Fruit Maturity and Quality of Splice-grafted and One-cotyledon Grafted Watermelon

Splice grafting with both cotyledons removed from the rootstock may significantly increase watermelon [Citrullus lanatus (Thunb.) Matsum. and Nakai] grafting efficiency, eliminate rootstock regrowth, and reduce costs of watermelon transplant production. We evaluated the efficacy of antitranspirant and sucrose treatments on the survival of splice-grafted transplants and assessed the effects of grafting method and rootstocks on fruit yield and quality. First, in a greenhouse experiment, four commercial antitranspirants, applied to rootstock seedlings before splice grafting, increased transplant survival 21 days after grafting (DAG) from 7% to 35% to 68% (P < 0.0001). In a second greenhouse experiment, survival of splice-grafted seedlings was 91% for plants that received 2% sucrose solution + antitranspirant, compared with 67% for plants receiving 2% sucrose alone and 25% for plants that received only water (P < 0.0001). Finally, in a field experiment we compared splice- vs. one-cotyledon grafting with two rootstocks (‘Shintosa Camelforce’ and ‘Tetsukabuto’) vs. nongrafted plants. At 54 days after transplanting (DAT), survival of all grafted transplants averaged 96% with a plant vigor rating of 7.7/10 (10 = most vigorous), compared with 84% survival (5.8/10 vigor rating) for nongrafted transplants. Flowering was delayed by an average of 2 days for splice-grafted watermelon (37 DAT) vs. one-cotyledon grafted and nongrafted plants (P < 0.0001), but harvest date was the same for all treatments (70 DAT). Fruit were harvested 0, 7, and 14 days after fruit reached physiological maturity, and there was no difference in total yield or fruit quality between grafted and nongrafted treatments, with two exceptions. Fruit with splice-grafted ‘Shintosa Camelforce’ rootstock had the firmest flesh (8.2 N) compared with nongrafted transplants (5.3 N), and lycopene increased from 16.7 µg·g−1 at physiological maturity to as high as 31.4 µg·g−1 when harvested 7 days after physiological maturity (P = 0.0002). These results indicate that application of sucrose with antitranspirant to rootstock seedlings before grafting can increase the survival of splice-grafted watermelon, and splice-grafted watermelon perform similarly to one-cotyledon grafted and nongrafted watermelon plants in field production.

Effect of Environment on Survival of Eggplant, Pepper, and Tomato in a Small-scale Healing Chamber

Many small-scale vegetable growers in the United States who graft their own vegetable transplants use healing chambers inside a greenhouse to heal their grafted plants. Under these conditions, light and relative humidity (RH) can fluctuate during the healing process, and growers need more research-based information regarding the impact of these factors on the survival of grafted transplants. To address this need, this study investigated the effect of different targeted levels of light (0%, 25%, and 50%) and RH (50% and 100%) (six combinations) in a small-scale healing chamber within a greenhouse, where the healing chamber was opened for increasing periods of time for 8 days, at which time plants were fully exposed to greenhouse conditions. The survival and growth of self-grafted eggplant (Solanum melongena), pepper (Capsicum annuum), and tomato (Solanum lycopersicum) were measured up to 25 days post grafting. Percent light in the closed healing chambers was similar for the 50% and 100% RH levels of each light treatment. When the healing chambers were closed, compared with the greenhouse, there was 0.1% light in the 0% light treatments, 25% light on average in the 25% light treatments, and 43% light on average in the 50% light treatments. On days 2 to 5 after grafting, when chambers were opened up to 1 hour, average RH in the healing chambers was 96% to 98% for the 100% RH treatments, and was 42% to 49% for the 50% RH treatments. On days 6 and 7, when chambers were opened for 3 to 8 hours, RH was 79% to 82% for the 100% RH treatments, and was 39% to 46% for the 50% RH treatments. Survival of grafted plants following healing was greatest when the healing chamber treatment was 100% RH and 50% or 25% light (95% and 90% survival, respectively), and plant survival with these two treatments did not significantly decline from 11 to 21 days after grafting, indicating plants were fully healed and acclimated when they were removed from the healing chambers on day 8. At 22 to 25 days following grafting, plants healed with 100% RH and 50% or 25% light had greater plant height, number of leaves per plant, and stem diameter than plants healed in the other light and RH combinations. SPAD reading and nitrate-nitrogen of fresh petiole sap were unaffected by any of the healing treatments tested in this experiment, or by crop type. Tomato and pepper had 14% greater survival rates on average than eggplant at all measurement dates, while tomato tended to have greater plant growth, followed by eggplant and pepper. Additional research is needed to improve survival of grafted eggplant.

