Fusarium oxysporum f.sp. niveum (Fusarium wilt of watermelon).

Fusarium wilt of watermelon occurs throughout the world and is often a limiting factor in watermelon production. In China, 20-30% of watermelon production is normally lost in infested areas, and 100% mortality has been observed in fields planted with susceptible cultivars in Zhejiang Province (Lin, 1990). In a survey of 62 watermelon crops grown in plastic tunnels throughout the main production area of Cyprus, Fusarium wilt was found in all fields sampled despite the use of resistant cultivars (mainly Crimson Sweet). Mean incidence ranged from 37 to 70% in 1985 and 1986, and mean yields of marketable fruit were 38 and 10 t/ha, respectively (Ioannou and Poullis, 1991). In Aydin Province, Turkey, incidence ranged from 0.2 to 12% in fields in which the pathogen was isolated from symptomatic plants (Erİncİk and Döken, 2018). In Spain, in soil infested with unidentified races of F. oxysporum f.sp. niveum, yield loss in a triploid cultivar was 42 to 68% (Miguel et al., 2004). In South Carolina and Georgia, USA, yield losses in research fields naturally infested with race 2 averaged 62 and 83%, respectively, which represented a 91 and 55% loss in net returns per hectare, respectively, based on an average price of $USD 0.35 per kilogram of seedless watermelon fruit.

Fusarium oxysporum f.sp. niveum (Fusarium wilt of watermelon).

Fusarium wilt of watermelon occurs throughout the world and is often a limiting factor in watermelon production. In China, 20-30% of watermelon production is normally lost in infested areas, and 100% mortality has been observed in fields planted with susceptible cultivars in Zhejiang Province (Lin, 1990). In a survey of 62 watermelon crops grown in plastic tunnels throughout the main production area of Cyprus, Fusarium wilt was found in all fields sampled despite the use of resistant cultivars (mainly Crimson Sweet). Mean incidence ranged from 37 to 70% in 1985 and 1986, and mean yields of marketable fruit were 38 and 10 t/ha, respectively (Ioannou and Poullis, 1991). In Aydin Province, Turkey, incidence ranged from 0.2 to 12% in fields in which the pathogen was isolated from symptomatic plants (Erİncİk and Döken, 2018). In Spain, in soil infested with unidentified races of F. oxysporum f.sp. niveum, yield loss in a triploid cultivar was 42 to 68% (Miguel et al., 2004). In South Carolina and Georgia, USA, yield losses in research fields naturally infested with race 2 averaged 62 and 83%, respectively, which represented a 91 and 55% loss in net returns per hectare, respectively, based on an average price of $USD 0.35 per kilogram of seedless watermelon fruit (Keinath et al., 2019a).

Predicting Hollow Heart Incidence in Triploid Watermelon (Citrullus lanatus)

In triploid (seedless) watermelon [Citrullus lanatus var. lanatus (Thunb. Matsum. and Nakai)], hollow heart (HH) is a disorder that is expressed as a crack in the center of the fruit that expands to an open cavity. Although HH incidence and severity is part of a screening process for marketable watermelon fruit during cultigen evaluations, HH incidence is highly variable with growing season, even when the best cultural practices are used. Placental tissue firmness is also measured because firmness is related to the marketability of watermelon and may be related to HH. Genetic and environmental factors can influence watermelon HH development, including plant genetics, pollen amount and viability, pollinator activity, and temperature and rainfall fluctuations. We used seedless watermelon cultigen evaluation data collected over 3 years (2012–14) to determine the relationship between germplasm HH and tissue firmness. Transplanted watermelon representing 30 to 44 cultigens per year were grown at the Central Crops Research Station, Clayton, NC, and interplanted with pollenizers ‘Ace’ and/or ‘SP-6’. Harvested fruit were cut length-wise and rated for HH incidence and severity. Flesh firmness was determined by a handheld penetrometer at five locations in the flesh (stem end, top side, ground spot, blossom end, and heart). A common cultigen subset, consisting of 13 cultigens that were grown in all three experiments, was used for analysis of HH severity and incidence, and placental firmness. The presence of HH was negatively correlated with tissue firmness in both the large multiyear cultigen set (R2 = −0.32; P = 0.0001) and the common cultigen set (R2 = −0.78; P = 0.0001). Cultigens with lower watermelon tissue firmness values had higher HH incidence and severity. By using multiyear cultigen studies and logistic regression, we were able to detect trends for cultigen susceptibility to this highly variable disorder. Using logistic regression, the probability of HH development was highest for ‘Bold Ruler’, ‘Liberty’, and ‘Affirmed’, and lowest for ‘Maxima’ and ‘Captivation’. The identification of cultigens with a tendency for higher or lower rates of HH will be useful for further research of the causes of HH. Measurements of placental flesh firmness may be useful indicators of susceptible cultigens.

Evaluating Cucurbit Rootstocks to Prevent Disease Caused by Pythium aphanidermatum and P. myriotylum on Watermelon

Pythium species cause root and stem rot in watermelon (Citrullus lanatus), but cucurbit rootstocks used to graft watermelon have not been evaluated for resistance. P. aphanidermatum and P. myriotylum were inoculated onto 15 nongrafted watermelon, citron (Citrullus amarus), bottle gourd (Lagenaria siceraria), and interspecific hybrid squash (Cucurbita maxima × C. moschata) cultivars in a growth chamber. Watermelon was more susceptible than bottle gourd and interspecific hybrid squash at 20 and 30°C. Twenty-one cultivars were inoculated in a field with an equal blend of both Pythium species. Interspecific hybrid squash was less susceptible than bottle gourd and watermelon in 2018 and 2019. Seedless watermelon cultivar Tri-X 313 was grafted to one citron, one bottle gourd, and three interspecific hybrid squash rootstocks. Plants were inoculated in the field as described. Grafting to interspecific hybrid squash rootstocks reduced disease incidence compared with nongrafted controls in 2018 and 2019. Mefenoxam and propamocarb applied at transplanting did not affect disease compared with non-fungicide-treated plots. Grafting to interspecific hybrid squash Camelforce significantly increased total and marketable fruit numbers and total weight in 2019 compared with the nongrafted control. In summary, interspecific hybrid squash was consistently resistant to Pythium, demonstrating resistance and utility in watermelon grafting.

