Growth Of Watermelon Seedlings Research Articles

Genome-wide survey of KT/HAK/KUP genes in the genus Citrullus and analysis of their involvement in K+-deficiency and drought stress responses in between C. lanatus and C. amarus

BackgroundThe KT/HAK/KUP is the largest K+ transporter family in plants, playing crucial roles in K+ absorption, transport, and defense against environmental stress. Sweet watermelon is an economically significant horticultural crop belonging to the genus Citrullus, with a high demand for K+ during its growth process. However, a comprehensive analysis of the KT/HAK/KUP gene family in watermelon has not been reported.Results14 KT/HAK/KUP genes were identified in the genomes of each of seven Citrullus species. These KT/HAK/KUPs in watermelon were unevenly distributed across seven chromosomes. Segmental duplication is the primary driving force behind the expansion of the KT/HAK/KUP family, subjected to purifying selection during domestication (Ka/Ks < 1), and all KT/HAK/KUPs exhibit conserved motifs and could be phylogenetically classified into four groups. The promoters of KT/HAK/KUPs contain numerous cis-regulatory elements related to plant growth and development, phytohormone response, and stress response. Under K+ deficiency, the growth of watermelon seedlings was significantly inhibited, with cultivated watermelon experiencing greater impacts (canopy width, redox enzyme activity) compared to the wild type. All KT/HAK/KUPs in C. lanatus and C. amarus exhibit specific expression responses to K+-deficiency and drought stress by qRT-PCR. Notably, ClG42_07g0120700/CaPI482276_07g014010 were predominantly expressed in roots and were further induced by K+-deficiency and drought stress. Additionally, the K+ transport capacity of ClG42_07g0120700 under low K+ stress was confirmed by yeast functional complementation assay.ConclusionsKT/HAK/KUP genes in watermelon were systematically identified and analyzed at the pangenome level and provide a foundation for understanding the classification and functions of the KT/HAK/KUPs in watermelon plants.

Antagonistic effect of Bacillus and Pseudomonas combinations against Fusarium oxysporum and their effect on disease resistance and growth promotion in watermelon.

We aimed to develop an effective bacterial combination that can combat Fusarium oxysporum infection in watermelon using in vitro and pot experiments. In total, 53 strains of Bacillus and 4 strains of Pseudomonas were screened. Pseudomonas strains P3 and P4 and Bacillus strains XY-2-3, XY-13, and GJ-1-15 exhibited good antagonistic effects against F. oxysporum. P3 and P4 were identified as Pseudomonas chlororaphis and Pseudomonas fluorescens, respectively. XY-2-3 and GJ-1-15 were identified as B. velezensis, and XY-13 was identified as Bacillus amyloliquefaciens. The three Bacillus strains were antifungal, promoted the growth of watermelon seedlings and had genes to synthesize antagonistic metabolites such as bacilysin, surfactin, yndj, fengycin, iturin, and bacillomycin D. Combinations of Bacillus and Pseudomonas strains, namely, XY-2-3+P4, GJ-1-15+P4, XY-13+P3, and XY-13+P4, exhibited a good compatibility. These four combinations exhibited antagonistic effects against 11 pathogenic fungi, including various strains of F. oxysporum, Fusarium solani, and Rhizoctonia. Inoculation of these bacterial combinations significantly reduced the incidence of Fusarium wilt in watermelon, promoted plant growth, and improved soil nutrient availability. XY-13+P4 was the most effective combination against Fusarium wilt in watermelon with the inhibition rate of 78.17%. The number of leaves; aboveground fresh and dry weights; chlorophyll, soil total nitrogen, and soil available phosphorus content increased by 26.8%, 72.12%, 60.47%, 16.97%, 20.16%, and 16.50%, respectively, after XY-13+P4 inoculation compared with the uninoculated control. Moreover, total root length, root surface area, and root volume of watermelon seedlings were the highest after XY-13+P3 inoculation, exhibiting increases by 265.83%, 316.79%, and 390.99%, respectively, compared with the uninoculated control. XY-13+P4 was the best bacterial combination for controlling Fusarium wilt in watermelon, promoting the growth of watermelon seedlings, and improving soil nutrient availability.

