Muskmelon Cultivars Research Articles

Comparison of the volatile compositions and flavour properties of cantaloupe, Galia and honeydew muskmelons

Aroma compounds were extracted from three cultivars of muskmelon ( Cucumis melo L.) by solid-phase microextraction and analysed by gas chromatography–mass spectrometry. Sulfur-containing esters and compounds containing a straight six-carbon chain were present at high concentrations in cantaloupe melons. Compounds containing a straight nine-carbon chain were at high concentrations in honeydew melons. Methyl esters were present at the highest levels in Galia melons. The sensory properties of the three melons were also compared. Cantaloupe melons were associated with sweet, floral and fruity aromas and a persistent aftertaste. Galia melons possessed the strongest cucumber-like flavours, while cucumber aroma and sweet flavour scored highly in honeydew melons.

IDENTIFIKASI BERAT, DIAMETER, DAN TEBAL DAGING BUAH MELON (Cucumis melo, L.) KULTIVAR ACTION 434 TETRAPLOID AKIBAT PERLAKUAN KOLKISIN

Indonesian farmers are very dependence on certificated seed from another countries. In the other side the natural resources and men powers very abundance. For these reason it is properly developed the research in agriculture sector, especially on plants breeding. It can be hoped that in the future the dependence on certificated seed from another countries can be minimized. The objective of this research were: (1) to find out the concentration and dipping period which is effective to induce polyploid in musk melon plant, (2) identify the weight, diameter, dan flesh thickness of tetraploid musk melon as result of colchicines treatment. The sample of this research was Action 434 musk melon cultivar, product of Chia-Thai Seed, Thailand. The number of sample was 480 plants, which plants on field randomly. There were four colchicines concentration as an independent variable: 0.0 percent, 0.05 percent, 0.10 percent and 0.2 percent. The dipping period were 12, 16, 20, and 24 hours for each concentration respectively. Completely Random Design was used in three replications. Data measurement were analyzed with Two Way ANOVA, DMRT, and LSD. From this research can be concluded that: (1) 0.2 percent colchicine is the most effective concentration to induce polyploid on musk melon, with dipping period effective varied from 16–24 hours, (2) there are changes in weight, diameter, and flesh thickness characters, with the increased tendency of each character in definite norm.

IDENTIFIKASI BERAT, DIAMETER, DAN TEBAL DAGING BUAH MELON (Cucumis melo, L.) KULTIVAR ACTION 434 TETRAPLOID AKIBAT PERLAKUAN KOLKISIN:

Indonesian farmers are very dependence on certificated seed from another countries. In the other side the natural resources and men powers very abundance. For these reason it is properly developed the research in agriculture sector, especially on plants breeding. It can be hoped that in the future the dependence on certificated seed from another countries can be minimized. The objective of this research were: (1) to find out the concentration and dipping period which is effective to induce polyploid in musk melon plant, (2) identify the weight, diameter, dan flesh thickness of tetraploid musk melon as result of colchicines treatment. The sample of this research was Action 434 musk melon cultivar, product of Chia-Thai Seed, Thailand. The number of sample was 480 plants, which plants on field randomly. There were four colchicines concentration as an independent variable: 0.0%, 0.05%, 0.10% and 0.2%. The dipping period were 12, 16, 20, and 24 hours for each concentration respectively. Completely Random Design was used in three replications. Data measurement were analyzed with Two Way ANOVA, DMRT, and LSD. From this research can be concluded that: (1) 0.2 % colchicine is the most effective concentration to induce polyploid on musk melon, with dipping period effective varied from 16–24 hours, (2) there are changes in weight, diameter, and flesh thickness characters, with the increased tendency of each character in definite norm.

Effect of Meloidogyne javanica and M. incognita on Resistance of Muskmelon Cultivars to Fusarium Wilt