PENGARUH ANTHESIS JANTAN DAN WAKTU POLINASI TERHADAP TINGKAT KEBERHASILAN PEMBENTUKAN BENIH SEMANGKA TANPA BIJI (Citrullus Lanatus Thunberg.)

Triploid watermelon seeds are produced from the crossing between watermelon diploid as males and tetraploid watermelons as females. The success of triploid seed formation is influenced by the success of pollination determined by pollen viability which is characterized by the period of anthesis and peptic receptivity by the time of pollination. This experiment was conducted in Jember on 2018. The Factorial Randomized Block Design, 3x3 with three replications, was concucted to determine the effect of male anthesis period and pollination time on the success rate of seedless watermelon seed formation. The results showed that no significant interaction of the male anthesis period and the time of pollination effect. Pollens harvested during pre anthesis give the best pollination results. On the other hand, the best pollination can be done at 07.30 – 08.30 am Keywords: anthesis, pollination, seeds, seedless watermelon.

Organic matter and moringa leaf extract’s effects on the physiology and fruit quality of red seedless watermelon (Citrullus lanatus)

This study was designed to assess the effects of different types of organic matter on the quality and biochemical properties of red seedless watermelon. The research was a single factor experiment, which involved six (6) treatments and four (4) replications. Watermelon grown and harvested from five (5) different organic matter sources, namely; vermicompost (VC), poultry manure (PM), cow dung (CD), goat dung (GD), and moringa leaf extract (MLE), at the rates of 10 ton, 20 ton, 30 ton, 30 ton, and 3000 L ha-1, respectively, were used in this study. The results revealed that the treatment of vermicompost improved the chlorophyll content, chlorophyll fluorescence, stomatal conductance, internal carbon dioxide, net photosynthetic rate, fruit weight and mineral nutrient content of watermelon. The application of cow dung reduced the rind thickness and increased the TSS and antioxidant activity of the watermelon. The goat dung treatment significantly affected fruit size, juice content and the pH content of the watermelon’s fruit juice. The poultry manure (PM) and moringa extract (MLE) treatments resulted in the highest anthocyanin content of all the watermelon. Although all the organic matter, in their unique ways, improved the quality of red seedless watermelon, the study shows that the vermicompost application had better growth, yield and improvement in the quality of watermelon.

Intercropping Seedless Watermelon and Cotton

Intercropping of seedless watermelon [Citrullus lanatus (Thumb.) Matsum. & Nak.] and cotton [Gossypium hirsutum (L.)] in the eastern geographical area of South Carolina requires changes in normal crop-management programs but has the potential to improve grower profits compared with typical production of each crop separately. The alteration and timing of several normal crop-production practices for both crops can present challenges and must be well-defined for successful intercropping of watermelon and cotton in the region. Notable adjustments in production for watermelon are delayed planting date, reduced row spacing and bed width, and modification of herbicide applications. Significant changes in normal cotton production also include modification of herbicide applications, but additional considerations, such as temporal limits on side-dressed fertilizer and insecticide applications, are needed because of the raised beds and plasticulture used for watermelons and also because of labeling restrictions for pesticides across crops. Research was conducted to 1) identify modifications in standard crop-management procedures for watermelon and cotton intercropping; and 2) determine the feasibility and profitability of intercropping the crops. Although there was a slight numerical reduction in intercropped watermelon yield each year, there were no significant differences in total watermelon yield between intercropping and watermelon monoculture in any of the years. There were also no significant differences in watermelon fruit quality parameters (size, brix, hard seed, hollow heart) in any of the years. Intercropped cotton yield was significantly less than monoculture cotton yields in each of the three years. The net income from intercropping in each year was slightly less than the net income from watermelon monoculture.

Improving the grafted-plant rate in triploid watermelons by optimizing the water moisture in substrates and the usage of scion

The cost of growing triploid watermelon seedlings has increased due to their low-efficiency grafting. The first priority in growing seedless watermelon seedlings is increasing the grafted-plant and seed-utilization rates. This study aimed to improve the grafted-plant rate by screening the most suitable substrate formulation, optimizing water moisture in the substrate, and evaluating the effect of different scions to improve seed-utilization rate. Five combinations of substrate (S1 to S5) and seven relative humidity levels (45%, 50%, 55%, 60%, 65%, 70%, and 75%) were used. Three types of scions (yellow bud, Ts-1; two cotyledons did not unfold, Ts-2; and first true leaf appeared, Ts-3) were tested. Results showed that the combination of S1 exhibited the best seed-utilization rate which was 71.6%. Moreover, the most suitable water moisture in the substrate ranged from 50% to 55%. The usage of the scion from Ts-3 significantly increased the grafting survival, grafted plant and seed-utilization rates by 13.7%, 10.1% and 22%, respectively, compared with the conventional method. Our study suggested that the best time to use the scion and the rootstock was during the seedling stage when the first true leaf unfolded. The proposed method decreased the production cost of seedlings and significantly improved the efficiency of grafting procedures. The results of this work are applicable to the technique of growing seedlings and can thus guide growers of high-quality grafted plants of triploid watermelon.