Coatings are generally applied to fruit as microemulsions, but nanoemulsions are still experimental. ‘Nova’ mandarins (Citrus reticulata) were coated with shellac or carnauba (Copernica cerifera) microemulsions or an experimental carnauba nanoemulsion; these were compared with an uncoated control during storage for 7 days at 20 °C. Coatings were also tested on ‘Unique’ tangors (C. reticulata × C. sinensis) stored for 14 days at 10 °C followed by a simulated marketing period of 7 days at 20 °C. Fruit quality evaluations included weight loss, gloss, soluble solids (SS), titratable acidity (TA), pH, SS/TA ratio, internal CO2, O2, fruit juice ethanol, and other aroma volatile content. Sensory visual shine and tangerine (C. reticulata) flavor rank tests after storage were conducted, followed by an off-flavor rating. The carnauba waxes resulted in less weight loss compared with the uncoated control and shellac coating during both experiments. There were no differences in gloss measurements of ‘Nova’ mandarins; however, shellac-coated fruit ranked highest for shine in a sensory test. For ‘Unique’ tangors, initially, shellac showed the highest gloss (shine) measurement; however, at the end of storage, the nanoemulsion exhibited the highest gloss, although it was not different from that of the microemulsion. Similarly, after storage, the nanoemulsion ranked highest for visual shine, although it was not different from that of the microemulsion. There were only minor differences in SS, TA, pH, and SS/TA among treatments. The internal CO2 gas concentration and juice ethanol content generally increased and internal O2 decreased during storage. The highest levels of CO2 and ethanol were found for the shellac treatment, as was the lowest O2, indicating anaerobic respiration. There were only minor differences among the other coating treatments; however, they were only sometimes different from those of the control, which generally had the highest O2, lowest CO2, and lowest ethanol. Shellac and the carnauba microemulsion also altered the volatile profile more than the control and the nanoemulsion did, especially for ‘Unique’ tangors. For ‘Unique’ tangors, the control and nanoemulsion ranked highest for tangerine flavor and had the least off-flavor at the end of storage. Among the coatings tested, the carnauba emulsions demonstrated less water loss, imparted more sustainable gloss, and caused less ethanol production than shellac, with the nanoemulsion exhibiting higher gloss measurements, less modifications of the atmosphere and volatile profile, and, consequently, better flavor compared with the microemulsion.
Marcela Miranda, Xiuxiu Sun, Christopher Ference, Anne Plotto, Jinhe Bai, David Wood, Odílio Benedito Garrido Assis, Marcos David Ferreira, and Elizabeth Baldwin
Rachel P. Naegele and Mary K. Hausbeck
Phytophthora capsici causes root and fruit rot and foliar blight of pepper. Multiple sources of resistance to Phytophthora root rot have previously been identified, but most display only partial resistance. One source, CM334, has broad spectrum root rot resistance to multiple pathogen isolates but has only low to moderate fruit rot resistance. This study evaluated previously identified pepper lines for resistance to two P. capsici isolates, OP97 and 12889, and compared root rot resistance to fruit rot resistance and genetic structure. CM334 was confirmed as a broad spectrum resistance genotype, whereas all other sources of resistance evaluated were susceptible to infection by one or both isolates evaluated. Although not completely resistant, PI 566811 displayed moderate resistance to fruit and root rot to both P. capsici isolates. Fruit rot resistance had a significant but small to moderate positive correlation (r = 0.26–0.63) with root rot resistance depending on the isolate and length of exposure. Pepper accessions with resistance to Phytophthora root and fruit rot belonging to different genetic subpopulations were identified and could serve as candidates for partial-resistance loci to incorporate into pepper breeding programs.
