Two isoenzyme systems, glucose phosphate isomerase and phosphoglucomutase, were identified for use as starch gel electrophoretic markers of plum × peach (Prunus salicina × Prunus persica) interspecific hybrids. Two distinct regions of banding were associated with each enzyme system. Different unique banding patterns for each species were observed for plum and peach at 3 of 4 banding regions. Interspecific hybrid plants exhibited hybrid enzyme patterns with bands from both plum and peach in each region. Consequently, interspecific plum × peach hybrid genotypes may be distinguished from parental plum or peach genotypes. These enzyme systems may be used in breeding programs to identify plum × peach hybrid seedlings.
‘Alderman’ is a large, sweet, cold-hardy, Japanese-type plum hybrid involving Prunus salicina Lindl. and P. americana Marsh. It is being introduced by the Univ. of Minnesota Agricultural Experiment Station for use in cold climates where other high-quality, Japanese-type plums may suffer winter injury. ‘Alderman’ was named after W.H. Alderman in commemoration of his 100th birthday in 1985 and in recognition of his many accomplishments as a scientist and administrator in horticultural science at the Univ. of Minnesota.
Influence of various concentrations of hydrogen cyanamide (HC) on fruit thinning of `Rome Beauty' apple (Malus domestica Borkh.), `Friar,' and `Simka' plums (Prunus salicina Lindley) were studied. A full bloom application of HC at all tested concentrations decreased `Rome Beauty' apple fruit set and yield, and increased fruit weight. Hydrogen cyanamide at 0.25% (V/V) resulted in adequate apple thinning, indicated by the production of an ideal fruit weight. Prebloom and full bloom applications of HC at greater than 0.75% reduced plum fruit set and yield in `Friar.' Full bloom application of HC at 0.25% to 0.50% showed a satisfactory fruit set, yield, and fruit size in `Friar' plum. Full bloom application decreased fruit set and yield in `Simka' plum. Hand thinning, as well as chemical thinning, is recommended for plums.
Diploid plums such as Prunus salicina, P. simonii, P. cerasifera, P. americana, P. angustifolia, P. mexicana, and their hybrids have a high level of RAPD polymorphisms. Of 71 successfully used primers, there are 417 reproducible RAPD markers and only 55 (13%) markers are not polymorphic. Genetic relationships of these diploid plums based on RAPD data is estimated using genetic distance (GD) defined as GDij = 1 – Sij, where Sij is similarity coefficient. Two similarity coefficients, Jaccard's and simple matching coefficient, are compared. Simple matching always yields higher similarity coefficients. Genetic distance within and between each gene pool: California, southeastern U.S., foreign, is estimated. Genetic distances of these diploid plums ranged from 0.32 to 0.68, and agreed well with the natural geographic distribution of the species. The cluster analysis using unweighted pair-group methods using arithmetic averages (UPGMA) was used to construct phenograms to summarize the relationships among these cultivated diploid plums and plum species.
The dwarfing characteristics of St. Julien and Pixy rootstocks, measured by shoot growth, were evident with `AU-Amber' and `AU-Producer' plum (Prunus salicina Lindl.) scions. Dwarfing did not occur with `AU-Rubrum'. Trunk cross-sectional area (TCA) was reduced with `AU-Amber', `AU-Producer', and `AU-Rubrum' scions on St. Julien and Pixy rootstocks. After 3 years, tree survival was 94% for Lovell; 89%, Halford; 57%, Nemaguard; 75%, Nemared; 83%, St. Julien; and 47%, Pixy. Tree survivability was significantly lower on Nemaguard and Pixy rootstocks than on Lovell and Halford. Multiple regression of total shoot growth, TCA, and survivability against foliar nutrient content resulted in the following significant equations: 0.460Mg - 0.210Mn, 0.236B - 0.487Mn, and 0.359N + 0.398Ca - 0.267P - 0.360Fe for each, respectively. Growth, survivability, and foliar nutrient content are significantly affected by rootstock in plum production.
