ASHS 2024 Conference

Producing sweetpotatoes involve several phases presenting unique challenges, most notably during transplanting. Sweetpotato slips, used for asexual reproduction, have non-uniform characteristics, making transplanting difficult. Additionally, the transition from a greenhouse to a field condition poses environmental risks and challenges, resulting in low transplant survival rates. A high slip mortality rate creates economic and logistical problems for producers. Plant growth regulators (PGRs) have been found to induce lignification or thickening of cell walls, which can alleviate environmental stresses in other crops; however, their impact remains unexplored in sweetpotato slips. Therefore, a study at Mississippi State University was conducted with the primary goal to enhance sweetpotato slip quality and improve transplant establishment rates. The study involves two greenhouse trials to identify the most effective PGR types and concentrations, and two histology trials to illustrate the effects of PGRs on sweetpotato slip lignin and cell wall. The greenhouse trials utilize a randomized complete block design to assess four different PGR types and thirteen concentrations on three replications of sweetpotato slips with 38 subsamples per treatment per replication. Data on plant height, stem diameter, number of nodes, SPAD, leaf area, and dry weight and fresh weight of the slips and roots were collected to determine the effects of PGRs on the plants. The histology trials included the same PGR treatments and concentrations to the slips. The slips were then collected, cross-sectioned, stained, and evaluated and measured under a microscope. The study proved that PGRs do have an effect on sweetpotato slips, by altering plant height, dry weight, and fresh weight, while not impacting the number of nodes. Thickening of the cell wall was also observed in slips treated with certain PGRs and it is hypothesized that this thickening of cell walls can contribute to reduced slip mortality when transplanting greenhouse produced slips to the field.

Almond (Prunus dulcis) is one of the most important crops in California. This commodity represented an economic impact of over 3.5 billion dollars for the state in 2022. During that year, 1,630,000 million planted acres were reported. In 2023, this number dropped by 74,000 acres, continuing the trend of decline due to numerous challenges that the industry has been facing. These include volatile prices, high input costs, reduced water allocations, climate unpredictability, and high temperatures during key phenological timings. The almond crop is highly sensitive to environmental factors, and photosynthetic rates can significantly decrease when temperatures reach 94F, heat levels are easily reached during the hot summer months in California’s production areas. To this matter, significant contributions are needed to support the industry. There are over 700 peer-reviewed scientific publications that evidence the benefits of using biologicals, which include plant biostimulants (PBS), in agriculture. It has been shown that season-long exogenous applications of cytokinin-containing PBS can support higher marketable yields. It is important to understand the physiological timings in which these applications have the most impact, in terms of maximizing the yield and quality potential. In 2023, a randomized complete-block design (RCBD) study was conducted on 5th leaf Var. Nonpareil in California’s Central Valley. The objective was to evaluate the yield and quality effects of an application of X-CyteTM, a 0.04% cytokinin-containing biostimulant registered for use on almonds in California, at different standalone phenological timings. These included early bloom, full bloom, petal fall, may spray, and hull-split. The trial consisted of six four-tree replications per treatment. Yield and quality data were subjected to a one-way ANOVA using IBM® SPSS® Statistics, and means were separated using Tukey’s HSD. The standard grower practice (SGP) produced 1801.5 marketable pounds of kernel meat per acre. X-Cyte™ treatment yields of 1845.16, 2140.16, 2215.66, 2137.67, and 2318.33, were observed for early bloom, full bloom, petal fall, may spray, and hull-split timings, respectively. Statistically significant differences were observed (p-value: 0.003). The hull-split and petal fall timing applications represented the higher yield increases (516.8 and 414.2 lbs/A, respectively) overall, compared to the SGP. It has been documented that taking place at these timings are key phenological stages deemed as major contributors to the components of yield: fruit set and nut fill. Significant differences in kernel size were not observed (p-value: 0.549). These findings further support and help fine-tune the use of biologicals and PBS in agricultural production systems.

