The effect of soluble potassium silicate applied to cucumber (Cucumis sativus L.), muskmelon (C. melo L.), and zucchini squash (Cucurbita pepo L.) on the severity of powdery mildew was examined. Application methods included amending nutrient solutions to a concentration of 1.7 mm Si and foliar sprays containing 1.7, 8.5, 17, and 34 mm Si. Untreated plants and plants sprayed with distilled water were used as controls. The leaves of all plants were inoculated with known concentrations of conidia of Sphaerotheca fuliginea (Schlecht.:Fr.) Poll. (cucumber and mu&melon) or Erysiphe cichoracearum DC.: Merat (zucchini squash) 1 day after the sprays were applied. Inoculated leaves on plants receiving the Si-amended nutrient solution or foliar sprays of ≥ 17.0 mm Si developed fewer powdery mildew colonies than those on control plants. Results of a separate experiment that included a potassium spray, indicated that the active ingredient of the potassium silicate sprays appears to be Si. Experiments to test the persistence of Si foliar sprays on cucumber demonstrated that a 17 mm Si spray applied 7 days before inoculation with S. fuliginea reduced mildew colony formation.
Jim Menzies, Pat Bowen, David Ehret, and Anthony D.M. Glass
R. E. Williamson and T. N. Gray
Cabbage, Brassica oleracea, var. Capitata L.; squash, Cucurbita pepo Alef.; and tendergreen, Brassica perviridis Bailey were grown at various water table depths in sheltered soil tanks on a fine sandy loam and a loam soil to evaluate the effects of high water table and soil type on growth and yield of these vegetable crops. Yields of the 3 species increased with water table depth to a depth of 76 to 102 cm. On both soil types the 15-cm water table depth caused considerable yield reduction and chlorosis for the 3 species. For maximum yields deeper water table depths were needed with loam than with sandy loam soil. Yield of cabbage was not significantly increased at water table depths greater than 30 cm in either soil. Squash yield was highest at water table depths of 61 to 76 cm in the fine sandy loam and 91 to 102 cm in the loam soil. Tendergreen yield was not significantly increased by water table depths greater than 61 cm in either soil.
Jack A. Hartwigsen and Michael R. Evans
Seed of Pelargonium ×hortorum L.H. Bailey `Freckles' (geranium) and Tagetes patula L. `Bonanza' (marigold) were soaked for 12, 24, or 48 h in solutions containing 0 (deionized water), 5000, 10,000, or 15,000 mg·L-1 humic acid (HA) or nutrient controls (NC) containing similar levels of nutrients prior to planting. Soaking in deionized water (DI) and NC treatments had no significant effect on root fresh weight. However, several of the HA treatments increased root fresh weight of marigold seedlings, and all increased geranium root fresh weight. Percentage of germination and shoot fresh weight were not significantly affected by treatment. Seed of Cucumis sativus L. `Salad Bush' (cucumber), Cucurbita pepo L. `Golden Summer Crookneck' (squash), `Freckles' geranium and `Bonanza' marigold were sown into 15-cell plug trays (5 mL volume), and the substrate was drenched with DI, 2500 or 5000 mg·L-1 HA, or 2500 or 5000 mg·L-1 NC. DI and NC treatments did not affect root fresh weight. However, cucumber, squash, and marigold seedlings germinated in substrate drenched with 2500 and 5000 mg·L-1 HA and geranium seedlings germinated in substrate drenched with 2500 mg·L-1 HA had significantly higher root fresh weight than did seedlings from all other treatments. Percentage of germination and shoot fresh weight were not significantly affected by treatment. `Salad Bush' cucumber and `Golden Summer Crookneck' squash seedlings germinated on germination towels soaked with 2500 or 5000 mg·L-1 HA, had significantly higher root fresh weight than did seedlings germinated on towels soaked with DI or NC solutions. Treatment with HA did not affect shoot fresh weight or the number of lateral roots. However, HA treatment increased the total length of lateral roots. The increase in lateral root growth occurred primarily in lateral roots developing from the lower hypocotyl.
Erik B. G. Feibert and Clint C Shock
Eight winter squash varieties (Table Ace Acorn, Sweet Dumpling, Waltham Butternut, Honey Boat, Sugar Loaf, Spaghetti, Gold Keeper, and Kabocha) were placed in storage 3 weeks after harvested and were stored for 6, 12, or 16 weeks at 5, 10, or 15°C and 50, 60, or 70 percent relative humidity. Before storage Spaghetti squash had low dry weight and low sugars while Kabocha, Sugar Loaf, and Honey Boat had high dry weight and high sugars. Squash of all varieties suffered high spoilage when stored at 5°C. Water losses increased with temperature or with storage at 50 percent relative humidity. Considering both spoilage and water loss, marketable fruit was highest when squash was stored at 10°C or 15°C and 60 or 70 percent relative humidity. Squash sugars were maintained with storage at 5°C and 10%. Squash can be stored for several months at 10°C and 60 to 70 percent relative humidity with little fruit loss or loss of sugar.
