collected, AS and HLB, because it was not possible to find trees that qualified as HLB-B trees. Samples were taken on 19 Jan., 3 and 19 Feb., and 3 Mar. 2014 in the same manner as for ‘Hamlin’. Fruit detachment force. The FDF was measured using a digital
Hong Chen, Greg McCollum, Elizabeth Baldwin, and Jinhe Bai
Kay P. Gersch, Carl E. Motsenbocker, and Gregory A. Lang
Cayenne pepper fruit adhere tightly to the calyx/receptacle, increasing the cost of hand harvest and restricting mechanical harvest. Eight (8) cayenne pepper genotypes were selected from field observations to characterize fruit detachment forces(FDFs) and examine potential relationships between FDF and other fruit parameters. A preliminary greenhouse experiment revealed two genotypes with consistently lower FDFs and two with consistently higher FDFs over several progressive harvest. A field experiment confirmed these characteristics. No correlation between any fruit parameter and FDF was found to be consistent over the genotypes studied.
Kelly T. Morgan, Smita Barkataky, Davie Kadyampakeni, Robert Ebel, and Fritz Roka
that reduces long-term productivity. The objective of the current field study was to determine the effect of short-term drought stress before and/or after harvesting on: 1) fruit detachment force required to remove fruit at harvest; 2) tissue loss and
Lisa Tang, Shweta Chhajed, and Tripti Vashisth
, there was no obvious difference in peel color for tight fruit and loose fruit (irrespective of HLB severity). Fig. 2. The percentages of tight and loose fruit (fruit detachment force >6 and ≤6 kgf, respectively) collected 3 weeks before harvest from
Luis Pozo and Jacqueline K. Burns
America Corp., Aurora, IL). In the 2007–2008 cropping year, fruit detachment force (FDF, kg-force) was measured 6 d after spray treatments in both mature and developing fruit with a digital force gauge (Force Five; Wagner Instruments, Greenwich, CT). For
Rongcai Yuan, Ulrich Hartmond, and Walter J. Kender
Endogenous concentrations of IAA and ABA in the peel, pulp, seed, and abscission zone of mature `Valencia' oranges [Citrus sinesis (L.) Osbeck] were determined by high-performance liquid chromatography and enzyme-linked immunosorbent assay from early November 1998 to mid-June 1999. Ethylene production of mature `Valencia' oranges during the same period was determined by gas chromatography. IAA concentrations in the pulp and seed were three to five times lower than those in the peel over the 7-month observation period. IAA concentration in the abscission zone and peel was high from late April to mid-May, the period of less responsiveness to abscission chemicals. ABA concentration in the pulp was low over the entire observation period. ABA concentration in the abscission zone and peel was low during the less responsive period. Ethylene production was always low except for a slight increase during late December and early February. The IAA to ABA ratio was high in the fruit abscission zone during the less responsive period. Fruit detachment force of CMN-pyrazole-treated fruit was positively correlated with the ratio of endogenous IAA to ABA or endogenous IAA, but negatively to endogenous ABA in the fruit abscission zone. These data suggest the balance between IAA and ABA in the fruit abscission zone may be an important factor in determining sensitivity and thereby the response of mature `Valencia' orange fruit to abscission chemicals. Chemical names used: abscisic acid (ABA); indole-3-acetic acid (IAA); 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMN-pyrazole).
Luis Pozo, Ana Redondo, Ulrich Hartmond, Walter J. Kender, and Jacqueline K. Burns
Two formulations of the plant growth regulator dikegulac (2,3:4,6-di-O-isopro-pylidene-α-L-xylo-2-hexulofuranosoic acid), consisting of dikegulac-sodium (Atrimmec) or dikegulac:ascorbic acid (1:1) (DAA), as well as 5-chloro-3-methyl-4-nitro-pyrazole at 200 mg·L-1, were applied as foliar sprays to `Hamlin' and `Valencia' orange trees (Citrus sinensis L. Osbeck) at two dates during the harvest season for each cultivar (11 Nov. and 10 Jan. for `Hamlin', 22 Mar. and 25 May for `Valencia'). Fruit detachment force was evaluated 10 days after application, whereas cumulative leaf abscission was monitored up to 60 days after application. In both cultivars, Atrimmec and DAA at 3,000 mg·L-1 induced moderate fruit loosening when applied at the earlier application date, but fruit loosening improved when applied at the later application date. In `Hamlin', both formulations caused higher leaf abscission when applied at the later date. DAA applications resulted in low leaf loss in `Valencia' regardless of application time, whereas Atrimmec caused unacceptably high leaf loss at either application date. No differences in internal fruit quality were found as a result of any abscission material treatment. The results indicate that DAA could be a promising option to induce fruit loosening in late harvested `Valencia' orange trees with minimal undesirable side effects.
