Watermelon Cv Research Articles

Impact of heat stress on sucrose metabolism of watermelon

High temperatures (HT) are a significant threat for crop production, and strategies for maintaining high crop yields and quality under HT stress are crucial agricultural objectives. The changes in sugar metabolism during HT stress were examined in watermelon cv. Crimson Tide leaves. The leaves obtained from plants were subjected to 35, 40, 45, 50, 55 and 60°C. Heat-stress tolerance (HST; LT50), hydrogen peroxide (H2O2), sucrose (Suc), reducing sugars and starch contents and some sucrolytic enzyme activities in leaf samples held at each temperature for 30 minutes were determined. The HST and H2O2 content, rose with increasing temperatures, most noticeably between 50-55°C. As a result, the LT50 value was determined to be 53.84°C. The Suc content increased almost 2-fold between 50-55°C. The reducing sugars and starch content sharply decreased with HT up to 50°C comparing to the control, however both increased almost 2-fold between 50-55°C. The H2O2 may act as a signal molecule at 40-45°C and triggers sucrose metabolism. It was determined that alkaline-INV and SuSy activities were at the maximum level at 40°C. The increase in enzyme activities has been associated with increased energy needs under stress conditions. The findings revealed that sugar metabolism contributes significantly to HST.

An Experimental Study on the Effect of Cutting Angle on the Growth of Grafted Watermelon Seedlings Using the One-Cotyledon Grafting Method

The labor-efficient automation of grafting has been recognized as a key factor in the wider adoption of grafting. In growing cucurbits, the root pruned one-cotyledon grafting method is the most commonly used method with grafting machines. The cutting angle, which affects the matching of the rootstock and scion, is key to the survival of the graft seedling. In the production of cucurbit graft seedlings, the cutting parameters are established based on experience, leading to low grafting success. To determine accurate cutting parameters, the watermelon cv. ‘Zaojia84-24′ was used as the scion and the pumpkin cv. ‘Zhenzhuang’ was used as rootstock, and two one-way experiments investigating the cutting angle of the watermelon scion and the rootstock as factors were conducted. The cutting angle of the rootstock and scion had no significant effect on the xylem reconnection rate or the grafting survival rate. A larger cutting angle for the rootstock and scion led to a delay in the reconnection of the phloem. Different cutting angles for the scion significantly affected the growth of the scion after grafting. Compared with a scion graft cutting angle of 10° (SL), graft cutting angles of 14° (SM) and 20° (SS) led to significantly greater scion dry weights, with increases of 16.00% and 18.61%, respectively. Different cutting angles of the rootstock significantly affected the growth of roots after grafting. Compared with a rootstock graft cutting angle of 10° (RL), graft cutting angles of 17° (RM) and 27° (RS) led to significantly greater root dry weights, with increases of 29.33% and 22.54%, respectively. The results of this study can provide a reference for the design of cutting mechanisms for cucurbit grafting robots, improving the cutting precision of grafting robots.

Mulch Application and Plant Spacing Influence on Growth Traits, Pests, Insects and Weeds in Cotton (Gossypium hirsutum L.) Varieties

Mulch Application and Plant Spacing Influence on Growth Traits, Pests, Insects and Weeds in Cotton (Gossypium hirsutum L.) Varieties

Comparative efficacy of cucurbitacin phytonematicides and Velum on growth and fruit quality of watermelon cultivar ‘Congo’ and suppression of Meloidogyne enterolobii under field conditions

ABSTRACT Globally, the guava root-knot nematode (Meloidogyne enterolobii) is becoming an emerging threat of note in crops with or without Mi resistance genes. Watermelon (Citrullus lanatus) cultivars are highly susceptible to Meloidogyne species, with all cultivars without genotypes with resistance to the genus. In contrast, nematode management options for watermelon production had since the withdrawal of fumigant nematicides been constrained. The objective of this study was to investigate the comparative efficacy of the locally-developed cucurbitacin phytonematicides and commercially available synthetic chemical nematicide Velum on growth and fruit yield and quality of watermelon cv. ‘Congo’, along with its accumulation of foliar nutrient elements and suppression of M. enterolobii population densities under field conditions. Nemarioc-AL and Nemafric-BL phytonematicides were each applied biweekly at 2% per seedling using 500 ml solution, while Velum was applied once using 500 ml solution at 0.08 ml/15 L chlorine-free water. At 90 days after the treatments, relative to untreated control, the two phytonematicides and Velum (a.i. fluopyram) significantly increased plant growth, fruit yield and quality, although with the accumulation of phosphorus in leaf tissues, with efficacies of the three products being comparable. Similarly, relative to untreated control, the three products significantly reduced nematode eggs and juveniles in roots and juveniles in soil, with efficacies that were significantly comparable. In conclusion, the benefits of phytonematicides on the productivity of watermelon cv. ‘Congo’ and suppression of population densities of M. enterolobii were comparable.

