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J.R.A. Santos and D.I. Leskovar

Germination bioassays were conducted to assess if water-soluble extracts of broccoli (Brassica oleracea L. var. italica L.) affect germination of broccoli, cabbage (Brassica oleracea L. var. capitata L.), and cauliflower (Brassica oleracea L. var. botrytis L.). Greenhouse experiments also examined the phytotoxic potential of soil previously cropped with broccoli and broccoli plant parts on seedling growth of those species. The first bioassay used nonsterile extracts (NSEs) and filter-sterilized extracts (FSEs) of broccoli leaves. The second bioassay used nonsterile and filter-sterilized leaf extracts (LEs), stem and root extracts (SREs), and whole broccoli plant (leaves, stems, and roots) extracts (WPEs). Broccoli and cabbage germination were not affected by NSEs or FSEs, but the latter reduced cauliflower germination by 22%. LEs and SREs decreased germination speed for broccoli, cabbage and cauliflower. Greenhouse seedlings were grown in soil previously cropped with broccoli or fallow soil at three fertilizer levels. Broccoli soil was phytotoxic to cauliflower but enhanced broccoli and cabbage seedling growth. The differential sensitivity to broccoli plant residue was in the order of cauliflower > broccoli = cabbage, with SR residue having the highest phytotoxic potential.

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S. Grange, D.I. Leskovar, L. Pike, and G. Cobb

Triploid watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] consumption is increasing in the United States However, some of the original problems, poor and inconsistent germination, still exist. Seeds of several triploid and diploid watermelon cultivars were subjected to a variety of treatments to improve germination. Control and scarified seeds, by nicking, were incubated at 25 or 30 °C in either 5 or 10 mL H2O or hydrogen peroxide (H2O2). Triploid seed germination was strongly inhibited in all cultivars when seeds were at 10 mL of H2O or H2O2; both nicking and H2O2 increased germination but not equal to rate of the control in 5 mL H2O or H2O2. Germination of diploid cultivars was unaffected by any treatment. Seed morphological measurments indicated that triploid seed has a smaller embryo with a large and highly variable (cv = 105%) air space surrounding the embryonic axis as compared with the diploid seed. These data suggests that triploid watermelon seed germination is not inhibited by the seed coat thickness alone. Seed moisture plays a significant role in germination, emergence, and stand uniformity.

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D.I. Leskovar, P. Perkins-Veazie, and A. Meiri

Water conservation strategies are being investigated for watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] production in the Winter Garden region of southwest Texas. Our objective was to determine how yield and fruit quality of a triploid (cv. Summer Sweet 5244) and hybrid (cv. Summer Flavor 710) watermelon were affected by irrigation based on evapotranspiration (ET) rates and timing of application during spring. Irrigation treatments included constant 1.0 and 0.5 ET, three with varying ET before or after fruit set, and one with cycles of 1.0 and 0.5 ET. Fruit quality characteristics were measured at the unripe, ripe, and overripe maturity stages. Water deficit before or after fruit set decreased yield and fruit number. Flesh color was not affected by irrigation at any maturity stage. Soluble solid content at the ripe stage increased only in triploids irrigated with constant 0.5 ET or with 0.5 ET applied after fruit set. Triploid plants exposed to frequent cycles of water deficit set more and smaller fruit than hybrids. These data suggest that triploid watermelon types may have a different acclimation response to drought stress than diploid hybrids.

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S. Grange, D.I. Leskovar, L. Pike, and G. Cobb

Triploid watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] consumption is increasing in the U.S. However, some of the original problems, poor and inconsistent germination, still exist. Seeds of several triploid and diploid watermelon cultivars were subjected to a variety of treatments to improve germination. Control and scarified seeds, by nicking, were incubated at 25 or 30 °C in either 5 or 10 mL H2O or hydrogen peroxide (H2O2). Triploid seed germination was strongly inhibited in all cultivars when seeds were at 10 mL of the H2O or H2O2; both nicking and H2O2 increased germination, but not equal to rate of the control in 5 mL H2O or H2O2. Germination of diploid cultivars was unaffected by any treatment. Seed morphological measurments indicated that triploid seed has a smaller embryo with a large and highly variable (CV = 105%) air space surrounding the embryonic axis as compared with the diploid seed. These data suggests that triploid watermelon seed germination is not inhibited by the seedcoat thickness alone. Seed moisture plays a significant role in germination, emergence, and stand uniformity.