Gregory E. Frey, Tarik Durmus, Erin O. Sills, Fikret Isik, and Marcus M. Comer
Shiitake (Lentinula edodes) is an edible mushroom-producing fungus. “Natural log-grown” shiitake mushrooms are favored by consumers and are often produced by small farmers and hobbyists in the United States. The tree species most often recommended as a substrate for shiitake is white oak (Quercus alba), which has many other economic uses. We tested two strains of shiitake in log substrates of three common, low-value tree species in the southeastern United States to identify potential alternatives to white oak. We found that sweetgum (Liquidambar styraciflua) was a good substitute for white oak, both in terms of mushroom production and financial returns. Red maple (Acer rubrum) had less potential, with lower production and marginal financial returns, and ailanthus (Ailanthus altissima) was not a suitable alternative substrate. Of the two shiitake strains tested, a commercially available strain performed better than a naturalized strain that was isolated from an uninoculated log. Further research is needed to identify other potential alternative substrates and production techniques in the southeastern United States and other regions.
Guirong Li, Ran Quan, Chaohui Yan, Xiaojin Hou, and Huiling Hu
Grape (Vitis vinifera) is among the world’s most important fruit crops and is a commonly used woody plant for genomics and post-genomics research. NAC transcription factors play central roles in plant growth and development, floral organ morphogenesis, and responses to biological stress. It is therefore important to identify key transcription factors from grape and clarify their mechanisms of action to generate genetic resources for grape molecular improvement. Our research group previously cloned a NAC transcription factor from V. vinifera ‘Yatomi Rosa’ [drought and leaf roll gene 1 (DRL1)] and demonstrated that it caused dwarfing of tobacco (Nicotiana benthamiana) plants when overexpressed. In the present work, we demonstrate that overexpression of DRL1 in transgenic tobacco delays flowering time and markedly reduces pollen viability. Furthermore, crosses between male DRL1 transgenic tobacco and female wild-type tobacco exhibit substantially lower fruit set, fruit and seed weights, fruit and seed shape indices, and seed germination rates than selfed wild-type plants or crosses with a transgenic female parent. DLR1 overexpression strongly influences flowering time and reproduction in transgenic tobacco, primarily through its effects on pollen development. These results provide a foundation for further functional characterization of DLR1 in grape.
Hong Su, He Zhang, Chaoxia Wang, Jianquan Huang, Jiayin Shang, Na Zhang, Dan Wang, and Kai Li
The addition of pulverized grape pruning wood to grape soils has a positive effect on fruit quality. However, its effects on the soil microecology of the root zone and the growth of the grape plants are not fully understood. To address this, ‘Shine Muscat’ grapes were cultivated in media consisting of garden soil and crushed grape pruning material at different mass ratios [100:1 (T1), 50:1 (T2), 30:1 (T3), 20:1 (T4), and 10:1 (T5)] and in garden soil without the pruning material, as a control. The changes in the plant fresh weight, leaf area, soil and plant analyzer development (SPAD) value, root development, soil organic carbon, microbial biomass carbon, and soil enzyme activity were determined over time. High-throughput sequencing technology was used to determine the soil bacterial community structures. The pruning supplementation increased the grape plants fresh weight, leaf area, and SPAD values. The T2 and T3 treatments increased the grape root length, surface area, and the projected area and number of the root tips; the soil organic carbon content, microbial biomass carbon content, soil invertase activity, amylase activity, and β-glucosidase activity were also significantly increased. The addition of the grape pruning material was found to increase the bacterial diversity and richness 60 and 150 days after treatment. At the phylum level, Proteobacteria, Acidobacteria, and Actinobacteria were the dominant groups, and the grape pruning material increased the relative abundance of the Acidobacteria and Actinobacteria after 60 and 150 days. The relative abundance of the Actinobacteria in the T2 treatment was 1.7, 1.3, 1.5, and 1.3 times that of the control, after 60, 90, 120, and 150 days, respectively. The T2 treatment was identified as the optimal treatment for grapes in the field because it improved the soil microecology and promoted root and tree development the most compared with the other treatments tested.
