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Sylvie Jenni, Daniel C. Cloutier, Gaétan Bourgeois, and Katrine A. Stewart

Growth of `Earligold' muskmelon (Cucumis melo L.), expressed as plant dry weight from transplanting to anthesis, could be predicted using a multiple linear regression based on air and soil temperatures for 11 mulch and rowcover combinations. The two independent variables of the regression model consisted of a heat unit formula for air temperatures, with a base temperature of 14C and a maximum reduced threshold of 40C, and a standard growing-degree day formula for soil temperatures with a base temperature of 12C. Based on 2 years of data, 86.5% of the variation in the dry weight (on a log scale) could be predicted with this model. The base temperature for predicting developmental time to anthesis of perfect flowers was established at 6.8C and the thermal time ranged between 335 and 391 degree days in the 2 years of the experiment.

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Lynn Brandenberger and Bob Wiedenfeld

Using polyethylene mulches has increased earliness, yields, and fruit quality in muskmelon, resulting in their extensive use for melon production with numerous commercial products. However, two problems are associated with polyethylene use: removal and disposal following production. Organic mulches are potential alternatives but, in this study, resulted in significantly lower soil temperatures than all other treatments and generally had lower yields. Soil temperature, yield, fruit size and percent soluble solids were increased by polyethylene mulches compared to bare soil. Crop response differences between polyethylene mulches were not significant for most characteristics measured. There were significant differences in durability and ease of removal of polyethylene mulches. Based our results, durability and ease of removal are the main characteristics on which to base selection. Proper mulch selection can reduce removal costs and enable commercial producers to leave a mulch in place for the production of a second crop.

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Samuel Mendlinger and Michael Fossen

The muskmelon (Cucumis melo L.) cultivars Topmark, Galia, No. 1, and BG-84-3 (BG) were examined in a field test for the influence of increased salt concentration (700, 2500, 5000, 7500, and 10,000 ppm) on flower production, vegetative growth, yield, and fruit quality. Increased salinity did not affect the number or timing of staminate and pistillate flowers produced. Increased salinity significantly and to the same extent reduced vegetative growth in the four cultivars. Increased salinity did not affect the number of fruit produced in the four cultivars but reduced mean fruit weight in three. Mean fruit weight and yield of `BG' were not reduced; i.e., `BG' was salt tolerant. Increased salinity increased the soluble solids concentration and slightly improved fruit appearance of all cultivars.

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Dean E. Knavel

Short-internode (SI) muskmelon (Cucumis melo L.) genotypes Ky-P7 (si-1 gene for SI) and Main Dwarf (si-3 gene for SI) were compared with the normal-internode (NI) cultivar Mainstream at various plant spacings or planting densities over 3 years. SI `Honey Bush' (si-1 gene for SI) and `Bush Star' (si-1 gene for SI) were included in 2 years. At double the population, SI plants (si gene type) produced ≈35% fewer fruit than `Mainstream' plants grown at one-half the population density. Spacing generally had no effect on average fruit weight, but increasing plant density of SI genotypes decreased the number of fruit per plant. Generally, doubling the density reduced leaf area and total plant dry weight, but had minimal effect on the amount of shaded leaf area. Ky-P7, `Honey Bush', and `Bush Star' plants had more leaf shading than `Mainstream' and Main Dwarf plants.

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Kimberly A. Klock, Henry G. Taber, and William R. Graves

Horticultural species vary in growth response to high root-zone temperature (RZT), but little is known about the effects of RZT on nutrient uptake. We determined P, K, Ca, Mg, Zn, and Mn total plant content of tomato (Lycopersicon esculentum Mill. cv. Jet Star), muskmelon (Cucumis melo L. cv. Gold Star), and honey locust (Gleditsia triacanthos L. var. inermis Willd.) grown in nutrient solution kept at 24, 27, 30, 33, and 36C. RZT effects on plant dry mass gain and gain in nutrient per plant varied by species. Honey locust and tomato total plant gain in P decreased linearly with increasing RZT, while melon P content increased linearly to 36C. Trends in total Mg and Mn content will be presented, as well as results from further research on correlations between supraoptimal RZT, root respiration, and shoot and root P content of tomato.