A growth chamber experiment was conducted to study the interaction between Meloidogyne javanica and/or M. incognita and the Fusarium wilt fungus Fusarium oxysporum f. sp. melonis, using three muskmelon cultivars differing in their resistance to the fungus. Inoculations were carried out l. with the wilt fungus alone, 14 and 28 days after transplanting; and 2. with the wilt fungus plus one or both root-knot nematodes, either directly upon transplanting, or 14 or 28 days after transplanting. In the course of the test all muskmelon cultivars, irrespective of their initial resistance to the wilt, almost completely lost their resistance when infected with M. javanica; resistance was also impaired but to a lesser extent with M. incognita. Wilting of 100% in the resistant and moderately resistant muskmelon cultivars inoculated with M. javanica + F. oxysporum f. sp melonis occurred 14 days earlier than in muskmelon inoculated with the fungus alone. Also, M. javanica was more severe on the plants than M. incognita. In all three cultivars, both root-knot nematode species hastened expression of plant wilting, which took 12.1 days with M. javanica, 14.8 days with M. incognita, and 12.3 days with both species combined, compared with 22.7 days for plants inoculated with Fusarium oxysporum f. sp. melonis alone. Moreover, the onset of wilting required 9–13.3 days when the nematode infection preceded F. oxysporum f. sp. melonis inoculation by two weeks, compared with 16.7– 19.7 days when the nematode and fungus were inoculated simultaneously 14 days after transplanting, indicating plant preconditioning by the nematode.

Extended Shelf Life in Transgenic `Galia' Melon (Cucumis melo L. var. reticulatus Ser.)

`Galia' is a high-quality muskmelon cultivar that is grown in green-houses or tunnels to maximize fruit yield and to help improve fruit quality. Maximum fruit quality and flavor are achieved when `Galia' are harvested at maturity. This however leads to reduced firmness and short shelf life. In vitro regeneration and transformation of `Galia' melon is a strategy that can be used to increase fruit shelf life. Melon cotyledons were transformed with the ACC oxidase gene in antisense orientation according to the protocol described by Nunez-Palenius et al. (2001, 2003). Experiments were conducted to compare fruit quality parameters between transgenic (TT) and wild type (WT) fruits from plants grown in greenhouse conditions. The melon plants were grown using commercial growing practices that included pruning and training to one vertical stem and the use of soilless media and drip fertigation. Wild type fruits were harvested at 37, 42, and 50 days after pollination (DAP), whereas transgenic fruits were harvested at 42, 50, and 56 DAP. TT fruits were harvested with that delaying period since their ripening process was slower than WT. Thirteen preharvest parameters were evaluated in transgenic and wild type fruits. Wild type and transgenic weight, lenght, width, soluble solids, tritatable acidity, pH, firmness, flesh thickness, seed cavity size and seed number parameters were not significantly different. Ethylene production and ACC oxidase from 42 DAP wild type fruits were greater than from transgenic fruits. Transgenic (ACC oxidase) galia melon fruits had a delayed fruit ripening process compared with wild type fruits.

Muskmelon seed priming in relation to seed vigor

A number of important factors may affect seed priming response, including seed quality. Effects of seed vigor on seed priming response were investigated using seed lots of two muskmelon (Cucumis melo L.) cultivars. Seeds of muskmelon, cvs. Mission and Top Net SR were artificially aged at 43°C for 0, 20 and 40 hours. Seeds were primed for six days in darkness at 25°C in KNO3 (0.35 mol L-1) aerated solution. Aged seeds germinated poorly at 17°C. Priming increased germination rate at 17 and 25°C and germination percentage at 17°C. An interaction effect on germination performance between vigor and priming was observed, especially at low temperature. Priming increased germination performance in seeds of low vigor, and the response was cultivar dependent.

Photosynthetic responses of muskmelon (Cucumis melo L.) to photon flux density, leaf temperature and CO2 concentration

Two cultivars (Huanghemi and Elizabeth) of muskmelon (Cucumis melo L.) were evaluated to determine the effect of photon flux density (PFD), leaf temperature, and CO,2 concentration on the net photosynthetic rate (Pn). The cultivars were evaluated under open field and solar-heated greenhouse conditions in northwest China. The Pn increased as the PFD increased, and then the rate of increase in Pn declined for Huanghemi and decreased for Elizabeth. Elizabeth registered 22 µmol m-2 s-1 for light compensation and 1127 µmol m-2 s-1 for light saturation, which, respectively, were 50 and 70% of those required by Huanghemi. The Pn increased with increasing leaf temperatures in the range of 9.8 to 50.8°C. The optimum temperature for photosynthesis was 35.3°C for muskmelon grown in open field, 2.4°C (7%) greater than that for muskmelon grown in the greenhouse. At optimal temperatures, the field-grown muskmelon had the Pn of 19.8 µmol m-2 s-1, 30% greater than that for the greenhouse-grown muskmelon. Both cultivars responded positively to CO2 concentrations of below the CO2 saturation points, whereas Huanghemi exhibited greater (51%) Pn and higher (49%) carboxylation efficiency than Elizabeth at optimal CO2 level. The two cultivars exhibited greater photosynthesis in open field than when grown in solar-heated greenhouses, while Elizabeth performed better than Huanghemi when light conditions were poor. Selective use of cultivars with low requirements for light and temperatures will enhance the photosynthesis and productivity of muskmelon grown in solar-heated greenhouses of northwest China. Key words: Light compensation, light saturation, photon flux density, transpiration