The Effect of Bacillus velezensis LJ02 Compounded with Different Fungi on the Growth of Watermelon Seedlings and Microbial Community Structure

The application of beneficial microbial consortium can effectively improve plant disease resistance and its growth. Various fungi were compounded with Bacillus velezensis LJ02 and applied to watermelon plants in this paper. The results showed that the microbial consortium T2 (compounded Bacillus velezensis LJ02 with Aspergillus aculeatus 9) can effectively control gummy stem blight and powdery mildew in watermelon, while the control effect reached 83.56% and 70.93%, respectively (p &lt; 0.05). Compound treatment improved the diversity and richness of the rhizosphere microbial community structure, and the relative abundance of Caulobacterales and Xanthomonadaceae significantly increased after applying T2 to the soil. Meanwhile, the internode length was significantly decreased 28% (p &lt; 0.05), and the maximum leaf length increased 10.33% (p &lt; 0.05). In addition, the microbial consortium delays the maturity of watermelon vegetables. By studying the effects of microbial consortium on watermelon seedlings, our study provides a theoretical basis for the popularization and application of the compound inoculant.

Control effect of root exudates from mycorrhizal watermelon seedlings on Fusarium wilt and the bacterial community in continuously cropped soil.

Watermelon (Citrullus lanatus) is susceptible to wilt disease caused by Fusarium oxysporum f. sp niveum (FON). AMF colonization alleviates watermelon wilt and regulates the composition of root exudates, but the effects of mycorrhizal watermelon root exudates on watermelon Fusarium wilt is not well understood. Root exudates of watermelon inoculated with AMF (Funeliformis mosseae or Glomus versiformme) were collected in this study. Then the root exudates of control plants and mycorrhizal plants were used to irrigate watermelon in continuous cropping soil, respectively. Meanwhile, the watermelon growth, antioxidant enzyme activity, rhizosphere soil enzyme activities and bacterial community composition, as well as the control effect on FON were analyzed. The results indicated that mycorrhizal watermelon root exudates promoted the growth of watermelon seedlings and increased soil enzyme activities, actinomyces, and the quantity of bacteria in rhizosphere soil. The proportion of Proteobacteria and Bacteroides was decreased, and the proportion of Actinobacteria, Firmicutes, and Chloroflexi in rhizosphere soil was increased when the seedlings were watered with high concentrations of mycorrhizal root exudates. The dominant bacterial genera in rhizosphere soil were Kaistobacter, Rhodanobacter, Thermomonas, Devosia, and Bacillus. The root exudates of mycorrhizal watermelon could reduce the disease index of Fusarium wilt by 6.7-30%, and five ml/L of watermelon root exudates inoculated with F. mosseae had the strongest inhibitory effect on watermelon Fusarium wilt. Our results suggest mycorrhizal watermelon root exudates changed the composition of bacteria and soil enzyme activities in rhizosphere soil, which increase the resistance of watermelon to Fusarium wilt and promoted the growth of plants in continuous cropping soil.

Variation of Soil Microbial Community and Sterilization to Fusarium oxysporum f. sp. niveum Play Roles in Slightly Acidic Electrolyzed Water-Alleviated Watermelon Continuous Cropping Obstacle.

It is critical to exploit technologies for alleviating watermelon continuous cropping obstacle which frequently occurs and results in the limiting production and economic losses of watermelon. This study aimed to explore the effects of slightly acidic electrolyzed water (SAEW) on watermelon continuous cropping obstacles. The results showed that SAEW significantly improved the growth of watermelon seedlings cultivated in continuous cropping soil and caused a mass of changes to the diversity of the soil microbial community. Compared with Con, SAEW decreased the diversity index of bacteria by 2%, 0.48%, and 3.16%, while it increased the diversity index of fungus by 5.68%, 10.78%, and 7.54% in Shannon, Chao1, and ACE index, respectively. Besides, the enrichment level of Fusarium oxysporum f. sp. niveum (FON) was remarkably downregulated by 50.2% at 14 days of SAEW treatment, which could decrease the incidence of Fusarium wilt disease. The wet and dry weights of FON mycelia in the fluid medium were depressed more than 93%, and the number of FON colonies in continuous cropping soil was reduced by 83.56% with SAEW treatment. Additionally, a strong correlation between watermelon, FON, and SAEW was presented by correlation analysis. Furthermore, the content of endogenous reactive oxygen species (ROS) was over quadruply increased by SAEW, which may contribute to the sterilizing effect of SAEW on FON. Taken together, our findings demonstrated that exogenous SAEW could alter the soil microbial diversity and decrease the accumulation of FON, which improved the growth of watermelon seedlings and finally alleviated continuous cropping obstacles of watermelon.

