Search Results

You are looking at 21 - 30 of 449 items for :

  • " Citrullus lanatus " x
  • Refine by Access: All x
Clear All
Free access

Yun-Chan Huh, Seung-Ryong Cheong, and Jung-Myung Lee*

Common watermelons have an indeterminate growth habit with normal internode length, thus allowing the vine to grow indefinitely under the normal conditions. Watermelon breeders have identified four dwarf genes (dw-1, dw-1 s , dw-2, dw-3) and used these for developing dwarf watermelon cultivars. We discovered a naturally occurring new dwarf and seedless mutant (NDSM) from a landrace cv. Mudungsan that had been cultivated in the Mountain Mudung area nearby Gwangju City in Korea. The progenies of this mutant segregated in a ratio of 3 vine to 1 dwarf indicating a single recessive gene nature. Morphological characteristics of the NDSM were markedly different from those of the four known dwarf genotypes. NDSM plants grow shorter than 1 m in length with fan-shaped leaves and have fewer leaf lobes than normal plants, which could be clearly distinguished at 2 or 3 true leaf stage. Male and female flowers have just one petal and failed to open completely even at the anthesis. Even though there were some fertile pollen grains, the fruits of NDSM had no seed after fertilization. The F2 progenies, obtained from crossing `920533' (normal vine type) and NDSM, segregated in a ratio of 3 vine to 1 dwarf. All F1 plants from crosses between 2 dwarf types, `Sugar Bush' (dw-1dw-1) and `NH 9' (dw-2dw-2), and NDSM were normal, while F2 showed 9 vines, 3 dw-1 or dw-2 types, 3 NDSM types, and 1 double dwarf. The backcross generation segregated in a ratio of 1 vine to 1 dwarf. These results indicate that the genes for the NDSM and 2 dwarf types are non-allelic. We named this new dwarf genotype (NDSM) as dw-4 in addition to four dwarf genes previously identified.

Free access

Mike Stanghellini and Jonathan R. Schultheis*

In 1999 and 2000, a total of 28 diploid watermelon cultigens (released cultivars and advanced breeding lines) were evaluated for staminate flower and pollen grain production to assess their potential to serve as pollenizers (pollen source plants) in triploid watermelon production systems. Male reproductive output (staminate flower and pollen production) was quantified during the peak flowering and fruit setting phase of the cultigens under field conditions. The number of staminate flowers produced per plant per day, number of pollen grains produced per flower, and total number of pollen grains produced per plant per day (staminate flowers per plant x pollen grains produced per flower) differed greatly between cultigens (for all tests, P < 0.01). Staminate flower production by cultigens differed by year (P < 0.0003) and days-within-years (P = 0.0094), but pollen production between years by cultigens was stable (P = 0.3845). Total male reproductive output ranged from 134,206 pollen grains per plant per day for `Jamboree' to 321,905 pollen grains per plant per day for `Summer Flavor 500'. These studies demonstrate the genotypic variability in watermelon male reproductive output potential, and may assist growers in selecting an optimal diploid pollenizer for triploid watermelon production.

Free access

Michael S. Stanghellini, John T. Ambrose, and J.R. Schultheis

The need for alternative [non-honey bee (Apis mellifera L.)] pollinators continues to increase as the number of problems facing the American beekeeping industry increase. One readily available alternative pollinator source is commercially produced bumblebee (Bombus spp.) colonies. From 1997 to 1999, three studies were conducted to compare the pollination efficacy of bumblebee and honeybee pollinators on field-grown watermelon. The experiments documented 1) bee activity periods (the onset and termination of foraging behavior in association with watermelon anthesis and duration), 2) floral visitation rates (number of flowers visited per unit time by individual foragers), and 3) stigmatic pollen deposition (number of pollen grains deposited on stigmata during single bee visits to pistillate watermelon flowers over the course of anthesis). Bumblebees outperformed honeybees in all three comparative experiments. Bombus foragers initiated foraging activity 30 to 60 min before the appearance of the first honey bee foragers. Both bee types continued to forage throughout anthesis once appearing in the field. Individual bumblebees consistently visited two or more times the number of flowers per min than did honeybees (P < 0.0001) throughout the day excluding the initial 30 to 60 min when honeybees did not forage. The number of pollen grains deposited in an initial visit to stigmata by Bombus foragers was consistently greater than for honeybees (P < 0.001). For both bee types, pollen deposition was influenced by time of day, peaking at 0900 hr and then declining until 1200 HR, when the flowers closed. Both foraging rates and pollen deposition favored bumblebees over honeybees regardless of time of day.

Free access

N. Sari, K. Abak, M. Pitrat, J.C. Rode, and R. Dumas de Vaulx

Parthenogenetic haploid embryos of `Crimson Sweet', `Halep Karasi', `Sugar Baby' and `Panonia F1' watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] were obtained after pollination with γ-irradiated (200 or 300 Gy) pollen. Some globular and heart-shaped embryos were observed in fruit harvested 2 to 5 weeks after pollination. The number of embryos per 100 seeds was highest for `Halep Karasi'. After in vitro culture, 17 haploid plants were obtained and doubled haploid lines were generated after chromosome doubling using colchicine.

Free access

M.J. Lamb, G.H. Clough, and D.D. Hemphill Jr.