Seed Transmission of Acidovorax avenae subsp. citrulli in Cucurbits

Prevention of the introduction of bacterial fruit blotch of watermelon, caused by Acidovorax avenae subsp. citrulli, into the transplant house or field is the most effective control strategy. Watermelon seedlots currently are screened for A. avenae subsp. citrulli, but other cucurbits, often grown in the same transplant house or field, generally are not as carefully monitored. In 1997 and 1999 field tests, cultivars of watermelon, muskmelon, honeydew melons, acorn squash, butternut squash, yellow squash, zucchini squash, cucumber, and pumpkin were evaluated for foliar and fruit susceptibility to bacterial fruit blotch and for seed transmission of A. avenae subsp. citrulli. The bacterium was introduced into the field on infected watermelon transplants or by misting a bacterial suspension onto fruit of the cucurbits. Foliar and fruit symptoms were more extensive in the watermelon, muskmelon, and honeydew melons than in the other cucurbits. In greenhouse grow-out assays, seed transmission of A. avenae subsp. citrulli was detected in every cucurbit in at least one of the two seasons, even though there were no fruit symptoms in some of them. Thus, any cucurbit crop plant should be considered a potential source for the introduction of A. avenae subsp. citrulli into the transplant house or field.

Divergência genética entre cinco genótipos de melão rendilhado

Estimou-se a divergência genética entre cinco genótipos de melão rendilhado (Cucumis melo var. reticulatus Naud.) (JAB-20, JAB-21, JAB-22, JAB-23 e 'Bônus nº 2') e determinou-se qual a contribuição relativa das 16 características avaliadas [nº médio de flores masculinas, hermafroditas/planta; produção total de frutos/m², peso médio dos frutos comerciáveis; diâmetro médio transversal e longitudinal do fruto (DMTF e DMLF); diâmetro médio transversal da inserção do pedúculo (DMTP); espessura média do mesocarpo e epicarpo (EMM e EME); diâmetro médio longitudinal e transversal do lóculo (DMTL e DMLL); proporção da cavidade (PC); desprendimento de sementes (DS); teor de sólidos solúveis totais (SST), pH e acidez titulável (AT)] na divergência genética. Obtiveram-se dois grupos de similaridade: I- JAB-20, JAB-21 e 'Bônus nº2' e II- JAB-22 e JAB-23. As características DMLF, DMTP, DMLL, DS e SST foram as que mais contribuíram para a divergência genética entre os genótipos.

Relationships between volatile composition and sensory evaluation in eight varieties of netted muskmelon (Cucumis melo L var reticulatus Naud)

AbstractThe quality parameter of muskmelon (Cucumis melo L var reticulatus Naud) is often identified with the sugar content, particularly sucrose. However, high soluble solids concentration at harvest does not always correspond with high overall fruit quality and should be used in conjunction with the evaluation of aroma. In order to find quality indices, correlations were checked between aroma compounds detected on the melon pulp by headspace gas chromatography and sensory evaluation. Eight cultivars of muskmelon were analysed for their aroma content and other quality parameters. Aroma compounds were mainly esters, while (Z)‐6‐nonenal and (E)‐6‐nonenol, characteristic of melon, were not detected with the technique used. The data were subjected to statistical analyses in order to find significant correlations. High values of correlation were not found between chromatographic and sensory data, but a high correlation was found between total aromas and ethyl esters, both data of analytical source. This fact means that ethyl esters could be very important compounds for melon flavour and could be considered as markers of a good‐quality aroma.© 2002 Society of Chemical Industry

Rootstock resistance to fusarium wilt and effect on fruit yield and quality of two muskmelon cultivars

