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Han Yulin, Ha Huiquan, Xin Huipu, Zhao Pengxiang and Shi Xinwei

Stevia rebaudiana Bertoni was hydroponically raised on the matrices of sand or slag and sprinkled periodically with three different nutrient solutions (BD, KO, Knop) respectively. The conventional raising method of Hailin state farm was used as the control. The results showed that the seedlings grown on the matrix of sand and sprinkled with Knop nutrient solution were stronger with well-developed root systems, obvious spindle-shaped root tubers, and less plant diseases, no insect pests, and weeds, which was significantly better than the control method in respect to the root length, root fresh weight, stem height, shoot fresh weight, and number of leaves, and significantly better than other treatments in respect to the root length, root fresh weight and stem height. This raising method is worth extending.

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Desire Djidonou, Xin Zhao, Karen E. Koch and Lincoln Zotarelli

Growth and yield typically increase when tomato plants are grafted to selected interspecific hybrid rootstocks from which distinctive root system morphologies are envisioned to aid nutrient uptake. We assessed these relationships using a range of exogenous nitrogen (N) supplies under field production conditions. This study analyzed the impact of N on growth, root distribution, N uptake, and N use of determinate ‘Florida 47’ tomato plants grafted onto vigorous, interspecific, hybrid tomato rootstocks ‘Multifort’ and ‘Beaufort’. Six N rates, 56, 112, 168, 224, 280, and 336 kg·ha−1, were applied to sandy soil in Live Oak, FL, during Spring 2010 and 2011. During both years, the leaf area index, aboveground biomass, and N accumulation (leaf blade, petiole, stem, and fruit) responded quadratically to the increase in N fertilizer rates. Averaged over the two seasons, the aboveground biomass, N accumulation, N use efficiency (NUE), and N uptake efficiency (NUpE) were ≈29%, 31%, 30%, and 33% greater in grafted plants than in nongrafted controls, respectively. More prominent increases occurred in the root length density (RLD) in the uppermost 15 cm of soil; for grafted plants, RLD values in this upper 15-cm layer were significantly greater than those of nongrafted plants during both years with an average increase of 69% over the two seasons. Across all the grafted and nongrafted plants, the RLD decreased along the soil profile, with ≈60% of the total RLD concentrated in the uppermost 0 to 15 cm of the soil layer. These results demonstrated a clear association between enhanced RLD, especially in the upper 15 cm of soil, and improvements in tomato plant growth, N uptake, and N accumulation with grafting onto vigorous rootstocks.

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Charles E. Barrett, Xin Zhao and Alan W. Hodges

Growers are looking for sustainable alternatives to methyl bromide as a soil fumigant that are effective and economical. Increased demand for organically produced fruits and vegetables has also contributed to the need for environmentally friendly soil-borne disease control methods. Grafting may be a valuable tool for vegetable growers to cope with pest management challenges in production of cucurbits and solanaceous crops; however, there are concerns regarding the higher costs associated with the use of grafted plants in the United States. The main objective of this 2-year study was to determine if grafting with a resistant rootstock could be cost-effective to overcome root-knot nematodes (RKN) (Meloidogyne sp.) and maintain fruit yield in organic heirloom tomato (Solanum lycopersicum) production in Florida's sandy soils. The heirloom tomato cultivar Brandywine was grafted onto the rootstock ‘Multifort’. Nongrafted and grafted ‘Brandywine’ plants were grown organically in two fields that exhibited different levels of RKN infestations. Grafted and nongrafted transplants were estimated to cost $0.78 and $0.17 per plant, respectively. The cost of rootstock seeds accounted for 36% ($0.28/plant) of the total cost of the grafted transplants and 46% of the cost difference between grafted and nongrafted plants. Sensitivity analyses were conducted using these estimated transplant production costs and crop yield data from the field trials as well as price information for heirloom tomato. Results showed that under severe RKN pressure, grafting may be an economically feasible pest control measure to help maintain a profitable production given that the risk of economic crop losses due to RKN outweighed the higher cost of grafted transplants.