6-Benzyladenine alleviates NaCl stress in watermelon (Citrullus lanatus) seedlings by improving photosynthesis and upregulating antioxidant defences.

Soil salinity is a growing problem in agriculture, plant growth regulators (PGRs) can regulate plant response to stress. The objective of this study was to evaluate the effects of exogenous 6-benzyladenine (6-BA) on photosynthetic capacity and antioxidant defences in watermelon (Citrullus lanatus L.) seedlings under NaCl stress. Two watermelon genotypes were subjected to four different treatments: (1) normal water (control); (2) 20mgL-1 6-BA; (3) 120mmolL-1 NaCl; and (4) 120mmolL-1 NaCl+20mgL-1 6-BA. Our results showed that NaCl stress inhibited the growth of watermelon seedlings, decreased their photosynthetic capacity, promoted membrane lipid peroxidation, and lowered the activity of protective enzymes. Additionally the salt-tolerant Charleston Gray variety fared better than the salt-sensitive Zhengzi NO.017 variety under NaCl stress. Foliar spraying of 6-BA under NaCl stress significantly increased biomass accumulation, as well as photosynthetic pigment, soluble sugar, and protein content, while decreasing malondialdehyde levels, H2 O2 content, and electrolyte leakage. Moreover, 6-BA enhanced photosynthetic parameters, including net photosynthetic rate, stomatal conductance, intercellular CO2 concentration, and transpiration rate; activated antioxidant enzymes, such as superoxide dismutase, catalase, and peroxidase; and improved the efficiency of the ascorbate-glutathione cycle by stimulating glutathione reductase, dehydroascorbate reductase, and monodehydroascorbate reductase, as well as ascorbic acid and glutathione content. Principal component analysis confirmed that 6-BA improved salt tolerance of the two watermelon varieties, particularly Zhengzi NO.017, albeit through two different regulatory mechanisms. In conclusion, 6-BA treatment could alleviate NaCl stress-induced damage and improve salt tolerance of watermelons by regulating photosynthesis and osmoregulation, activating the ascorbate-glutathione cycle, and promoting antioxidant defences.

SALT STRESS AND AMBIENCE ON THE PRODUCTION OF WATERMELON SEEDLINGS

ABSTRACT The objective of this study was to evaluate the production of watermelon seedlings irrigated with saline waters and cultivated in different types of environments and substrates. The experimental design was completely randomized with split-split plots, in which the plot corresponded to two growing environments (EN1 = full sun and EN2 = 50% shade black net), the subplot to two types of irrigation water (IW1 = 0.8 and IW2 = 2.5 dS m-1) and the sub-subplot to four types of substrates (SB1 = vermiculite + coconut fiber, SB2 = manure + soil, SB3 = carbonized rice husk + soil, SB4 = biochar + soil), with four replicates of twenty-five seeds. The variables analyzed were: emergence percentage (EP), emergence speed index (ESI), mean time of emergence (MTE), number of leaves (NL), stem diameter (SD), seedling height (SH) and root length (RL), shoot dry mass (SDM), root dry mass (RDM) and total dry mass (TDM). The EN2 treatment provided better conditions for emergence and initial growth, and EN1 was also favorable to the emergence and initial growth of watermelon seedlings, when the substrates SB1 and SB2 were used.

