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Six ‘Ambersweet’-derived hybrids, similar to sweet orange fruit size, color, and taste and potential as new sweet orange cultivars, were selected to determine their fruit categorization by comparison of their volatile profiles with the parent and ‘Hamlin’, a typical sweet orange. All hybrids are at least ½ sweet orange and varying amounts of mandarin, grapefruit, Poncirus trifoliata, and sour orange in each pedigree. In total, 135 volatiles were detected in the eight hybrid lines/commercial cultivars over two harvests, and 20 compounds were detected in all samples, including terpenes (limonene, β-myrcene, α-pinene, α-terpinene, α-terpineol, and linalool), esters (ethyl butanote, ethyl pentanoate, and ethyl acetate), aldehydes (acetaldehyde, hexanal, and nonanal), and alcohols (ethanol and hexanol). Total abundance of volatiles in January-harvested fruits averaged 30% higher than for fruits of the same trees harvested in November. ‘Ambersweet’ contained the highest total amount of volatiles (mainly as a result of very high levels of monoterpenes), and of them, nootkatone and six other compounds were not detected in any of the hybrids, and some of them were also not detected in ‘Hamlin’. On the other hand, 12 compounds, including pentanal, ethyl 2-butenoate, and ethyl nonanoate, were not detected in ‘Ambersweet’ but were found in ‘Hamlin’ and some of the hybrids. Cluster analysis separated the cultivar/hybrid and harvest time combinations into three clusters. FF-1-76-50, FF-1-76-52 and January FF-1-75-55, all with the same parents (‘Ambersweet’ × FF-1-30-52), were close to FF-1-65-55, but they were separated from ‘Hamlin’ and further separated from ‘Ambersweet’. The cluster containing ‘Hamlin’ has three subclusters: January ‘Hamlin’ and November FF-1-74-14, a hybrid with one-eighth P. trifoliata, which includes a slight off-flavor frequently found in P. trifoliata hybrids, independent of each other, and both were separated from a group of November ‘Hamlin’, FF-1-64-97, and FF-1-75-55. The cluster containing ‘Ambersweet’ included January FF-1-64-97. A principle component analysis (PCA) separated ‘Ambersweet’ from all hybrids and ‘Hamlin’ along the PC1 axis and separated November harvests from January harvests along PC2. This volatile analysis supports the classification of the hybrids as sweet orange.

Thinning with BA reportedly increases size of 'Empire' fruit more than does thinning with NAA because of enhancement of cell division by BA. This study was conducted to determine the phenological stage at which BA application provides maximum fruit weight relative to degree of cropload reduction. In all years, treatments were applied at a range of timings: petal fall (PF), 5-, 10-, or 15-mm king fruitlet diameter (KFD). For each thinner, the same concentration was used throughout the study. In 1994, only Accel® at 75 mg·L^-1 was evaluated. In 1995, NAA (7.5 mg·L^-1) + carbaryl (600 mg·L^-1), Accel®, and a BA-only formulation were compared, but BA alone was applied only at PF, 10- and 15-mm KFD. In 1996, Accel® and NAA were compared with and without carbaryl at all timings. Most treatments reduced cropload and enhanced fruit weight. When data for all 3 years were combined, Accel® or BA increased cropload-adjusted fruit weight (CAFW) in 8 of 10 treatments made at 10- or 15-mm KFD, PF treatments never increased CAFW, and only one of four applications at 5-mm KFD increased CAFW. In contrast, NAA + carbaryl increased CAFW in four of four treatments applied at PF or 5-mm KFD, but in only one of four treatments at 10- or 15-mm KFD. Accel® was less effective than NAA in reducing fruit clusters to a single fruit per spur in most comparisons, either with or without carbaryl. Return bloom varied greatly across years, but was always influenced by application time and types of thinners. In 1994 and 1996, return bloom was closely related to cropload the previous year. Although return bloom was very low for most treatments in 1995, 10- and 15-mm KFD applications of NAA + carbaryl increased it three-fold in comparison with other treatments (NAA + carbaryl at PF or 5 mm or BA at 10-mm KFD) that had similar effects on cropload. Chemical names used: 6-benzyladenine (BA); naphthaleneacetic acid (NAA).

Foliar application of spray materials is an integral component of commercial citrus production. An intensive assessment of spray application practices has been stimulated by low fruit value and increased concern about potential surface water contamination in the Indian River citrus region of Florida. Many publications report research results regarding distribution of spray materials within orchards and off-target deposition, but interpretation is challenging because so many factors influence spray results, and integrating this information into practical recommendations is difficult. Canopy geometry and density are prominent factors contributing to variable deposition and spray drift. Environmental factors such as temperature, relative humidity, wind speed, and wind direction also greatly influence spray deposition and drift, and substantial changes can occur within seconds. In addition the physical and/or mechanical set up of the sprayer interact significantly with the other factors. A better understanding of these interactions should help growers optimize spray effectiveness and efficiency while reducing potential off-target effects.