Rootstock Improves High-tunnel Tomato Water Use Efficiency

The following study was conducted to address water use efficiency in grafted tomato (Solanum lycopersicum) in an on-farm environment. The commercial rootstock cultivars Beaufort (BE) and Shield (S) were chosen as these two have different root system morphologies that may benefit water use efficiency. The heirloom cultivar Cherokee Purple (CP) was grafted onto both rootstocks and used as the nongrafted control. The study was conducted in 2016 and 2017 on a 5-acre vegetable and cut flower farm in North Carolina’s Piedmont region. Plants were grown under protected, high-tunnel culture where they received either 100% (3 hours every other day) or 50% (1.5 hours every other day) of the grower’s normal irrigation regime. At 50% irrigation, ‘Beaufort’-grafted plants yielded significantly more than nongrafted ‘Cherokee Purple’ and ‘Shield’-grafted plants. Furthermore, ‘Beaufort’-grafted plants at 50% irrigation yielded more than nongrafted ‘Cherokee Purple’ receiving the 100% irrigation treatment. The ‘Beaufort’-grafted plants significantly improved irrigation water use efficiency (iWUE) at the 50% irrigation treatment compared with the other graft treatments. Yield and iWUE of ‘Shield’-grafted plants were comparable with the nongrafted ‘Cherokee Purple’ at both irrigation treatments. Regardless of irrigation treatment, grafting onto ‘Beaufort’ improved the quality of total fruit harvested. An economic assessment was conducted to determine the feasibility of using grafted plants in conditions lacking significant disease pressure. Purchasing grafted transplants would increase the initial investment by $5227.2 per acre. However, the increased yield obtained when using ‘Beaufort’ rootstock at 50% irrigation increased net revenue by $35,900.41 per acre compared with nongrafted ‘Cherokee Purple’ receiving 100% irrigation, amounting to a 44.6% increase in net revenue while saving ≈383,242 gal/acre of water per growing season. These results indicate that growers can select rootstocks to better manage water use in an environmentally friendly manner without limiting economic gains.

Improvement of Grafted Watermelon Transplant Survival as a Result of Size and Starch Increases Over Time Caused by Rootstock Fatty Alcohol Treatment: Part I

Application of fatty alcohol to rootstocks used for vegetable grafting has been shown to increase the efficiency of producing grafted transplants by controlling cucurbit (Cucurbitaceae) rootstock meristematic regrowth and by allowing the rootstocks to accumulate carbohydrates, especially starch, over time in the hypocotyl and cotyledon. A grafting experiment was conducted to determine the effect of increased carbohydrates on survival of watermelon (Citrullus lanatus) grafts using standard grafting procedures. ‘Carnivor’ interspecific hybrid squash (Cucurbita maxima × C. moschata) and ‘Macis’ bottle gourd (Lagenaria sicereria) rootstocks at 1, 7, 14, and 21 days after fatty alcohol treatment were grafted with ‘Tri-X 313’ seedless watermelon using the one-cotyledon method. Graft survival on ‘Macis’ rootstock was acceptable or significantly increased up to day 14, with a slight decrease at day 21. Graft survival on ‘Carnivor rootstock was also acceptable up to day 21, with a significant increase between days 1 and 7. The second experiment was conducted to determine whether the increased carbohydrates provide sufficient energy to successfully graft without the rootstock cotyledon, a method that has previously shown inconsistent results. Graft survival was improved by 90% using treated ‘Carnivor’ rootstock 7 days after fatty alcohol treatment and ‘Macis’ rootstock 14 days after fatty alcohol treatment. Adoption of the hypocotyl-only graft method in commercial production may increase efficiency by better using greenhouse space and could decrease disease probability by removing the cotyledons before grafting.