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Wenjing Guan, Xin Zhao, Richard Hassell and Judy Thies

Grafting with resistant rootstocks is an effective strategy to manage a variety of soilborne diseases and root-knot nematodes in solanaceous and cucurbitaceous vegetables. In addition, improved resistance to some foliar diseases and viruses has also been reported in grafted plants. Hence, grafting technology is considered an important and innovative practice of integrated pest management and a promising alternative for soil fumigants in vegetable production. Inherent resistance within rootstocks and improved plant nutrient uptake are generally suggested as the main reasons for improved disease control in grafted vegetables. However, increasing evidence indicated that systemic defense mechanisms may also play an important role in plant defense as a result of grafting. This review analyzes current literature on the use of grafting techniques for disease management in vegetable crops, discusses potential mechanisms associated with grafting-conferred plant defense, and identifies needs for future research to promote more effective and efficient use of grafting technology to support sustainable vegetable production.

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Xin Zhao, Edward Carey, James Nechols, Kim Williams and Weiqun Wang

Implications of dietary phenolic compounds for human health and disease prevention have been indicated by a body of literature. A greenhouse pot study was performed to investigate the impacts of fertilizer source and preventive insecticide application on phenolic compound levels in pac choi [Brassica rapa (L.) cv. Mei Qing]. A two-way randomized complete-block design with five replications was used in this experiment. Fertilizer source consisted of two levels: conventional fertilizer (pre-plant application of Osmocote slow-release fertilizer), and organic fertilizer (pre-plant application of vermicompost and fertigation with compost tea and fish emulsion). Insecticide application consisted of three levels: organic (pyrethrin) vs. conventional (permethrin), and a plain water control. At harvest, total phenolics and individual phenolic compounds in pac choi leaves (blades) were analyzed by Folin assay and HPLC, respectively. Head weight of pac choi was significantly higher under conventional fertilizer treatment, while it was not affected by insecticides. Total phenolic content of pac choi was significantly increased by organic fertilizer treatment. HPLC results indicated that organic fertilizer treatment resulted in significantly higher levels of individual phenolic compounds, including chlorogenic acid and ferulic acid. In contrast, preventive insecticide application showed little effect on the phenolics in pac choi. Correlation analysis excluded the influence of plant size (head weight) on phenolic content in pac choi. Differential N-forms, rates of nutrient release, and/or variable nutrient content in organic and conventional fertilizer treatments may contribute to elevated phenolic content in organically fertilized pac choi.

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Xin Zhao, Edward E. Carey and Fadi M. Aramouni

Consumers of organic food tend to believe that it tastes better than its conventional counterpart. However, there is a lack of scientific studies on sensory analysis of organic food. A consumer taste test was conducted to compare the acceptability of organically and conventionally grown spinach. Spinach samples were collected from organically and conventionally managed plots at the Kansas State University Research and Extension Center, Olathe. One hundred-twenty-two untrained panelists (80 female and 42 male) participated in this consumer study. Fresh and 1-week-old spinach leaves were evaluated by 60 and 62 consumers, respectively, using a 9-point hedonic scale (9 = like extremely, 5 = neither like nor dislike, 1 = dislike extremely). The ANOVA results showed that fresh organic spinach had a higher preference score than corresponding conventional spinach, although not at a significant level (P = 0.1790). For the 1-week-old spinach, the difference diminished, and instead, conventional spinach had a higher preference rating. Among 61 consumers who made comments regarding the sensory evaluation, 29 claimed that organic spinach was more tasty and flavorful; 19 consumers thought conventional spinach was better; 13 consumers could not tell the difference. Even though this consumer study did not reveal significant differences in consumer preference for organic vs. conventional spinach, further well-designed sensory tests are warranted given the trends indicated in our study. Assessment of sensory attributes of organic vegetables after storage also deserves further attention. Ideally, both consumer tests and descriptive analysis using trained panelists will be considered.