Rhuanito S. Ferrarezi, Arun D. Jani, H. Thomas James III, Cristina Gil, Mark A. Ritenour, and Alan L. Wright
The prevalence of Huanglongbing (HLB) in Florida has forced growers to search for new management strategies to optimize fruit yield in young orchards and enable earlier economic returns given the likelihood of HLB-induced yield reductions during later years. There has been considerable interest in modifying orchard architecture design and fertilizer and irrigation management practices as strategies for increasing profitability. Our objectives were to evaluate how different combinations of horticultural practices including tree density, fertilization methods, and irrigation systems affect growth, foliar nutrient content, fruit yield, and fruit quality of young ‘Valencia’ sweet orange [Citrus sinensis (L.) Osbeck] trees during the early years of production under HLB-endemic conditions. The study was conducted in Fort Pierce, FL, from 2014 to 2020 on a 1- to 7-year-old orchard and evaluated the following treatments: standard tree density (358 trees/ha) and controlled-release fertilizer with microsprinkler irrigation (STD_dry_MS), high tree density (955 trees/ha) with fertigation and microsprinkler irrigation (HDS_fert_MS), and high tree density with fertigation and double-line drip irrigation (HDS_fert_DD). Annual foliar nutrient concentrations were usually within or higher than the recommended ranges throughout the study, with a tendency for decreases in several nutrients over time regardless of treatment, suggesting all fertilization strategies adequately met the tree nutrient demand. During fruit-bearing years, canopy volume, on a per-tree basis, was higher under STD_dry_MS (6.2–7.2 m3) than HDS_fert_MS (4.3–5.3 m3) or HDS_fert_DD (4.9–5.9 m3); however, high tree density resulted in greater canopy volume on an area basis, which explained the 86% to 300% increase in fruit yield per ha that resulted in moving from standard to high tree density. Although fruit yields per ha were generally greatest under HDS_fert_MS and HDS_fert_DD, they were lower than the 10-year Florida state average (26.5 Mg·ha−1) for standard tree density orchards, possibly due to the HLB incidence and the rootstock chosen. Although tree growth parameters and foliar nutrient concentrations varied in response to treatments, management practices that included high tree density and fertigation irrespective of irrigation systems produced the highest fruit yields and highest yield of solids. Soluble solids content (SSC) and titratable acidity (TA) were lower, and the SSC-to-TA ratio was highest under STD_dry_MS in 2016–17, with no treatment effects on quality parameters detected in other years. Both drip and microsprinkler fertigation methods sufficiently met tree nutrient demand at high tree density, but additional research is needed to determine optimal fertilization rates and better rootstock cultivars in young high-density sweet orange orchards under HLB-endemic conditions in the Indian River Citrus District.
Mary C. Stevens, Rui Yang, and Joshua H. Freeman
A novel methyl bromide alternative, ethanedinitrile (EDN), has been reported to be efficacious against soil-borne pathogens, weeds, and plant-parasitic nematodes. Degradation products of EDN include NH4 +and NH3, but it is currently unknown at what quantities these degradation products are being released into the soil at a given use rate of EDN. To address this issue, field studies were performed using the raised-bed plasticulture system. Deposition of NH4 + and NO3 − in top 0–15-, 15–30-, and 30–45-cm soils were evaluated 3 weeks after fumigation with EDN applied at 336, 448, and 560 kg·ha−1. Change of pH and transformation of NH4 + to NO3 − in top 0–15- and 15–30-cm soils were tracked weekly after fumigation with EDN at 448 kg·ha−1 for 10 weeks. This study found that fumigation with EDN significantly increased soil pH of the top 0–15-cm soil and soil NH4 + in top 0–15- and 15–30-cm soils, but soil NO3 − was unaffected. Nitrification process in top 0–15-cm soil was inhibited by fumigation with EDN for at least 7 weeks. These results indicate that N deposited by fumigation with EDN could be an important preplant N source for crop production, and the inhibition of nitrification could help mitigate nitrate leaching. This study provides helpful information for quantification of N deposited from fumigation with EDN.