Economic Analysis of Grafted Tomato Production in Sandy Soils in Northern Florida

In addition to controlling soilborne diseases, grafting with selected rootstocks has the potential to enhance growth and yields in tomato (Solanum lycopersicum) production. However, information is rather limited regarding its economic viability in different production systems in the United States. The objective of this study was to compare the costs and returns of grafted vs. nongrafted fresh-market tomato production under common management practices in fumigated fields in northern Florida. The field trials were conducted in Live Oak, FL, during Spring 2010 and 2011. ‘Florida 47’ tomato was grafted onto two interspecific hybrid tomato rootstocks: ‘Beaufort’ and ‘Multifort’. Grafted and nongrafted ‘Florida 47’ plants were grown on fumigated raised beds with polyethylene mulch and drip irrigation using recommended commercial production practices for nutrient and pest management. The estimated costs of grafted and nongrafted transplants were $0.67 and $0.15 per plant, respectively, resulting in an additional cost of $3020.16 per acre for using grafted transplants as compared with nongrafted plants. Grafting also led to higher costs of harvesting and marketing tomato fruit as a result of yield improvement (1890 to 2166 25-lb cartons per acre for grafted plant vs. 1457 to 1526 25-lb cartons per acre for nongrafted plant). Partial budget analyses showed that using grafted transplants increased tomato production costs by $4488.03–$5189.76 per acre depending on the rootstock and growing season. However, compared with nongrafted tomato, the net farm return of grafted tomato production was increased by $253.32–$2458.24 per acre based on the tomato shipping point prices. Sensitivity analysis further demonstrated that grafting would be more profitable as the costs of grafted transplants decreased and the market tomato prices increased. These results indicated that although grafting increased the total cost of production, the increase in marketable fruit yield generated significant gross returns to offset costs associated with the use of grafted tomato transplants. Nevertheless, further research is warranted to provide more production budget and net return data about the economic feasibility of grafted tomato production based on a wide range of commercial growing conditions in Florida.

Cost Benefit Analysis of Using Grafted Transplants for Root-knot Nematode Management in Organic Heirloom Tomato Production

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.

Measurement of Leaf Vapor Conductance of Cucumber Transplants in the Greenhouse with Minimal Invasion

We estimated leaf vapor conductance (gl) of cucumber grafted transplants under greenhouse growing conditions. Fifty-six transplants were placed on a bench in the greenhouse. The transpiration rate (Tr) of the canopy was estimated by weighing the 16 transplants in the center using an electronic balance. The total vapor diffusion resistance (Rl+b) from inside the leaf to the atmosphere was estimated based on the vapor diffusion model, which incorporates the absolute humidity near the leaf surface and that inside the leaf as well as Tr. Next, gl was estimated from Rl+b and the resistance of leaf boundary layer evaluated with a model leaf. The Tr in the afternoon tended to be larger than that in the morning at the same photosynthetic photon flux (PPF) level. By contrast, the gl in the afternoon tended to be smaller than that in the morning at the same PPF level. The decrease of gl in the afternoon seems to be induced by the excessive transpiration resulting from an increase of vapor pressure deficit at the leaf surface.

