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  • Author or Editor: S.M. Southwick x
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Abstract

Ethylene production by senescing flowers of calamondin (Citrus madurensis Lour.), at rates as high as 15 nl/g fresh weight-hour did not necessarily induce absicission. Moreover, combinations of gibberellic acid (GA), calcium dihydrophosphate and 6-benzylamino purine (BA), which are known to increase fruit set in citrus, did not significantly decrease ethylene production. Abscission of calamondin fruitlets and increases in fruit set appear to be independent of ethylene production.

Open Access

Abstract

Whole-tree sprays of gibberellic acid (GA) plus calcium dihydrophosphate Ca(H2PO4)2 increased fruit set of navel orange [Citrus sinensis (L.) Osb.] during 1979 and 1980. Gibberellic acid alone or a combination with Ca(H2PO4)2 or 6-benzylamino purine (BA) increased fruit set in 1980. Benzylamino purine did not increase fruit set or the fruit-setting effectiveness of GA. Calcium dihydrophosphate increased fruit set for approximately 5.5 weeks in 1980 even though leaves did not show signs of calcium deficiency. However, no increase in fruit set was observed 8.5 weeks after application. Fruit sprayed with GA were smaller than untreated fruit initially; however, no size differences were noted 8.5 weeks after full bloom.

Open Access

Soil applied potassium (K) may not alleviate K deficiency in fine textured California soils when high numbers of prunes per tree are produced leading to leaf necrosis and limb death. Because K demand is increased by fruit, K nitrate (KN) sprays appear to be a corrective option for growers in this situation. Our objectives were to determine best seasonal KN spray liming strategies to minimize K deficiency, quantify K uptake into leaves after spray and to evaluate spray effects on productivity. Results indicated that regardless of spray timing leaf K was increased by approximately 0.3% and three weeks later decreased 0.2%. Average leaf K in sprayed trees was 0.7% higher than untreated trees at harvest. Fruit fresh to dry weight ratios were lower (better) from summer sprayed trees than spring. Summer KN sprayed trees had yield efficiencies equal to those having soil applied K. Fruit size was similar regardless of K application method. Foliar KN sprays may be a viable K augmentation to soil application in heavy crop years on fine textured soils.

Free access

Abstract

Treatments that inhibit production of citrus flowers, such as the presence of fruit, gibberellic acid (GA3) spray, and branch pruning, were examined on container-grown ‘Tahiti’ lime (Citrus latifolia Tan.) trees induced to flower by severe water stress lasting from 2 to 5 weeks. The presence of (or effects of recently removed) fruit located at the apex of branches inhibited production of new shoots as well as expression of the vegetative and floral nature of those shoots in basipetal lateral buds. Fruit ranging in size from 0.76 to 5.0 cm in equatorial diameter inhibited the shooting response. Shoot production and floral expression were normal on other branches. Fruit size or the amount of time fruit were present on branches were associated with the reduction in shoot and flower production. Aqueous GA3 sprays at 10−3 m concentration, applied at the onset or end of the floral inductive water stress treatment, inhibited expression of both vegetative and floral shoots. This inhibitory response dissipated as time elapsed after treatment. Pruning three branches from each tree replicate did not modify the flowering response in nonpruned water-stressed branches. The shooting response of branch units on these small trees responded independently to the presence or absence of fruit, GA3 treatment, and branch pruning.

Open Access

`Bing' sweet cherry is the most widely planted cultivar grown in the Western US because of widespread market acceptance. High prices are associated with early maturing `Bings' so growers are inclined to plant in early maturing growing regions. High numbers of less marketable, abnormally shaped (deep sutures, spurs, doubles) fruit tend to be produced in these regions. It is thought that abnormal fruit development is associated with high summer temperatures. Dataloggers equipped with thermocouples were located in 7 California cherry growing regions. Thermocouples were positioned throughout tree canopies, monitoring flower bud temperatures for 2 seasons from May to October. A Richard's function was used to describe the relation of average daily temperature (July, August, September to the percentage of fruit with deep suture. Correlation coefficients (R2) of 0.85 and higher were found, with increases in average daily temperatures above 22C associated with the formation of abnormal fruit shapes. Heat lamps were used to increase spur temperatures 5-7C above ambient during the July through September period, High percentages of abnormal flowers were produced in the season after 2 July, but not after 21 August heating, Strategies to lower high summer canopy temperatures helped to reduce abnormal fruit shapes.