Persimmon is an important fruit crop gown all over the world due to its unique fruit taste and nutritional quality. The skin color is one of the key attributes in persimmon fruit to determine the harvest maturity. Poor color development in early maturing cultivars causes losses to the growers. The present study was aimed at evaluating the effects of preharvest S-ABA spray application on advancing color development and improving fruit quality at harvest. ‘Yoho’ persimmon trees grown in Western Australia were sprayed with S-ABA (0, 25, 50, 75 mg L-1) two weeks before anticipated harvest. The preharvest spray application of S-ABA showed significant increase in color indicators such as color index, a*, b*, and chroma of persimmon fruit harvested after one and two weeks of spray application. S-ABA (25 and 50 mg L-1) spray application showed significantly higher soluble solids content (SSC), and slightly reduced firmness in harvested fruit. Additionally, the 50 mg L-1 S-ABA spray application markedly increased carotenoids content in fruit harvested after one week, while fruit harvested after two weeks exhibited higher carotenoids in 25 mg L-1 and 50 mg L-1 S-ABA treatments. Moreover, the total phenolics, flavonoids and antioxidants were enhanced by S-ABA treatments as compared to control. In conclusion, the preharvest spray application of S-ABA (50 mgL-1) triggers fruit ripening sharply even after one week, while 25 mg L-1 S-ABA treatment showed significant improvement in color after two weeks of application. A single spray application of S-ABA could be employed for advancing harvest maturity, color development, and promoting overall persimmon fruit ripening quality.

Understanding the sink-to-source relationship on leafy crops offers valuable insights into optimizing resource allocation for enhanced plant growth and quality. Variations in growth rates and carbon pools across individual leaves or groups of leaves at similar developmental stages allow us to understand the plant strategies of carbon allocation and partitioning. We hypothesized that products that enhance the carbon source-to-sink relationship during leaf development can lead to increased growth and dry matter accumulation. This project aimed to determine if the exogenous application of a cytokinin and B-Mo-based product during leaf development would impact carbon source-to-sink relationship and, hence, influence plant growth and quality. The experiment was a complete randomized design with two treatments consisting of a negative control and the application of the product twice during the growing cycle. The experimental unit consisted of a deep-water culture reservoir with three lettuce plants. Destructive sampling was conducted at five sampling points. At each sampling point (n=4 per experimental run), the phenological stage was determined, and root and shoot length and dry matter, leaf length, width, area, and non-structural carbon and chlorophyll contents were measured. This data was used to estimate growth rates. Results indicate that the cytokinin and B-Mo-based product increased the number of true unfolded leaves by 1 ± 0.4 and the overall size of the lettuce head by 9%. The treated lettuce reached a marketable size four days earlier than the control treatment. Statistically significant differences were observed in the shoot and root dry matter accumulation and foliar length and width at some sampling points. Some of the growth indices indicate an increase in leaf surface area investment and enhanced conversion efficiency of assimilates into biomass in plants treated with the product. Plants exhibiting these alterations had higher sucrose and total soluble sugar content. There was a noticeable pattern of higher concentrations of non-structural carbohydrates, proteins, and amino acids in the leaves compared with the roots across all plants and treatments. Overall, our study on using a cytokinin and B-Mo-based product to strengthen the source-to-sink relationship during the development of a leafy crop provides new insights into non-structural carbohydrate metabolism and the role of CKs, B, and Mo in generating a high-quality plant in a shorter timeframe.

