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- Author or Editor: W. R. Okie x
- Journal of the American Society for Horticultural Science x
Abstract
Parental, F1, F2, and backcross generations of tomato (Lycopersicon esculentum Mill.) lines Morden MEL2668170G (MEL) and ‘Walter’ (WA) were screened as seedlings for resistance to verticillium wilt (Verticillium dahliae Kleb.) race 2. Disease reaction means, based on the number of leaves and cotyledons with symptoms 5.5 weeks after inoculation, were 2.7 for MEL and 4.6 for WA. Resistance in MEL appeared to be recessive with narrow sense heritability estimated at 0.25 or less. Disease severity was sometimes inadequate to avoid the selection of escapes in advanced generations. Analysis of F3 progenies, however, indicated 3 genes or less might be involved. Results suggest race-2 resistance can be maintained in advanced generations by the elimination of highly susceptible plants and by progeny testing to insure recovery of the most resistant individuals rather than escapes.
Abstract
Commercial and exotic cultivars and selections of peach and nectarine [Prunus persica (L.) Batsch] were evaluated for reaction to gummosis caused by Botryosphaeria dothidea (Moug. ex Fr.) Ces & de Not. (B. ribis Gross & Dugg.). Commercial germplasm was susceptible. Mature trees of several exotic lines showed very little natural infection. ‘Eagle Beak’, Plant Introduction (PI) 43289 from China, was the most resistant to gummosis. Artificially inoculated twigs of this line gummed only slightly, although the fungus could still be isolated from some wounds after 16 months.
Two unpruned narrow-leaf and two unpruned standard-leaf peach [Prunus persica (L.) Batsch.] selections were evaluated for physiological components related to water use efficiency {WUE [carbon assimilation (A) per unit of transpiration (T)]}. The purpose of the study was to assess the value of narrow-leaf phenotypes to improve WUE in peach and separate the environmental component of canopy geometry from the genetic components. The narrow-leaf characteristic itself did not confer improved WUE. The interception of light was a key determinant of WUE in these genotypes. Internal shading of the tree by excessive leaf area reduced daily WUE measured in gas exchange studies. Canopies that intercepted more than 75% of the photosynthetically active radiation (PAR) had reduced daily WUE. Dormant season pruning of the four genotypes lowered isotopic carbon discrimination and therefore increased seasonal WUE compared to unpruned trees. None of the genotypes had a significant correlation of seasonal WUE with leaf and fruit weight. Analysis of covariance indicated that `Bounty' and both narrow-leaf genotypes had greater leaf and fruit weight than `Redhaven' for a given level of PAR interception. `Bounty' had the least internal canopy shading of the four genotypes. Genetic differences in peach growth types can be selected for factors increasing WUE as well as increased productivity. Future work in peach breeding to improve WUE and productivity must take into consideration light interception, productivity, and WUE in an integrated manner to make real progress in the efficient use of water and light in the orchard environment.
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.
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.
Abstract
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.
Diploid plums (Prunus L. sp.) and their progenitor species were characterized for randomly amplified polymorphic DNA polymorphisms. Bootstrap analysis indicated the variance of genetic similarities differed little when the sample size was >80 markers. Two species from China (Prunus salicina Lindl. and P. simonii Carr.) and one species from Europe (P. cerasifera Ehrh.) contributed the bulk (72% to 90%) of the genetic background to the cultivated diploid plum. The southeastern plum gene pool was more diverse than those from California, Florida, or South Africa because of the greater contribution of P. cerasifera and P. angustifolia Marsh. to its genetic background.