Thermal stress and physiological changes in watermelon seeds

ABSTRACT Given that watermelon is a crop widespread around the world, there is considerable interest in verifying how its seeds physiologically behave under unfavorable temperature conditions. This study aimed to evaluate the biochemical changes mobilization and reserves degradation, as well as the enzyme activity, during seed germination and initial growth of watermelon seedlings subjected to thermal stress, using temperature, germination percentage, germination rate and relative germination frequency over the incubation time as evaluation parameters. The experimental design was completely randomized, in a 5 x 3 factorial scheme, with five temperatures (17 ºC, 20 ºC, 25 ºC, 30 ºC and 35 ºC) and three cultivars (Charleston Gray, Fairfax and Crimson Sweet), with 4 replicates of 50 seeds. Germination, seedling growth, reserve degradation and stress protection system were evaluated. Thermal stress caused deleterious effects on watermelon seeds with germination capacity at well defined temperature limits, being 25 ºC the ideal temperature, with the highest percentage of normal seedlings. Sub- (17 ºC) and supra-optimal (30 ºC) temperatures presented more than 80 % of abnormal seedlings. The α-amylase enzyme activity is intense only at the beginning of germination. Under thermal stress, the proline contents increase mainly in the cotyledons.

Melatonin pretreatment improves vanadium stress tolerance of watermelon seedlings by reducing vanadium concentration in the leaves and regulating melatonin biosynthesis and antioxidant-related gene expression

Vanadium (V) is an important heavy metal with ubiquitous presence in the Earth’s crust, but limited information is available as to its effect on plants and management strategies. Melatonin is a widely studied biomolecule; it acts as an antioxidant and a signaling molecule that enhances the abiotic stress tolerance of plants. Melatonin improves copper, zinc, and cadmium tolerance in plants. In this study, we investigated the response of watermelon seedlings to V stress and the potential role of melatonin in enhancing V stress tolerance of watermelon seedlings. The results showed that seedlings pretreated with melatonin (0.1μM) exposed to V (50mg/L) had a higher relative chlorophyll content (SPAD index), photosynthetic assimilation, and plant growth compared with non-melatonin pretreated seedlings. Melatonin pretreatment lowered leaf and stem V concentrations by reducing V transport from root to shoot. Melatonin pretreatment enhanced superoxide dismutase (SOD) and catalase (CAT) activities, and reduced the hydrogen peroxide (H2O2) and malondialdehyde (MDA) content of watermelon seedlings, by regulating melatonin biosynthesis and gene expression for superoxide dismutase, peroxidase, ascorbate peroxidase, glutathione peroxidase, and glutathione S-transferase. So far as we know, these results are the first evidence that melatonin improves plant growth of watermelon seedlings under vanadium stress conditions. Considering these observations, melatonin can be utilized to reduce the availability of V to plants, and improve plant growth and V stress tolerance.

English

Seeds of watermelon [Citrullus lanatus (Thunb.) Matsum and Nakai, cv. Crimson Sweet] were used to investigate the effects of different priming techniques on seed germination and early seedling growth. The seeds were soaked in solutions of 0.2% gibberellin (50 mg L–1 gibberellic acid), 0.2% cytokinin (90 mg L–1 kinetin), 0.2% potassium nitrate (2 g L–1 KNO3), 0.2% calcium nitrate [2 g L–1 Ca(NO3)2] or water (hydropriming) for 6 h at 25°C. After drying, five replicates of 25 seeds were distributed in plastic boxes with blotter paper and kept into a seed germinator at 26°C for 12 days. The different priming treatments significantly affect the measurements of the seed germination and growth of watermelon seedlings. The germination of watermelon seeds ranged from 0 to 100%, and was significantly greater when seeds were subjected to priming with GA3, KNO3, Ca(NO3)2 and water (control), and lower under cytokinin (CK) priming. The seed priming with 0.2% solution of CK resulted in 100% of abnormal seedlings, and therefore should not be used by watermelon growers. Seed priming with GA3, KNO3, Ca(NO3)2 and water (hydropriming) increased the shoot length, whereas GA3, Ca(NO3)2 and water priming improved the radicle length, as well as shoot dry matter watermelon seedlings. The KNO3 and water priming increased the root dry matter of watermelon seedlings. Seed priming with KNO3 and Ca(NO3)2 improved the germination rate and seedling vigor index. The results of this study show that seed priming with GA3, KNO3, Ca(NO3)2 and water (hydropriming) may be useful tools due to their positive effects on germination percentage and growth characteristics of watermelon seedlings. Key words: Citrullus lanatus, cytokinin, gibberellin, hydropriming.