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Desire Djidonou, Xin Zhao, Jeffrey K. Brecht and Kim M. Cordasco

Grafting is considered to be a unique component in sustainable vegetable production. In addition to its usefulness for managing soil-borne diseases, it has been suggested that grafting with vigorous rootstocks can improve crop growth and yield. The objective of this greenhouse study was to assess the effects of different interspecific hybrid tomato rootstocks (Solanum lycopersicum × Solanum habrochaites) on yield, growth, nutrient accumulation, and fruit composition of tomato (S. lycopersicum). Using the determinate tomato cultivar Florida 47 as the scion, plants were grafted onto four interspecific rootstock cultivars including Beaufort, Maxifort, Multifort, and RST-04-105. Overall, the use of rootstocks resulted in total and marketable fruit increase 53% and 66% higher than non-grafted and self-grafted scion plants, respectively. The increase in marketable yield by ‘Beaufort’, ‘Maxifort’, and ‘Multifort’ was largely attributed to an increased number of fruit per plant, whereas higher average fruit weight contributed to the yield increase in plants grafted onto ‘RST-04-105’. Self-grafting of ‘Florida 47’ resulted in similar yield as the non-grafted scion control. Analyses of plant growth parameters demonstrated significant enhancement of total leaf area at first fruit harvest in plants grafted onto interspecific rootstocks as compared with the non-grafted and self-grafted scion controls. In addition to plant growth and yield improvement, enhanced accumulation of nitrogen, potassium, and calcium was also observed in grafted plants. The enhancement in mineral nutrient accumulation was largely related to increased biomass accumulation rather than higher nutrient concentration (on a dry weight basis). The overall accumulation of phosphorus was not influenced markedly by the rootstocks used. In general, grafting with the interspecific rootstocks maintained fruit soluble solids content (SSC) and total titratable acidity (TTA), concentrations of vitamin C, carotenoids, and total phenolics at levels comparable with non-grafted plants, whereas harvest date showed a more pronounced effect on fruit composition.

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Xin Zhao, Qianru Liu, M. Tatiana Sanchez and Nicholas S. Dufault

Fusarium wilt of watermelon can be effectively managed by grafting with resistant rootstocks. Excision and regeneration of grafted seedling roots is a common practice among cucurbit-grafting nurseries that has not been thoroughly examined. The objectives of this study were to compare the performance of grafted and nongrafted watermelon plants under both greenhouse and field conditions when inoculated with Fusarium oxysporum f. sp. niveum (FON) race 2, and assess the effect of root excision on growth of grafted plants with Cucurbita moschata and Cucurbita maxima × C. moschata rootstocks. Two greenhouse experiments (Fall 2015 and Spring 2016) and one field trial (Spring 2016) of seedless watermelon ‘Melody’ were conducted in this study. In both greenhouse experiments, inoculated, nongrafted watermelon plants showed a significantly higher percentage of recovered Fusarium spp. colonies (70% to 75%) compared with grafted treatments (0% to 7.5%). Some plant growth measurements, including the longest vine length and aboveground fresh and dry weight, indicated less vigorous growth for nongrafted plants compared with the grafted treatments. Significantly higher percent recovery of Fusarium spp. below the graft union was observed in the grafted plants with root excision and regeneration treatment (3.7%) in contrast to the intact root treatment (0.5%), suggesting that the root excision method may possibly create entry points for FON infections. Overall, the root excision treatment showed little influence on aboveground growth and root characteristics of grafted plants. Yield of grafted watermelon with FON inoculation in the fumigated field trial was significantly higher than that of noninoculated, nongrafted ‘Melody’ (NGM) control as reflected by the increase of fruit number and size. Averaged over all the grafted treatments, the increase in marketable fruit number and weight reached 108.3% and 240.9%, respectively, and the total fruit number and weight increase was at 80.0% and 237.2%, respectively. However, grafted plants also exhibited greater levels of root-knot nematode infestation as indicated by the significantly higher root galling ratings. Results from this study demonstrated that grafting with squash rootstocks can effectively limit FON colonization in seedless watermelon plants, although more research in rootstock selection and testing is needed to optimize the use of grafted plants for improving plant growth and fruit yield.

