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Open access

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.

Open access

Ying Wang, Tingting Xue, Xing Han, Lingxiao Guan, Liang Zhang, Hua Wang, and Hua Li

Kaolin particle film (KPF) is an aqueous formulation of chemically inert mineral particles that can be sprayed on the surface of crops to form a protective film, resulting in increased fruit yield and quality. In this work, the effects of kaolin-based, foliar reflectant particle film on grape composition and volatile compounds in ‘Meili’ (Vitis vinifera L.) grapes were investigated under different growth stages over two growing seasons. The 100-berry weight and titratable acid content were decreased, and the sugar and soluble solid contents were increased in grapes of plants treated with kaolin over 2 years. Compared with grapes from plants not sprayed with kaolin, the levels of total phenol, flavonoid, flavanol, tannin, and anthocyanins of grapes from plants treated with kaolin for 2 years were mostly increased. High-performance liquid chromatography (HPLC) analysis also revealed an increased content of monomeric anthocyanin and changed anthocyanin composition. However, there was little effect on the volatile compounds in the grapes. These results demonstrate that KPF can facilitate the accumulation of sugar and phenolics, thereby improving grape quality even in a humid climate.

Open access

Alexander Miller, Petrus Langenhoven, and Krishna Nemali

Operational cost of producing lettuce (Lactuca sativa) during the winter in greenhouses is high in the northern regions of the United States due to the addition of supplemental lighting (SL) and heating. Crop productivity in greenhouses should increase to offset high operational costs and maintain profits. Factors including SL composition, heating efficiency, suitability of production systems (PS), and cultivar performance can affect crop productivity. Research-based information on optimizing the above environmental- and production-related factors is limited. This information is critical for growers to make informed decisions and increase profits during winter hydroponic production. We evaluated the interactive effects of SL composition, solution temperature, PS, and cultivar treatments on lettuce shoot dry weight (SDW, g·m−2) and shoot water content (SWC, %) in a greenhouse maintained at suboptimal air temperature (13.7 °C) using a split-plot design. There were three light treatments (sunlight without SL, sunlight + narrow-spectrum SL at nighttime, and sunlight + full-spectrum SL at nighttime), two solution temperature levels [heated (18.8 °C) and unheated (13.2 °C)], two hydroponic PS [constant flood technique (CFT) and nutrient film technique (NFT)], and eight cultivars included in the study. Results indicated that 1) a narrow-spectrum SL at nighttime in combination with heated solution resulted in maximum SDW of lettuce, 2) the SDW and SWC (major determinant of economic yield) increase between the heated and unheated solution temperature treatments was higher in the CFT than in the NFT, and 3) the positive effects of using heated solution were seen mainly in the green-color cultivars. Our research identified the optimal spectral composition of nighttime SL, tested the positive effects of alternate heating methods using heated solution on plant growth under suboptimal air temperature conditions, compared the suitability of two hydroponic PS for lettuce production, and quantified yield potential of several lettuce cultivars in hydroponic production during winter. Growers can use our research findings to make informed decisions about their investment and to maximize hydroponic lettuce productivity and profits during winter.

Open access

Coral Ortiz, Antonio Torregrosa, Enrique Ortí, and Sebastià Balasch

Thinning is the process of removing some flowers or fruit to increase fruit size at harvest. In the Valencia region of Spain, the thinning operation for citrus fruit (Citreae) is performed for some mandarin varieties. This is always performed manually; however, this method is very expensive. The goal of this research study was to assess the mechanical thinning of mandarin (Citrus reticulata) using a hand-held branch shaker. Different thinning treatments were conducted over a 3-year period. The gasoline-powered branch shaker was capable of detaching fruit four- to five-times faster than manual thinning. Final fruit size was significantly higher using manual and mechanical thinning compared with a no thinning treatment. Similar final fruit size was obtained with manual and mechanical thinning. However, no significant differences were found in final fruit yield by weight among no thinning, mechanical thinning, and manual thinning treatments. The use of a branch shaker could be recommended for thinning operations to increase efficiency, reduce labor costs, and obtain larger and higher-quality fruit.