Regulation of Plant Growth, Photosynthesis, Antioxidation and Osmosis by an Arbuscular Mycorrhizal Fungus in Watermelon Seedlings under Well-Watered and Drought Conditions.

Drought stress has become an increasingly serious environmental issue that influences the growth and production of watermelon. Previous studies found that arbuscular mycorrhizal (AM) colonization improved the fruit yield and water use efficiency (WUE) of watermelon grown under water stress; however, the exact mechanisms remain unknown. In this study, the effects of Glomus versiforme symbiosis on the growth, physio-biochemical attributes, and stress-responsive gene expressions of watermelon seedlings grown under well-watered and drought conditions were investigated. The results showed that AM colonization did not significantly influence the shoot growth of watermelon seedlings under well-watered conditions but did promote root development irrespective of water treatment. Drought stress decreased the leaf relative water content and chlorophyll concentration, but to a lesser extent in the AM plants. Compared with the non-mycorrhizal seedlings, mycorrhizal plants had higher non-photochemical quenching values, which reduced the chloroplast ultrastructural damage in the mesophyll cells and thus maintained higher photosynthetic efficiency. Moreover, AM inoculation led to significant enhancements in the enzyme activities and gene expressions of superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase, and monodehydroascorbate reductase in watermelon leaves upon drought imposition. Consequently, AM plants exhibited lower accumulation of MDA, H2O2 and compared with non-mycorrhizal plants. Under drought stress, the soluble sugar and proline contents were significantly increased, and further enhancements were observed by pre-treating the drought-stressed plants with AM. Taken together, our findings indicate that mycorrhizal colonization enhances watermelon drought tolerance through a stronger root system, greater protection of photosynthetic apparatus, a more efficient antioxidant system and improved osmoregulation. This study contributes to advances in the knowledge of AM-induced drought tolerance.

Effect of Nitrate/Ammonium Ratios on Growth, Root Morphology and Nutrient Elements Uptake of Watermelon (Citrullus Lanatus) Seedlings

Nitrogen is taken up by most plant species in the form of nitrate and ammonium. The objective of this study was to investigate the effect of different nitrogen forms on the growth of watermelon seedlings. Plants were grown in hydroponic culture with five nitrate (NO3−)/ammonium (NH4+) ratios (100/0, 75/25, 50/50, 25/75, 0/100). When the proportion of NH4+ was increased, the leaf number, leaf area, shoot height, net photosynthesis, biomass, and root growth were significantly decreased. Higher concentrations of nitrogen (N) and phosphorus (P) were observed when plants were supplied with mixed NO3− and NH4+ compared to NO3− or NH4+ alone, whereas the concentrations of potassium (K), calcium (Ca), and magnesium (Mg) were decreased with increasing NH4+. The microelements concentrations were generally increased with more NH4+ added. In addition, plants fed with higher NO3−/NH4+ ratios resulted in more minerals accumulation.

Effects of different potassium nutrition on growth and root morphological traits of watermelon seedling