Watermelon [Citrullus lanatus (Thunb.) Matsum. and Nakai `Crimson Sweet'] was seeded in a commercial peat medium in multicell containers. Five NO3: NH4 ratios and five levels of supplemental Ca were combined factorially in a 100N-31P-265K mg·liter-1 pretransplant nutrition regime. The medium was amended with CaCO3 in 1989; the medium was not amended in 1990. Dry-matter accumulation had decreased with increasing NH4-N 3 weeks after seeding both years. In 1989, increasing NH4-N also had decreased seedling growth by the last sampling date due to decreased NH+ 4 uptake. Shoot N concentration was higher in 1990 than 1989, but N uptake was similar. On the first sampling date in both years, increasing the Ca concentration decreased seedling growth and increased medium electrical conductivity (EC). In 1990, increasing the Ca concentration raised shoot N concentration but did not increase seedling growth or N uptake. Either N form at 100 mg N/liter and Ca at 4 to 8 mmol·liter-1 were optimal for watermelon transplant production, but Ca at >8 mmol·liter-1 suppressed transplant growth.

Free access

John R. Duval and D. Scott NeSmith

Seeds of triploid watermelons [Citrullus lanatus (Thunb.) Matsum & Nakai] often germinate poorly, which prevents adequate stand establishment in both field and greenhouse environments. Methods of improving germination and emergence of these expensive seeds would reduce overall risk to growers, thus increasing the crop's market prominence. Seeds of `Genesis' triploid watermelon were subjected to three treatments: 1) seedcoat removal; 2) clipping the seedcoat opposite the radicle end; or 3) no seedcoat alteration; and were germinated on agar in the presence of a 0%, 1%, 2%, 4%, or 8% aqueous H2O2 at constant 28 °C in the dark. Seedcoat removal, clipping, and all levels of H2O2 increased final germination percentages relative to the control (no seedcoat alteration, no H2O2) by as much as 70%. Hydrogen peroxide levels >2% resulted in severe injury to germinating seeds. These findings suggest that germination barriers of triploid watermelon are seedcoat related, and that seedcoat alteration and H2O2 can overcome these barriers.

Full access

Stephen M. Olson, George J. Hochmuth, and Robert C. Hochmuth

Studies were conducted at the NFREC, Quincy, and AREC, Live Oak, Fla., to compare watermelon {Citrullus lanatus [(Thumb.) Matsum & Nakai]} plant establishment by transplanting and direct-seeding. Cultivars used were `Charleston Gray' in 1984, 1985, 1986, and 1989; `Jubilee' in 1988 and 1989; and `Crimson Sweet' in 1987 to 1990. Early yields were greater with transplants for all three cultivars in all years. With `Charleston Gray', total yields with transplants were higher in 1985 and 1989, but not in 1984 or 1986. The average fruit weights with transplants were also greater in 1985 and 1989 than in 1984 or 1986. With `Jubilee', total yield with transplants was higher in 1989, but not in 1988. Average fruit weight with transplants was greater in 1989 than in 1988. With `Crimson Sweet', total yields were higher with transplants in 1989 and 1990, but not in 1987 or 1988, but fruits were larger with transplanting compared to direct-seeding only in 1990. In all experiments, yields with transplants were never less than those with direct-seeded plants.

Free access

D.L. Hopkins, C.M. Thompson, and G.W. Elmstrom

Seedlings of 22 watermelon [Citrullus lanatus (Thunb.) Matsum. and Nakai] cultivars and two plant introductions were screened in the greenhouse for resistance to the fruit blotch bacterium. There were significant differences in disease severity among cultivars, but no cultivar was immune to the bacterium. In field tests, fruit of 18 commercial cultivars were inoculated individually or became infected naturally from diseased foliage. Cultivars with relatively resistant fruit included `Sugar Baby', `Jubilation', `Mirage', `Calsweet', `Crimson Sweet', `Royal Sweet', and `Sangria'. The more susceptible cultivars generally had a light-colored rind. Cultivar level of resistance to bacterial fruit blotch may not be sufficient under conditions conducive to severe disease development.

Free access

G.E. Boyhan, J.D. Norton, B.R. Abrahams, and H.H. Wen

In an anthracnose [Colletotricum obiculare (Berk. & Mont.) Arx.] screening test of 76 plant introductions (PIs), commercial Chinese watermelons [Citrullus lanatus (Thunb.) Matsum. & Nakai], and `Crimson Sweet', PI 512385 had the highest disease resistance with a mean rating of 4.5 (1= resistant, 9 = susceptible). In a second test with PI 512385, which included material with previously reported resistance (PIs 270550,326515, 271775,271779,203551, 299379, and 189225), and `Crimson Sweet' (susceptible control), PI 512385 had significantly higher resistance than `Crimson Sweet' but was not significantly more resistant than the other PIs evaluated. PI 512385 had a mean rating of 2.2 in the second test.

Free access

Claude E. Thomas, Amnon Levi, and Ellis Caniglia

Two hundred sixty-six Citrullus lanatus (Thumb.) Matsum. & Nakai accessions (Plant Introductions and named cultivars) were tested against a race 2 Sphaerotheca fuliginea (Schlechtend.: Fr.) Pollacci isolate to evaluate for resistance to powdery mildew disease. Growth room-grown seedlings were artificially inoculated with conidia from watermelon host leaves at 2-day intervals from the appearance of the first true leaf until test results data were taken, when the second true leaf was fully expanded. Plants were evaluated on a 1 to 9 scale of increasing disease severity. Disease indices (DIs) were calculated as weighted averages for each entry. All genotypes with resistant plants (powdery mildew rating 1 to 3) were reevaluated in a replicated test of 3 replications of 10 plants each. Disease indices were again calculated. Twenty-two plant introductions (PIs) and one named variety displayed intermediate resistance to powdery mildew in the replicated test with DIs ranging from 5.0 to 6.0.