, 1987 ; Tromp, 1982 ). The presence or absence of gibberellins clearly influences flowering in apple, but the underlying mechanisms for that relationship are not well understood. Low return bloom in poorly thinned apple trees is often blamed on floral
Trees with about the same crop load were hand thinned to 1, <2, or <3 fruit per cluster or not thinned while the ovule was about one-half expanded. Treatments were replicated three times. Vegetative, and bearing terminal, lateral and shoots with secondary growth were tagged in October, and flowering was determined the following year. Shoots and roots were sampled during dormancy and analyzed for organically bound N, and K. Results indicated that branches with secondary growth produced substantially more shoots and flowers than other branch types. The unthinned trees produced fewer total flowers per branch, had a lower percentage of branches with flowering shoots, and smaller flower clusters than thinned trees. Organically bound N in the roots and shoots was not affected by crop load. Crop load appeared to be negatively related to K concentration in roots <1 cm in diameter, but not in roots >1 cm in diameter. The data suggest that neither N nor K were limiting in trees with large crops.
from the price paid per tree to determine crop value. Return bloom dynamics. Twenty-five spurs were randomly selected among five shoots (five spurs per 2-year-old segment of shoot) per tree, and the number of reproductive buds per spur recorded. Floral
United States to improve return bloom after moderate to heavy crops. Floral initiation inhibitors, specifically gibberellins, show potential as crop load management tools by reducing return bloom after light crops. Literature widely reports the effects of
The proportion of spurs blooming on `McIntosh' apples (Malus domestica Borkh.) was reduced significantly in 1986 and 1988, but not in 1987, following seasonal programs of six bitertanol or flusilazole treatments applied at two and three rates, respectively. The fungicides were not associated with any visible phytotoxic effect nor was shoot length reduced by any fungicide treatment. In two of three experiments conducted in May and June 1986, transpiration was reduced by the low rate of flusilazole and the high rate of bitertanol relative to both the captan and nonsprayed trees. In all three experiments, flusilazole at 1.4 g a.i./100 liter was associated with transiently reduced transpiration rates, lasting a minimum of 48 hours, relative to the nonsprayed control. Fungicides affected the diffusive resistance of apple leaves in all three experiments; however, there were no consistent treatment effects on diffusive resistance among the three experiments.
Overwintering buds and internodes of Vitis labruscana `Concord' were taken from minimal- (MP) and balance-pruned (BP) vines in Dec. 1993 and Dec. 1994 from canes whose weight, crop weight, total nodes, and nodes with periderm were known. Winter characters recorded were: node-5's primary bud basal area, total nodes, and developmental stage of cluster primordia; stage of largest cluster in the secondary bud; vascular area of cane internode 5. Fifty node-5 buds were tagged in each treatment and flower and fruit number per cluster later recorded. Regression analysis showed no effect of a shoot's crop, cane weight, node number, or nodes having periderm on any character measured in the overwintering buds or canes for either treatment. Regression analysis did show mean flower number per cluster was linearly related to mean winter stage per cluster in both treatments, with all values falling on one line. Differences between treatments were one of degree of cluster development; BP vines had more-developed winter and spring clusters and more flowers and fruit per shoot. The slope of the regression was identical the last 3 years, although the y intercept varied each year; thus, a given cluster stage in the overwintering bud was capable of producing a variable number of flowers the next season, depending on year. Flower number per shoot appeared positively related to growing-degree-days the previous season.
In a simple, yet elegant experiment conducted 30 years ago, Chan and Cain (1967) using 'Spencer Seedless', a facultatively parthenocarpic apple (Malus×domestica Borkh.) cultivar, proposed that seeds inhibited flowering and accentuated biennial bearing in apple. Their conclusions have been extrapolated widely to include apple and other species. We have tested the universality of their conclusions using 'Bartlett' pear (Pyrus communis L.), a commercially important, facultatively parthenocarpic cultivar. Unlike 'Spencer Seedless' apples and seedless 'Bartlett' pear grown in France, California-grown seedless 'Bartlett' pear fruit strongly inhibited flowering the following year. However, the presence of seeds increased 'Bartlett' pear fruit size relative to seedless fruit by 13% and 20% in nonthinned and heavily-thinned pear trees, respectively, indicating that seeds increased fruit sink strength.
Leaves and fruits on individual limbs of pecan (Carya illinoensis Koch cv. Stuart) were removed during the time of kernel development. Leaf removal decreased and fruit removal increased pistillate flower production and fruit set.
Several experiments were conducted to evaluate the influence of time, concentration, and number of GA4+7 applications on ‘McIntosh’, ‘Early McIntosh’, and ‘Empire’ apples (Malus domestica Borkh.). GA4+7 at 150 mg·liter−1 increased fruit set and inhibited flower bud formation on ‘McIntosh’ and ‘Early McIntosh’. Flower bud formation was inhibited on ‘McIntosh’ when GA4+7 was applied over a wide range of times from 6 days before full bloom to 34 to 35 days after full bloom. Applications made 45 and 60 days after full bloom had no effect. Following storage, ‘Empire’ fruit treated with GA4+7 were softer and had a higher incidence of senescent breakdown than controls. Postbloom sprays of GA4+7 increased fruit set on ‘Empire’ one year when applied from 0 to 150 mg·liter−1, while two applications of 50 mg·liter−1 on similar trees in another year caused thinning. GA4+7 sprays appeared to advance ripening of ‘Empire’ apples. Gibberellin sprays reduced seed number. GA4+7 inhibited flowering in ‘Empire’. Repeat applications 19 and 34 days after full bloom were only slightly more inhibitory to flowering than one application of 0, 50, 100, or 150 mg·liter−1 made 10 days after full bloom.
Regulation of biennial bearing in pome fruit is usually accomplished by chemically removing fruit during the “on” cycle. The advantages and disadvantages of regulating biennial bearing by inhibiting flowering in the “off” cycle were discussed. Gibberellins and the two phenyl urea cytokinin-like compounds, thidiazuron and CPPU have been shown to inhibit flowering in pome fruit. It was concluded that inhibition of flowering with commercially available gibberellins was not a commercially acceptable approach to regulate biennial bearing. The inhibition of flowering was erratic, fruit thinning and increased fruit set could not be predicted, and seed abortion following gibberellin application could predispose fruit to reduced postharvest life because of reduced calcium uptake. Regulation of flowering by inhibiting flower bud formation appeared to be a viable way to regulate cropping on nonbearing tress or trees that were not carrying a crop.