Pending the release of new genetic material with satisfactory resistance, grafting techniques may represent a quick, though expensive method for controlling race 1,2 of Fusarium oxysporum f. sp. melonis in Italian growing regions of melon ( Cucumis melo L.). We evaluated the potential of grafting for resistance to this pathogen in 13 commercial melon rootstocks and various Cucurbitaceae spp. and determined productivity and fruit quality characteristics of grafting on resistant rootstocks. Following inoculation, P360 and PGM 96-05 commercial rootstocks, as well as Benincasa hispida, Cucumis metuliferus, Cucumis ficifolius, Cucurbita maxima, Cucurbita moschata, and Lagenaria siceraria were resistant to the race 1,2 of Fusarium. Yield and quality attributes of scion cultivars (Supermarket and Proteo) grafted on P360 and PGM 96-05 rootstocks were not improved relative to ungrafted controls. Grafts onto B. hispida negatively influenced both yield and fruit quality, while C. metuliferus, and C. zeyheri had negative impacts on productivity and fruit quality, respectively. These results indicate that rootstock influences on disease resistance as well as productivity and quality of scion fruit are important in determining the potential utility of grafting applications.

Isolation of Nonpathogenic Mutants of Fusarium oxysporum f. sp. melonis for Biological Control of Fusarium Wilt in Cucurbits

ABSTRACT Two nonpathogenic mutant strains 4/4 and 15/15 of Fusarium oxysporum f. sp. melonis (race 1,2) were isolated by a continuous dipinoculation technique following UV mutagenesis of the virulent wild-type isolate FOM1.2. No disease symptoms or detrimental effects were observed following inoculation of muskmelon seedlings by strain 4/4. In contrast, strain 15/15 caused mortality of susceptible cultivars although to a lesser extent than the wild-type isolate. Strain 4/4 colonized a variety of muskmelon and watermelon cultivars. In muskmelon cv. Ein Dor, seedlings were dipped in a conidial suspension of strain 4/4 and planted in medium amended with the mutant to achieve 100% colonization of roots and between 30 to 70% of the lower stem tissues 7 days after planting. Similar percent colonization of watermelon seedlings by strain 4/4 was recorded. In cross-protection experiments with muskmelon cultivars, significant reduction in seedling mortality was observed between 4/4-colonized FOM1.2. challenged plants compared with that of wild-type challenged plants alone. Similarly, strain 4/4 was able to significantly reduce mortality of watermelon seedlings caused by F. oxysporum f. sp. niveum race 2. This novel approach of generating nonpathogenic mutants for biological control in Fusarium spp. and other fungal pathogens from virulent wild-type isolates may be beneficial for control, because the mutant strains, lacking only in pathogenicity, may compete more efficiently than other biocontrol organisms against the pathogen of origin.

Fusarium wilt of field-grown muskmelon in British Columbia

A wilt disease of field-grown muskmelon (Cucumis melo L. var. cantalupensis) was observed during the 1999 and 2000 growing seasons on three farms in the semi-arid interior region near the Okanagan Valley of British Columbia. Initial symptoms were yellowing and wilting of leaves, which sometimes occurred unilaterally; in some cases, this was followed by plant death prior to flowering. The crown area of diseased plants had dark brown lesions that progressed into lateral branches for distances of 45—75 cm. Some lesions also extended into the developing fruit, which frequently became infected and rotted. Stem lesions were accompanied by dark brown exudate droplets and necrosis extended into the cortical and vascular regions. Plants with fruit collapsed when temperatures exceeded 25-s30°C in mid-July and early August. White mycelium developed on the infected crown area and on fruits collected from mature plants in the field, after incubation under high humidity conditions, and macroconidia and microconidia of Fusarium oxysporum Schlechtend.:Fr. were produced. A number of muskmelon cultivars were affected, and the most susceptible were Galia and Castella, while Athena appeared unaffected in the field. Pathogenicity tests demonstrated that muskmelon was the only susceptible host and no disease symptoms developed on cucumber (Cucumis sativus L.), watermelon (Citrullus vulgaris Eckl. & Zeyh), or squash (Cucurbita pepo L.). Based on symptomology and host range, the pathogen was identified as F. oxysporum Schlechtend. f. sp. melonis (Leach & Currence) W.C. Snyder & H.N. Hans. Inoculation of a set of differential muskmelon cultivars revealed that the pathogen was F. oxysporum f. sp. melonis race 1. The pathogen was recovered from diseased transplants in a propagation greenhouse and from seed recovered from naturally infected fruits on mature plants in the field. This is the first report of fusarium wilt of muskmelon in British Columbia, and the first report of race 1 of F. oxysporum f. sp. melonis in Canada.

