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  • Author or Editor: Thomas G. Beckman x
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Preliminary results of a field trial of 49 different scion varieties grafted onto Nemaguard plus `Redhaven'/Lovell suggest that scion influence on incidence of peach tree short life (PTSL) may be comparable to that of rootstock. After 6 growing seasons survival of the various scion treatments ranged from 5 to 85%. Correlation analyses indicated that those scion varieties exhibiting either early bloom or late defoliation survived better and that those varieties exhibiting both characteristics survived the best. Results indicate that final testing of rootstock candidates for PTSL tolerance must be done with grafted materials and that it may be possible to recommend the planting of certain scion varieties on PTSL sites as well as particular rootstocks for maximum longevity.

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Two F1 hybrid Prunus rootstocks, K62-68 and P101-41, developed from a cross of `Lovell' [susceptible to both Meloidogyne incognita (Kofoid and White) Chitwood and M. javanica (Treub) Chitwood] and `Nemared' (resistant to both root-knot nematode species), were selfed to produce two F2 seedling populations. Vegetative propagation by herbaceous stem cuttings was used to produce four or eight self-rooted plants of each F2 seedling for treatment replications. Eggs of M. incognita and M. javanica were inoculated into the potted media where plants were transplanted, and plants were harvested and roots examined for signs and symptoms associated with root-knot nematode infection ≈120 days later. Segregation ratios in both F2 families suggested that resistance to M. incognita in `Nemared' is controlled by two dominant genes (Mi and Mij) and that to M. javanica by a single dominant gene (Mij). Thus, Mij conveys resistance to both M. incognita and M. javanica.

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Six commonly known peach rootstocks (i.e., Flordaguard, Guardian®, Halford, Lovell, Nemaguard, and Okinawa) were evaluated for their susceptibility to Meloidogyne mayaguensis in the greenhouse. All rootstocks were rated as either nonhosts (highly resistant) or poor hosts (resistant) of M. mayaguensis. Lovell generally supported greater numbers of M. mayaguensis eggs per plant and eggs per gram of dry root, whereas no nematode reproduction was noted on Flordaguard rootstock (nonhost). Root galling occurred on all six rootstocks. However, reproduction as measured by number of egg masses, eggs per plant, and eggs per gram of dry root was a better measure of host resistance than number of root galls per plant.

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Two peach cultivars were budded in 1988 to seedlings from 10 open-pollinated peach and plum lines selected from a 7-year-old peach tree short life (PTSL) field test. Lovell and Nemaguard seedling rootstocks were also budded as controls. The trees were planted in 1989 on a non-fumigated PTSL site near Columbia. South Carolina. Highly significant differences in bloom date, trunk cross-sectional area (TCSA), suckering, bacterial canker infection, and PTSL death were found among the rootstock/scion combinations after four years. Bloom dates when compared to trees on Lovell were advanced by 1-6 days with trees on Blue Goose and BY7446 plums blooming the earliest. Scion TCSA on BY520-8 and BY520-9 peach rootstocks was significantly greater than on Lovell. The plum rootstocks BY7446, Blue Goose, and Edible Sloe had the smallest TCSA. Nemaguard, BY7446, and Edible Sloe had significantly more suckers per tree than Lovell. BY520-9 and Edible Sloe trees had significantly less bacterial canker infection than Lovell. BY520-9, BY7446, and Edible Sloe had the lowest PTSL mortality, and thus hold the most promise as potential rootstocks to replace Lovell on PTSL sites.

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The primary focus of the stone fruit rootstock program at Byron, GA, has been the development of disease-resistant rootstocks for peach (Prunus persica L. Batsch). Historically peach tree short life (PTSL), aka bacterial canker complex, and Armillaria root rot (ARR) have been the two most important causes of premature mortality of commercial peach trees in the southeastern United States. Guardian®, a seedling peach rootstock, was cooperatively released in 1993 by the U.S. Department of Agriculture (USDA)-Agricultural Research Service (ARS) and Clemson University. It has since been widely adopted by the southeastern peach industry. As a result, trees losses to PTSL have declined sharply. However, Guardian, like most other peach seedling rootstocks, is susceptible to ARR. ARR has now moved to the forefront as the primary cause of premature peach tree death in the Southeast. In response to this threat, the USDA-ARS in cooperation with the University of Florida, released ‘Sharpe’, a plum hybrid rootstock in 2007. Despite its broad disease resistance, ‘Sharpe’ proved unsuited for widespread commercial utilization due to its relatively poor cropping performance. In 2011, ‘MP-29’, a semidwarf, clonal, plum × peach hybrid, was released for commercial trial. ‘MP-29’s broad disease and nematode resistance, in combination with its dwarfing ability and excellent productivity, offered great promise for use in this production area and in others suffering from similar issues. Since its release, testing of ‘MP-29’ has continued both in researcher and grower trials. To date, performance has exceeded all expectations.

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