Timothy Coolong

Nitrogen and sulfur influence nutrient usage and accumulation in onion

Abstract To study the effects of nitrogen (N) and sulfur (S) fertility on onion (Allium cepa L.) bulb pungency, bulb fresh and dry weight, nutrient uptake and accumulation in the bulb, “Granex 33” onions were greenhouse grown using nutrient solution culture. A factorial arrangement of solutions containing 1.7, 15.0, and 41.7 mg L−1 S and 10, 50, 90, and 130 mg L−1 N were used. Bulb pungency and bulb fresh and dry weight were affected by both S and N treatments. Depletion patterns for most of the macronutrients from the nutrient solutions during plant growth were affected by N and S levels, and differed depending on the N and S combination. In certain N and S combinations, magnesium (Mg) and calcium (Ca) usage were unaffected over time. Bulb N levels increased with N fertility and decreased slightly with S availability, while bulb phosphorous levels responded linearly to N fertility. Overall changes in bulb Ca and Mg levels were minor, but were influenced by N and S fertility. Bulb S content was affected by low S and N fertility, decreasing with each. Boron levels in onion bulbs decreased with increasing N and S fertility, while bulb manganese, iron, and zinc concentrations tended to increase with increasing N availability and decrease with increasing S. Potassium, copper, and molybdenum bulb concentrations were unaffected by N or S fertility. These results have the potential of being used as a reference in developing nutritional programs designed for optimal onion performance having specific flavor intensities.

Predator-prey trophic relationships in response to organic management practices.

A broad range of environmental conditions likely regulate predator–prey population dynamics and impact the structure of these communities. Central to understanding the interplay between predator and prey populations and their importance is characterizing the corresponding trophic interactions. Here, we use a well‐documented molecular approach to examine the structure of the community of natural enemies preying upon the squash bug, Anasa tristis, a herbivorous cucurbit pest that severely hinders organic squash and pumpkin production in the United States. Primer pairs were designed to examine the effects of organic management practices on the strength of these trophic connections and link this metric to measures of the arthropod predator complex density and diversity within an experimental open‐field context. Replicated plots of butternut squash were randomly assigned to three treatments and were sampled throughout a growing season. Row‐cover treatments had significant negative effects on squash bug and predator communities. In total, 640 predators were tested for squash bug molecular gut‐content, of which 11% were found to have preyed on squash bugs, but predation varied over the season between predator groups (coccinellids, geocorids, nabids, web‐building spiders and hunting spiders). Through the linking of molecular gut‐content analysis to changes in diversity and abundance, these data delineate the complexity of interaction pathways on a pest that limits the profitability of organic squash production.

Zinc Concentration in Hydroponic Solution Culture Influences Zinc and Sulfur Accumulation in Brassica rapa L

Abstract A rapid cycling population of Brassica rapa L. was grown hydroponically and subjected to solution zinc (Zn) concentrations ranging from 0.05 to 200 mg L−1. The objectives of the study were to determine how available Zn affected plant growth, and the accumulation of Zn, total sulfur (S), sulfate (SO4 2−) in B. rapa shoots. Plants exposed to Zn levels above 5 mg L−1 exhibited mild visual toxicity symptoms as well as stunted root and shoot growth. Plants exposed to Zn levels ≥50 mg L−1 had chronic toxicity symptoms after several days of exposure and did not measurably grow. Mineral analysis showed that Zn accumulated linearly in plant shoots in response to increasing Zn, despite the expression of varying levels of Zn toxicity symptoms. Total shoot S and SO4 2− accumulated at amounts greater than the control when exposed to Zn levels ≥25 mg L−1 Zn; even though solution S did not vary among treatments. At the higher Zn concentrations, shoot S did not differ from the control. Additionally, SO4 2− was responsible for the nearly all the S measured regardless of Zn exposure. This suggests that Zn uptake and accumulation differs from S when exposed to increasing Zn availability.

Impact of Supplemental Calcium Chloride on Yield, Quality, Nutrient Status, and Postharvest Attributes of Tomato

Little is known regarding the impact of calcium chloride applications during growth and development on tomato postharvest quality. This trial investigated supplemental calcium chloride applications on yield, nutrient content, texture, and postharvest quality of tomato fruit. Calcium (Ca) nutrient solution concentrations were: 60, 180, and 360 mg·L−1 calcium, while foliar applications were (0, 1, and 2% calcium chloride w/v). Plants grown with 60 mg·L−1 Ca had a high incidence of blossom end rot, which was not affected by calcium chloride sprays. Fruit nutrient concentrations were affected by calcium delivered through the nutrient solution. As fruit cluster position increased, fruit nutrient concentrations significantly decreased. Foliar calcium chloride sprays affected fruit soluble solids content and dry weight, but did not affect texture. Pericarp elasticity increased concomitantly with calcium in the nutrient solution. Postharvest disease incidence was not affected by calcium treatment, though weight loss during storage was negatively affected by calcium chloride sprays.

