Commercial Melon Research Articles

A temporal genetic analysis of disease resistance genes: resistance to melon vine decline derived from Cucumis melo var. agrestis

AbstractMelon vine decline causes severe economic losses to melon crops all over the world. Two fungi. Acremonium cucurbitacearum and Monosporascus cannonballus, have been reported as the main causal agents of root damage, responsible for the decrease in root water and nutrient uptake capacity. However, melon vine decline aetiology is not completely understood, so screening assays must be conducted under natural infestation conditions. In field assays, the erratic effect of uncontrolled environmental factors makes the study of the trait's genetics difficult. The percentage of asymptomatic plants scored at individual moments during the infection process in the field is an imprecise indicator of the resistance level of each genotype. The analysis of disease progress curves does allow for the minimization of the stochastic fluctuations caused by environmental factors at various moments in time. Using this analysis the mode of inheritance of the partial resistance to melon vine decline derived from the accession Pat 81 of Cucumis melo var. agrestis was further studied. Data from the six generations assayed (susceptible and resistant parents. F1, F2, and backcrosses BC1 and BC2 were fitted to an additive/dominance model without epistatic effects using a scaling test. Monogenic control was proposed as the simplest model to explain the data. Assuming this simple model, the method of analysis also allowed for the characterization of the incomplete penetrance of resistance, which varies as a log probit function of the time. Simple genetic control would simplify the use of Pat 81 in breeding programmes aimed at developing commercial melon varieties with resistance to vine decline.

Stable isotope ratios of carbon and nitrogen in natural populations of Drosophila species and their hosts

Abstract1. Stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) were determined in seven species of wild‐caught Drosophila (see Patterson & Stone 1952) and their natural hosts in order to assess if any relationships existed between isotope signatures of the flies and their hosts. The species included the cosmopolitan D. hydei, D. arizonae, D. simulans and D. pseudoobscura collected from rotting fruit (commercial melons), and the cactophilic D. nigrospiracula, D. mojavensis and D. pachea collected from their specific host plants (Saguaro, Organpipe and Senita Cactus, respectively).2. Isotope signatures were clearly different among the natural hosts, with fruit and each species of cactus segregating into a non‐overlapping pattern on plots of δ13C vsδ15N.3. Wild‐caught Drosophila exhibited interspecific differences in isotope signatures that reflected the patterns observed for their natural hosts. For most species, values for δ15N were 3·0–5·‰ higher in the flies, in agreement with the expected δ15N enrichment with increased trophic level.4. For D. nigrospiracula, changing food resources from the natural host (Saguaro) to a laboratory diet of yeast for only 24 h resulted in a shift in stable isotope signatures toward the values of the new resource.5. The results suggest that stable isotope analysis can be a valuable tool in studies of resource ecology and feeding habitats in Drosophila, and is sensitive enough to detect recent feeding history.

Characterization of the seed oils of some commercial cultivars of melon

Proximate analysis of the seeds from three commercial melon cultivars (Honey Dew, Hy-mark and Orange Flesh) showed high percentage of lipids (25.7—27.6%) and proteins (15.2—19.2%). The physico-chemical properties of the hexane-extracted oil from the seeds of these cultivars were determined. Gas chromatographic analysis of the oils showed the presence of almost all fatty acids starting from C6— C24 except that of C11 , C21 C23 , C18:2 being the principal fatty acid followed by C18:1 , C16:0 , and C18:0 fatty acids. The number of fatty acids, which were present in concentrations higher than 0.01% of total fatty acids, was 17, 14, and 13, respectively, in these cultivars

Characterization of the seed oils of some commercial cultivars of melon

Proximate analysis of the seeds from three commercial melon cultivars (Honey Dew, Hy-mark and Orange Flesh) showed high percentage of lipids (25.7—27.6%) and proteins (15.2—19.2%). The physico-chemical properties of the hexane-extracted oil from the seeds of these cultivars were determined. Gas chromatographic analysis of the oils showed the presence of almost all fatty acids starting from C6— C24 except that of C11 , C21 C23 , C18:2 being the principal fatty acid followed by C18:1 , C16:0 , and C18:0 fatty acids. The number of fatty acids, which were present in concentrations higher than 0.01% of total fatty acids, was 17, 14, and 13, respectively, in these cultivars

Occurrence, Distribution, and Relative Incidence of Mosaic Viruses Infecting Field-Grown Melon in Spain.