Open access

James A. Schrader, Paul A. Domoto, Gail R. Nonnecke, and Diana R. Cochran

An accurate predictive model for estimating the timing of seasonal phenological stages of grape (Vitis L.) would be a valuable tool for crop management. Currently the most used index for predicting the phenological timing of fruit crops is growing degree days (GDD), but the predictive accuracy of the GDD index varies from season-to-season and is considered unsatisfactory for grapevines grown in the midwestern United States. We used the methods of multiple regression to analyze and model the effects of multiple factors on the number of days remaining until each of four phenological stages (budbreak, bloom, veraison, and harvest maturity) for five cold-climate wine grape cultivars (Frontenac, La Crescent, Marquette, Petit Ami, and St. Croix) grown in central Iowa. The factors (predictor variables) evaluated in models included cultivar, numerical day of the year (DOY), DOY of soil thaw or the previous phenological stage, photoperiod, GDD with a base temperature of 10 °C (GDD 10), soil degree days with a base temperature of 5 °C (SDD 5), and solar accumulation. Models were evaluated for predictive accuracy and goodness of fit by calculating the coefficient of determination (R 2), the corrected Akaike information criterion (AICc), and the Bayesian information criterion (BIC); testing for normal distribution of residuals; and comparing the actual number of days remaining until a phenological stage with the number of days predicted by models. The top-performing models from the training set were also tested for predictive accuracy on a validation dataset (a set of data not used to build the model), which consisted of environmental and phenological data recorded for one popular Midwest cultivar (Marquette) in 2019. At all four phenological stages, inclusion of multiple factors (cultivar and four to six additional factors) resulted in predictive models that were more accurate and consistent than models using cultivar and GDD 10 alone. Multifactor models generated from data of all five cultivars had high R 2 values of 0.996, 0.985, 0.985, and 0.869 for budbreak, bloom, veraison, and harvest, respectively, whereas R 2 values for models using only cultivar and GDD 10 were substantially lower (0.787, 0.904, 0.960, and 0.828, respectively). The average errors (differences from actual) for the top multifactor models were 0.70, 0.84, 1.77, and 3.80 days for budbreak, bloom, veraison, and harvest, respectively, and average errors for models that included only cultivar and GDD 10 were much larger (5.27, 2.24, 2.79, and 4.29 days, respectively). In the validation tests, average errors for budbreak, bloom, veraison, and harvest were 1.92, 1.31, 0.94, and 1.67 days, respectively, for the top multifactor models and 10.05, 2.54, 4.23, and 4.96 days, respectively, for models that included cultivar and GDD 10 only. Our results demonstrate the improved accuracy and utility of multifactor models for predicting the timing of phenological stages of cold-climate grape cultivars in the midwestern United States. Used together in succession, the models for budbreak, bloom, veraison, and harvest form a four-stage, multifactor calculator for improved prediction of phenological timing. Multifactor models of this type could be tailored for specific cultivars and growing regions to provide the most accurate predictions possible.

Open access

Yingchao Lin, Dejun Kong, Zhihong Wang, Yi Chen, Zhixiao Yang, Chun Wu, Hui Yang, and Lili Chen

Tobacco is traditionally an industrial crop that is used for manufacturing cigarettes. However, due to health concerns and global tobacco control movements, alternative uses of tobacco are urgently needed to support tobacco farmers and vendors. Tobacco is also an oilseed crop with an oil yield ranging from 30% to 40 of its dry weight. However, there is still no information on the effects of nitrogen application on tobacco seed yield and seed oil production. The objective of this study was to evaluate the effects of N fertilization (90, 120, 150, and 180 kg·ha−1 N) on the seed yield, oil content, fatty acid composition, and seed germination characteristics of tobacco plants at two locations. The results showed that applying increasing amounts of N to tobacco plants significantly increased their total seed yields and oil content. Nitrogen application also modified the fatty acid composition of the seed oil, as more unsaturated fatty acids were produced under the increasing N application rate treatments than under the control. Moreover, increasing the N application rate generally significantly increased the yields of individual fatty acids as well. Nevertheless, the increased seed oil content and altered fatty acid composition did not affect seed germination traits, as the seed germination potential and rate showed no obvious change among treatments or the control. The height and size of the tobacco plants also increased with the increasing N application rate, which would be beneficial for increasing biomass production for bioenergy. This study shows for the first time the feasibility of increasing the seed and oil yields and modifying the fatty acid composition of tobacco plants by increasing N addition.