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D.I. Leskovar, J.C. Ward, and A. Meiri

Reductions in the supply of high-quality irrigation water from underground aquifers is affecting production and irrigation management in the Winter Garden of southwestern Texas. This study was conducted to determine how growth, yield, and quality of watermelons [Citrullus lanatus (Thunb.) Matsum. & Nakai] grown with subsurface drip are affected by synchronizing irrigation with specific growth stages. In 1995 irrigation rates were: 1.0 evapotranspiration (ET) throughout the entire growth period (T1); 1.0ET until fruit set followed by 0.6ET until final harvest (T2); 1.0ET until fruit set followed by 0.6ET until first fruit maturity followed by 0.4ET until final harvest (T3); 1.0ET until fruit set followed by 0.6ET until first fruit maturity followed by 0.2ET until final harvest (T4). In 1996, two irrigation rates were constant 1.0ET (T1) and 0.5ET (T4), and two with varying ET rates throughout the entire growth period. Varying irrigation rates with specific growth stages had more influence on fruit set and early yield than on leaf and vine growth. Total marketable fruit yield ranged from 94.4 to 71.8 Mg·ha–1 when 569 mm (T1) and 371 mm (T4) of irrigation water, respectively, were applied in Spring 1995, and from 90.3 to 80.9 Mg·ha–1 when 881 mm (T1) and 577 mm (T4) of irrigation water, respectively, were applied in Spring 1996. However, plants irrigated with constant 0.5ET demonstrated greater water use efficiency than those with 1.0ET. Information on water use will assist farmers in designing management strategies that minimize risks due to uncertainties in weather and water supplies.

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D.I. Leskovar, L.A. Stein, and F.J. Dainello

This study was conducted to determine the effect of within-row plant spacing and mulching on growth, quality, and yield of an experimental semi-savoy spinach (Spinacia oleracea L.) genotype `Ark-310' to produce a high-quality fresh-market product. Spinach transplants were established in the field on 13 Nov. 1995 and 3 Dec. 1997. Within-row spacings were 15 and 25 cm, and mulching treatments were bare-soil and black polyethylene mulch. Plants were destructively sampled weekly (1996) or bi-weekly (1998) for leaf area (LA), leaf number, leaf dry weight (LDW); and root dry weight (RDW) measurements. Plants grown on plastic mulch at 25-cm spacing had the greater LA, LDW, and RDW than when grown at 15-cm spacing on mulch or bare-soil. Leaf number and specific leaf area (LA/LDW) were less affected by either spacing or mulching. The amount of soil on harvested leaves was lowest on plants grown on plastic mulch in both years. In one year, total yields (MT/ha) were 42% higher when plant spacing decreased from 25 cm to 15 cm, while mulch increased yields by 20 %, a response that was independent of plant spacing. These effects were not evident in the year with higher rainfall. It appears that for a root-cut or loose leaf spinach, yield efficiency and product cleanliness of `Ark 310' spinach may be further improved by combining high plant density with efficient irrigation and fertilization programs under mulch and drip.

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V. Esensee, D.I. Leskovar, and A.K. Boales

Nonomura and Benson (1992) reported that foliar applications of dilute solutions of methanol caused growth and yield increases and reduced water use in several crops. The request from commercial growers for explicit information regarding this report prompted our experiments using the same procedures. Growth of cantaloupe, pepper, cabbage, cauliflower and onion seedlings and mature plants were evaluated in the laboratory and greenhouse in 1993 and in the field in 1993 and 1994. Treatments of 0%, 10%, 20%, 30%, or 40% methanol (v/v water) with 0.1% surfactant generally did not cause significant growth differences. Stem diameters or lengths, shoot fresh and dry weights, or root fresh and dry weights of seedlings were unaffected as a result of methanol treatment. In the field, cabbage head weight was slightly higher after methanol application only in 1993, whereas cantaloupe fruit weight and number were significantly lower in 1993, but not in 1994.

