Approximately twenty native almond species have been described. Representative germplasm from seven of these are present in UC collections and have been used in crossing. Three specific breeding lines utilizing these species are described. One (1980 series) involved increasing yield potential through selection of high blossom density following gene introgression from Prunus fenzliana. A second involved incorporation of self-fertility, late bloom, smaller tree size, early maturity, high blossom density, and desirable nut characters from Prunus webbii into commercial breeding lines. A self-fertile selection resembling `Nonpareil' has been obtained from this material. The third line involves transmission of a unique thin, netted-surfaced, hard-shell phenotype from Prunus argentea.
Dale E. Kester and Thomas M. Gradziel
Thomas L. Davenport
Pruning is an unavoidable necessity of virtually all arboreal fruit crops. In the tropics and subtropics, pruning of mango (Mangifera indica L.) is particularly important due to its tendency for frequent flushes, especially in humid tropics. Commercial orchards must maintain control of both tree size and orchard productivity in order to remain productive. Tip, formation, and severe pruning can be used in a variety of circumstances to produce predictable and useful results for a variety of purposes. For example, tip pruning can be used to encourage frequent flushing and branching of young trees to bring them into commercial production years earlier than if left alone. It can also stimulate timely flushes of lateral stems in an annual program to maintain tree size and prepare trees for synchronous flowering. Formation pruning shapes trees in an overgrown orchard to receive the maximum amount of light for high productivity and sets them up for annual pruning in a flowering management program. Severe pruning coupled with subsequent tip pruning of huge, nonproductive trees facilitates rapid restoration of orchard production. Each of these types of pruning can be used to get mango trees into production quickly and thereafter maintain maximum annual production while maintaining their desired size.
Peter M. Hirst and David C. Ferree
Two-year-old branch sections of `Starkspur Supreme Delicious' apple (Malus domestics Borkh.) trees growing on 17 rootstock were studied over 6 years to determine the effects of rootstock on shoot morphology and spur quality and describe how these factors may be related to precocity and productivity. Shoot length was affected by rootstock and was positively related to trunk cross-sectional area within each year, but the slope of the regression line decreased as trees matured. The number of spurs on a shoot was largely a product of shoot length. Spur density was inversely related to shoot length, where rootstock with longer shoots had lower spur densities. Flower density was not related to spur density, and shoot length only accounted for a minor part of the variation in flower density. The proportion of spurs that produced flowers was closely related to flower density, indicating that rootstock influence flower density by affecting the development of individual buds rather than by the production of more buds. More vigorous rootstock generally had spurs with larger individual leaves and higher total leaf area per spur, but fewer spur leaves with lower specific leaf weights. More precocious rootstock were also more productive over a 10-year period when yields were standardized for tree size. Tree size was the best indicator of precocity and productivity, which could be predicted with a high degree of certainty as early as the 4th year.
C. Gregoriou and C.V. Economides
Growth, yield, and fruit quality were recorded for Ortanique tangor (Citrus reticulata Blanco) on 11 rootstocks until the trees were 12 years old. Trees on Volkameriana (C. volkameriana Pasq.), rough lemon, and `Estes rough lemon (C. jambhiri Lush.) were more productive per unit of tree size, and their cumulative yields per tree were significantly higher than those of trees on the other rootstocks. There was no significant difference between cumulative yields of Ortanique on the following rootstocks: sour orange (C. aurantium L.), `Palestine' sweet lime (C. limettioides Tan.), `Red' rough lemon (C. jambhiri Lush.), Rangpur (C. limonia Osbeck), and Amblycarpa (C. limonellus var. amblycarpa Hassk.). However, yield on these rootstocks was significantly higher than on Carrizo and Troyer citranges [C. sinensis (L.) Osbeck × Poncirus trifoliata (L.) Raf.] and `Swingle' citrumelo [C. paradisi Macf. × P. trifoliata (L.) Raf.]. The high productivity per unit of tree size of `Palestine' sweet lime suggested that this rootstock could be used advantageously in closely spaced plantings. Rootstocks affected fruit size, weight, rind thickness, juice content, total soluble solids concentration (SSC), and total acids, but the differences were not large enough to be of practical importance.
G.H. Neilsen and J. Yorston
In an apple (Malus domestica Borkh.) orchard with a severe replant problem, tree size was increased by the 2nd year and number of fruit by the 3rd year by treating the planting hole soil with formalin or mancozeb plus monoammonium phosphate (MAP) fertilizer. Growth increases were evident each year for 4 years only for the MAP + formalin treatment. In a second orchard, with a less severe replant problem, planting-hole treatment with formalin or dazomet + MAP increased tree size by year 2. Number of fruit in year 2 was increased by formalin and mancozeb + MAP treatments, although this effect persisted in year 3 only for mancozeb + MAP. Leaf P concentrations were increased to high values in the first year by MAP fertilization but declined in subsequent years. Leaf Mn concentration also increased in one orchard, a consequence of fertilizer-induced acidification of planting hole soil and Mn uptake from the fungicide mancozeb. Chemical names used: tetrahydro-3,5-dimethyl-2 H -l,3,5-thiadiazine-2-thione (dazomet); 37% aqueous solution formaldehyde (formalin); Zn, Mn ethylene dithiocarbamate (mancozeb).
