caused by Botryosphaeria dothidea [(Moug.:Fr.) Cos & de Not.] is widespread throughout the southeastern United States. Until recently, its economic impact on peach [Prunus persica (L.) Batsch] has been impossible to estimate, since no effective controls were known. Significant, though not total, suppression of gummosis on `Summergold' peach trees was achieved with an intensive 5-year spray program with captafol. Captan was far less effective than captafol. Both trunk diameter and fruit yield were negatively correlated with disease severity. After eight growing seasons, trees treated with captafol were 18% larger than the untreated trees. Yield of mature captafol-treated trees was 40% to 60% high er than that of untreated ones. Following termination of the spray program after 5 years, disease severity gradually increased on both captafol- and captan-treated trees. However, through eight growing seasons, disease severity was significantly lower on captafol-treated trees. This study demonstrates that peach tree fungal gummosis significantly depresses tree growth and fruit yield on susceptible peach cultivars.