QUANTUM YIELD, PHOTOSYNTHETIC PIGMENTS AND BIOMASS OF MINIWATERMELON UNDER IRRIGATION STRATEGIES AND POTASSIUM1

ABSTRACT This study was conducted with the objective of evaluating the quantum yield, photosynthetic pigments and biomass accumulation of mini watermelon cv. Sugar Baby, under strategies of irrigation with saline water and potassium fertilization. The experiment was conducted in a randomized block design, in a 8 × 3 factorial scheme, with three replicates, corresponding to eight strategies of irrigation with saline water applied at different phenological stages of the crop (control - irrigation with low-salinity water throughout the crop cycle, and salt stress in the vegetative, vegetative/flowering, flowering, flowering/fruiting, fruiting, fruiting/ fruit maturation and fruit maturation stage) and three potassium doses (50, 100 and 150% of the recommendation). The dose of 100% corresponded to 150 mg of K2O kg-1 of soil. Two levels of electrical conductivity of water were used: 0.8 and 4.0 dS m-1. Irrigation with water of 4.0 dS m-1 continuously in the vegetative and flowering stages increased the initial fluorescence and decreased the quantum efficiency of photosystem II of mini watermelon fertilized with 100 and 150% of K recommendation. Fertilization with 50% recommendation did not interfere in the fluorescence parameters of the mini watermelon, regardless of the irrigation management strategy. Chlorophyll a synthesis is inhibited by salt stress in the vegetative/flowering, flowering, flowering/fruiting, fruiting/maturation stages, as well as for total chlorophyll, except for the flowering stage. Application of 4.0 dS m-1 water in the flowering, fruiting/maturation and maturation stages promoted greater biomass accumulation in mini watermelon.

HEAT STRESS-INDUCED ALTERATIONS IN ANTIOXIDATIVE ENZYMES OF SOME PLANTS OF CUCURBITACEA FAMILY

The effects of high temperatures on melon cvs. Miranda and Poli, watermelon cv. Crimson Tide and zucchini cv. Asma leaves. The leaves obtained from plants were subjected to 35, 40, 45, 50, 55 and 60°C temperatures with gradual increments every 30-minutes. Samples, obtained at each treatment, were analyzed for ascorbic acid content, NADP(H) oxidase, catalase, gluthatione reductase, peroxidases activities and isoperoxidase patterns. The ascorbic acid content slightly increased parallel to temperature increment in zucchini but did not change in watermelon and in both melon cultivars. Melon cv. Poli exhibited comparatively less oxidative damage than cv. Miranda with a lower NAD(P)H oxidase activity. Heat stress induced NAD(P)H activity in watermelon and zucchini comparing to control plants. Results revealed that antioxidative enzyme activities were increased generally up to 50°C then decreased gradually in melon cultivars. Besides cv. Poli generally had higher enzyme activities than cv. Miranda. The activity of catalaes become prominent in watermelon while the activity of ascorbate peroxidase become prominent in zucchini. Acidic isoperoxidase bands with different relative mobility values were found in all species. Besides, basic isoperoxidase band could not be determined in both melon cultivars and watermelon while a basic isoperoxidase band was found in zucchini.