J. Brent Loy
Premature harvest of acorn squash is a widespread problem because fruits reach maximum size and optimum color within 20 days after pollination (DAP), well before peak dry matter and sugar content occur. The present study was conducted to determine the relationship between harvest date and physiological factors affecting eating quality in Cucurbita pepo L. squash. In the summer of 2005, C. pepo squash cultivars were evaluated at three harvest dates, 25, 35, and 45 days after pollination (DAP), with or without a 10-day storage period at 21 °C. Four F1 hybrid cultivars carrying powdery mildew tolerance (PMT) were evaluated: a semi-bush, commercial acorn cultivar (`Tip Top'), a high quality experimental acorn, bush hybrid (NH1634), and two sweet dumpling-type, semi-bush hybrids (NH1635 and 1636). Data were collected on mesocarp DW, oBrix (soluble solids), and partitioning of biomass between mesocarp tissue and developing embryos during storage. Peak DWs of 20% to 21% occurred at 25 DAP in NH1634, 1635 and 1636, and at 35 DAP in Tip Top (19.5 %). At 25 DAP, Brix was low (means of 5.9 to 7.2) across all cultivars. With harvest at 25 DAP plus 10 days storage, oBrix was low in Tip Top (7.1), but was higher than 10 in NH1634 and NH1636. Brix reached near maximum (13 to 15) at 45 DAP in NH1634, 1635 and 1636, and at 55 DAP in Tip Top (12). Embryos were small (DW = 8 to 19 mg) at 25 DAP and grew fairly linearly to a maximum at 55 DAP. Mean embryo DW at 55 DAP was 87.5 mg for Tip Top, 76.9 mg for NH1636, 57.1 mg for NH1634, and 28.5 mg for NH1635. The proportion of total fruit biomass expressed as energy equivalents (kJoules) allocated to embryos in mature fruit (45 DAP + 10 days storage) was 11.8% in NH1635, 18.7% in NH1634, 27.4% in Tip Top, and 30.2% in NH1636. Reallocation of assimilates from mesocarp tissue to developing embryos was a major contributing factor, along with respiration, to a reduction in mesocarp dry matter during storage.
Mark E. Herrington, Svenning Prytz, Ross M. Wright, Ian O. Walker, Peter Brown, Denis M. Persley, and Ray S. Greber
1 E-mail address: firstname.lastname@example.org 2 Retired. We acknowledge the financial support for the development of the resistant squashes: 'Dulong QHI' from HRDC (Horticultural Research and Development Corporation); AUSVEG and QFVG (Queensland
Qi Zhang, Andy Medina, and Chuck Lyerly
Summer squash are generally regarded as any variety of Cucurbita used immature as a table vegetable, but more commonly refer to any cultivated type of Cucurbita pepo that produces immature fruit for consumption ( Herrington and Persley, 2002
R. J. Hopp and Haydon Rochester Jr.
Greenhouse studies of the effect of N-dimethyl amino succinamic acid on the early growth stages of Butternut squash (Cucurbita moschata Poir.) were followed in 1965 by a replicated field trial in which the plants could by grown to maturity. In addition to controls the treatments in the field consisted of 1000 and 5000 ppm N-dimethyl amino succinamic acid used in the form of Alar, a 50% wettable powder formulation. The first application was made when all plants had at least one true leaf (June 22); a second application was made about six weeks later (August 6). Alar was applied as a fine mist spray to runoff point; Triton X-100 was added as a spreader. Growth measurements were taken at weekly intervals until 11 weeks after the initial treatment. Some of the effects of the Alar treatments compared to the controls are summarized in Table 1.
L. E. Francois
The salt tolerance of 2 squash cultivars (Cucurbita pepo L. ‘White Bush Scallop’ and ‘Aristocrat Zucchini’) was determined in artificially salinized field plots. Saline treatments were imposed by irrigating with water that contained equal weights of NaCl and CaCl2. Relative yields of ‘Scallop’ and ‘Zucchini’ fruit were reduced 15.9% and 14.7% for each unit increase in salinity of saturated soil extracts (κe) above 3.2 and 6.0 decisiemens per meter (dS/m), respectively [dS/m = millimhos per centimeter (mmho/cm)]. ‘Scallop’ was moderately sensitive and Zucchini moderately tolerant to salinity for both fruit yield and vegetative growth. Germination response to salinity was determined in the laboratory using artificialiv-salinized sand cultures. Both cultivars proved to be more salt-tolerant during germination than during vegetative, flowering, or fruiting stages of growth.
Judy G. Schmalstig and Heather J. McAuslane
Squash silverleaf (SSL) is a physiological disorder of vegetables in the genus Cucurbita L. caused by feeding of nymphs of the silverleaf whitefly (SLW) (Bemisia argentifolii Bellows & Perring). SSL causes a silvering of the leaves and a blanching of fruit. Leaf silvering is caused by developmental separation of the upper epidermis and the palisade mesophyll layer resulting in additional air space and altered light reflection. The anatomical development of SSL was analyzed in young leaves of zucchini squash (Cucurbita pepo L.) using two susceptible genotypes (`Elite' and YSN347-PMR) and two tolerant genotypes (ZUC76-SLR and ZUC33-SLR/PMR). SLW nymphs were allowed to feed only on the mature leaves and the anatomy of the developing leaves was observed by light microscopy and transmission electron microscopy. Silvering began at the apex of young leaves and developed basipetally. The increased percentage of air space that resulted between the upper epidermis and palisade layers was the result of an increase in the duration of air space development in young, developing leaves. Chloroplasts in silvered tissue of mature leaves and in tissue of young leaves that later became silvered, were smaller and contained less starch than chloroplasts in tissue from noninfested plants. In contrast, development of genetic silvering, a condition not related to whitefly feeding, occurred throughout the entire leaf at one time, beginning as yellowed tissue in the axils of leaf veins then turning silver. Chloroplasts were normal in genetically silvered tissue of genotype YSN421-PMR. The SSL-tolerant genotype, ZUC76-SLR, did not show alteration in chloroplast structure or air space development when challenged with SLW; however, it had shorter and paler petioles, as did the susceptible genotypes. SSL symptoms were induced with spraying of gibberellic acid synthesis inhibitor chlormequat chloride in SSL-susceptible but not in SSL-tolerant genotypes. Reciprocal grafting between susceptible and tolerant plants showed that tolerance resides in the developing tissue and not the mature tissue on which the whiteflies feed.