Rongcai Yuan, Ulrich Hartmond, Angela Grant, and Walter J. Kender
Influence of young fruit, shoot, and root growth on response of mature `Valencia' oranges [Citrus sinensis (L.) Osbeck] to the abscission chemical CMN-pyrazole was examined in 1999 and 2000. CMN-pyrazole dramatically increased ethylene production in mature fruit and reduced the fruit detachment force (FDF), except during a period of reduced response to CMN-pyrazole in early May when spring vegetative growth, young fruit of the following year's crop, and mature fruit were all on the trees. Removal of spring flushes, which included spring vegetative shoots and leafy and leafless inflorescences, prevented any young fruit and shoot growth, but did not inhibit root growth. However, trunk girdling in combination with removal of spring flushes not only prevented growth of young fruit and shoots but also inhibited root growth. During the responsive period, there were no differences in either ethylene production or FDF of CMN-pyrazole-treated mature oranges between 1) the nonmanipulated trees and those manipulated by either 2) removal of spring flushes alone, or 3) in combination with trunk girdling. However, during the less responsive period, ethylene production in CMN-pyrazole-treated mature oranges was significantly lower while the FDF was higher in nonmanipulated trees than in trees treated by either removal of spring flushes alone, or in combination with trunk girdling. There was no difference in either fruit ethylene production or FDF between trees manipulated by (2) removal of spring flushes alone, and (3) removal of spring flushes in combination with trunk girdling regardless of CMN-pyrazole application. Shoot growth terminated at least 2 weeks before the onset of the less responsive period. Removal of young fruit increased response of mature fruit to CMN-pyrazole during the less responsive period. This suggests that hormones from rapidly growing young fruit may be responsible for the occurrence of the less responsive period. Chemical name used: 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMN-pyrazole).
Jacqueline K. Burns, Richard S. Buker III, and Fritz M. Roka
An abscission agent [5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP)] was applied to `Hamlin' and `Valencia' orange (Citrus sinensis) trees at concentrations ranging from 0 to 500 ppm in a volume of 300 gal/acre. Four days after application, fruit were mechanically harvested with either a trunk shake-and-catch or a continuous canopy shake-and-catch system commercially used in Florida. Harvesting conditions were varied by limiting the actual trunk shake time of the trunk shaker to 2, 4, or 7 seconds, or by altering the ground speed of the canopy shaker (1.0, 1.5, or 2.0 mph). In general, increasing duration of shake and the application of CMNP increased percent mature fruit removal and decreased the amount of fruit remaining in the tree. Increasing CMNP concentration decreased fruit detachment force but increased post-spray fruit drop. Comparison of short duration shake times in CMNP-applied trees with trees harvested at longer durations either sprayed or not sprayed with CMNP indicated no significant difference in percent mature fruit removal. The results demonstrate that CMNP application increases harvesting capacity of trunk and canopy shakers by reducing time necessary to harvest each tree while maintaining high percent mature fruit removal.
Rongcai Yuan, Ulrich Hartmond, and Walter J. Kender
Effects of NAA, TIBA, ethephon, and CMN-Pyrazole on fruit detachment force (FDF) of mature `Valencia' and `Hamlin' orange [Citrus sinensis (L.) Osb.] fruit were examined in 2000 and 2001. NAA effectively inhibited the reduction in FDF or fruit abscission caused by ethephon when applied to the abscission zone 24 hours before ethephon application, but had no significant effect when applied to the fruit without contacting the abscission zone, or to the peduncle ≈4 cm above the abscission zone. TIBA, an auxin transport inhibitor, decreased FDF of mature fruit and promoted fruit abscission when applied alone as a spray to the canopy or directly to the fruit peduncle. This response was dependent on TIBA concentration. TIBA was more effective when applied in combination with ethephon or CMN-Pyrazole than alone. These results are consistent with our previous data that endogenous auxin concentration in the abscission zone of mature `Valencia' orange fruit is one of the factors controlling the sensitivity and thus the responsiveness of the abscission zone of mature fruit to abscission chemicals. Chemical names used: 5-chloro-3-methyl-4-nitro-pyrazole (CMN-Pyrazole); 2-chloroethylphosphonic acid (ethephon); naphthalene acetic acid (NAA); 2,3,5-triiodobenzoic acid (TIBA).