Gas exchange, growth, and production of mini-watermelon under saline water irrigation and phosphate fertilization

In the semi-arid region of Northeastern Brazil, due to the occurrence of excess salts, both in the water and soil, plants are constantly exposed to various conditions of abiotic stress. Thus, it is extremely important to identify methods capable of minimizing the effects of salt stress on plants as a way to ensure the expansion of irrigated areas. In this context, the objective of this study was to evaluate the gas exchange, growth, and production of mini-watermelon irrigated with saline waters and fertilized with phosphorus. The experiment was conducted in pots under greenhouse conditions in Pombal, PB, Brazil, using a randomized block design in a 5 x 4 factorial scheme, corresponding to five levels of electrical conductivity of irrigation water—ECw (0.3, 1.3, 2.3, 3.3, and 4.3 dS m-1), four phosphorus doses— PD (60, 80, 100, and 120% of the recommendation), and with three replicates. Watermelon plants cv. Sugar Baby were sensitive to water salinity greater than 0.3 dS m-1, with more pronounced inhibition of gas exchange, growth, and production. Reduction in the CO2 assimilation rate of watermelon plants cv. Sugar Baby was associated with factors of stomatal and non-stomatal origin. Phosphorous doses corresponding to 73 and 88% of the recommended values promoted an increase in the intercellular CO2 concentration and stem diameter of mini-watermelon plants. P2O5 doses ranging from 60 to 120% of the recommendation did not mitigate the effects of salt stress on the cultivation of watermelon cv. Sugar Baby.

Production of watermelon irrigated with saline water in mulched Entisol with potassium fertilization

The adjustment in the growing season associated with cultural practices can mitigate the negative effects of salinity on crop production. In this context, the objective of this study was to evaluate the production components of watermelon cv. Crimson Sweet under the effects of irrigation with saline water, soil cover and potassium doses in crops during dry and rainy seasons. The treatments were arranged in a split plot with 2 x 2 x 4 scheme, with the electrical conductivity of the irrigation water (0.3 and 3.0 dS m-1) in the main plot, and the combinations between soil mulch (without and with) and doses of potassium (0, 40, 80 and 120 kg ha-1 of K2O) in the subplots, distributed in randomized blocks. Final stand, number of fruits per plant, average fruit weight, production per plant and yield were evaluated. The data were subjected to analysis of variance and potassium doses were evaluated by regression. In the rainy season, watermelon was more productive than in the dry season even under irrigation, with higher number of fruits and production per plant and yield. Irrigation using water with electrical conductivity of 3.0 dS m-1 should be used with moderation in watermelon crop, as it did not compromise yield. Potassium chloride application is not recommended in soil with intermediate potassium content, because it reduced the number of fruits per plant and yield. The use of mulch is recommended in watermelon cultivation, since it increased the number of fruits and production per plant.

Effect of Citrullus amarus accessions on the population dynamics of Meloidogyne incognita and M. javanica and watermelon yield

The aims of this study were to determine i) the effect of grafted watermelon cv. Sugar Baby onto C. amarus accessions BGV0005164 and BGV0005167 on M. incognita and M. javanica population growth estimated by means of the values of maximum reproduction rate, maximum nematode density and equilibrium density in pot experiments; ii) the effect of increasing nematode densities on plant productivity in pot experiments; and iii) the effect of repeated cultivation of watermelon cv. Sugar Baby grafted onto both C. amarus accessions and onto C. lanatus ‘Robusta’ during two seasons in a plastic greenhouse on M. incognita reproduction, disease severity, crop yield and selection for nematode virulence. In pot experiments, the values of maximum reproduction rate, maximum nematode density and equilibrium density of M. incognita were 37 %, 72 % and 68 % lower in watermelon grafted onto BGV0005164 than in ungrafted, and 28 %, 76 % and 77 % lower when grafted onto BGV0005167. Regarding M. javanica, the values of maximum reproduction rate, maximum nematode density and equilibrium density in watermelon grafted onto BGV0005164 were 88 %, 65 % and 14 % lower than in ungrafted, and 80 %, 76 % and 33 % lower when grafted onto BGV0005167. Dry shoot weight of ungrafted and grafted watermelon inoculated with a range of nematode densities between 0 and 1200 s-stage juveniles per 100 cm3 of soil was not affected, irrespective of the nematode isolate. In the plastic greenhouse experiment, M. incognita reproduced less in grafted than in ungrafted watermelon. Disease severity was higher in ungrafted than in grafted watermelon. The level of resistance of both C. amarus accessions was not affected after two-year cultivation, but it decreased from moderately resistant in 2017 to slightly resistant in rootstock ‘Robusta’. Watermelon grafted yielded between 2.9 and 5.6 kg more per plant than the ungrafted in 2017, and between 2.0 and 2.7 kg more per plant in 2018. In conclusion, C. amarus accessions BGV0005164 and BGV0005167 performed as poorer hosts to M. incognita and M. javanica. Watermelon grafted onto these C. amarus accessions improved fruit yield when they were cultivated in nematode infested soils without affecting its level of resistance to M. incognita after two consecutive crops.

