Gene E. Lester

Melon Fruits: Genetic Diversity, Physiology, and Biotechnology Features

Among Cucurbitaceae, Cucumis melo is one of the most important cultivated cucurbits. They are grown primarily for their fruit, which generally have a sweet aromatic flavor, with great diversity and size (50 g to 15 kg), flesh color (orange, green, white, and pink), rind color (green, yellow, white, orange, red, and gray), form (round, flat, and elongated), and dimension (4 to 200 cm). C. melo can be broken down into seven distinct types based on the previously discussed variations in the species. The melon fruits can be either climacteric or nonclimacteric, and as such, fruit can adhere to the stem or have an abscission layer where they will fall from the plant naturally at maturity. Traditional plant breeding of melons has been done for 100 years wherein plants were primarily developed as open-pollinated cultivars. More recently, in the past 30 years, melon improvement has been done by more traditional hybridization techniques. An improvement in germplasm is relatively slow and is limited by a restricted gene pool. Strong sexual incompatibility at the interspecific and intergeneric levels has restricted rapid development of new cultivars with high levels of disease resistance, insect resistance, flavor, and sweetness. In order to increase the rate and diversity of new traits in melon it would be advantageous to introduce new genes needed to enhance both melon productivity and melon fruit quality. This requires plant tissue and plant transformation techniques to introduce new or foreign genes into C. melo germplasm. In order to achieve a successful commercial application from biotechnology, a competent plant regeneration system of in vitro cultures for melon is required. More than 40 in vitro melon regeneration programs have been reported; however, regeneration of the various melon types has been highly variable and in some cases impossible. The reasons for this are still unknown, but this plays a heavy negative role on trying to use plant transformation technology to improve melon germplasm. In vitro manipulation of melon is difficult; genotypic responses to the culture method (i.e., organogenesis, somatic embryogenesis, etc.) as well as conditions for environmental and hormonal requirements for plant growth and regeneration continue to be poorly understood for developing simple in vitro procedures to culture and transform all C. melo genotypes. In many cases, this has to be done on an individual line basis. The present paper describes the various research findings related to successful approaches to plant regeneration and transgenic transformation of C. melo. It also describes potential improvement of melon to improve fruit quality characteristics and postharvest handling. Despite more than 140 transgenic melon field trials in the United States in 1996, there are still no commercial transgenic melon cultivars on the market. This may be a combination of technical or performance factors, intellectual property rights concerns, and, most likely, a lack of public acceptance. Regardless, the future for improvement of melon germplasm is bright when considering the knowledge base for both techniques and gene pools potentially useable for melon improvement.

Impact of potassium nutrition on postharvest fruit quality: Melon (Cucumis melo L) case study

Among the many plant mineral nutrients, potassium (K) stands out as a cation having the strongest influence on quality attributes that determine fruit marketability, consumer preference, and the concentration of critically important human-health associated phytonutrients. However, many plant, soil, and environmental factors often limit adequate uptake of K from the soil in sufficient amounts to satisfy fruit K requirements during development to optimize the aforementioned quality attributes. The objectives of this review are 1) to summarize published study abstracts on the effects of soil and/or foliar K fertilization as well as diverse K forms, on fruit phytonutrient concentrations; and 2) to illustrate the important role of K forms on fruit quality with a case study of Cucumis melo L (muskmelon) fruit produced with optimal soil applied K . The muskmelon studies will compare commercial sources (forms) of K applied to examine seasonal effects (spring vs. autumn) and the number of foliar K applications during fruit development on fruit marketability (maturity, yield, firmness, soluble solids, sugars, relative sweetness), consumer preference attributes (sugar content, sweetness, texture), and phytochemical concentrations (K, ascorbic acid, and β-carotene concentrations). Numerous studies have consistently demonstrated that specific K fertilizer forms, in combination with specific application regimes, can improve fruit quality attributes. Potassium fertilizer forms in order of effectiveness (Glycine (Gly)-complexed K = K2SO4 ≥ KCl > no K > KNO3) when applied wet (foliar or hydroponic) vs. dry (soil) were generally superior in improving fruit marketability attributes, along with many human-health nutrients. The muskmelon case study demonstrated that two K forms: Gly-complexed K and K2SO4, combined with a silicone-based surfactant, applied weekly, as a foliar spray, during fruit development, from both autumn and spring-grown plants, had the greatest impact on improving fruit marketability attributes (maturity, yield, firmness, and sugars), as well as fruit quality attributes (human-health bioactive compounds K, ascorbic acid, and β-carotene). Among several foliar applied K salts studied under field conditions so far, salts with relatively low salt indices appeared to have the greatest impacts on fruit quality when applied during the mid- to late-season fruit development periods.