Janet S. Mrosek and Stephen C. Myers
The relationship between cell division, nonstructural carbohydrates and fruit size was investigated using 5-year-old `Encore' peach [Prunus persica (L.) Batsch]. The trees, which were trained to two opposing scaffolds, were selected for uniformity based on tree size and floral bud density. One-year-old shoots ranging in size from 20 to 30 cm were tagged from throughout the canopy. At anthesis, one entire scaffold was thinned of 75% of its flowers, leaving 25% in the mid-section of each shoot. The opposing scaffold served as the control. Samples were taken at three intervals for histological analysis: Anthesis, 30 days, and 45 days after full bloom. Nonstructural carbohydrates were analyzed on samples taken at five intervals: Anthesis, 10, 20, 30, and 45 days after full bloom. Volumetric size increased 29% by 30 days after full bloom, and 64% by 45 days after full bloom. Final fruit size (volumetric) was increased 8% by harvest.
Kim D. Bowman
Citrus tree size and growth form are important traits that can be influenced by the genotype of both scion and rootstock cultivars. However, there have been very few reports of size or growth habit traits within Citrus or sexually compatible genera that might be transmitted genetically in breeding programs. A procumbent growth habit has been described for `Cipo' (Citrus sinensis [L.] Osbeck), a unique sweet orange cultivar maintained in the USDA germplasm repository. Sexual hybrids were produced between this selection and four related species, and these progenies were evaluated for two distinct traits associated with the unusual growth habit of `Cipo'. Inheritance of both drooping petiole and horizontal shoot growth were observed among the `Cipo' hybrids. Investigations are continuing on these four populations to verify segregation patterns and identify individuals possessing favorable combinations of growth habit with other desirable tree characteristics.
Kim D. Bowman
`Cipo' sweet orange [Citrus sinensis (L.) Osbeck] is distinctive among citrus selections because of reduced tree height and procumbent growth habit. Open-pollinated seeds were collected from `Cipo' orange and `Pineapple' sweet orange (C. sinensis) at Riverside, California, and grown under cool greenhouse conditions. Seedlings of `Cipo' were relatively uniform in morphology (including drooping shoot habit) and were presumed to be apomicts derived from nucellar embryos. `Cipo' seedlings were distinctly different from `Pineapple' in several characteristics, including smaller shoot altitude/extension ratios (a measure of uprightness) and broader stem-petiole angles (`Cipo' 1.33 radians; `Pineapple' 0.84 radians). The procumbent habit of `Cipo' appeared to be related to a preference for horizontal shoot orientation rather than a weakness of stem structure. Some increased sensitivity to ethylene was observed in the `Cipo' seedlings. `Cipo' is proposed as a resource for hormone research and a potential parent in breeding for unique tree morphology and reduced tree size.
William H. Olson, Steve Southwick, and Jim Yeager
French prunes growing on marianna 2624 (P. cerasifera × P. munsonianna; M 2624), myrobalan seedling and 29C (P. cerasifera; MS and M 29C, respectively) were planted in 1981 on a clay type soil, and evaluated for growth and yield components over a 10 year period. Thirty replicate trees per treatment were pruned and grown under uniform irrigation and fertility regimes. There were no tree size differences among rootstocks after 10 years growth even though initial and seasonal trunk cross sectional area differences were observed. Trees on MS rootstock were highest yielding in the initial 2 years of fruiting, but cumulative yields were not different as a function of rootstock. More rootstock suckers were counted on M 2624 than myrobalan rootstocks. Excavations revealed that trees on MS had a deeper root distribution. No statistical differences were observed with regard to fruit size and fresh to dry fruit weight ratios.
D.C. Elfving and I. Schechter
Annual yields per tree for `Starkspur Supreme Delicious' apple (Malus domestica Borkh.) trees on nine size-controlling rootstock were related linearly to number of fruit per tree at harvest each year, independent of rootstock. Mean fruit weight was inversely and less closely related to number of fruit per tree when adjusted for tree size (fruit load). Annual yield-fruit count data for 9 years analyzed together showed that the number of fruit per tree was the principal factor determining yield, regardless of rootstock or tree age. A curvilinear relationship between yield and fruit count per tree during 9 years suggests that the sink strength of an apple crop is nearly, but not precisely, proportional to the number of fruit per tree.