ECONOMICS OF GRAFTED VS CONVENTIONAL WATERMELON PLANTS

Grafting of watermelons has been used in many countries to provide control of, or resistance to, certain soil borne diseases such as Fusarium wilt. The impact of grafting on postharvest quality has not been thoroughly examined. This report deals with the comparison of the costs of production between grafted versus conventional watermelons and the potential net revenue of the two. A 2-year study was conducted on the effects of grafting watermelon (Citrullus lanatus) onto rootstocks of squash and gourd at Lane, Okla., in both 2004 and 2005. Details of the research methodology are outlined in “Year Two: Effects of Grafting on Watermelon Yield and Quality” by Roberts et al. Costs of using grafted transplants increased the costs of production from $1,209 to $1,914 or $705/acre at 1,500 plants/acre. Results of the 2-year study indicated grafted watermelons had slightly lower yields per acre, similar sugar in some grafted combinations the first year but slightly lower the second year, similar lycopene content, and much higher firmness. Results of a 10-day storage study indicated that firmness of fresh-cut flesh for all watermelons declined after ten days on the shelf. However, the grafted watermelon flesh was firmer after ten days than the nongrafted fruit at the beginning of the ten days. This improved shelf life should interest the cut-fruit industry and should lead to contract price enhancement for the growers. A market price of $0.02/lb for grafted watermelons above the market price of nongrafted watermelons would be needed to provide similar net revenues at the same yield per acre.

(56) Transpiration and Photosynthesis of Grafted Watermelon Transplants as Affected by Environmental Factors during Graft Union Formation

Grafted transplants are widely used for watermelon culture in Korea mainly to reduce the yield and quality losses caused by soil-borne diseases. It is normal practice to cure the grafted transplants under high relative humidity (RH) and low photosynthetic photon flux (PPF) conditions for a few days after grafting to prevent the wilting of the transplants. Transpiration rate (TR) and net photosynthetic rate (NPR), however, could be suppressed under those environmental conditions. In the present study, TR and NPR of the grafted watermelon transplants were compared during graft union formation under 18 environmental conditions combining two air temperatures (20 and 28 °C), three RHs (60%, 80%, and 100%), and three PPF s (0, 100, and 200 μmol·m-2·s-1). Percentages of graft union formation and survival were also evaluated. TR and NPR dramatically decreased just after grafting but slowly recovered 2 to 3 days after grafting at 28 °C. The recovery was clearer at higher PPF and lower RH. On the other hand, the recovery of TR and NPR was not observed in 7 days after grafting at 20 °C. Differences in TR and NPR affected by RH were nonsignificant. Percentage of graft union formation was 98% when air temperature, RH, and PPF were 28 °C, 100%, and 100 μmol·m-2·s-1, respectively, which was the highest among all the treatments. Percentage of survival was over 90% when air temperature was 28 °C and RH was higher than 80% (when vapor pressure deficit was lower than 0.76 kPa). In addition, higher PPF enhanced TR and NPR and promoted rooting and subsequent growth of grafted transplants. Results suggest that the acclimation process for grafted watermelon transplants can be omitted by properly manipulating environmental factors during graft union formation.

Advantages and Limitations of Grafted Vegetable Transplants in Israel

Grafting technology for vegetable transplants was introduced to Israel eight years ago by Hishtil Nurseries, Inc. The main goal of grafting was to find a substitute for methyl bromide, the elimination of which was pending. The use of grafted watermelon transplants soon followed. Presently, more than 40% of watermelon transplants are grafted. The chief reason for the success of grafted transplants is their tolerance to soil-borne pathogens, including Fusarium, Monosporascus, and Macrophomina. Yields of grafted transplants are often much higher, and it has been shown possible to grow watermelons with saline water (4.5). A limitation of grafted transplants is that presently, we do not have a good solution for nematodes. A drawback is that in order to get good watermelon taste and flavour, the grower needs the experience to adjust agrotechniques, especially determining the best harvest date. Grafted tomato transplants were also introduced early on. Grafted tomato transplants can have excellent resistance to fusarium crown rot, corky root, and other soil-borne pathogens. Some rootstocks have been observed to tolerate water salinity of 8 ec and still produce commercially acceptable yields. Limitations to the use of grafted tomato transplants are the lack of compatibility of some of the cultivars with the rootstocks and the breakdown of nematode resistance at high soil temperatures. Melons, eggplants, and cucumbers are grafted under some conditions.