Alternate-bearing trees produce a heavy on-crop followed by a light off-crop. Whereas climatic events initiate alternate bearing, it is perpetuated by endogenous tree factors. For citrus, the mechanism and underlying physiology by which fruit influence floral intensity the next spring was unresolved. To determine whether reduced return bloom of on-crop trees was due to inhibition of vegetative shoot production and, thus, a lack of “wood” on which to bear next spring's inflorescences or, alternatively, to inhibition of phase transition and inflorescence development on an adequate number of vegetative shoots, fruit were removed from individual shoots monthly or from entire on-crop `Pixie' mandarin trees during periods critical to shoot initiation (summer) and phase transition (winter). Fruit removal provided clear evidence that the on-crop exerted a significant effect on return bloom during the summer by reducing summer–fall shoot growth and, hence, the number of flowers borne on these shoots as well as on old wood of fruit-bearing shoots. The on-crop had less effect in winter on phase transition and return bloom. Buds collected during the summer from on-crop `Pixie' mandarin trees were characterized by high indoleacetic acid and low isopentenyladenosine concentrations compared to buds from off-crop trees. The starch level of the buds was not affected. No differences in hormone concentrations were detected for buds collected during winter from on- and off-crop trees, but buds of on-crop trees had less starch. The results demonstrate that the on-crop reduces return bloom predominantly by inhibiting summer-fall vegetative shoot growth by a mechanism similar to apical dominance, not a lack of available carbohydrate.
In three trials, 2004 crop loads were adjusted at the balloon stage of blossom development on heavily cropped whole apple trees by clipping all flower pedicels within a cluster while leaving the spur intact. Trees were adjusted to 0% crop (all flowers removed), 50% crop (half of all clusters removed), or left as 100% crop (no flowers removed). On `Cameo'/Bud.9, 400 ppm GA4+7 were applied to trees of each crop level at petal fall, 10 mm, 20 mm, or left unsprayed. At each crop load, GA4+7 marginally diminished the 2005 return bloom regardless of application timing, but the 2004 crop level was far more influential in 2005 flowering. In a second `Cameo'/Bud.9 trial, 0, 300, 600, or 900 ppm ethephon were applied to whole trees of each crop level at 45 DAFB. Ethephon generally demonstrated a rate response in improving the 2005 return bloom, but the 2005 flowering was more dramatically influenced by 2004 crop levels. On `Honeycrisp'/M.9, 300 ppm GA4+7 were applied to whole trees of each crop level at 10 mm. GA4+7 diminished 2005 return bloom at the 50% crop load, but spray effects were not as clear at the extreme 2004 crop levels. These results suggest that commercial floral inhibitors and promoters have difficulty overcoming endogenous effects of heavy or light bloom and crop in severely alternating apple trees. In a fourth trial, lightly cropped organic `Fuji'/MM.106 trees were sprayed with 0, 150, 300, or 450 ppm GA4 at petal fall, 10 mm, or 20 mm timings in 2004. The 2005 return bloom was inversely correlated with spray rates, with 10 mm showing more floral inhibition than other timings. Overall, `Cameo' was less sensitive to GA and ethephon than `Honeycrisp' or `Fuji'.
Biennial bearing has long been thought to occur in cranberry (Vaccinium macrocarpon Ait). Researchers have shown that percent return bloom on fruiting uprights can range from 12% to 65% depending on year, bed vigor and cultivar. Resource limitation and/or hormonal factors in a fruiting upright may be related to flower bud initiation and, thus, percent return bloom the following year. This research was undertaken to determine the extent of biennial bearing by cranberry cultivar and growing region. Seven cultivars were studied; three found in all states (MA, NJ, WI, OR), two common to MA and NJ, and two different cultivars in WI and OR representing cultivars commercially grown in these areas. In the fall or winter of 1989/1990 six 2-m transects were randomly selected within a cranberry bed for each cultivar. Along the transect, 60 uprights that fruited in 1989 were tagged. In the summer of 1990, fifty of the uprights will be sampled to determine percent return bloom and percent set.
