Citrus production under enclosed structures can exclude the Asian citrus psyllid (ACP, Diaphorina citri) and eliminate the negative effects of citrus greening or huanglongbing (HLB) disease caused by Candidatus Liberibacter asiaticus to the grapefruit (Citrus paradisi) fresh fruit industry. Physically impeding the insect vector from accessing trees is a logical method to have disease-free groves. Our objectives were to assess the ability of enclosed screenhouses to exclude the ACP, stop HLB inoculation and dissemination, and improve fruit yield of in-ground and container-grown 6-year-old “Ray Ruby” grapefruit at super-high planting densities relative to open-air trees. We built a large structure to allow commercial-scale trials and tested two production systems (screenhouse and open-air), two planting systems (in-ground and potted), and two rootstocks (“Sour Orange” [Citrus × aurantium] and “US-897” [Citrus reticulata × Poncirus trifoliate]). The experimental design was a randomized complete block design split-split-plot with four replications. Four passively ventilated 1,080-m² completely enclosed screenhouses were constructed using a 50-mesh monofilament high-density polyethylene screen. The main support for each enclosed, covered structure consisted of pressure-treated, wooden utility poles. Trees were planted in Sept/2013 on a density of 1,957 trees/ha. Irrigation was performed on-demand using two 7.6-LPH drip emitters per tree, and fertigation was applied three times/week using 15N-2.6P-22.4K water-soluble fertilizer at 180 kg N/ha. Psyllids were monitored using sticky cards and detected inside the screenhouses post-Hurricane Irma, which damaged the screen structures in Sept/2017, leaving openings until repairs were completed in Apr/2018. Screen aging and a tropical storm in April/2019 caused another major screen opening fixed in Oct/2019. Despite the weather-related damages to the screens, only trees cultivated in open-air tested positive for Candidatus Liberibacter asiaticus after 6 years. There was fast disease progression for all outside treatments, with 100% infection. Covered, in-ground trees exhibited the highest trunk diameter and canopy volume (P < 0.0001). Trees grown inside screenhouses exhibited higher fruit yield than outside trees, with the highest yield observed for in-ground trees on “US-897” (51,081 kg/ha) (P < 0.0001). Several open-air treatments particularly in containers did not produce any fruit. On the other hand, potted grapefruit trees cultivated inside the enclosures had the highest soluble solids content (P < 0.001). The screenhouses provided disease exclusion, increased fruit yield, and fruit quality, representing an alternative for growers interested in producing high-quality fruit for the fresh market. Production cost and economic viability still need to be evaluated for large-scale implementation.

Lasiodiplodia theobromae is a fungal pathogen associated with perennial tropical fruit plants worldwide. In citrus, L. theobromae causes stem-end rot (Diplodia stem-end rot), a damaging postharvest disease that is aggravated when trees are also infected with the citrus greening bacteria ‘Candidatus Liberibacter asiaticus’. Due to the latent infection of L. theobromae during the preharvest stage, it becomes difficult to control the disease by chemical or physical treatment. In the current study, we sequenced and assembled strain CITRA15, the first genome of L. theobromae obtained from diseased Citrus paradise ‘Flame’ grapefruit in Florida, and thereby provided a genomic resource for future research on diagnostics, and postharvest and preharvest disease management of citrus and other fruit crops.

The Southeastern United States is facing agriculture crises, such as the ongoing epidemic of citrus greening disease that has forced the region to begin looking into alternative crops. Some of these belong to the Rosaceae genus Prunus, which encompasses many economically important species such as peaches, almonds, cherries, plums, and more. Peach production in Florida has become a very promising alternative to citrus; however, there are different limitations and challenges that peach production faces in this region. Differing climates coupled with edaphic challenges such as salinity, alkalinity, and waterlogging have been the focus of much of the research into the viability of peach production in the region. Using the genetic diversity of the Prunus genus is crucial to the success of peach as an alternative crop, due to the nature of its propagation on rootstocks. The development of new rootstock cultivars has been—and continues to be—the most efficient way not only to deal with the variety of problems associated with the climate and soil mentioned above but also to mitigate the effects of pests and diseases. The vegetative propagation of stone fruit rootstocks also has distinct advantages that seed propagation cannot achieve, including tree performance uniformity and the multiplication of interspecific hybrids. Tools used to select the best-performing rootstocks for the area such as the root system architecture (RSA) analysis are fundamental to this development process to ensure that the rootstock cultivars with the traits needed for success in the region are selected. This narrative review lays out all the challenges facing southeastern peach production in detail, discussing the research into these challenges and highlighting the tools that are most crucial to the success of peach production in the region to create a resource for researchers, growers, and breeders to more easily access this information.