The Florida citrus industry has seen a steady decline in production since the arrival of Huanglongbing (HLB), or citrus greening disease, in Southern Florida in 2005. Following infection, trees experience a steady decline in health and productivity. HLB has since spread throughout all of Florida’s citrus producing regions resulting in nearly 100% infection rates in traditional field settings. Lamentably, no cure has been found for HLB, so research efforts have focused on mitigating the symptoms associated with this disease. Among the myriad of symptoms associated with HLB, the increased rates of mature fruit (preharvest fruit drop) is a major concern for growers. Not only do more fruit drop in HLB-affected trees, but fruit also begin dropping earlier in affected trees as well. This loss of mature, and potentially marketable, fruit in the months leading up to harvest represents a visual loss of revenue for the growers. The authors have previously reported that the likelihood of a fruit to drop during preharvest fruit drop is related to the size of that fruit; the relatively smaller fruit on the tree are more likely to drop during the preharvest fruit drop window. As plant growth regulators (PGRs) have had promising results in preventing fruit drop in many crop species, the efficacy of PGR applications in reducing preharvest fruit drop was evaluated. Thirty small and thirty large fruit were tagged on four 12-year-old ‘Valencia’ on ‘Swingle’ rootstock trees. Small fruit were those that were a ½ standard deviation below the average fruit size for that tree whereas large fruit were those that were a ½ standard deviation above the average. Ten of the small tagged fruit and ten of the large tagged fruit were then dipped into ProGibb® (33 ppm Gibberellic Acid [GA]), Citrus Fix® (106 ppm 2,4-Dichlorophenoxyacetic Acid [2,4-D]), or left untreated (control). Citrus Fix® improved retention in both small and large fruit whereas ProGibb® only improved retention in the large fruit. As GA prevents drop by delaying the senescence process, the lack of effect in the small fruit may suggest that they have already entered the senescence process. To further explore why the small and large fruit differ in their likelihood to drop and why they respond differently to PGR applications, additional biochemical and molecular analyses are underway.

Spring frost is the primary cause of yield reduction in southern highbush, representing a significant challenge to blueberry production in the southeastern United States. Plant growth regulators are used as aids in different agricultural industries to either advance or delay growth and development process. Ethephon influences fruit set, size, and yield and has also been used as a tool to delay bloom in order to avoid freeze damage. This study examined the efficacy of ethephon to delay flower bud growth stages in three Southern Highbush Blueberry cultivars (‘Farthing’, ‘Georgia Dawn’, and ‘Kee Crisp’). Ethephon was applied at different concentrations of 200, 400, and 800 ppm, and a control treatment water/surfactant was also included. Flower buds were visually assessed from January until March. No relevant results were found for ‘Farthing’; however, for ‘Georgia Dawn’ and ‘Kee Crisp', ethephon at 800 ppm had the highest effect on delaying blooming development compared to the control. These results suggest that ethephon might delay flower bud growth stages in Georgia Dawn and Kee Crisp, offering potential advantages in reducing susceptibility to spring chill injury.

Increased consumption of blueberries has led to a prominent rise in demand. However, Georgia blueberry production is limited by challenges including short orchard life of southern highbush (SHB; tetraploid) and fruit quality issues associated with rabbiteye (RE; hexaploid) varieties. Interspecific hybridization can bring in beneficial alleles to improve the local adaptability and fruit quality of commercial varieties. Many of the wild blueberry germplasm with valuable soil adaptability and fruit quality traits such as V. fuscatum are diploids. Heteroploid crossings between SHB and diploid wild blueberry were shown to have a very low level of success. Ploidy induction through tissue culture is promising to circumvent the ploidy barrier and improve the efficiency of wide-hybridization. The objective of this research focuses on developing a ploidy induction protocol using two SHB varieties ‘Emerald’ and ‘Rebel’. SHBs previously initiated in tissue culture, were treated with 0%, 0.02% and 0.2% colchicine. SHBs were segmented into single and double node segments and put into woody plant medium (WPM) culture media containing either 6-(γ,γ-Dimethylallylamino)Purine (2iP) or trans-Zeatin. The treatments, along with non-treated control, were grown in a growth chamber of 26°C with 16/8 day and night cycles. The number and length of new shoots were recorded 35 and 50 days after treatment (DAT). Significant longer axillary stem growth was observed in the non-treated control compared to that of colchicine-treated segments for both SHBs indicating the suppressive effect of stem growth from colchicine treatments. Several Octo- and mix ploidy-shoots of ‘Emerald’ and ‘Rebel’ were identified among colchicine-treated SHB explants after ~ 21 weeks using a flow cytometer. Both levels of colchicine treatments generated octoploids. These new synthetic octoploid blueberries will be useful to cross with SHB and RE blueberries. The established ploidy induction protocol will be utilized to double the chromosomal levels of diploid V. fuscatum species and make them cross-compatible with SHB varieties.