Cultivars of sweet cherry (Prunus avium L.), nectarine [P. persica (L.) Batsch var. nectarina (Ait.) Maxim.] peach [P. persica (L.) Batsch], pear (Pyrus communis L.) and plum (Prunus salicina Lindl.) differed in their phytotoxic responses to methyl bromide (MB) fumigation treatments designed to control the Mediterranean fruit fly (Ceratitis capitata Wied.) without use of a subsequent cold treatment. Phytotoxic responses were relatively mild or negligible in most cultivars fumigated at 21°C with 48 g MB/m3 for 2 hours, 48 g/m3 for 3 hours, or 32 g/m3 for 4 hours. A few of the cultivars tested were very susceptible to MB injury. In some cultivars, both the control and fumigated lots exhibited symptoms of injury that apparently were not related to the fumigations but were caused by packinghouse handling or orchard practices. The fumigations slowed the ripening of cherries and plums. Decay of nectarines was slightly greater in fumigated than in control lots of fruit.
Root growth is restricted in compact soil zones irrespective of whether the zones result from cultural equipment or are genetic in origin. Because yield may be reduced and production costs increased, proper diagnosis is important. To that end, penetrometer soil strength measurements were used in the field to characterize root-limiting soil-impedance characteristics for ‘Eldorado’ plums (Prunus salicina Lindl.). A penetrometer soil strength of 16 bars, measured at a volumetric water content of 16.9% (field capacity), was sufficient to lower root density to about 50% of that observed for low-strength soil. Tree growth (trunk circumference) was highly correlated with the averageprofile root density and the amount of silt present at a mid-profile depth. Low values of these parameters most probably were related to a water stress condition that reduced tree growth.
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.
Commercially grown apricots (Prunus armeniaca), peaches (Prunus persica), nectarines (Prunus persica), plums (Prunus salicina and Prunus domestica), and pluots (Prunus salicina × Prunus armeniaca) have a tendency to produce high numbers of flowers. These flowers often set and produce more fruit than trees can adequately size to meet market standards. When excessive fruit set occurs, removal of fruit by hand-thinning is common to ensure that fruit size meets market standards. Over the years there have been numerous attempts to find chemical or physical techniques that would help to reduce costs associated with and improve efficiencies of hand-thinning; however, using alternate strategies to hand-thinning have not been widely adopted in stone fruit production. In the past 10 years, through the continuing efforts of scientists throughout the world in public and private institutions and business, it appears that there are chemical sprays capable of reducing the need for hand-thinning in stone fruit. Management of flowering by reducing the number of flowers on apricot, peach, nectarine, plum, and prune has shown promise under climatic conditions such as those found in the San Joaquin Valley of California. By applying gibberellins during May through July, flowers in many stone fruit cultivars can be reduced in the following season. The reduction in flower number does not generally lead to an increase in fruit set. As a result, fruit numbers are reduced, the need for hand thinning can be reduced, and in some cases eliminated. There are risks associated with reducing flower number before climatic conditions during bloom or final fruit set are known. However, given the changes in labor costs and market demands, especially in the developed world, the benefits may outweigh the risks. The application and implications of these summer gibberellin applications toward reducing flower numbers will be discussed as it relates to commercial stone fruit growing.
Twenty-nine commercial and experimental Prunus rootstocks, most with incorporated root-knot nematode [Meloidogyne javanica (Traub.) Chitwood] resistance, were evaluated against mixtures comprising nine populations of the root-lesion nematode Pratylenchus vulnus Allen and Jensen. Nearly all tested materials were susceptible. Five cultivars with high resistant levels were further challenged with seven P. vulnus populations individually. `Redglow' (Prunus salicina Lindl. × P. munsoniana Wight and Hedrick) was the only rootstock that showed broad resistance to all populations. The rootstocks `Torinel' (P. domestica L.), AC-595 (P. domestica × P. insititia L.), `Marianna 4001' (P. cerasifera Ehr. × P. munsoniana), and `Felinem' [P. dulcis (Mill.) D. A. Webb × P. persica (L.) Batsch] showed resistance to one or a few P. vulnus populations. Several supposedly resistant sources proved to be susceptible. Tests of crosses made between parents of diverse genetic background with partial resistance to P. vulnus indicate that a descendant with potential P. vulnus resistance is difficult to obtain. Pathogenic diversity among P. vulnus populations appears to be high.