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J.T. Baker, D.I. Leskovar, V.R. Reddy, and F.J. Dainello

A temperature experiment with two cultivars of muskmelon (`Gold Rush' and `Mission') was conducted in growth chambers to determine how main vine leaf appearance rates responded to temperature. We identified three cardinal temperatures for leaf appearance rate: the base temperature (10 °C) at which leaf appearance rate was zero, an optimum temperature where leaf appearance rate was at a maximum (34 °C) and an upper threshold temperature (45 °C) where leaf appearance rate returned to zero. Using these three cardinal temperatures, we constructed a simplified thermal unit accumulator for hourly measurements of air temperature. Main vine plastochron interval (PI), thermal time to harvest and final yield was determined for three cultivars of muskmelon (`Explorer', `Goldrush', and `Mission') grown in the field over six transplanting dates. The PI was calculated for each cultivar-transplanting date combination as the reciprocal of the slope of main vine node number vs. accumulated hourly thermal units (Tu). The PI was significantly affected by both cultivar and transplanting date. Final yield was sharply reduced in the last two planting dates, presumably due to high temperature stresses impacting reproductive development. As air temperatures warmed during the field experiment, the time interval from transplanting to 10% final harvest were reduced by between 21 to 28 days among the three cultivars and the first four transplanting dates. Our goal was to construct a simple muskmelon phenology model that could be run with easily obtainable weather station data and used by growers to quantify phenological development and aid in projecting harvest dates. We also wanted to test whether main vine node number was a useful description of vegetative development for muskmelon.

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S.L. Grange, D.I. Leskovar, L.M. Pike, and B.G. Cobb

Poor and inconsistent germination is a problem in triploid watermelon. Nicking was shown effective in improving germination in triploid cultivars. In this experiment, we examined the effects of high and low medium moisture, and nicking on diploid and triploid seed germination. Germination for the diploid cultivar was unaffected by any treatment. At high moisture conditions, triploid seed germination was severely reduced to less than 15%, while nicking significantly improved germination up to 40%. However, this increase is still not commercially acceptable. When seed morphological components were measured for each cultivar, triploid seeds had a larger and highly variable air space as compared to the diploid seed. The data confirm that seed germination is not inhibited by the seedcoat alone, but appears to be highly sensitive to excessive water conditions.

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E.W. Stover, P.J. Stoffella, S.A. Garrison, D.I. Leskovar, D.C. Sanders, and C.S. Vavrina

A commercial mixture of 1-naphthaleneacetamide and 1-naphthaleneacetic acid (Amcotone) was applied to tomato (Lycopersicon esculentum Mill.) and pepper (Capsicum annuum L.) at various timings from early bloom through early fruit development to evaluate effects on fruit size and both early and total marketable yield. Amcotone was applied at rates from 10 to 40 mg·L-1, at three sites for each of the species studied. Measured yield response variables in tomato did not differ between the control and Amcotone treatments, regardless of location. Amcotone treatments did not affect yields or fruit size for pepper at the New Jersey or Texas sites. However, at Ft. Pierce, Fla., early marketable yield of pepper was increased in plots receiving three Amcotone applications at 10 mg·L-1, but total marketable yield was significantly reduced in all plots receiving more than two Amcotone sprays, and mean fruit weight was reduced by all Amcotone treatments. Early and total marketable yield of pepper at Ft. Pierce were markedly reduced in plots receiving four applications of 40 mg·L-1, which was a high rate used to assess potential phytotoxicity. While minimal benefit from auxin application was observed in this study, earlier studies suggest that these results may have been influenced by favorable environmental conditions for fruit development or negative effects on unopened flowers during all Amcotone spray applications.