Rootstock and Plastic Mulch Effect on Watermelon Flowering and Fruit Maturity in a Verticillium dahliae–Infested Field

Separately, grafting and the use of plastic mulch can increase yield, quality, and early harvest of watermelon (Citrullus lanatus), especially when plants are under biotic and/or abiotic stress. A 2-year field study was conducted to evaluate the combination of four different rootstocks and two types of plastic mulch (black and clear) on date of watermelon first flowering, fruit ripening, yield, and fruit quality when plants were exposed to Verticillium dahliae. Seedless watermelon cv. Secretariat was grafted onto rootstocks Lagenaria siceraria cv. Pelop, Benincasa hispida cv. Round, and two interspecific hybrid squash rootstocks Cucurbita maxima × C. moschata cvs. Super Shintosa and Tetsukabuto, with nongrafted ‘Secretariat’ as the control. Fruit were harvested 0, 7, and 14 days after both the leaflet and tendril attached to the fruit pedicel were completely dry (fruit considered to be physiologically mature). The area under the disease progress curve (AUDPC) values for verticillium wilt were not different for mulch type in either year, although the overall AUDPC value was greatly reduced in the four grafted treatments (227) compared with nongrafted (743). There was no difference in days to male or female flowering due to mulch type or year, and rootstock did not affect first flowering of male flowers. Female flowering was 14 and 11 days later in 2018 and 2019, respectively, for ‘Secretariat’ grafted onto bottle gourd ‘Round’ compared with ‘Secretariat’ grafted onto ‘Tetsukabuto’. Female flowering of ‘Secretariat’ on ‘Round’ was also 7 days later compared with nongrafted ‘Secretariat’ both years. However, days to first harvest was not different with mulch or rootstock and was 92 days after transplanting (DAT) in 2018 and 114 DAT in 2019. There was no difference in yield (fruit number and weight) due to year, harvest date, or mulch, but there was a difference due to grafting. ‘Secretariat’ grafted onto ‘Super Shintosa’ had the greatest total number and weight of fruit per plant (3.7 and 14.8 kg, respectively), and nongrafted ‘Secretariat’ had the lowest (0.7 and 3.2 kg, respectively). Fruit quality attributes hollow heart formation (rating 3.2/5 on average), hard seed count (6 on average), total soluble solids (11% on average), and lycopene content were not different among mulch type, rootstock treatment, or harvest date; however, lycopene content did differ due to year (52.44 and 32.51 µg·g−1 in 2018 and 2019, respectively). Flesh firmness was highest for watermelon grafted onto ‘Super Shintosa’ rootstock (6.7 N) and lowest for nongrafted watermelon (4.3 N). Overall, rootstocks reduced verticillium wilt severity and increased fruit yield whereas mulch had no effects, and 5 V. dahliae colony forming units (cfu)/g of soil may be the minimum level for impact on watermelon fruit yield.

Initial development of watermelon in fuction of substrates and irrigation with saline water