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Gene Lester

Lipoxygenase (LOX) activity was assayed on hypodermal- and middle-mesocarp tissues from netted muskmelon (Cucumis melo L.) fruit 10, 20, 30, and 40 days postanthesis and after 12 days of storage at 4 or 21C. Highest LOX activity was obtained using a phosphate buffer at pH 7 and 20C. LOX activity was detected only in hypodermal-mesocarp (hypodermic) tissue at 30 days postanthesis, and activity increased with fruit age and storage temperature. Antioxidants, which inhibit LOX, were detected only in hypodermic tissue from 10 through 30 days postanthesis fruits. Linoleic plus linolenic free fatty acids, substrates for LOX, in hypodermic tissue had declined at 30 days postanthesis, as did plasma membrane integrity, and both continued to decline in association with increased LOX activity.

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Gerald E. Wilcox, Paul R. Adler, and Mohamad Errebhi

A study was made to investigate the effects of liming and N source fertilization on soil acidity, nutrient uptake an yield of muskmelon on a Princeton loamy-sand (fine sandy, mixed, mesic, type Hapludalf) at Southwest Purdue Agricultural Center, Vincennes, IN. The experiment consisted of lime and no lime treatments with five N treatments of 0 N, 50 kg·ha-1 N as urea and 100 kg·ha-1 N as urea, NH4NO3, and (NH4) SO4. The unlimed soil tested pH 4.6, 4.2 and 4.1 and the limed soil was pH 5.5, 5.6 and 5.2 with 100 kg N·ha-1 as urea, NH4NO3 and (NH4) SO4, respectively. With NH4NO3 the NO3-N declined from 268 ppm on 6/1 to 64 ppm on 7/7 in the saturation extract (SE). Highest NH4-N was from (NH4)2SO4 followed by NH3NO4 and urea. The NH4-N concentration from (NH4)2SO4 in the SE decreased from 152 ppm to 19 ppm during the season on unlimited soil and from 56 ppm to 8 in the SE decreased from 152 ppm on limed soil. Symptoms of Mn toxicity in the leaves became apparent on unlimed plots 7 weeks after transplanting. As the rate of N increased in the range of 0, 50 and 100 kg·ha-1 from urea the Mn contents were 372,459 and 607 ppm respectively. The muskmelon fruit yield increase due to 100 kg N·ha-1 was 13279 kg·ha-1, 12161 kg·ha-1 and 8502 kg·ha-1 for ureas, NH4NO3 and (NH4)2SO4 respectively.

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Yasuyoshi Hayata, Xin-Xian Li, and Yutaka Osajima

To clarify the cause of low sucrose accumulation in seedless `Crest Earl's' netted muskmelon [Cucumis melo L. (Reticulatus Group)] fruit induced by CPPU, the activity level of sucrose metabolizing enzymes was compared between seeded and seedless fruit. CPPU promoted growth of the ovary in both pollinated and nonpollinated flowers until 10 days after anthesis (DAA), and thereafter the growth rate of nonpollinated fruit was lower than in the controls. Sucrose accumulation of seedless fruit remained lower than in seeded fruit, but there was no difference in fructose and glucose content between seeded and seedless fruit. Acid invertase activity declined sharply 20 DAA in seeded and seedless fruit, and was hardly detectable at 35 DAA, when sucrose accumulation began. Neutral invertase (NI) activity in both seeded and seedless fruit decreased from 20 DAA until 35 DAA; thereafter, NI activity in seeded fruit remained relatively constant, with a small but insignificant increase in maturity. Sucrose synthase (SS-c: sucrose cleavage direction) activity in seeded fruit decreased from 20 to 30 DAA, and then increased as fruit matured, while SS-c activity in seedless fruit did not change during development. Sucrose phosphate synthase (SPS) activity in seeded fruit increased from 25 to 30 DAA and remained relatively constant until harvest. SPS activity in seedless fruit declined gradually from 30 to 45 DAA, then remained at a low level. Sucrose synthase (SS-s: sucrose synthesis direction) activity in seeded fruit increased rapidly after 30 DAA, concomitant with sucrose accumulation. In contrast, SS-s activity in seedless fruit increased only slightly after 30 DAA indicating levels of SS-s activity are closely related to sucrose accumulation in parthenocarpic seedless muskmelons. Chemical name used: [1-(2-chloro-4-pyridyl)-3-phenylurea] (CPPU).