Rahmatallah Gheshm and Rebecca Nelson Brown
Annually, Americans consume an average of 24.5 lb of lettuce (Lactuca sativa) per capita, more than half of which is head lettuce. This study examined the impacts of using black and white-on-black polyethylene mulches on three crisphead lettuce cultivars for spring production in the open field, with data collected on the soil temperature and lettuce yields. Black polyethylene, white-on-black polyethylene, and bare ground were compared for effects on soil temperature, lettuce yields, and lettuce head height and diameter. Mean soil temperatures at a 5 cm depth were 18.9 °C under black polyethylene, 17.7 °C under white-on-black polyethylene, and 17.1 °C in bare ground plots. Changes in the lettuce canopy size presented a similar trend over the growing season in all treatments. Both mulch type and cultivar significantly (P < 0.01) affected the canopy growth in head lettuce. Lettuce on black polyethylene mulch grew significantly (P < 0.01) faster than lettuce on white-on-black polyethylene or bare ground. However, the black and white-on-black mulches produced similar yields, averaging 5.76 and 5.71 kg·mˉ2, respectively. Meanwhile, bare ground plot yields were significantly (P < 0.01) lower at 4.57 kg·mˉ2. Cultivar rank order was consistent across treatments, and Crispino and Garmsir at 5.82 and 5.47 kg·mˉ2 fresh weight had significantly higher yields than Nevada at 4.75 kg·mˉ2 (P < 0.01).
Esther McGinnis, Alicia Rihn, Natalie Bumgarner, Sarada Krishnan, Jourdan Cole, Casey Sclar, and Hayk Khachatryan
The millennial generation, born between 1981 and 1996, is the largest demographic age group in the United States. This generation of plant enthusiasts has experienced financial setbacks; nevertheless, they collectively wield immense economic power. In 2018, this generation made one-quarter of all horticulture purchases. Consumer horticulture (CH) is challenged to develop targeted programming and outreach methods to connect with this influential and information-hungry generation. To examine the possibilities, the CH and Master Gardener Professional Interest Group held a workshop on 23 July 2019, in Las Vegas, NV, at the American Society for Horticultural Science (ASHS) annual conference. The workshop first actively engaged participants to build points of connection by discussing nontraditional terminology that resonates with younger audiences. Suggested terminology included plant parent, plant enthusiast, plant babies, apartment-friendly, sustainable, and urban agriculture. After the opening discussion, three presentations explored innovative content, marketing and outreach in the areas of social media, retail promotions, and public gardens. The social media presentation focused on building a two-way partnership with millennials on Instagram that emphasized shared values of sustainability, local foods, and wellness. During the second presentation, the speaker highlighted retail point-of-sale promotions that appeal to younger audiences. The final presentation described creative programming used by botanical gardens to engage younger visitors. A facilitated discussion followed the presentations to identify and evaluate techniques and content that could be incorporated into CH research, teaching, and extension to reach and interact with new millennial audiences. Based on the workshop presentations and the facilitated discussions, the ASHS CH and Master Gardener Professional Interest Group concluded that more CH professionals should engage in social media outreach tailored to the needs and preferences of younger generations. To support this valuable outreach, research of consumer behavior and retail marketing should be encouraged to identify the preferred terminology and subject matter that appeal to millennials. Finally, CH can learn from and partner with public gardens as they implement multidisciplinary programming and exhibitions.
Jiffinvir Khosa, Derek Hunsaker, and Michael J. Havey
The amounts and types of epicuticular waxes on onion (Allium cepa) leaves affect feeding damage by onion thrips (Thrips tabaci). This study used gas chromatography mass spectrometry (GCMS) to establish the identities of waxes and measure over time wax amounts on leaves of inbred onion plants with glossy, semiglossy, and waxy foliage. Nine waxes were detected on leaves of all inbreds, and higher coefficients of variation (cv) were observed for less abundant waxes on foliage of doubled haploid onions. Older leaves had higher amounts of waxes compared with younger leaves on the same plant. Except for one minor wax, amounts of individual waxes on leaves were not significantly different for plants of different ages. There was a significant inbred by sampling date interaction due to lower amounts of waxes on the leaves of older plants from the semiglossy inbred. These results indicate that there is little advantage to multiple samplings of leaves over time from the same plant and resources may be better used to evaluate more plants. The relatively large cvs for amounts of specific waxes may reduce response to selection for unique epicuticular wax profiles to develop onion populations that suffer less feeding damage by onion thrips.