Profiling Polyphenols in Five Brassica species Microgreens by UHPLC-PDA-ESI/HRMSn

Brassica vegetables are known to contain relatively high concentrations of bioactive compounds associated with human health. A comprehensive profiling of polyphenols from five Brassica species microgreens was conducted using ultrahigh-performance liquid chromatography photodiode array high-resolution multistage mass spectrometry (UHPLC-PDA-ESI/HRMS(n)). A total of 164 polyphenols including 30 anthocyanins, 105 flavonol glycosides, and 29 hydroxycinnamic acid and hydroxybenzoic acid derivatives were putatively identified.The putative identifications were based on UHPLC-HRMS(n) analysis using retention times, elution orders, UV-vis and high-resolution mass spectra, and an in-house polyphenol database as well as literature comparisons. This study showed that these five Brassica species microgreens could be considered as good sources of food polyphenols.

Antioxidant, sugar, mineral, and phytonutrient concentrations across edible fruit tissues of orange-fleshed honeydew melon (Cucumis melo L.).

Orange-fleshed, non-netted honeydew ( Cucumis melo L.) is a relatively new melon in the marketplace and has shown a lot of potential as an alternative to netted muskmelons (cantaloupes), which are often prone to surface contamination by enteric bacteria. Orange-fleshed honeydew is a cross between orange-fleshed cantaloupe and non-netted, green-fleshed honeydew. This glasshouse study investigated the nutritional profile (phytonutrient and sugar contents) in different tissues of mature orange-fleshed honeydew melon fruit. The equatorial mesocarp of ripe fruit was segmented into hypodermal (subpeel), outer, middle, and inner (near the seed cavity) tissues and then assayed for total sugars, mineral nutrients, phytonutrients, total proteins, and enzymatic antioxidant activities. The concentrations of soluble solids, sucrose, total sugars, beta-carotene, and 5-methyltetrahydrofolic acid increased in an inward direction from the subpeel mesocarp tissues toward the seed cavity. The activities of ascorbate peroxidase, catalase, and superoxide dismutase also increased in an inward direction. The concentrations of calcium, iron, magnesium, manganese, and sodium all decreased in the inward direction. When expressed on a dry weight basis, the concentrations of ascorbic acid, boron, copper, fructose, glucose, phosphorus, potassium, and zinc were higher in the subpeel region compared to the inner mesocarp tissues, but the reverse was true when data were expressed on a fresh weight basis. These data reveal that there is considerable variation in sugars, minerals, and phytonutrients across the mesocarp regions and that expressing the data on a fresh or dry weight basis can alter interpretations of the nutritional significance and health benefits of fruit. The data also confirm that orange-fleshed honeydew melon can be a rich source of many human health-related nutrients.

Organically versus Conventionally Grown Produce: Common Production Inputs, Nutritional Quality, and Nitrogen Delivery between the Two Systems

One distinguishing conclusion found in most reviews of research studies comparing organically and conventionally grown produce is that variables shared alike by organic and conventional produce during production, harvest, and postharvest handling and storage were not applied. As a result, accurate and meaningful conclusions comparing the nutritional quality of organic and conventional produce are difficult to ascertain. Pairing common production variables such as the physical, biological, and chemical/nutritional attributes of soils, the irrigation sources and amounts, crop varieties, crop maturities and harvest dates, pre- and postharvest processing, handling, and/or storage methods, individually and collectively, provide greater clarity as to how inputs unique to organic and conventional systems affect produce quality. Variables to be paired during production, harvest, and postharvest handling and storage studies comparing organic and conventional produce are discussed along with findings indicating that organic crops often have higher dry matter, ascorbic acid, phenolic, and sugar and lower moisture, nitrate, and protein contents and yields than conventionally grown crops. Recent studies of nutritional quality in organic versus conventional produce also indicate that soil nitrogen delivery rates strongly affect nutritional quality. Nitrogen profiling is a promising new approach to improving the nutritional quality of both organic and conventional produce.

