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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.
Rootstock influence on bloom date and fruit maturation of `Redhaven' peach [Prunus persica (L.) Batsch] was studied over a 3-year period. Rootstock included seedlings (Lovell, Halford, Bailey, and Siberian C) and cuttings (GF677, GF655.2, Damas 1869, and `Redhaven'). Bloom dates of the various combinations differed in all 3 years, with a range of 3.6, 9.1, and 7.3 days in 1988, 1989, and 1990, respectively. Fruit development period differed each year with a range of 3.9, 5.8, and 4.4 days in 1988, 1989, and 1990, respectively. `Weighted-average harvest date also differed with a range of 3.6,2.9, and 5.6 days in 1988, 1989, and 1990, respectively. `Redhaven'/Lovell was the latest blooming and maturing combination in all 3 years of the study.
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.