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Seedlings of eight Prunus taxa were evaluated for variation in susceptibility to a single, 4- or 5-day flooding period and root rot caused by Phytophthora cryptogea Pethybr. & Lafferty. Survival, plant defoliation, disease severity index, root necrosis, and net photosynthesis indicated that the combination of flooding and pathogen was significantly more severe to all taxa than either individual treatment. Most response variables reflected early plant dysfunction but were not correlated with long-term survival. Long-term survival was 70% in the combination treatment compared to 99% in the control group. Flooding injured seedlings more than the pathogen in most taxa. Taxa differed only slightly in tolerance to the treatments, as measured by survival rate. Prunus takesimensis Nakai had the highest survival rate of 100% and along with P. mahaleb L. and P. yedoensis Matsum. showed some tolerance to flooding and the pathogen. Prunus sargentii Rehd. had the lowest survival rate of 81% and appeared to be least tolerant to the pathogen.
Abstract
Autotetraploid watermelons were produced by treating the growing points of diploid seedlings with aqueous colchicine solution or by soaking diploid seeds in colchicine solution. The soaking method was more effective.
Diploid pollen was apparently more viable than tetra-ploid pollen. Examination of germinating tetraploid pollen revealed that while over two-thirds germinated normally a small percentage sent forth 2, 3 or 4 normalsized pollen tubes or a single bifurcated tube. Germinating diploid pollen always put forth only one unbranched pollen tube. Tetraploid plants did not set fruit when pollinated with pollen from tetraploids; however, they did set fruit when pollinated with pollen from diploids.
Cytological observations were made of pollen mother cells of both diploid and tetraploid plants. Meiosis in diploids was regular; however, irregularities were observed in tetraploids. Examination of some pollen mother cells of tetraploids at the quartette stage revealed micro sporocytes in addition to the 4 microspores. The abnormal quartette formations and lower pollen viability of tetraploids were believed associated with irregularities observed at meiosis. Preliminary investigations of megaspore formation revealed no apparent differences between the diploid and tetraploid megaspores. Although meiotic irregularities were found, a sufficient amount of apparently viable pollen was observed. A physiological basis for the self-sterility is suggested.
Abstract
Peach trees (Prunus persica L. Batsch cv. Regina) were subjected to three levels of postharvest irrigation between 15 June and 15 Oct. 1983. Wet-treatment (control) trees were irrigated at 3-week intervals, medium-treatment trees received one, and dry-treatment trees received no postharvest irrigations. Significant differences in seasonal patterns of stomatal conductance were found among all treatments, with conductance varying in proportion to irrigation level. Wet-treatment pre-dawn water potential (ψw) remained nearly constant at −0.3 MPa throughout the postharvest season, whereas the dry-treatment readings became more negative as the season progressed. Differences in mid-day ψw were less distinct, but generally reflected pre-dawn water status. The seasonal increase in trunk radius of the dry-treatment trees was reduced by 33% relative to either wet or medium treatments. The amount of daily trunk radial shrinkage was inversely proportional to irrigation level. Dormant pruning weights were 13% less in dry treatments than wet treatments. Return bloom of dry-treatment trees in Spring 1984 was 30% and 40% greater than medium- and wet-treatment return bloom, respectively. Dry-treatment fruit set was 70% greater than medium- or wet-treatment fruit set. Following fruit thinning, there were no significant differences among treatments for fruit yield or fruit size, but fruit maturity was slightly delayed in the dry treatment.
Abstract
Trees of Malus domestica (Borkh.) ‘Miller Sturdeespur’ were hand thinned to achieve light, medium, and heavy fruit loads. A heavy European red mite (ERM), Panonychus ulmi (Koch), infestation was encouraged by mite seeding and predator elimination in half the trees for each fruit load. The effect of these treatments were determined on fruit number, number and percentage of drops, fruit size, color, soluble solids, titratable acidity, pH, firmness, and percentage of foliar concentration for 5 macronutrients. Mite feeding increased the percentage of drop and reduced red pigmentation, soluble solids, and leaf phosphorus and calcium. Deleterious effects of mite feeding increased with increasing fruit load. With light fruit loads, heavy mite feeding had a negligible effect on fruit quality.