The study was carried out by a pot experiment supplied with five K levels [0(K0),60 kg·hm 2(K1),240 kg·hm 2(K2),500 kg·hm 2(K3),700 kg·hm 2(K4)] to probe into effects of different application of potassium fertilizer on watermelon seedling growth and root morphology traits.Results indicated that under 240 kg·hm 2 potassium application,stem fresh weight,leaf fresh weight,stem dry weight,leaf dry weight,leaf area,stem diameter,plant height,total root length,specific root length,surface area,root volume,root tips and root average diameter were 46.05%,31.31%,57.56%,29.87%,2.92%,12.71%,37.18%,67.23%,64.00%,64.03%,58.88%,154.11% and 6.25% higher than those under no potassium application.Under 700 kg·hm 2 potassium application,stem fresh weight,leaf fresh weight,stem dry weight,leaf dry weight,leaf area,stem diameter and plant height were 40.24%,25.31%,36.90%,23.08%,31.09%,9.81% and 41.44% lower than those under 240 kg·hm 2 potassium application.The effect of 700 kg·hm 2 potassium application on root morphological traits were not obvious.Additionally,the root length in root diameter ≤ 1.0 mm was above 90%,the root tips in root diameter range ≤ 0.5 mm was above 98%,specific root length,surface area and root volume in root diameter ≤ 2.0 mm was above 50% of total amount,respectively.Root length,specific root length,surface area and root volume of root diameter ≤ 2.0 mm,2.5 mm diameter ≤ 3.0 mm,3.5 mm diameter ≤ 4.0 mm were significant affected by K level.Morphological traits were determined by specific root length,surface area,root volume and tips in root diameter ≤ 2.0 mm.Because of relatively stronger absorption and the largest proportion of fine roots,the impact of potassium deficit on potassium nutrition of watermelon seedling was more serious than that on roots growth.Appropriate potassium concentration was beneficial to the growth of watermelon seedlings,it could improve the quality of seedlings growth,root growth and development.No potassium application and high potassium restrained the growth of seedlings,but the inhibition of high potassium on the root growth was not obvious.Under this experimental condition,the 240 kg·hm 2 potassium application treatment was the best.

End-of-Day Light Treatments Regulate Watermelon Seedling Growth with No Subsequent Effects on Fruit Production After Transplanting to the Field

While using end-of-day (EOD) red or far-red (FR) light had been previously successful in regulating the seedling growth of selected vegetable transplants, no study has evaluated this transplanting regulating technique for watermelon, or whether it has effects on fruit production after the seedlings are transplanted to the field. As such, the influence of end-of-day (EOD) red (R) or far-red (FR) light on watermelon [Citrullus lanatus (Thunb) Matsum and Nakai], cv. Sugar Baby, seedling growth and subsequent fruit production after transplanting to the field was investigated. Seedlings were exposed to low intensity EOD R (15 min), EOD FR (15 min), EOD FR + R (15 min of FR followed by a 15 min of R treatment), or no EOD light (control) treatments at the end of each photoperiod to determine if these light treatments affected plant growth in a manner that might be beneficial for transplant production (e.g., shorter more stocky plants that might be less prone to lodging and more easily used with mechanical transplanters, or larger taller plants that might have greater early growth after transplanting) without deleterious effects on subsequent fruit production. EOD FR treated seedlings had longer petioles and internodes than seedlings in any of the other EOD R and EOD FR + R or control light treatments. EOD R treated seedling growth was not different than control seedlings. The EOD FR + R treatment negated the EOD FR light growth effects suggesting involvement of phytochrome in the light regulated growth of watermelon seedlings. When EOD treated watermelon seedlings were transplanted to the field there were no subsequent effects on fruit production.

INFLUENCE OF PLUG CELL SIZE FOR ROOT VIGOR AND SEEDLING QUALITY ON GRAFT WATERMELON SEEDLING

INFLUENCE OF PLUG CELL SIZE FOR ROOT VIGOR AND SEEDLING QUALITY ON GRAFT WATERMELON SEEDLING

Effect of Hypocotyl Morphology on Survival Rate and Growth of Watermelon Seedlings Grafted on Rootstocks with Different Emergence Performance at Various Temperatures