Parts I and II of this series revealed substantial opportunities for improving spraying of Indian River citrus (Citrus spp.). In this segment of our work we develop guidelines for growers to select the spray parameters providing an optimal balance between efficiency and efficacy while minimizing environmental contamination.

It is proposed that these guidelines could be codified in a simple expert system to make them easier to use. We propose that understanding limiting conditions may be the key to choosing spray options. Wind is a major factor influencing spray deposition and offtarget drift. Based on weather records, wind speeds below 5 mph (8.0 km·h^-1) are only routinely observed from 2000 HR until 0800 HR, making night spraying a good choice for low-volume applications. The importance of adjusting sprayer set-up for individual groves is demonstrated, with economic estimates of the cost of failing to make these adjustments. Routine use of careful sprayer adjustments is also likely to reduce off-target drift. Improvements in equipment and spray chemicals are also discussed. Use of non-orchard buffer areas and/or windbreaks appear to offer considerable opportunity for reducing off-site spray movement.

EcoLyst, a formulation of N-N-diethyl-2-(4-methylbenzyloxy) ethylamine hydrochloride containing 1 g/floz [4.5 oz/gal (33.8 g·L^-1)] a.i., is a plant growth regulator that has been reported to increase soluble solids concentration (SSC) in juice oranges by 0.6% to 1.2%. Our objectives were to determine the effectiveness of EcoLyst application for increasing SSC in Florida oranges (Citrus sinensis) and grapefruit (C. paradisi), and to identify the optimum rate and time of application. Experiments were conducted for three seasons using `Hamlin,' `Pineapple,' and `Valencia' sweet oranges; and for two seasons using `Flame,' `Marsh,' and `Ray Ruby' grapefruit, all in commercial groves. EcoLyst was applied at 6 and 12 floz/acre (0.44 and 0.88 L·ha^-1) for oranges and 16 and 32 ppm (mg·L^-1) [effectively 9 and 18 floz/acre (0.66 and 1.32 L·ha^-1) in most sprays] for grapefruit, and included Silwet L-77 adjuvant at 0.05%. Applications were made at several stages of development from prebloom to initial fruit set. In all cases, SSC was determined as juice corrected SSC, by adjusting refractometer readings based on titratable acidity. In 13 trials with sweet orange only five displayed significant increases in SSC (P ≤ 0.05) resulting from EcoLyst application. Two additional trials produced SSC increases significant at P < 0.10. Even where significant increases in SSC occurred they were typically observed in only one harvest and at one time of application and were always relatively low in magnitude (highest increase over controls was 0.38%). No rate or timing of EcoLyst application was consistently associated with best response, although eight of nine SSC increases observed in orange occurred with applications ranging from prebloom to 25% open flowers. Only one significant increase in SSC was observed in five trials with grapefruit. In these studies, increases in SSC resulting from EcoLyst application were neither sufficiently consistent nor large enough to justify a recommendation for commercial use in Florida citrus.

Adjacent but separate trials of `Oroblanco' and `Melogold', both triploid pummelo [Citrus grandis (L.) Osbeck] × grapefruit (Citrus paradisi Macf.) hybrids, were established on nine rootstocks in the Indian River citrus region of Florida in 1993. The trees on the citrandarin rootstock ×639 [Cleopatra mandarin (C. reticulata Blanco) × trifoliate orange (Poncirus trifoliata L.)] were significantly more productive than trees on any other rootstock tested for `Oroblanco' and all rootstocks except Swingle citrumelo (C. paradisi × P. trifoliata) and Cleopatra mandarin for `Melogold'. Cumulative production of `Oroblanco' on ×639, through year 9, was 50% higher than for Swingle or Volkamer lemon [C. limon (L.)], which were the next highest in yield. `Melogold' displayed extremely low yield, with 45% of trees producing fewer than 50 fruit total in the 9 years of this study. Carrizo citrange (C. sinensis Osbeck × P. trifoliata) produced the smallest trees with both scion varieties, reflecting poor adaptation of this rootstock to the calcareous soil at the trial site. As expected, acidity of `Oroblanco' and `Melogold' was much lower than would be observed for grapefruit when fall harvested, with similar total soluble solids (TSS), and much higher TSS: titratable acidity ratio. Some rootstock effects on internal quality were observed.