Open access

Andre Luiz Biscaia Ribeiro da Silva, Joara Secchi Candian, Lincoln Zotarelli, Timothy Coolong, and Christian Christensen

Soil nitrogen (N) is easily leached in cabbage (Brassica oleracea var. capitata) production areas of southeastern United States characterized by sandy soils with low water-holding capacity. Soil N leaching in these areas is increased after rainfall events; consequently, growers increase the fertilizer N application to protect against N deficiencies and yield loss. The objective of this study was to evaluate the effects of three fertilizer N rates on yield and head quality for common cabbage cultivars used by Florida and Georgia growers during four cabbage growing seasons. Field experiments were conducted in Hastings, FL, in 2016 and 2017, and in Tifton, GA, in 2018 and 2019. A randomized complete block design was used with a split-plot design of fertilizer N rate and cabbage cultivar. Fertilizer N rate treatments consisted of the application of 170, 225, and 280 lb/acre N and were assigned as the main plot. Cabbage cultivars Bravo, Bronco, Bruno, Capture, Cheers, and Ramada were assigned as the sub-plots. Weather conditions were monitored during all growing seasons, and total, marketable, and unmarketable yields, as well as cabbage head polar and equatorial diameters, and core height and width were measured. In Florida, there was a significant interaction for growing season and fertilizer N rate. The Florida 2016 cabbage season experienced 10.5 inches of rainfall, and fertilizer N rates had no effect on cabbage yields. Total and marketable yield averaged 45,391 and 38,618 lb/acre among fertilizer N rates in 2016, respectively. Rainfall accumulated 2.1 inches during the 2017 study in Florida, which was less than the crop evapotranspiration. In response, total and marketable yield were higher for the applications of 225 lb/acre N (51,865 and 49,335 lb/acre, respectively) and 280 lb/acre N (54,564 and 52,219 lb/acre, respectively) compared with the application of 170 lb/acre N (47,929 and 43,710 lb/acre, respectively). In Georgia, there were no significant interactions between production season and fertilizer N rates. In addition, there were no significant main effects of season or fertilizer N rate. Rainfall events accumulated 20.9 and 7.8 inches during the 2018 and 2019 growing seasons, respectively. Total and marketable yields averaged 37,290 and 33,355 lb/acre, respectively for the two growing seasons in Georgia. Cabbage cultivar had no interaction with fertilizer N rate in any location. ‘Cheers’ (52,706 lb/acre) had the highest total yield in Florida, and ‘Ramada’ (38,462 lb/acre) and ‘Bronco’ (39,379 lb/acre) had the highest total yields in Georgia. In conclusion, the application of 225 lb/acre N was sufficient to sustain cabbage yields, but yields of the 170- and 225-lb/acre N treatments were not different when rainfall events exceeded crop evapotranspiration.

Open access

Ji-Jhong Chen, Heidi Kratsch, Jeanette Norton, Youping Sun, and Larry Rupp

Shepherdia ×utahensis ‘Torrey’ (‘Torrey’ hybrid buffaloberry) is an actinorhizal plant that can fix atmospheric nitrogen (N2) in symbiotic root nodules with Frankia. Actinorhizal plants with N2-fixing capacity are valuable in sustainable nursery production and urban landscape use. However, whether nodule formation occurs in S. ×utahensis ‘Torrey’ and its interaction with nitrogen (N) fertilization remain largely unknown. Increased mineral N in fertilizer or nutrient solution might inhibit nodulation and lead to excessive N leaching. In this study, S. ×utahensis ‘Torrey’ plants inoculated with soils containing Frankia were irrigated with an N-free nutrient solution with or without added 2 mm ammonium nitrate (NH4NO3) or with 0.0 to 8.4 g·L−1 controlled-release fertilizer (CRF; 15N–3.9P–10K) to study nodulation and plant morphological and physiological responses. The performance of inoculated plants treated with various amounts of CRF was compared with uninoculated plants treated with the manufacturer’s prescribed rate. Plant growth, gas exchange parameters, and shoot N content increased quadratically or linearly along with increasing CRF application rates (all P < 0.01). No parameters increased significantly at CRF doses greater than 2.1 g·L−1. Furthermore, the number of nodules per plant decreased quadratically (P = 0.0001) with increasing CRF application rates and nodule formation were completely inhibited at 2.9 g·L−1 CRF or by NH4NO3 at 2 mm. According to our results, nodulation of S. ×utahensis ‘Torrey’ was sensitive to N in the nutrient solution or in increasing CRF levels. Furthermore, plant growth, number of shoots, leaf area, leaf dry weight, stem dry weight, root dry weight, and N content of shoots of inoculated S. ×utahensis ‘Torrey’ plants treated with 2.1 g·L−1 CRF were similar to those of uninoculated plants treated with the manufacturer’s prescribed rate. Our results show that S. ×utahensis ‘Torrey’ plants inoculated with soil containing Frankia need less CRF than the prescribed rate to maintain plant quality, promote nodulation for N2 fixation, and reduce N leaching.

Open access

Ivette Guzman, Danise Coon, Krystal Vargas, and Paul W. Bosland