Summary A single application of either prohexadione-calcium (Ca) at 250 mg l–1, or of prohexadione-Ca at 250 mg l–1 plus ethephon at 180 mg l–1, dissolved in water acidified with 1.0 g l–1 citric acid was applied to young ‘Burlat’ sweet cherry trees (Prunus avium L.). In the year of application, both chemicals provided effective growth control over the entire season, with prohexadione-Ca plus ethephon being more restrictive to growth than prohexadione-Ca alone. This pattern of growth suppression was observed in the dynamics of shoot elongation, mean shoot length, internode length, and total shoot extension. Both chemical treatments increased flower bud set on previous-season shoots. Residual effects (i.e., in the year following treatment, with no additional chemical application) were produced by prohexadione-Ca plus ethephon, which reduced the mean shoot length to 56.6% of untreated control trees, and by both treatments significantly limiting the length of all internodes relative to the controls. No residual effects were observed on the numbers of flower buds in year-2.

Nursery trees of apple hybrids NY73334-35, NY75413-30 and NY75414-1 were treated once or twice with the plant growth regulator (PGR) Accel or Promalin, alone or in combination, to induce branching. Regardless of the PGR used. or the rate and frequency of application. treated trees produced more shoots per tree than untreated control trees for all three hybrid selections. Medium [750 mg.L-1 N-(phenylmethyl)-1H-purine-6-amine (6 benzyladenine or BA)] or high rates (1000 mg.L-1 BA) of both compounds were more efficient in shoot induction than low rates (500 mL, L-1 BA). When comparable rates of both chemicals were applied, no differences in the number of lateral shoots. shoot length distribution, total tree extension growth and apical dominance among chemical treatments were noted. Regression analysis on rates of Accel and Promalin vs. total number of shoots demonstrated that Accel promoted a linear increase in this characteristic, whereas Promalin Caused a parabolic effect on branching. The trees treated once or twice in the nursery at medium rates of either compound were transplanted into the orchard, One year after transplanting the trees exhibited a pronounced increase in the total number of shoots and their extension growth, and also considerable reduction in apical dominance. It is believed that those changes may facilitate canopy training, and thus accelerate the onset of bearing.

To estimate the amount of direct sunlight intercepted by any part of an apple tree canopy, a modified point quadrat method was developed. The relative direct light interception by different components within apple tree canopies was estimated by a laser scanning method, based on moving a laser beam above the canopy in set patterns. The percent of contacts of the laser-simulated ‘sunbeam’ on leaves on different shoot types or other parts of the canopy was determined in several different tree forms. The laser was positioned by two different methods: a two-axis laser positioner and a solar arc positioning device. Two two-axis laser positioner allowed an above-canopy laser to be rotated accurately in both vertical and horizontal planes to provide a grid of positions surrounding the canopy surface. The solar arc positioning device was designed to move the pole-mounted laser along an artificial solar track to simulate the movement of the sun throughout a day. Various sampling schemes were examined to develop efficient sampling procedures for evaluating the proportion of relative direct light interception by different components of the tree canopy. No particular patterns of light interception by different shoot types were found in three tree forms. From these analyses, to overcome the natural variations in tree canopy characteristics, general recommendations are to use a solar are positioning device to provide an angular range over which measurements can be taken, to use 75–100 laser samples per tree and to distribute the sampling points over the whole canopy with 3–4 are heights per tree.

Fruit maturity, quality, calcium concentration and economic value of `Starkrimson Delicious' ( Malus domestica Borkh.) apples, under a range of crop levels and European red mite [ Panonychus ulmi (Koch)] cumulative mite-days (CMD), were best explained by local surface regression models involving CMD and crop load. Fruit from trees with low CMD and a light crop (125 fruit/tree, about 20 t/ha) were the most mature at harvest. Those fruit had higher ethylene concentrations, starch pattern indices, soluble solids concentrations, and watercore incidence at harvest than fruit from trees with low CMD and a normal crop (300 fruit/tree, about 40 t/ha), or with high CMD at any crop level. Those fruit also had higher incidences of watercore and internal breakdown after 4 months of cold storage. Calcium concentrations in fruit increased as crop load and CMD increased. Whole-canopy net CO 2 exchange rate per fruit related better to fruit quality and calcium concentrations than either crop load or CMD alone, but was always a much worse predictor than local surface regressions. Low CMD and normally cropped trees had the highest crop value; lightly cropped trees had an intermediate crop value; while high CMD and normally cropped trees had the lowest crop economic value. Crop load should be considered when defining action thresholds for mites, and harvest schedules for apples should reflect crop load and mite populations on apple trees.