Wind-induced blemishing known as windscar and lesions from the disease melanose (caused by Diaporthe citri) are two of the most important causes of fresh grapefruit (Citrus paradisi) cullage in Florida. Copper hydroxide fungicides are the primary means of controlling melanose, but high air velocities from passing sprayers have been suspected of increasing windscar. In 1998 and 1999, airblast applications of Cu(OH)₂ (1.7 kg·ha^-1 Cu) were made at a range of early fruit development stages to a fresh grapefruit orchard in the Indian River region of Florida. These applications supplemented aerial sprays of Cu(OH)₂ that were made uniformly across the entire experimental site at biweekly intervals beginning near full bloom. During the commercial harvest period fruit were sampled from three regions (interior, upper exterior, and lower exterior) of each treatment tree and were evaluated for percentage of fruit surface covered by windscar and severity of melanose. Airblast applications did not affect windscar in either year, but windscar was significantly greater from the upper exterior of the canopy, which is likely to experience the highest natural wind velocities. From these data, it appears unlikely that airblast applications significantly contribute to windscar of Indian River grapefruit. In 1998, no trees receiving airblast applications had significantly lower melanose incidence than the trees sprayed only via aircraft; however, trees receiving four airblast applications were scored as having higher apparent melanose on exterior samples than trees receiving most other treatments. This is consistent with high levels of Cu injury on these fruit which can superficially resemble melanose. Following treatment in 1999, trees receiving four airblast applications of Cu(OH)₂ had significantly lower melanose scores than trees receiving either no or only early airblast applications, but were not significantly different from trees receiving a single spray 5.5 weeks postbloom. A computer model, which estimates Cu levels on fruit based on fruit growth, rainfall, and application parameters, indicated exterior fruit receiving four airblast sprays had >3 μg·cm^-2 [Cu] for 40 days in 1998 but only 10 days in 1999, which reflects increased probability of Cu damage in 1998. It appears that aerial application supplemented by airblast merits further study as an economical means of melanose control.

The U.S. Department of Agriculture citrus scion breeding program is urgently working on developing huanglongbing (HLB; pathogen Candidatus Liberibacter asiaticus)-tolerant cultivars with excellent fruit quality and productivity when HLB-affected. The slow process of assessing new citrus hybrids is a major impediment to delivery of these much-needed cultivars. We generate thousands of hybrids each year, germinate the seedlings, grow them for 2 years in the greenhouse, plant them at high density in a field where the disease HLB is abundant, grow them for 5 to 10 years, and make selections based on tree performance and fruit quality of these HLB-affected trees. Based on promising reports of accelerated citrus growth when grown in a metallized reflective mulch (MRM) system, we tested the hypothesis that the MRM system may accelerate growth and selection of new hybrid seedlings compared with conventional soil culture (CSC). In the MRM system, tree rows are covered with a layer of metallized plastic film and drip irrigation is installed beneath the plastic. In 2 years of analysis, tree canopy volume was significantly greater with MRM in 2020 (27% greater than CSC) but not in 2021, and MRM tree height was greater in 2021 (7% greater than CSC). Mortality was significantly greater with MRM in both 2020 and 2021(in 2021: 32% vs. 17% under CSC), and MRM trees had more chlorotic leaves. Because of staff limitations, plant debris and soil were not routinely cleared from MRM, thus diminishing any benefit from the reflective surface. Better maintenance might have resulted in more sustained evidence of MRM growth benefits. With the current resource availability, the MRM system does not appear to accelerate the assessment of hybrid seedling trees.

Three citrus hybrids, containing 50% to 75% sweet orange (Citrus sinensis) genome in their pedigrees and similar to sweet orange in fruit size, color, and taste, were tested for their potential to be classified as new “sweet orange” cultivars. ‘Hamlin’, ‘Midsweet’, and three other early to midseason sweet oranges, along with ‘Dancy’ tangerine (Citrus reticulata), a typical mandarin, were used for comparison. Fruit were picked on 23 Jan. 2014, 30 Dec. 2014, and 27 Jan. 2015. A total of 114 volatiles were detected and separated into seven groups by detection frequency: three groups with 43 volatile components did not show differences and thus contributed little information for classification of sweet orange vs. mandarin, and the remaining four groups with 71 volatiles contributed to distinctions between orange and mandarin. Among the hybrids, the pattern of volatile detection frequency for hybrid FF-1-74-52 was virtually identical to sweet orange, and cluster analysis agreed with the classification. The number of average peaks were 55 to 62 in sweet oranges, 67 in FF-1-74-52, and 17 to 37 in tangerine and other hybrids. Quantity analysis of individual volatiles and chemical classes indicated that FF-1-74-52 and sweet oranges were rich in total volatile abundance, and almost all chemical classes including mono and sesquiterpenes, aldehydes, alcohols, ketones, and esters. This was especially true for ethyl butanoate, which contributes a fruity top note, and valencene and all sesquiterpene hydrocarbons, which only contribute to citrus flavor indirectly through their contribution to headspace partitioning. Two other hybrids, FF-1-75-55 and FF-1-76-51, each had some similarity to sweet oranges in several chemicals and classes, but not in the overall volatile profile. All three sweet orange–like hybrids met the standards for mandarins and oranges in soluble solids content, titratable acidity (TA), and the ratio. The above volatile and nonvolatile flavor chemical profile comparisons strongly support a proposal to classify FF-1-74-52 as a “sweet orange” commercially, and all three hybrids were previously shown to be more similar to sweet orange in their volatile profile than is ‘Ambersweet’. ‘Ambersweet’ was a hybrid that was legally classified as a “sweet orange” in 1995 based on its volatile profile.