Two of the major postharvest diseases impacting grapefruit shelf life and marketability in the state of Florida (USA) are stem-end rot (SER) caused by Lasiodiplodia theobromae and green mold (GM) caused by Penicillium digitatum. Here, we investigated the in vitro and in vivo efficacy of vapors of thymol, a natural compound found in the essential oil of various plants and the primary constituent of thyme (Thymus vulgaris) oil, as a potential solution for the management of GM and SER. Thymol vapors at concentrations lower than 10 mg L⁻¹ significantly inhibited the mycelial growth of both pathogens, causing severe ultrastructural damage to P. digitatum conidia. In in vivo trials, the incidence and lesion area of GM and SER on inoculated grapefruit were significantly reduced after a 5 d exposure to 50 mg L⁻¹ thymol vapors. In addition, the in vitro and in vivo sporulation of P. digitatum was suppressed by thymol. When applied in its vapor phase, thymol had no negative effect on the fruit, neither introducing perceivable off-flavor nor causing additional weight loss. Our findings support the pursuit of further studies on the use of thymol, recognized as safe for human health and the environment, as a promising strategy for grapefruit postharvest disease management.

Traditionally, peach rootstocks are propagated by seeds due to their high availability, low cost, and easy storage and handling. However, stem cuttings allow the propagation of interspecific hybrids and keep the genetic uniformity of heterozygous genotypes. This study compared the effect of four different concentrations of K-IBA (indole-3-butyric acid potassium salt) on softwood cuttings of three peach backcrosses (peach × (peach × almond)) for rootstock propagation in two propagation systems: aeroponics and germination trays. The four concentrations of K-IBA applied were: 0.0% (w/v) as a control, 0.1% (w/v), 0.2% (w/v), and 0.4% (w/v). Data were collected on the survival rate (%), rooting rate (%), and root growth parameters. The relevance of auxin for peach cuttings rooting was evidenced. K-IBA at 0.2% showed the best rooting effect for peach softwood cuttings, evidenced by its high rooting rate and higher survival rate. K-IBA at 0.4% and 0.2% produced the highest number of adventitious roots. The highest root growth parameters were obtained in germination trays, confirming the suitability of this system for root growth. However, aeroponics was demonstrated to be as efficient as the traditional germination trays for the rooting of peach cuttings, allowing for a more controlled environment with a better use of resources.

The focus of this study was to develop technologies using chlorine dioxide (ClO₂) gas to control postharvest stem-end rot of citrus caused by Lasiodiplodia theobromae. Mycelial growth of L. theobromae on potato dextrose agar (PDA) plugs was completely inhibited by a 24-h ClO₂ exposure provided by 0.5 g of solid ClO₂ generating granular mixture in a 7.7-liter sealed container. In vivo experiments were conducted on artificially inoculated Tango and naturally infected U.S. Early Pride mandarins. When ClO₂ treatments were initiated 0 to 6 h after inoculation, decay development was significantly reduced as compared with the control, and higher ClO₂ doses were more effective. A ClO₂ treatment (using 3 g of generating mixture per 7.7-liter sealed container) administered 0 h after inoculation resulted in 17.6% Diplodia stem-end rot incidence compared with 95.6% in the control, whereas the same treatment administered 24 h after inoculation was much less effective, resulting in 63.0% incidence compared with 85.4% in the control. Diplodia stem-end rot incidence of naturally infected fruit after using 6 or 9 g of generating mixture per 24-liter sealed box was 23.8 or 25.7%, respectively, compared with 47.9% for control fruit. The ClO₂ treatments had no negative effects on fruit quality characteristics including weight loss, firmness, puncture resistance, titratable acids (TAs), total soluble solids (TSSs), and rind color. Albedo pH at wounds was significantly reduced from 6.0 to 4.8 by the ClO₂ treatments, whereas undamaged albedo remained at 5.8. In addition, no visible physiologic defects, such as peel browning and bleaching, were observed on ClO₂-treated fruit. These results indicate that ClO₂ gas has the potential to be developed as a component of an integrated citrus postharvest decay control system to minimize fruit losses.