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- Author or Editor: T. A. Wheaton x
- Journal of the American Society for Horticultural Science x
Abstract
Substantial improvement in the external color of harvested citrus fruit was achieved by holding at optimum temperature and ethylene concentration. Under specific conditions, marked improvement in orange and red pigmentation occurred. Initial color development was most rapid at 30°C but carotenoid accumulation ceased after a few days. Best color was obtained with fruit held at 15-25°C for longer periods of time. Optimal ethylene concentration decreased as temperature decreased. At the lowest temperature, high ethylene concentration inhibited color development.
Growth and nitrogen (N) accumulation relationships based on tree size, rather than age, may provide more generic information that could be used to improve sweet orange [Citrus sinensis (L.) Osbeck] N management. The objectives of this study were to determine how orange trees accumulate and distribute biomass and N as they grow, investigate yearly biomass and N changes in mature orange trees, determine rootstock effect on biomass and N distribution, and to develop simple mathematical models describing these relationships. Eighteen orange trees with canopy volumes ranging between 2 and 43 m3 were dissected into leaf, twig, branch, and root components, and the dry weight and N concentration of each were measured. The N content of each tree part was calculated, and biomass and N distribution throughout each tree were determined. The total dry biomass of large (mature) trees averaged 94 kg and contained 0.79 kg N. Biomass allocation was 13% in leaves, 7% in twigs, 50% in branches/trunk, and 30% in roots. N allocation was 38% in leaves, 8% in twigs, 27% in branches/trunk, and 27% in roots. For the smallest tree, above-/below-ground distribution ratios for biomass and N were 60/40 and 75/25, respectively. All tree components accumulated biomass and N linearly as tree size increased, with the above-ground portion accumulating biomass about 2.5 times faster than the below-ground portion due mostly to branch growth. The growth models developed are currently being integrated in a decision support system for improving fertilizer use efficiency for orange trees, which will provide growers with a management tool to improve long-term N use efficiency in orange orchards.
Abstract
The uptake, translocation, and metabolism of 14C-gibberellic acid (14C-GA3) was studied in 3-year-old container-grown ‘Marsh’ grapefruit trees (Citrus paradisi Macf.). A total of 1.65 × 105 disintegrations per min (dpm) in 200 μl of solution was applied evenly over the entire fruit surface, or, on both surfaces of 3 to 5 subtending leaves of a fruit. Absorption of 14C-GA3 by leaves and peel began within 1 hr of application and continued for 8 hr. Translocation of labeled material from leaves to peel and the reverse began 4 to 8 hr after application and continued for 4 weeks. No labeled material was recovered from juice or seeds. Labeled material persisted in albedo, flavedo, and leaves for 8 weeks with the highest accumulations in the peel. Separation of 14C-GA3 metabolites from the 95% EtOH extract by reversed-phase HPLC produced 2 14C-labeled peaks. Analysis of these 2 peaks by β-D-glucosidase hydrolysis, n-butanol partitioning, and cochromatography with 14C-GA3 standards suggested that the major component was 14C-GA3 and the other a polar metabolite.
A factorial experiment begun in 1980 included `Hamlin' and `Valencia' sweet-orange scions [Citrus sinensis (L.) Osb.], and Milam lemon (C. jambhiri Lush) and Rusk citrange [C. sinensis × Poncirus trifoliata (L.) Raf.] rootstocks, tree topping heights of 3.7 and 5.5 m, between-row spacings of 4.5 and 6.0 m, and in-row spacings of 2.5 and 4.5 m. The spacing combinations provided tree densities of 370, 494, 667, and 889 trees ha. Yield increased with increasing tree density during the early years of production. For tree ages 9 to 13 years, however, there was no consistent relationship between yield and tree density. Rusk citrange, a rootstock of moderate vigor, produced smaller trees and better yield, fruit quality, and economic returns than Milam lemon, a vigorous rootstock. After filling their allocated space, yield and fruit quality of trees on Milam rootstock declined with increasing tree density at the lower topping height. Cumulative economic returns at year 13 were not related to tree density.