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Charles E. Barrett, Xin Zhao, Charles A. Sims, Jeffrey K. Brecht, Eric Q. Dreyer and Zhifeng Gao

Grafting has many purposes in vegetable production. It is used for control of soilborne pathogens, season extension in protected culture, and improving productivity in cucurbitaceous and solanaceous crops. Consumers desire heirloom tomatoes (Solanum lycopersicum) for their perceived excellent flavor. Heirloom tomatoes are susceptible to many soilborne diseases and may benefit from grafting onto more robust, disease-resistant rootstocks especially under organic production. In this two-year study, heirloom tomato ‘Brandywine’ was grafted onto tomato hybrid ‘Survivor’ and interspecific tomato hybrid ‘Multifort’ rootstocks to determine the effects of grafting on fruit quality attributes such as soluble solids content (SSC), pH, total titratable acidity (TTA), and vitamin C. Nongrafted and self-grafted ‘Brandywine’ tomatoes were included as controls. Consumer sensory tests were also conducted to assess the effects of grafting on overall appearance and acceptability, firmness, tomato flavor, and sweetness. No significant differences in vitamin C, SSC, pH, or TTA were found in fruit from the nongrafted, self-grafted, and ‘Brandywine’ grafted with the two rootstocks either year. The SSC of all tomatoes in 2010 was lower than that of 2011. In 2010, fruit from ‘Brandywine’ grafted onto the rootstock ‘Survivor’ was scored significantly lower in appearance, acceptability, and flavor than the nongrafted ‘Brandywine’ treatment. All grafted treatments resulted in a significant decrease in acceptability ratings in the consumer sensory test. No significant differences were observed between nongrafted and grafted treatments in 2011. Consumers who reported more frequent consumption of fresh tomato tended to give lower ratings for most sensory attributes evaluated. Harvest time and fruit ripeness need to be considered in future research to better understand the influence of grafting with selected rootstocks on fruit composition and sensory attributes of heirloom tomatoes.

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Wenjing Guan, Xin Zhao, Danielle D. Treadwell, Michael R. Alligood, Donald J. Huber and Nicholas S. Dufault

Interest in producing specialty melons (Cucumis melo) is increasing in Florida, but information on yield performance, fruit quality, and disease resistance of specialty melon cultivars grown in Florida conditions is limited. In this study conducted at Citra, FL, during the 2011 Spring season, 10 specialty melon cultivars were evaluated, in both certified organic and conventionally managed fields, including: Creme de la Creme and San Juan ananas melon (C. melo var. reticulatus), Brilliant and Camposol canary melon (C. melo var. inodorus), Ginkaku and Sun Jewel asian melon (C. melo var. makuwa), Arava and Diplomat galia melon (C. melo var. reticulatus), and Honey Pearl and Honey Yellow honeydew melon (C. melo var. inodorus). ‘Athena’ cantaloupe (C. melo var. reticulatus) was included as a control. ‘Sun Jewel’, ‘Diplomat’, ‘Honey Yellow’, and ‘Honey Pearl’ were early maturing cultivars that were harvested 10 days earlier than ‘Athena’. ‘Athena’ had the highest marketable yield in the conventional field (10.7 kg/plant), but the yield of ‘Camposol’, ‘Ginkaku’, ‘Honey Yellow’, and ‘Honey Pearl’ did not differ significantly from ‘Athena’. Under organic production, ‘Camposol’ showed a significantly higher marketable yield (8.3 kg/plant) than ‘Athena’ (6.8 kg/plant). ‘Ginkaku’ produced the largest fruit number per plant in both organic (10 fruit/plant) and conventional fields (12 fruit/plant) with smaller fruit size compared with other melon cultivars. Overall, the specialty melon cultivars, except for asian melon, did not differ significantly from ‘Athena’ in terms of marketable fruit number per plant. ‘Sun Jewel’, ‘Diplomat’, and ‘San Juan’ showed relatively high percentages of cull fruit. ‘Honey Yellow’, ‘Honey Pearl’, and ‘Sun Jewel’ exhibited higher soluble solids concentration (SSC) than ‘Athena’ in both organic and conventional fields, while ‘Brilliant’, ‘San Juan’, and ‘Ginkaku’ also had higher SSC than ‘Athena’ under organic production. ‘Honey Yellow’, ‘Sun Jewel’, ‘Brilliant’, and ‘Camposol’ were less affected by powdery mildew (caused by Podosphaera xanthii) and downy mildew (caused by Pseudoperonospora cubensis) in the conventional field. ‘Honey Yellow’ and ‘Camposol’ also had significantly lower aboveground disease severity ratings in the organic field compared with ‘Athena’, although the root-knot nematode (RKN) (Meloidogyne sp.) gall rating was higher in ‘Honey Yellow’ than ‘Athena’.