We evaluated the initial development of watermelon cv. Crimson Sweet seedlings grown in different organic substrates and electrical conductivity of irrigation water. The experiment was carried out in a greenhouse between January and March of 2017. The experimental design was in randomized blocks with factorial arrangement 3 x 5. The treatments were combinations of three substrates: soil + bovine manure (SBM) (1:1); soil + sheep manure (SSM) (1:1) and commercial substrate Basaplant® (CS), and five electrical conductivity of irrigation water (ECiw): C1 – 0.3 dS m-1; C2 – 1.5 dS m-1; C3 – 2.7 dS m-1; C4 – 3.9 dS m-1 and C5 – 5.1 dS m-1. Plant height, number of leaves, stem diameter, root fresh mass, stem fresh mass, leaf fresh mass, root dry mass, stem dry mass, and leaf dry mass were evaluated at 37 days after sowing (DAS). The interaction between substrate x ECiw significantly affected the variables plant height, number of leaves, stem fresh mass and leaf fresh mass; all the analyzed variables were affected by substrate factor, while plant height, number of leaves, root dry mass, stem dry mass, and leaf dry mass were affected by ECiw. It is possible to produce watermelon cv. Crimson Sweet seedlings using water with electrical conductivity up to 2.86 dS m-1 associated with commercial substrate and up to 2.67 dS m-1 associated with sheep manure. It can be inferred that the use of commercial substrate is more suitable for the production of watermelon cv. Crimson Sweet seedlings.

Application strategies of saline water and nitrogen doses in mini watermelon cultivation

Salt stress is highlighted as one of the limiting factors for the establishment of agriculture in the semiarid region of Northeastern Brazil. In this context, it is essential to look for new strategies aiming at minimizing the effects of salt stress on the crops. The present work aimed to evaluate the photochemical efficiency, photosynthetic pigments, and growth of the watermelon cv. Sugar Baby under different use strategies with saline waters and nitrogen fertilization. The experiment was conducted in a protected environment at the Center of Technology and Natural Resources of the Federal University of Campina Grande, municipality of Campina Grande, Paraíba. An experimental design in randomized blocks was adopted, arranged in a 6 x 2 factorial scheme, with six management strategies of water salinity and two nitrogen doses (corresponding to 50 and 100% of the recommendation), with five replications. Two salinity levels of the irrigation water were studied, one with low and another with a high level of electrical conductivity of the water (ECw = 0.8 and 3.2 dS m-1). The watermelon cv. Sugar Baby expressed higher sensitivity to salt stress in the flowering phase, with a decrease in the synthesis of chlorophyll b, chlorophyll total, and carotenoids. The 50% dose of N provided an increment in the initial fluorescence, stem diameter, and the number of leaves of the watermelon cv. Sugar Baby. The length of the main branch of the watermelon plants decreased with the salt stress applied in the fructification phase; however, the fertilization with 100% of N stimulated a higher growth when the irrigation with saline waters was performed at the vegetative and flowering phases.

CRESCIMENTO E MARCHA DE ACÚMULO DE NUTRIENTES EM MELANCIA cv. TOP GUN EM VARZÉA IRRIGADA NO TOCANTINS

Um dos empecilhos ao crescimento da área cultivada com melancia tem sido a escassez de informações técnicas, sobretudo relativas à nutrição da cultura, o que pode afetar diretamente na produtividade e qualidade dos frutos. A marcha de absorção de nutrientes é uma ferramenta fundamental para o conhecimento da exigência nutricional da planta em diferentes estádios fenológicos, mostrando a época certa para aplicação dos nutrientes. Diante o exposto, este trabalho teve como objetivo determinar o crescimento e marcha de acúmulo de macronutrientes pela cultura da melancia cv. Top Gun em área de várzea no município da Lagoa da Confusão – TO. O experimento foi conduzido em propriedade rural localizada no município da Lagoa da Confusão – TO, no período de junho a agosto de 2016. O delineamento experimental utilizado foi em blocos casualizados com cinco épocas de coleta das plantas (15, 30, 45, 60 e 75 dias após a semeadura), em quatro repetições, sendo que em cada repetição foram coletadas duas plantas. Após cada coleta, as plantas foram fracionadas em parte aérea (ramas e folhas) e frutos, para determinação da matéria seca constante. Posteriormente realizou-se a determinação dos teores dos nutrientes N, P, K, Ca, Mg e S, sendo utilizado o método de extração por digestão nitro-perclórica. Os nutrientes mais acumulados pelas plantas de melancia durante o ciclo foram K, N, Ca, Mg, P e S, com 101,27, 75,54, 59,45, 14,91, 13,09 e 5,84 kg ha-1, respectivamente. Os nutrientes mais transportados pelos frutos foram K, N, P, Mg, Ca e S, correspondendo a 80,56, 50,96, 11,16, 6,45, 5,93 e 4,88 kg ha-1, respectivamente. O período de maior acúmulo de matéria seca em plantas de melancia cv. Top Gun foi de 30-45 DAS para a parte aérea (ramas e folhas) e 60-75 DAS para os frutos.
 Palavras-chave: Citrullus lanatus L.; desenvolvimento de plantas; macronutrientes; marcha de absorção.

