Perry E. Nugent
Robert L. Long, Kerry B. Walsh, David J. Midmore, and Gordon Rogers
A common practice for the irrigation management of muskmelon (Cucumis melo L. reticulatus group) is to restrict water supply to the plants from late fruit development and through the harvest period. However, this late fruit development period is critical for sugar accumulation and water stress at this stage is likely to limit the final fruit soluble solids concentration (SSC). Two field irrigation experiments were conducted to test the idea that maintaining muskmelon plants free of water stress through to the end of harvest will maximise sugar accumulation in the fruit. In both trials, water stress before or during harvest detrimentally affected fruit SSC and fresh weight (e.g., no stress fruit 11.2% SSC, weight 1180 g; stress fruit 8.8% SSC, weight 990 g). Maintaining plants free of water stress from flowering through to the end of harvest is recommended to maximise yield and fruit quality.
D.J. Gray, D.W. McColley, and Michael E. Compton
A protocol for high-frequency somatic embryogenesis in Cucumis melo L. was developed using `Male Sterile A147 as a model cultivar. Basal halves of quiescent seed cotyledons were cultured on embryo induction (EI) medium containing concentration ranges of the auxin 2,4-D and the cytokinins BA, Bin, TDZ, or 2iP before transfer to embryo development (ED) medium. Medium with 2,4-D at 5 mg·liter-1 and TDZ at 0.1 mg·liter-1 was superior, with 49% of explants responding and an average of 3.3 somatic embryos per explant (6.8 somatic embryos per responding explant). More explants produced embryos when incubated on EI medium for 1 or 2 weeks (30% and 33%) than for 3 or 4 weeks or with no induction. However, 2 weeks was 2.9 times better than 1 week in terms of number of embryos per explant. One week of initial culture in darkness, followed by a 16 hour light/8 hour dark photoperiod, produced more responding explants (26%) than two or more weeks in darkness or no dark period at all; but 1 and 2 weeks of darkness resulted in a similar number of embryos per explant (2.1 and 2.8). Sucrose concentration in EI and ED media had a highly significant effect on embryo induction and development. EI medium with 3% sucrose resulted in more embryogenic explants than EI medium with 1.5% or 6% sucrose. However, treatments with 3% sucrose in EI medium and 3% or 6% sucrose in ED medium produced significantly more embryos per explant (8.5 and 11.9) than other treatments. Treatments did not affect embryo induction directly and regeneration per se but, instead, frequency and efficiency of somatic embryo development. The optimal treatments were tested with 51 other commercial varieties. All varieties underwent somatic embryogenesis, exhibiting a response of 5% to 100% explant response and 0.1-20.2 embryos per explant. Chemical names used: N-(phenylmethyl)-lH-purin-6-amine (benzyladenine or BA); N-(2-furanylmethyl)-lH-purin-6-amine (kinetin or BIN); N-phenyl-N'-1,2,3-thiadiazol-5-ylurea (thidiazuron or TDZ); N-(3-methyl-2-butenyl)-lH-purin-6-amine (2iP); (2,4-dichlorophenoxy) acetic acid (2,4-D).
Thomas J. Kalb II and D. W. Davis
Combining ability and heterosis for yield, maturity, and plant traits in bush muskmelon (Cucumis melo L.) were estimated through the use of a 6-parent diallel evaluated in 1981 at Excelsior, Minn. and at Santa Paula, Calif. The variance of GCA was greater than that of SCA for all traits. Minnesota 266 was the best general combiner for yield weight characteristics. Minnesota 101 was exceptional for GCA in those traits associated with earliness, and U.C. Perlita Bush and U.F. G508 combined well for main crop yield. Correlations between the performance of parental lines and the average of their hybrids were consistently positive and often significant. Favorable heterosis over the midparent was found for all traits but days to first fruit. Favorable heterosis over the superior parent was found for plant health and all yield traits except total number of fruit per plant. In a 3 × 10 design II at Excelsior, estimates of additive variance exceeded those of dominance variance in general, providing for moderately high heritability estimates (40–70%) for most traits.