The emergence performance of different rootstocks and watermelon cultivars at different temperatures, and the effect of hypocotyl structure on grafting success and survival rate were investigated. Evaluated rootstocks were Cucurbita moschata (landrace), C. maxima (Ar›can local cultivar), Strong Tosa (C. maxima x C. moschata), P360 (C. maxima x C. moschata), Luffa cylindrica, Benincasa hispida, Lagenaria siceraria (landrace), Skopje (Landrace), and 2 Lagenaria hybrids, 216 and FR Gold. The Crimson Tide watermelon cultivar was used as scion. Emergence tests at 14 …C, 18 …C and 25 …C were carried out for all rootstocks and scion seeds in a growth chamber. Cucurbita type rootstocks showed better emergence performance at low temperatures than did other rootstocks and scion. However, B. hispida, L. cylindrica, Lagenaria type rootstocks and scion did not emerge at 14 …C and they were rotten. At 18 …C, the earliest emergence was recorded in Cucurbita type rootstocks while the latest emergence was observed in B. hispida and L. cylindrica. Rootstocks and scion did not show any difference in emergence rate at 25 …C. B. hispida and L. cylindrica had the thinnest and shortest hypocotyls which made grafting difficult. The survival rate of grafted plants was inversely correlated with the difference in diameters of scion and rootstock. At the same time survival rate was significantly affected by the rootstocks genotype. Rootstocks had different numbers of vascular bundles but the survival rate was not affected by the number of vascular bundles whereas the plant growth rate was positively affected. In general, Lagenaria type rootstocks had a higher survival rate than did other rootstocks. The hole insertion grafting technique had a significantly lower survival rate than did the approaching technique in Cucurbita type rootstocks. All graft combinations produced higher plant biomass than did the control plant, except for the L. cylindrica. The study showed that rootstock influences survival rates and plant growth in the use of grafting applications in watermelon.

Watermelon seedling growth and mortality as affected by Anasa tristis (Heteroptera: Coreidae).

Adult squash bugs, Anasa tristis (De Geer), were confined on seedling watermelon plants at densities of zero, one, two, and four per plant. Squash bugs were allowed to feed on the plants until plants died or reached 30 cm in height. Number of leaves and length of plant vine were recorded at 2- or 3-d intervals. Seedling foliage, stems, and roots were harvested and dried after plants reached 30 cm in height. Growth of seedlings was regressed on number of squash bugs and results indicated that an increasing density of squash bugs feeding on seedlings resulted in a significant reduction in plant growth. Additionally, increased density of squash bugs resulted in reduced weight of foliage and root dry biomass. Seedling mortality increased as the density of squash bugs increased.

Influence of Cyclic Cold Temperature Stress on Watermelon Seedling Growth, Earliness, Yield, and Quality

Watermelon seedlings may be repeatedly exposed to temperatures alternating between almost freezing and optimal temperatures for growth during stand establishment in coastal South Carolina. `Carnival' watermelon transplants were exposed to 2 °C for 3, 6, and 9 h, for 1, 3, 6, and 9 days in a walk-in cooler and then to warm temperatures (24 °C) immediately prior to field planting. Our objective was to determine the long term effect of early season cold temperature exposure on seedling growth, earliness, yield and quality by simulating the cold/warm alternations possible in the field. Cold-stressed transplants were field planted after the risk of ambient cold stress was negligible. Exposure to cycling cold temperatures generally did not affect earliness, total productivity and quality, although seedling growth characteristics were reduced in response to the longer cold-stress treatment. Therefore, cold temperature stresses occurring in the field at transplanting have negligible beneficial or detrimental effects on yield potential of `Carnival' watermelon.

スイカの健苗育成への鉱物粉末施用の効果

野生のユウガオ台木 (品種名 : ドンK) に接ぎ木したスイカ (品種名 : 縞王MAX) を, 台木の自根を切除後, 鉱物粉末 (商品名, ミネラルの素) を添加したポットおよび無鉱物粉末添加区のポットに挿し木した.その結果, ポット (乾土約200g) に2g程の鉱物粉末を添加した区で, 特に根の伸長, さらに地上部生体重の増加が無添加区に比較して有意に高い値を示した.また, 鉱物粉末添加区では, ポット内に分布した根量は, 明らかに多かった.このことは, 本実験で用いた鉱物粉末がこれまでの知見のように根の伸長促進に効果のあることを示唆している.

Effects of Powders of Some Mineral Substances on the Growth of Watermelon Seedlings

Effects of Powders of Some Mineral Substances on the Growth of Watermelon Seedlings