The hypothesis that carbon balance is the basis for differences in responses by lightly and normally cropped apple trees to European red mite (ERM) [ Panonychus ulmi (Koch)] damage was tested. Mature `Starkrimson Delicious' ( Malus domestica Borkh.)/M.26 apple trees were hand-thinned to light (125 fruit/tree, about 20 t/ha) or normal (300 fruit/tree, about 40 t/ha) target crop levels and infested with low [<100 cumulative mite-days (CMD)], medium (400 to 1000 CMD) or high (>1000 CMD) target levels of ERM. A range of crop loads and CMD was obtained. Mite population density, fruit growth, leaf and whole-canopy net CO 2 exchange rates (NCER) were measured throughout the growing season of 1994. Leaf area and vegetative growth per tree were also measured. Yield and final mean fruit size were determined at harvest. Return bloom and fruiting were determined the following year. Total shoot length per tree was not affected by crop load or mite damage. ERM reduced leaf and whole-canopy NCER. Normally cropped trees showed fruit weight reduction earlier and more severely than lightly cropped trees with high mite injury. Variation in final fruit weight, return bloom and return fruiting was much better related to whole-canopy NCER per fruit than to CMD.

The expolinear growth model of Goudriaan and Monteith (1990) is proposed as a new model for the inherent growth pattern of fruit of apple (Malus domestica Borkh.), defined as growth pattern under apparently non-limiting conditions This function has three parameters: maximum relative growth rate, maximum absolute growth rate, and ''lost time'' (x intercept of the linear growth phase). Apple fruit growth (weight basis) at very low crop loads and apparently optimum environmental conditions, displays an early positive curvilinear growth followed by linear growth to harvest, and is described well by the expolinear function. The model also fits growth patterns of 'Empire' and 'Golden Delicious' apple fruit differing in the rate of growth in the exponential phase due to differences in the crop load. Estimates of cortical cell numbers in 'Empire' fruit from related studies suggest that during the linear phase in mid-season, different growth rates among crop load treatments were apparently controlled by differences in numbers of cells in the fruit, since estimated growth rates per cortical cell were essentially constant over several treatments.

After convectional drying, bean seeds (Nadwislanski variety) were subjected to impact trials conducted in a specially constructed centrifugal impactor. The influences of rotational speed of 1000-2500 rev/min, seed moisture content of 14-21% w.b., and drying air temperature of 25-55°C on seed damage and germination were examined. To make the results more useful, a theoretical analysis of the mechanical forces acting on the seed was conducted to determine impact velocities. Values of impact velocity, below 4·0m/s and seed moisture contents above 18% w.b. were associated with acceptable seed damage of 5%. The test conditions, within the ranges given above, had little effect on seed germination capacity.

The cowpea [Vigna unguiculata (L.) Walp] is an important crop in many countries of tropical Africa, Asia and South America. Compared with other leguminous crops, little is known about the population structure of the cowpea and the partitioning of genetic diversity between cultivated and wild cowpea. One hundred and twelve accessions of cultivated cowpea (V. unguiculata ssp. unguiculata) and 43 of wild cowpea (V. unguiculata ssp. dekindtiana) were evaluated for genetic diversity at 26 isozyme loci. Cultivated accessions were characterized by very low genetic diversity (Ht = 0.029), with only six polymorphic loci. Four of these polymorphic loci displayed one very common allele and one rare allele. Accessions possessing these rare alleles were dispersed throughout Africa and a geographical center of isozyme diversity was not evident. Cultivated groups biflora (the catjang) and sesquipedalis (the yard‐long bean) could not be differentiated from the cowpea. Wild cowpea, on the other hand, were highly diverse (Ht = 0.168), with 19 out of 26 loci polymorphic. Our data indicate introgression from wild to cultivated must be very rare. Six wild accessions displayed high identity with the cultivated cowpea. Wild cowpea may, therefore, be the progenitor of the cultivated cowpea. Because these wild accessions were dispersed throughout equatorial Africa, there is no isozyme evidence for a narrowly defined center of domestication.