Thomas J. Kalb II and D. W. Davis
A 6-parent diallel was established in 1981 at Excelsior, Minn, and at Santa Paula, Calif, to analyze combining ability and heterosis for fruit quality of traits in bush muskmelon (Cucumis melo L.). GCA variance exceeded SCA variance for all traits. Minnesota breeding lines were superior in GCA for most interior quality traits, but inferior to Florida and California lines in exterior quality. Correlations between the performance of parents and the average of their hybrids were consistently positive, and often significant. Favorable heterosis over the midparent was shown for soluble solids, net density, and net rope, and, to a lesser extent, for flesh amount, rind thickness, cavity amount, and cavity dryness. A 3 × 10 design II at Excelsior showed estimates of additive variance exceeding those of dominance variance for all traits except fruit weight, shape index, and vein tract. The large estimates of additive variance provided for moderately high (40–70%) estimates of heritability for most traits.
D. L. Hughes, Judy Bosland, and M. Yamaguchi
Individual leaves of Cucumis melo L. acropetal to a developing fruit were treated with a pulse of 14CO2. The level of 14C in the leaves, internodes, and fruits was determined after various periods of time when the leaf at the 3rd node acropetal to the fruit was treated. Leaves at the same node as the fruit, the 2nd, the 3rd, the 6th, and the 18th node acropetal to the fruit were treated and the level of 14C in the leaf, internodes, and fruit was determined after 2 hours. The percent of the incorporated 14C which was exported from the leaf was strongly affected both by time and leaf position relative to the fruit. Leaves which were 3 nodes acropetal to the fruit exported 65% of the label in 6 hours, while those further from the fruit retained the label longer. The influence of the fruit on the movement of 14C label is limited to a few internode lengths along the branch.
John A. Wells and Perry E. Nugent
‘Edisto’ and ‘Saticoy Hybrid’ muskmelon (Cucumis melo L.) were grown at 2 soil moisture levels. Soil moisture was negatively correlated with soluble solids content (SSC) in the fruit of both cultivars and negatively correlated with dry matter, ascorbic acid, β-carotene, and sucrose content in ‘Edisto’ and with ascorbic acid content in ‘Saticoy’. In both cultivars, SSC was highly correlated with ascorbic acid, sucrose, and dry matter content. The SSC, a commonly used measure of fruit quality, may be misleading unless the effect of soil moisture is considered.
Laurie Hodges, Entin Daningsih, and James R. Brandle
Field experiments were conducted over 4 years to evaluate the effects of antitranspirant (Folicote, Aquatrol Inc., Paulsboro, N.J.) and polyacrylamide gel (SuperSorb, Aquatrol Inc., Paulsboro, N.J.) on early growth of transplanted muskmelon grown either protected by tree windbreaks or exposed to seasonal winds. A randomized complete block design (RCBD) with split plot arrangement was used with wind protection (sheltered and exposed) areas as the main treatment and use of an antitranspirant spray or gel dip as subtreatments. Based on destructive harvests in the field, treatments and subtreatments did not affect dry weight or leaf area index in the first 2 years. Specific contrasts, however, showed that gel application significantly increased fresh weight, dry weight, and leaf area index over that of the untreated transplants whereas the spray application tended to reduce these factors during the first 3 weeks after transplanting. Significant differences between gel and spray subtreatments disappeared by 5 weeks after transplanting. Shelterbelts ameliorated crop microclimate thereby enhancing plant growth. Significantly, wind velocity at canopy height was reduced 40% on average and soil temperatures were about 4% warmer in the sheltered plots compared to the exposed plots during the first 5 weeks post-transplant. Muskmelon plants in the sheltered areas grew significantly faster than the plants in the exposed areas in 2 of the 3 years reported, with the 3-year average fresh weight increased by 168% due to wind protection. Overall transplanting success and early growth were enhanced the most by wind protection, followed by the polyacrylamide gel root dip, and least by the antitranspirant foliar spray. We conclude that microclimate modification by wind speed reduction can increase early muskmelon plant growth more consistently than the use of polyacrylamide gel as a root dip at transplanting or the use of an antitranspirant spray. A polyacrylamide gel root dip generally will provide more benefit during early muskmelon growth than the use of an antitranspirant spray.
Yigal Cohen, Helena Eyal, and Avraham Cohen
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.