Biennial bearing has long been thought to occur in cranberry (Vaccinium macrocarpon Ait). Researchers have shown that percent return bloom on fruiting uprights can range from 12% to 65% depending on year, bed vigor and cultivar. Resource limitation and/or hormonal factors in a fruiting upright may be related to flower bud initiation and, thus, percent return bloom the following year. This research was undertaken to determine the extent of biennial bearing by cranberry cultivar and growing region. Seven cultivars were studied; three found in all states (MA, NJ, WI, OR), two common to MA and NJ, and two different cultivars in WI and OR representing cultivars commercially grown in these areas. In the fall or winter of 1989/1990 six 2-m transects were randomly selected within a cranberry bed for each cultivar. Along the transect, 60 uprights that fruited in 1989 were tagged. In the summer of 1990, fifty of the uprights will be sampled to determine percent return bloom and percent set.
In the article titled “Ethephon as a Blossom and Fruitlet Thinner Affects Crop Load, Fruit Weight, Fruit Quality, and Return Bloom of ‘Summerred’ Apple (Malus ×domestica) Borkh.,” by Mekjell Meland and Clive Kaiser [HortScience 46(3):432-438; March
The efficacy of Prohexadione-Ca on vegetative and reproductive parameters was tested for 3 years on three apple cultivars (Golden Delicious, Braeburn, and Fuji) at concentrations ranging from 125 up to 350 ppm. The Prohexadione-ca was applied after shoots reached 5 cm length, for 1 month. In all cases, Prohexadione-Ca reduced shoot growth, showed the tendency to increase fruit size and to enhance return bloom. In addition, it increased leaf coloration and higher chlorophyll content, and it induced higher photosynthetic efficiency than the control. The relationships among shoot reduction, chlorophyll content and photosynthetic efficiency are discussed.
Apogee at rates of 125 and 250 ppm applied at 2-cm average shoot growth and a split application of 125 ppm applied at 2-cm shoot growth and 2 weeks later reduced vegetative growth of `Pink Lady', `Gala', and `Fuji' in 1997 and 1998. Cultivar response varied with rate and year. Fruit size was significantly increased in `Gala' at the low rate and split low rate applications and in `Fuji' at the low and high rate single application in 1998. There was no effect on return bloom or fruit color.
Abstract
‘Richared Delicious’ trees received 10 μW·cm−2 of red light, peaking at 660 nm for 1.5 or 15 min nightly at midnight from full bloom until the end of “June drop” in early July. Both light treatments reduced abscission during the June drop period. ‘McIntosh’ apple trees received 10 or 200 μW·cm−2 of red light for 15 min at midnight, beginning in mid-August and continuing nightly until mid-October. Preharvest drop of fruit was delayed considerably one year and slightly reduced the 2nd year. With either cultivar, light treatment had no effect on fruit size, fruit quality, or return bloom in either year.
Abstract
The inhibitory effect of cropping on return bloom in fruit trees is well-known. Previous work suggests the presence of fruit inhibits vegetative meristems from initiating flowers (2). Root pruning promotes flower formation in fruit trees (4). In 1984, we began a study to investigate the interactions between cropping and root pruning on flowering and other physiological processes in field-grown apple trees. In May 1986, the trees that had been deblossomed for three consecutive years underwent a second flush of bloom. This occurrence has not been documented adequately for apple.
Abstract
Foliar sprays of (2-chloroethyl)phosphonic acid (ethephon) were applied at 50, 100, and 150 ppm to French prune trees at 50% petal fall and when seed length was 8.3 to 9.4 mm. All concentrations thinned fruits within 3 to 4 weeks after treatment. The treatments increased soluble solids and fruit size, and in some instances decreased dry tonnage. Return bloom the following year was greater on treated trees than on controls. Also, fall coloration patterns appeared earlier on the treated trees. No phytotoxic effects from the treatments were evident on the fruits.