Free access

Lack of pollen dispersal was noted in various sites and cultivars of sweet cherry (Prunus avium) following one of California's warmest recorded winters (≈550 hours @ 7°C in the Central Valley). `Bing' cherry is thought to require 850 to 880 hours for adequate budbreak and bloom development. Cross pollination is required by most sweet cherry cultivars for fruit set, including `Bing'. Complete anther dehiscence averaged 13% in `Bing' trees sampled, compared to 52% in `Rainier', 65% in `Brooks', 84.5% in `Burlat', 33% in Van, 23% in `Larian', and 86% in `Black Tartarian'. A range of degree of dehiscence from none to half-open was widely apparent, again by cultivar. Many partially dehiscent anthers did not shed pollen normally but appeared to have the mass of pollen completely adherent inside the pollen sacs. `Black Tartarian', `Larian', and `Burlat' shed pollen readily, however, pollen from dehiscent anthers of other cultivars generally appeared to stick together on the everted locule walls and required direct manipulation to be withdrawn from the pollen sac. Anther morphology ranged from normal size to half normal size, anthers appearing to be without pollen altogether that shriveled on drying, and lobes that were aborted. Pollen germination was low overall: 19% `Bing', 18% `Rainier', 20% `Brooks', 57% `Burlat', 14% `Van', 48% `Larian', and 48% `Black Tartarian'. Poor fruit set in low chill years is often attributed to lack of bloom overlap with pollenizers, however, inadequate chilling also may contribute to low fruit set by inhibiting anther and pollen growth and development. The implications of a critical chilling requirement for normal floral differentiation are that in cherry-growing areas where low chill years are common, pollen may not be viable or transferrable from pollenizers and female gametophytic development also may be impaired.

Free access

During the fruit growing season, April through August 1990, 1991, and 1992, four sprays of 20-22 liters/tree of KNO3 were applied to `French' prune trees (Prunus domestica L. syn. `Petite d'Agen). Spray applications of KNO3 were compared to single annual soil applications of KCl (1.4-2.3 kg/tree) and sprays of urea + KNO3 with respect to leaf K and N, fruit size, drying ratio, and dry yield. Potassium nitrate sprays were as effective, or better, than soil-applied K in maintaining adequate levels of leaf K throughout the season. Treatment effects were not carried over into the next year. Lowest leaf K was found in trees where no K had been applied. Those values were below the adequate level of 1.3% K and the untreated group developed K deficiency symptoms. Consistent effects on leaf K were not obtained when urea was applied and no negative effect on leaf K was demonstrated. Equivalent dry yields per tree were obtained by foliar and soil K applications. There was no best time for KNO3 sprays. Yield per tree was not enhanced when foliar K-N sprays were applied to trees that had levels of 1.3% K or more as of 15 Apr. 1992. Trees that were below optimum K in April tended toward improved dry yields after four K-N sprays. Trees that had no applied K were lowest yielding. Drying ratios and fruit size (number of fruit per kilogram) were not different among K treatments. Dry yields per tree were increased without a decrease in fruit size or an increase in drying ratio with either soil or foliar K application. These results suggest that foliar KNO3 sprays applied four times throughout the growing season can be used to correct incipient K deficiency in `French' prune and to obtain dry yields equivalent to those obtained with soil applications of KCl.