Analisis Strategi Pengembangan Agribisnis Semangka (Citrullus lanatus) Pada CV Tani Makmur Di Kabupaten Jombang

Fruits are a source of vitamins and minerals needed by the body. Apart from being a source of vitamins and minterals, watermelon is one type of fruits that have a high economic value. One company that seizes the watermelon business opportunity is CV Tani Makmur. To maintain the business of watermelon fruit, CV Tani Makmur party needs to do a strategy for the company to grow and avoid the loss. The purpose of this research is (1) An analize the development strategi of watermelon agribusiness, (2) Identify development strategi of internal and external area. This research was conducted from February to June 2017. The results of internal environmental analysis with IFE matrix shows that the business of watermelon CV Tani Makmur has a total score of 3.1234. This value is above the average value of 2.5 indicating that the development of the watermelon business CV Tani Makmur is above average, ie the company is able to utilize its strength quite well. In addition, the company can minimize its weaknesses quite well. While the results of external environmental analysis with the EFE matrix shows that the business of watermelon CV Tani Makmur has a total score of 2.3079. This value is below the average score of 2.5 indicating that in the business development of watermelon fruit, CV Tani Makmur less respond to opportunities that exist. In addition, firms are less able to avoid threats to the watermelon business. Companies can be managed with grow and build strategies. The result of the strategy with the SWOT matrix resulted in seven alternative strategies. The QSP matrix resulted in the priority of the alternative strategy in the business strategy of watermelon fruit of CV Tani Makmur with the highest STAS (Sum Total Attractivity) score is to develop the human resources performance to increase the production and the broader target market with STAS of 5.4266. This strategy is a strategy of utilizing the company's strength to overcome the weakness of the watermelon business of CV Tani Makmur.

Arbuscular Mycorrhizal Fungi Inoculation to Enhance Chilling Stress Tolerance of Watermelon

In this study the positive effects of Glomus intraradices symbiosis on growth, physiological and biochemical attributes of watermelon (Citrullus lanatus) cv. “Crimson Sweet” and “Charleston Gray” in response to chilling stress were investigated. When subjected to chilling stress, arbuscular mycorrhizal fungi (AMF)-inoculated watermelon seedlings exhibited significantly higher root and shoot dry mass than non-AMF-inoculated plants. AMF symbiosis also improved chilling stress in watermelon seedlings via alterations in chlorophyll content and photosynthesis efficiency. Notably, AMF inoculation resulted in reduced chilling-induced oxidative stress evident by significantly decreased accumulation of H2O2 and malondialdehyde (MDA). Chilling stress enhanced leaf electrolyte leakage of watermelon seedlings, while inoculation of AMF significantly ameliorated electrolyte leakage by 9.91 and 11.58% in “Crimson Sweet” and “Charleston Gray”, respectively, under 36 h of chilling stress. AMF symbiosis combined with 36 h chilling stress significantly induced peroxidase (POX) activity (1.26- and 1.17-fold in “Crimson Sweet” and “Charleston Gray”, respectively) compared with non-AMF-inoculated seedlings. These results indicate that AMF symbiosis could play an important role in improving chilling resistance of watermelon seedlings by restoring photosynthesis efficiency and relieving chilling-induced oxidative stress.