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Sylvie Jenni, Katrine A. Stewart, Gaétan Bourgeois, and Daniel C. Cloutier

A simple method to predict time from anthesis of perfect flowers to fruit maturity (full slip) and yield is presented here for muskmelon (Cucumis melo L.) grown in a northern climate. Developmental time for individual muskmelons from anthesis to full slip could be predicted from several heat unit formulas, depending on the temperature data set used. When temperature at 7.5 cm above soil level was used, the heat unit formula resulting in the lowest coefficient of variation (cv=6.9%) accumulated daily average temperatures with a base temperature of 11 °C and an upper threshold of 25 °C. With temperatures recorded at a meteorological station located 2 km from the experimental field, the method showing the lowest cv (8.9%) accumulated daily maximum temperatures with a base temperature of 15 °C. This latter method was improved by including a 60-degree-day lag for second cycle fruit. The proportion of fruit volume at full slip of 22 fruit from the first cycle could be described by a common Richards function (R 2=0.99). Although 65% of the plants produced two fruit cycles, fruit from the first cycle represented 72% of total yield in terms of number and mass. The blooming period of productive flowers lasted 34 days, each cycle overlapping and covering an equal period of 19 days. Counting the number of developing fruit >4 cm after 225 degree days from the start of anthesis (when 90% of the plants have at least one blooming perfect flower) could rapidly estimate the number of fruit that will reach maturity.

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Melkizedek O. Oluoch and Gregory E. Welbaum

The viability and vigor of osmotically primed (0.3 m KNO3, 6 days, 25C) and nonprimed `PMR 45' muskmelon (Cucumis melo L.) seeds were compared after storage for 9 years at <20C and 6% moisture content (MC, dry weight basis). Viability was compared at 20, 25, and 30C at water potentials of 0, -0.2, -0.4, -0.6, and -0.8 MPa and in soil. Additionally, stored primed and nonprimed seeds were either primed, aged (15% MC and 45C) for up to 8 days, or aged for 72 hours and primed. The force required to puncture 5-mm-long, micropylar seed pieces was measured using an Instron universal testing machine. Less force was required to puncture primed seed pieces at 0, 5, 15, 20, and 25 hours of imbibition, demonstrating that osmotic priming weakens the perisperm envelope tissue that the radicle must penetrate for germination to occur. In an earlier report, germination rate and final germination percentages were higher for osmotically primed seeds both in laboratory tests and field emergence studies conducted immediately after priming. After 9 years in storage, nonprimed seeds germinated to higher percentages in water at 30C and reduced water potential at all temperatures, while primed seeds germinated to higher percentages in water at 20 and 25C and exhibited a higher percentage of seedling emergence at a soil MC of 17%. Priming durations of ≤5 days had no effect on the viability, while longer durations decreased the viability of stored primed and nonprimed seeds. Priming generally decreased the log mean time to germination of stored nonprimed seeds but increased values for stored primed seeds. Controlled deterioration increased the log mean time to germination and decreased the viability of primed seeds faster than nonprimed seeds. Priming following controlled deterioration had no effect on nonprimed seeds and reduced the percent viability of primed seeds by 20%. Osmotic priming has a deleterious effect on the seed storage life of muskmelon seeds.