Influence of cultivar and osmotic dehydration time on aroma profiles of muskmelon ( Cucumis melo, cv reticulatus Naud.) spheres

Among several factors affecting the osmotic dehydration process, the raw material characteristics play a fundamental role. As aroma is one of the major determinants of fruit quality, the influence was studied of both the cultivar and the processing time of dewatering–impregnation–soaking (DIS) on the aroma profiles of muskmelon spheres, in order to optimise the technique as a pre-treatment to further processing. Muskmelon cultivar Mirado and Rony, manually cut into 28 mm diameter spheres, were subjected to osmotic dehydration at 25°C for 1, 2, 4 and 6 h in a 60% (wt/wt) sucrose syrup. Both muskmelon cultivars showed higher uptake of soluble solids when compared with other fruit and there was a higher water loss in cultivar Mirado than cultivar Rony during the whole process. The aroma profile of melon cultivar Rony was less modified by DIS, indicating a better suitability for this type of pre-treatment. `Positive' aroma compounds did not decrease in cultivar Rony, and `negative' ones significantly increased only after 6 h of DIS. Possible differences in tissue structure could account for the different behaviour of the two cultivars.

Temperature Effects on Phenological Development and Yield of Muskmelon

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. A growth chamber experiment was conducted with two cultivars of muskmelon (‘Gold Rush’ and ‘Mission’) 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 (34°C) at which the rate of leaf appearance was maximal; and an upper threshold temperature (45°C) at which 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 were determined for three cultivars of muskmelon (‘Explorer’, ‘Gold Rush’ and ‘Mission’) grown in the field at Overton, TX, USA, over six transplanting dates from March to June 1998. 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 (ΣTu). 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 impairing reproductive development. As air temperatures increased during the field experiment, the time interval from transplanting to 10% final harvest was reduced by 21 to 28d among the three cultivars and the first four transplanting dates. Main vine node number was a useful descriptor of vegetative development for muskmelon.

A Simple Phenological Model of Muskmelon Development

Utilizing information gathered in previous growth chamber and field experiments, we developed a simple temperature-driven crop phenology model of muskmelon (Cucumis melo L.) to help commercial growers time crop phenological events and predict harvest dates. The model quantifies vegetative development in terms of main vine node numbers which allows the model to simulate either a direct-seeded or a transplanted crop. The model operates on an hourly time-step but requires only daily weather data and a few cultivar-specific parameters including plastochron interval and thermal time requirements to reach six predefined developmental stages. The model was tested against an independent data set consisting of three muskmelon cultivars grown at five transplanting dates. Tests of the model indicate an average ability to predict main vine node numbers to within one to two nodes of observed values. Estimated harvest date predictions were more variable than those for main vine node number but an average model accuracy of 1 to 3d was obtained in model tests with a data set used to construct the model. Procedures for calibrating the model for different cultivars, cultural practices or environments are outlined.

Muskmelon Fruit Soluble Acid Invertase and Sucrose Phosphate Synthase Activity and Polypeptide Profiles during Growth and Maturation