Cucurbitaceae Germplasm Resistance to Verticillium Wilt and Grafting Compatibility with Watermelon

Grafting is used in watermelon [Citrullus lanatus (Thunb.) Matsum and Nakai] production as a means to combat soilborne diseases. To support the development of new rootstock cultivars in the United States, we screened cucurbit germplasm accessions for resistance to verticillium wilt (caused by Verticillium dahliae Kleb.) and for compatibility as watermelon rootstocks. Screening was done using a field naturally infested with V. dahliae [5 and 7.5 colony-forming units (cfu)·g−1 soil in 2017 and 2018, respectively], and plants were inoculated at transplanting (1.5 and 104 cfu of V. dahliae per plant in 2017 and 2018, respectively). In 2017, 56 germplasm accessions from three genera commonly used as rootstocks, Cucurbita, Lagenaria, and Benincasa, were sourced from the U.S. Department of Agriculture (USDA) National Plant Germplasm System and area under the verticillium wilt (disease) progress curve (AUDPC) values ranged from 16 to 397. The 14 accessions with the lowest AUDPC values and good germination (>40%) were used as rootstocks along with the commercial rootstock cv. Tetsukabuto (control), and all were grafted with watermelon cv. Secretariat as the scion in 2018. Grafted plant survival rate was greatest for ‘Tetsukabuto’ (90%) and the accession PI 381840 (L. siceraria) (89%), and ranged from 22% to 85% for all other accessions. All grafted treatments that produced mature fruit in 2018 tended to flower at the same time as nongrafted ‘Secretariat’, with first male and female flowers occurring in 45 to 50 days and 44 to 51 days after transplanting, respectively. There were no significant differences in AUDPC values due to grafting or when accessions were compared with ‘Tetsukabuto’. Only six accessions produced mature fruit when grafted with ‘Secretariat’, indicating they were compatible for watermelon grafting. Fruit weight and number as well as total soluble solids, pH, lycopene content, rind firmness and thickness, and dry matter content were similar for all accessions and ‘Tetsukabuto’ grafted on ‘Secretariat’. Only fruit flesh firmness differed and was highest for ‘Secretariat’ grafted on ‘PI 491316’ and lowest for ‘Secretariat’ grafted on ‘PI 49174’. The six verticillium wilt-tolerant accessions that were compatible with watermelon could potentially be used as rootstocks or as sources of genetic resistance in rootstock breeding programs.

WATERMELON INITIAL GROWTH UNDER DIFFERENT HYDROGEL CONCENTRATIONS AND SHADING CONDITIONS

ABSTRACT Watermelon (Citrullus lanatus) belongs to the plant family Cucurbitaceae. It is cultivated in many regions of Brazil, particularly in rainfed areas; thus, it is subject to the problems arising from irregular rainfall. Hydrogel is a soil conditioner used to retain and provide water to plants for long periods of time. Therefore, incorporating hydrogel into the soil should increase water availability for watermelon cultivation, and may be an alternative method to reduce the risk of water deficit. This study evaluated the effect of different concentrations of hydrogel on the initial growth of watermelon cv. 'Crimson Sweet' under different shading conditions. The experiment was carried out in a greenhouse with completely randomized design with a 4×3 factorial scheme. The treatments consisted of four hydrogel doses (0.0; 1.5; 3.0; and 6.0 g L-1 substrate), three shading conditions (under full sun; black shade net, and red shade net, both with 50% shading), and five replicates per treatment. The variables evaluated were plant height; stem diameter; shoot, root, and total dry matter; and leaf area. The best hydrogel dose for watermelon cultivation was 1.5 g L-1, but the higher doses impaired plant growth, regardless of shading conditions. The black net improved biomass accumulation in 'Crimson Sweet' watermelon, whereas the red net induced plant etiolation.

Standardization of Regeneration, Agrobacterium-Mediated Transformation, and Introduction of Nucleocapsid Gene of Watermelon Bud Necrosis Virus in Watermelon