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A 2-ac block of `Bing'/Colt, Mahaleb or GM61/1 was planted 8×15′, Feb 1991 so that 7 treatments were arranged in 6 blocks. We imposed water stress during 2 distinct periods, June or July in 1992. Once trees had stopped growing water was added (estimated @ 50% ETc) to maintain leaf turgor, but not to initiate further shoot growth. Well-watered (100% ETc) trees were summer pruned to check growth. Water stress was monitored by measuring water potential of basal bagged leaves with a pressure chamber at midday. Shoot growth was stopped by water stress. Shoot growth ceased at a trunk water potential of approximately -17 bars in both Colt and Mahaleb rootstocks although Colt rootstock went into stress more rapidly than Mahaleb. Colt may be more sensitive to water deprivation at this site than Mahaleb rootstock. Well-watered GM 61/1 trees had tree sizes much like those of water stressed Colt trees. A combination of early season stress and summer pruning (heading) may be the best combination used to control growth. Flower bud formation was noticed by season's end in these 2nd leaf trees. Water stress can be used to control tree growth, save water and encourage fruitfulness when integrated into an appropriate orchard system.

Free access

ReTain™, a commercial derivative of aminoethoxyvinylglycine, was applied as a single application at 124 g·ha-1 a.i. to `Bartlett' pear (Pyrus communis L.) trees 28, 21, 14, or 7 days prior to initial commercial harvest and at 62 g·ha-1 a.i. in combination with naphthaleneacetic acid (NAA) at 92 g·ha-1 a.i. 14 days prior to initial commercial harvest. Maturity and quality of treated fruits at harvest and following storage were compared with those of nontreated pears in 1996 and 1997. Ethylene production by mature green pears at harvest was not significantly affected by ReTain™ treatments, although softening, loss of chlorophyll, and starch clearance were usually inhibited by the 14- or 7-day treatment. ReTain™ suppressed ethylene production, softening and loss of chlorophyll in ripening pears and mature green pears cold-stored for 4 months, although loss of chlorophyll did not differ in the cold-stored fruit in 1997. ReTain™ had little effect on softening during a ripening period of 6 days after 4 months of cold storage. Application at 14 or 7 days prior to initial harvest appeared most effective, often with little difference between the two timings, and the 28- or 21-day treatment or combined ReTain™ and NAA treatment were seldom more effective. ReTain™ applied 14 or 7 days before initial harvest delayed fruit maturation by 4-10 days depending on the maturity index. The maturity or ripeness of pears from the combined ReTain™ and NAA, NAA only, and control treatments was often similar or differed only slightly. Premature ripening, prevalent in 1997, was dramatically suppressed in fruit treated with ReTain™. Ripening of both ReTain™- and non-ReTain™-treated fruit with ethylene reduced premature ripening by ≈50%.

Free access

Secondary or “rat-tail” bloom, a major site for fireblight infection of `Bartlett' pear, comprised 10% of the total bloom in 1997 and 20% in 1998. We are striving to find production practices that can be economically applied to reduce the number of “rat-tails.” Of the five known types of secondary clusters in pear, four occur on `Bartlett', the most numerous being types I and V. Type I rat-tails occur on the bourse at the base of normal clusters and bloom from 10 to 30 days after normal bloom. Type V rat-tails occur mostly at pruning sites and have one to three flowers per cluster, blooming 20 to 50 days after normal bloom. GA 3 or GA4+7 + BA were applied at 100 mg•L-1 in 1997 to reduce rat-tail bloom in 1998. In 1998, neither GA3 nor GA4+7 + BA had an effect on normal bloom or type I rattails. GA3 reduced type V rat-tails when applied at either 2 June, 2 July, or 15 Aug. but had no effect on type V clusters when applied at full bloom, petal fall, 16 June, or 15 July. GA4+7 + BA reduced the number of type V rat-tails when applied at either 2 June, 16 June, 2 July, and 15 July but had no effect when applied at full bloom, petal fall, or 15 Aug. Dormant pruning horizontal shoots resulted in as many rat-tails as vertical shoots, and heading cuts a similar number as stubbing cuts. Dormant pruning 1-year wood resulted in fewer rat-tails than 2-year wood. Summer pruning 21 or 49 days after bloom resulted in fewer rat-tails than pruning 10 days after harvest, but was similar to pruning 89 days after bloom. These and other results from ongoing work will be presented toward development of an integrated fire blight reduction strategy.

Free access