Muskmelon [Cucumis melo L. (Reticulatus Group)] fruit sugar content is the single most important consumer preference attribute. During fruit ripening, sucrose accumulates when soluble acid invertase (AI) activity is less then sucrose phosphate synthase (SPS) activity. To genetically heighten fruit sugar content, knowledge of sugar accumulation during fruit development in conjunction with AI and SPS enzyme activities and their peptide immunodetection profiles, is needed. Two netted muskmelon cultivars, Valley Gold a high sugar accumulator, and North Star a low sugar accumulator, with identical maturity indices were assayed for fruit sugars, AI and SPS activity, and immunodetection of AI and SPS polypeptides 2, 5, 10, 15, 20, 25, 30, 35, or 40 (abscission) days after anthesis (DAA). Both cultivars, grown in the Fall, 1998 and Spring, 1999, showed similar total sugar accumulation profiles. Total sugars increased 1.5 fold, from 2 through 5 DAA, then remained unchanged until 30 DAA. From 30 DAA until abscission, total sugar content increased, with `Valley Gold' accumulating significantly more than `North Star'. During both seasons, sucrose was detected at 2 DAA, which coincided with SPS activity higher than AI activity, at 5 through 25 DAA, no sucrose was detected which coincided with SPS activity less than AI activity. At 30 DAA when SPS activity was greater than AI activity, increased sucrose accumulation occurred. `Valley Gold' at abscission had higher total sugar content and SPS activity, and lower AI activity than `North Star'. `North Star' had AI isoforms at 75, 52, 38, and 25 kDa (ku) that generally decreased with maturation, although the isoform at 52 ku remained detectable up to anthesis (40 DAA). `Valley Gold' had the same four AI isoforms, all decreased with maturation and became undetectable by 20 DAA. Both `Valley Gold' and `North Star' had one SPS band at 58 ku that increased with DAA, and coincided with SPS activity. `Valley Gold' had a more intense SPS polypeptide band at abscission than `North Star'. Thus, netted muskmelon fruit sugar accumulation may be increased, either by genetic manipulation or by selecting for cultivars with a specific number of down-regulated AI isoforms, and higher SPS activity during fruit ripening.

591 MelonMan: A Simple Phenology Model of Muskmelon Development

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.

174 Muskmelon Fruit Soluble Acid Invertase and Sucrose Phosphate Synthase Activity and Polypeptide Profiles during Growth and Maturation

Muskmelon [Cucumis melo L. (Reticulatus Group)] fruit sugar content is the single most important consumer preference attribute. During fruit ripening, sucrose accumulates when soluble acid invertase (AI) activity is less then sucrose phosphate synthase (SPS) activity. To genetically heighten fruit sugar content, knowledge of sugar accumulation during fruit development in conjunction with AI and SPS enzyme activities and their peptide immunodetection profiles is needed. Two netted muskmelon cultivars [`Valley Gold' (VG), a high sugar accumulator, and `North Star' (NS), a low sugar accumulator] with similar maturity indices were assayed for fruit sugars, AI, and SPS activity and immunodetection of AI and SPS polypeptides following 2, 5, 10, 15, 20, 25, 30, 35, and 40 (abscission) days after anthesis (DAA). Both cultivars, grown in spring and fall, showed similar total sugar accumulation profiles. Total sugars increased 1.5 fold, from 2 through 5 DAA and then remained unchanged until 30 DAA. From 30 DAA until abscission, total sugar content increased, with VG accumulating significantly more sugar then NS. In both cultivars, during both seasons, sucrose was detected at 2 DAA, which coincided with higher SPS activity than AI activity. At 5 through 25 DAA, SPS activity was less then AI activity resulting in little or no sucrose detection. It was not until 30 DAA that SPS activity was greater than AI activity resulting in increased sucrose accumulation. VG at abscission had higher total sugar content and SPS activity and lower AI activity than NS. Total polypeptides from both cultivars 2 through 40 DAA, were immunodetected with antibodies: anti-AI and anti-SPS. NS had Al isoforms bands at 75, 52, 38, and 25 kDa that generally decreased wtih DAA. One isoform at 52 kDa remained detectable up to anthesis (40 DAA) VG had the same four Al isoforms, all decreased with DAA and became undetectable by 20 DAA. It is unclear if one or all AI isoforms correspond with detected enzyme activity. VG and NS had one SPS band at 58 kDa that increased with DAA and concomitantly with SPS activity. VG had a more intense SPS polypeptide band at abscission then did NS. Thus, netted muskmelon sugar accumulation may be increased by selecting for cultivars with a specific number of AI isoforms, which are down-regulated, and with high SPS activity during fruit ripening.

A study of oxalate-induced systemic resistance of muskmelon to squash mosaic virus

By treatment with oxalate muskmelon cultivar “Wangwenxiang”, which is sensitive to squash mosaic virus (SqMV), develops systemic resistance to SqMV significantly. The challenge inoculation experiments indicate that the symptom of oxalate-treated plants gets much slighter, the virus content is only 4% reduced to. The peroxidase activity increases by five times, three new isoperoxidases are induced, and lignin content increases by 82.9 %. These results indicate that oxalate induces systemic resistance of muskmelon to SqMV while it induces increase of peroxidase activity, new isoperoxidases and content of lignin in the plants treated with oxalate.