Abstract
The effects of 2 light levels, (full sun and 47% shade) 3 nitrogen and 3 potassium levels (672, 2018, and 3362 kg/ha yr-1) on light compensation point, shoot and root growth, canopy distribution and leaf tissue nutrient content of Ficus benjamina were determined. The 47% shade treatment during 7 months of production significantly decreased light compensation point levels. N level slightly affected compensation point and K level had no effect. Higher N levels increased shoot growth, while K levels played a dominant role in root development. Light level interacted with both of these effects. N level was positively correlated to percent of the plant canopy contained in the upper half of the plant and this in turn closely was correlated with plant light compensation point.
Buffalograss [Buchloë dactyloides (Nutt.) Engelm] is a drought-resistant, dioecious species, native to the Central Great Plains, which shows excellent potential as a low-maintenance turfgrass. Although buffalograss can be propagated vegetatively, there is a need for seeded turf-type cultivars. To assist in developing seeded cultivars, heritabilities of turf characteristics were estimated. Heritabilities from maternal half-sib analyses ranged from h2 = 0.04 ± 0.03 for the 1988 uniformity rating to h2 = 0.62 ± 0.26 for the 1989 spring color rating. Heritability estimates calculated from offspring-parent regression were also variable and generally lower than maternal half-sib analysis. The results suggest that some turf characteristics are highly heritable and that growing conditions markedly affect heritability estimates.
Current recommendations for fruit thinning of processing clingstone peaches in California suggest that growers delay thinning until an assessment of fruit size is made at reference date (10 days after first indications of pit hardening) and then adjust the crop load according to the fruit size attained. Recent research on modelling peach fruit growth indicates that delaying thinning until reference date (usually mid-May) can substantially limit final fruit size potential and crop yield when initial fruit set is heavy. In 1991 we initialed a field study to lest these model predictions and evaluate the yield response and economic feasibility of fruit thinning within 50 days of bloom to a specific crop load. The experiment was conducted in commercial orchards of the extra-early maturing cling peach cultivars Loadel and Carson. Three thinning treatments involved thinning different sets of trees on April 10, April 30, (∼30 and 50 dafb) and May 23 (reference date). Although costs of thinning at the earlier dates were 140-290% of thinning at reference date the increase in yield resulting from early thinning more than compensated for the higher thinning costs. There were no major effects of thinning treatment on the occurrence of split pits or other quality characteristics. This research has stimulated a re-evaluation of commercial fruit thinning practices used for clingstone peaches in California.
Abstract
Leaf diffusion resistances of Ficus benjamina grown in full sun were lower than those from 47% light exclusion. Scanning electron micrographs revealed 53% more stomata on sun leaves. High KC1 increased transpiration rates and foliar levels of K were increased in sun grown plants, but unaffected in shade grown plants.
Field tests at two locations examined the influence of length and spacing of root propagules on blackberry plant establishment. Root propagules 10.2 cm long spaced 61 cm resulted in greater emergence, plant stand, and shoot growth than 5 cm and 2.5 cm root propagules. Differences in emergence and shoot growth between 10.2 cm progagules spaced 61 cm and 5 cm propagules spaced 61 cm were non-significant. Greenhouse tests compared four lengths of root propagules (15.2 cm, 10.2 cm, 5cm, 2.5 cm) for production of nursery plants. Percent emergence, time of emergence, and number of shoots per propagule produced from 2.5 cm propagules were comparable to results from 15.2 cm and 10.2 cm propagules.
Abstract
Plants of Ficus benjamina L. had less leaves in the upper half of sun and shade-grown plants with higher N rates. Potassium affected leaf distribution only in bottom portion of canopy and had no effects on LCP. High N levels increased light compensation point (LCP) of sun-grown plants, but reduced LCP of shadegrown plants. Increased number of leaves in upper half of sun-grown plants reduced LCP but shade-grown plants showed an opposite effect.