Seven types of explants (proximal cotyledon, distal cotyledon, distal cotyledon leaves, proximal cotyledon leaves, distal hypocotyls, proximal hypocotyls, and basal petioles) of watermelon (Citrullus lanatus) cv. Sugar Baby were tested for their regeneration capacity on MS medium supplemented with different concentrations and combinations of hormones (BAP 0–3 mg/l alone and IAA 0–0.5 mg/l and BAP 0–3 mg/l together). The results showed that the proximal petiole cultured in MS + BAP (3 mg/l) showed the highest percentage of callus induction (28%) and shoot production (24%). The proximal cotyledons cultured in MS + BAP (2 mg/l) + IAA (0.1 mg/l) showed the highest regeneration frequency (76%). Agrobacterium tumefaciens strain EHA 105 carrying a binary vector pBI121 containing the GUS gene (s-glucuronidase) and kanamycin-resistance gene, nptII, was used to transform petiole explants of watermelon cv. Sugar Baby. Various conditions such as the agrobacterial concentration of OD600 0.6, infection time of 20 min, co-cultivation duration of 2 days and selection at 100 mg/l kanamycin were found as important parameters for the successful Agrobacterium-mediated transformation of watermelon. Further, a transgene construct using the nucleocapsid protein (NP) gene from watermelon bud necrosis virus (genus Tospovirus family Peribunyaviridae) was developed in pBI121 and used to transform watermelon. The successful transformation of petiole explant of watermelon with the GUS gene as well as the NP gene was confirmed by molecular assays, which showed a transformation efficiency of 14.2% and 0.375% with the GUS and NP gene, respectively.

Rootstock effects on seed yield and quality in watermelon

This research was conducted to investigate rootstock effects on seed yield and quality in watermelon. The work was conducted in the experimental fields and laboratories of the Department of Horticulture of the University of Cukurova in the 2016 and 2017 growing seasons. Watermelon cv. Crimson sweet (CS) scion was grafted onto three different rootstocks (Cucurbita ‘NUN-9075’, Lagenaria ‘Argentario’, and citron watermelon ‘PI296341’). Plants were assessed according to their main stem length, main stem diameter, number of nodes, biomass, pollen production and development, fruit yield and quality, and seed yield and quality. NUN-9075/CS and Argentario/CS graft combinations resulted in higher average stem length, plant biomass, fruit yield and quality, seed yield, seed emergence, and germination percentage. There was no significant difference observed between graft combinations in pollen viability, pollen germination, and normal pollen production. No significant difference was observed between graft combinations in accelerated ageing (AA), and the seed germination decreased after AA of 192 h. In the second year (2017), there was higher main stem length, main stem diameter, total fruit yield, seed yield, and number of seeds per fruit compared to the first year (2016). Based on the results of this study, NUN-9075 rootstock performed better than other rootstocks; hence, it is recommended as the best rootstock.

Response of two Citrullus amarus accessions to isolates of three species of Meloidogyne and their graft compatibility with watermelon

The response of two Citrullus amarus accessions, BGV0005164 and BGV0005167, was assessed against different Meloidogyne arenaria, Meloidogyne incognita, and Meloidogyne javanica isolates in pot experiments and against M. incognita in plastic greenhouse. In the pot experiments, plants were inoculated with a second-stage juvenile per cm3 of sterile sand and maintained in a growth chamber at 25 °C for 50 days. The watermelon cv. Sugar Baby was included as a susceptible control for comparison. At the end of the experiments, the number of egg masses and eggs per plant was determined, and the reproduction index was calculated as the percentage of the number of eggs produced in the C. amarus accessions with regard to that produced in the susceptible cv. Sugar Baby. In the plastic greenhouse experiment, the ungrafted watermelon cv. Sugar Baby and watermelons grafted onto each of the C. amarus accessions and onto the watermelon rootstock cv. Robusta were cultivated from May to August 2016 in plots with nematode densities from 46 to 1392 J2 per 250 cm3 of soil at transplantation. At the end of the experiment, the galling index and the number of eggs per plant were determined, and the reproduction index was calculated. Additionally, the compatibility of the two accessions with the watermelon cv. Sugar Baby and the effect on fruit quality (weight, size, shape, firmness, pH, total soluble solids, and flesh color) were assessed under a hydroponic system in a greenhouse. The commercial rootstocks cv. Cobalt and cv. Robusta were also included. All the Meloidogyne isolates produced less egg masses and eggs per plant on the accessions than on Sugar Baby. Both accessions performed as resistant against M. arenaria, and from highly to moderately resistant to M. incognita and M. javanica in pot experiments. In the plastic greenhouse experiment, both C. amarus accessions performed as resistant to M. incognita. Both C. amarus accessions were compatible with the watermelon cv. Sugar Baby, but only the BGV0005167 accession did not influence the fruit quality. Then, the BGV0005167 accession is a promising rootstock for managing the three tropical root-knot nematode species without influencing watermelon fruit quality.