Flow Injection Mass Spectral Fingerprints Demonstrate Chemical Differences in Rio Red Grapefruit with Respect to Year, Harvest Time, and Conventional versus Organic Farming

Spectral fingerprints were acquired for Rio Red grapefruit using flow injection electrospray ionization with ion trap and time-of-flight mass spectrometry (FI-ESI-IT-MS and FI-ESI-TOF-MS). Rio Red grapefruits were harvested 3 times a year (early, mid, and late harvests) in 2005 and 2006 from conventionally and organically grown trees. Data analysis using analysis of variance principal component analysis (ANOVA-PCA) demonstrated that, for both MS systems, the chemical patterns were different as a function of farming mode (conventional vs organic), as well as growing year and time of harvest. This was visually obvious with PCA and was shown to be statistically significant using ANOVA. The spectral fingerprints provided a more inclusive view of the chemical composition of the grapefruit and extended previous conclusions regarding the chemical differences between conventionally and organically grown Rio Red grapefruit.

Calcium alters senescence rate of postharvest muskmelon fruit disks

Abstract Percent total chlorophyll loss in whole muskmelon (Cucumis melo L. var. reticulatus Naud.) fruit disks incubated in control (no salt), 0.02, 0.04, 0.08, 0.16 or 0.32 M CaCl2, MgCl2 or KCl plus 0.35 M mannitol for ten days at 22 °C in the dark was delayed only in calcium solutions, with the greatest retention occurring in 0.04 M content. Percent total chlorophyll loss was hastened in 0.16 and 0.32 M concentrations regardless of the cation. Differences in the chemical, senescence-associated, properties of the plasma membrane (PM) from hypodermal mesocarp tissue of postharvest muskmelon disks were compared before and after floating disks in control, 0.04 or 0.16 M CaCl2, MgCl2 or KCl plus 0.35 M mannitol for ten days at 22 °C in the dark. Total phospholipid, protein, and H+-ATPase (EC 3.6.1.35) activity loss, in the PM were delayed only with 0.04 M CaCl2 and hastened with most all other chloride solutions vs. no salt. The free sterol:phospholipid ratio and percent unsaturation of phospholipid fatty acids was the highest in the PM from fruit disks incubated in 0.04 M CaCl2 and were the highest and lowest, respectively, in 0.16 M CaCl2 vs. no salt. This study suggests that muskmelon fruit senescence is affected by calcium treatment, by affecting the PM, possibly involving the regulation of phospholipid composition and content.

Preharvest furrow and drip irrigation schedule effects on postharvest muskmelon quality

Abstract A two-year study was conducted on the effects of furrow or drip irrigation applied 1, 2 or 4 days prior to harvest (following all plots having been watered 8 days prior to harvest) on the postharvest quality of muskmelon ( Cucumis melo L. var. reticulatus) fruits cv. Magnum 45. Fruit firmness was not affected by irrigation method or application time. Regardless of irrigation method, water applied at 4 days prior to harvest produced fruit with significantly lower soluble solids concentration SSC (10.8% vs. 12.2%) greater volume (1684 vs. 1508 cm 3 ) and greater moisture content (88.5% vs. 87.4%) compared to no watering after 8 days prior to harvest. No consistent differences were found with fruit SSC, volume moisture content or taste of fruits from plots where water was applied 1 or 2 days prior to harvest compared to fruits receiving no water after 8 days. Significantly lower sweetness and overall preference ratings were found for fruit from plots drip-irrigated 4 days prior to harvest compared to those that received no water after 8 days. In contrast, only sensory ratings of fruits from furrow-irrigated plots might indicate that watering 1 and 2 days prior to harvest may be as detrimental to quality as water applied at 4 days prior to harvest.