The main areas for field-grown melon (Cucumis melo) production in Spain were surveyed for the occurrence and relative incidence of cucumber mosaic virus (CMV), papaya ringspot virus-watermelon strain (PRSV-W), watermelon mosaic virus-2 (WMV-2), and zucchini yellow mosaic virus (ZYMV) during the growing seasons of 1995 and 1996. Samples from 1,152 plants showing symptoms of virus infection were collected from commercial melon fields and analyzed by enzyme-linked immunosorbent assay (ELISA). CMV and WMV-2 were the most frequently found viruses, both by the number of locations and by their incidence in each location. In contrast, PRSV-W and ZYMV were detected in fewer sites and at lower incidences. PRSV-W was not found in 1996. In 79% of the samples, only one virus was detected; 15% of the samples were doubly infected. Both the incidence of plants showing symptoms of viral infection and the relative incidence of each of the four viruses varied according to the region, while the main trends of virus distribution were similar for 1995 and 1996.

Evaluation of U.S. Honeydew-type Melons for Resistance against Downy Mildew and Alternaria Leaf Blight

Seventeen U.S. honeydew-type cultivars of melon (Cucumis melo L.) and three control cultigens were evaluated in replicated, artificial inoculations under controlled conditions for resistance against downy mildew and Alternaria leaf blight. All cultivars tested were susceptible to downy mildew. However, all of the tested cultivars were significantly more resistant to Alternaria leaf blight than the susceptible control. Twelve of these cultivars were not significantly more susceptible to Alternaria leaf blight than the two resistant controls. These cultivars may provide useful sources of Alternaria leaf blight resistance for incorporation into other commercial melon types.

Resistance mechanisms of Cucumis melo var. agrestis against Trialeurodes vaporariorum and their use to control a closterovirus that causes a yellowing disease of melon

One of the yellowing diseases that affects melon (Cucumis melo) crops cultivated under plastic greenhouses in southern Europe is caused by a closterovirus transmitted by the greenhouse whitefly Trialeurodes vaporariorum. A Cucumis melo var. agrestis accession shows a certain level of resistance to that virus. Under free‐choice conditions, the reproduction of T. vaporariorum on this accession was significantly lower than on the susceptible control accession C. melo cv. ‘Bola de Oro’, and this suggests that T. vaporariorum prefers to colonize other accessions before C. melo var. agrestis. Under no‐choice conditions, we observed that T. vaporariorum reproduction on C. melo var. agrestis was less than on the susceptible controls. The results showed the participation of both antixenosis and antibiosis resistance mechanisms against T. vaporariorum in C. melo var. agrestis. It is difficult to cultivate melon completely free from T. vaporariorum and yellowing disease. However, success in breeding commercial melon cultivars which incorporate the antixenosis and antibiosis found in C. melo var. agrestis together with biological or chemical insect control, or a combination of these, would reduce the insect population and, therefore, the melon‐yellowing disease would occur later and in less severe form.

Protoplast regeneration and fusion in Cucumis: melon × cucumber

The aim of this investigation was to develop a protocol to be used in asymmetric protoplast fusions with breeding material of melon and cucumber. Efficient methods for plant regeneration from unfused protoplasts of commercial melon lines were established and are reported. Ploidy levels of explant material and plants, regenerated from protoplasts were analyzed. Electrofusion was carried out between melon protoplasts and irradiated and non-irradiated donor protoplasts of cucumber. Although initial plating efficiencies of heterokaryons were high, development stopped after a few divisions. In control experiments, shoots were regenerated at high frequencies. In only two fusion experiments, development continued to the callus stage, but further development was not observed. When analyzed with PCR using arbitrary primers, the majority of these calli DNA were identical to the melon DNA. However, a few of the examined calli, although being mainly homologous to melon, were observed to have new bands corresponding to bands specific for cucumber. Due to sexual incompatibility, successful hybridization between cucumber and melon was never obtained by sexual crosses. We suggest that the failure to regenerate plants in our fused material could be explained partially by an analogous somatic incompatibility reaction.

Control of Striped Cucumber Beetle in Muskmelon, 1987

Abstract A comparison of soil systemics to presently used foliars for control of cucumber beetle on muskmelon was made in a commercial melon field near Belle Plaine, Minn. Plots were a single row, 50 ft long, replicated 4 times, and arranged in a randomized complete block design. The granular Furadan was distributed by hand over the row immediately behind the plants and lightly covered. The Furadan 4F was applied in 25 gal water/acre in a 4-inch band over the row immediately after transplanting. Transplant date was 2 Jun. The entire field was irrigated due to extreme drought. Soils were sandy loam. Foliar applications were made on 10 and 24 Jun and 6 and 25 Jul using a CO2 sprayer at 40 psi pressure and 17 gal/acre total material. Phytotoxicity, wilted plants, and row width—a measure of growth—were recorded.