Search Results
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.
Early maturing peach trees [Prunus persica (L.) Batsch cv. Regina] growing on a deep sandy loam soil were subjected to three levels of postharvest irrigation over 4 years. The control treatment was irrigated with ≈ 10 to 15 cm of water at 2- to 3-week intervals, the medium treatment received a single irrigation (20 to 30 cm) in early August, and the dry treatment was not irrigated between early to mid-June and mid-October. All received a predormancy irrigation of 10 to 15 cm in mid- to late October. Flower and fruit density were greater in the dry treatment than the control. The occurrence of double fruit was also greatly increased in the dry treatment but not in the medium treatment, when compared with the control. After normal commercial hand thinning, yields and fruit size were no different among the three treatments over all 4 years. Vegetative growth as measured by dormant pruning weights, trunk radial growth, and canopy shaded area was reduced in the dry treatment, but there was no indication of progressively declining vigor. Soil moisture determinations indicate that water use by the control occurred mainly in the upper soil profile. In the dry treatment, as the upper profile dried, water was extracted progressively deeper, down to at least 300 cm. The main disadvantage of severe postharvest water stress was the substantial increase of double fruits.
Abstract
Equal volumes of peanut hulls, pine bark, and sphagnum peatmoss were combined into 5 media. Particle size distribution, total porosity, air space, easily available water, water buffering capacity, and bulk density were determined for each medium. Top dry weight, root dry weight, and percent growth of Rhododendron indicum (L.) Sweet cv. George L. Taber were measured 14 weeks after potting in 1-liter containers. Peanut hulls increased particle size, total porosity, and air space, and decreased easily available water, water buffering capacity, and bulk density of media. Peatmoss generally reduced total porosity and air space and increased easily available water, water buffering capacity, and bulk density regardless of other component combinations. Top dry weight, root dry weight, and percent growth were greater in peanut hull-containing media. Addition of peatmoss to the container media tended to produce less growth.
Seasonal patterns of soil water content and diurnal leaf water potential (LWP), stomatal conductance(gs), and net CO2 assimilation (A) were determined in a high-density peach [Prunus persica(L) Batsch cv. Cal Red] subjected to regulated deficit irrigation scheduling. The regulated deficit irrigation treatment caused clear differences in soil water content and predawn LWP relative to control irrigation treatments. Treatment differences in midday LWP, gs, and A were also significant, but not as distinct as differences in predawn LWP. Leaves on trees subject of the deficit irrigation treatment were photosynthetically more water-use-efficient during the latter part of the stress period than were the nonstressed trees. Midday LWP and gs, on trees that received the regulated deficit irrigation treatment did not recover to control treatment values until more than 3 weeks after full irrigation was resumed at the beginning of state III of fruit growth, because of water infiltration problems in the dry soil caused by the deficit irrigation. The regulated deficit irrigation treatment caused only a 8% reduction in trunk growth relative to the control, but resulted in a 40% savings in irrigation requirements.
Abstract
Resistance in Pisum sativum to Aphanomyces euteiches was evaluated in the laboratory by the number of oospores formed in excised root tips inoculated with zoospores of the pathogen. Significantly lower mean numbers of oospores formed in root tips of 3 moderately resistant breeding lines than in those of 3 susceptible cultivars. Results were reproduceable if test procedures were adequately controlled. A sample size of 40 root tips gave 95% confidence in detecting a 40 oospore/root tip difference between means of resistant and susceptible genotypes.
Lower mean numbers of oospores formed in excised root tips of genotypes which were resistant in greenhouse tests. Inoculum concentrations of 10 to 100 zoospores/plant caused severe disease in susceptible cv. New Era, while greater amounts of inoculum were needed to cause comparable disease in 2 resistant breeding lines.
Abstract
A computer simulation of asparagus growth is developed and used to evaluate the effects of various harvest strategies on short and long term commercial yield of asparagus (Asparagus officinalis L.). At present asparagus is harvested until the canners stop buying, usually in the 3rd or 4th week of June in southern Michigan, purchase generally being terminated by the reduction of spear diameter (whips), increase in fiber content of the spears or opening of the bracts. The simulation shows that this stragety is economically optimal for any single year; however, if the grower terminates the harvest every year on June 1, then the average yearly yields are significantly greater than those derived from the previous strategy. Skipping strategies, in which the grower skips a harvest every nth year (2nd, 3rd, or 4th), produced significantly lower 15 year average yields than either of the other 2 strageties, but produced significantly greater yields per plant.
Abstract
‘Idlewild’ peach [Prunus persica (L.) Batsch] was released by the Louisiana Agricultural Experiment Station to provide a 500- to 600-hr chilling-requirement cultivar which produces a good quality fruit. ‘Idlewild’ produces a heavy crop of medium to large semi-freestone fruit that ripen 36 days before ‘Elberta’ or about June 9 in southeastern Louisiana. ‘Idlewild’ has exhibited good resistance to bacterial leaf spot [Xanthomonas campestris pv. pruni (Smith 1903) Dye 1978] when grown under southeastern Louisiana conditions.