Comparing a Smartphone Irrigation Scheduling Application with Water Balance and Soil Moisture-based Irrigation Methods: Part I—Plasticulture-grown Tomato

A new smartphone irrigation scheduling application (VegApp) was compared with current irrigation scheduling recommendations and an automated soil moisture sensor (SMS)–based irrigation system in southern Georgia during Spring 2016 and 2017. Plants were grown using plastic mulch and drip irrigation following standard production practices for watermelon (Citrullus lanatus) in Georgia. The VegApp irrigation regime was based on evapotranspiration (ETo) values calculated from real-time data collected from a nearby weather station. Current irrigation scheduling recommendations use a water balance (WB) method. The WB method uses historic averages for determining ETo rates for the season. Water applied, soil water tension at 6-, 10-, and 14-inch depths, yield, and fruit quality were evaluated. In 2016, the SMS-based irrigation plots applied the least water. In 2017, the lowest amount of water was applied to plants grown using the VegApp. Total marketable yields were not significantly affected by irrigation regime. However, 45-count fruit yields were affected by irrigation in 2017. Plants grown using SMS-based irrigation had significantly higher yields of 45-count fruit than those grown using theWBmethod. Irrigationwater use efficiency (IWUE)was affected by irrigation treatment and year. The SMS-irrigated plants had the greatest IWUE, although it was not significantly different from plants grown using the VegApp irrigation program. Internal quality parameters including, firmness, hollow heart, and total soluble solids (TSS) were not significantly affected by irrigation scheduling during the study. The results suggest that overall water applications may be reduced and yields maintained when using VegApp compared with traditional WB methods of irrigation scheduling.

Interaction of Onion Cultivar and Growth Stages on Incidence of Pantoea ananatis Bulb Infection

Center rot, caused by Pantoea ananatis, has been one of the most important bacterial diseases of onion leading to considerable economic losses. Symptoms can be expressed in the onion foliage and bulb, with the pathogen moving from the infected leaves to bulb scales. However, little is known regarding which growth stage the plant is most susceptible to bulb infection and if there are differences in susceptibility to bulb infection among sweet onion cultivars. In this study, five cultivars of sweet onion (Pirate, Sweet Harvest, 1518, Granex YPRR, and 1407) were inoculated by clipping the tips of onion foliage and depositing 1 ml of 1 × 108 CFU/ml of P. ananatis suspension into the central leaf cavity. The inoculations were done at three growth stages (first leaf senescence, bulb initiation, and bulb swelling). Center rot incidence was assessed for precured and cured onion bulbs. In addition, total bulb incidence of center rot for each cultivar inoculated at three growth stages were also calculated. Total bulb center rot incidence was significantly higher for Granex YPRR (84%) compared with other cultivars. Also, cultivars 1518 (49%) and 1407 (33%) had significantly lower incidence of bulb infection compared with other tested cultivars. Onions were significantly more susceptible to bulb infection when inoculated during first leaf senescence (62%) as compared with bulb initiation (37%) and bulb swelling (31%) stages in precured bulbs (P = 0.041). Significantly higher incidence of center rot was observed for bulbs whose foliage were inoculated during first leaf senescence stage (64%) compared with bulb initiation (55%) and bulb swelling (52%) stages (P = 0.048). Interactions between onion cultivar and inoculation stage on center rot bulb incidence were not significant (P ≥ 0.218), when evaluated at different assessment periods. However, different cultivars displayed significant variability in susceptibility to bulb infection. The outcomes of this study may have implications in devising management strategies aimed at protecting most susceptible onion growth stages against P. ananatis.

Yellow Squash and Zucchini Cultivar Evaluation in Georgia

Ten yellow squash (Cucurbita pepo) and nine zucchini (C. pepo) cultivars were evaluated in southwest Georgia during spring and fall growing seasons in 2014 and 2015. Plants were grown using plastic mulch and drip irrigation following standard production practices for squash in Georgia. Plants were harvested 10 to 13 times during each study season. Fruit were graded into fancy, medium, and culls. Virus pressure was low during the trials. For yellow squash yields, there were significant cultivar by season interactions; however, Solstice, a straightneck yellow squash, and Gentry, a crookneck cultivar, were consistently among the highest yielding yellow types. Despite having no documented virus resistance, ‘Gentry’ performed well during the fall season. However, ‘Precious II’, a yellow straightneck cultivar with the presence of the precocious yellow gene, experienced high cull rates in the fall due to virus effects on the fruit. There was a year by season by cultivar interaction for zucchini yield. Despite this interaction, ‘Respect’ was ranked among the highest yielding cultivars in all four seasons of the trial. Differences were also observed between seasons for yellow and zucchini squash, with fall yields generally being lower than those in the spring. The results of this study suggest significant differences in the adaptability of squash cultivars for spring and fall production in Georgia. In addition, virus resistance, while important, should not be the exclusive factor for determining cultivars for fall-planted squash in Georgia.