Galia' melons were grown under controlled conditions and pruned to bear two fruits with 19 leaves per plant. Leaves and fruits were sampled and analysed at eight different stages. Pericarp cell division ,and enlargement occurred during the first week after anthesis but only cell enlargement was responsible for fruit growth thereafter. An increase in fruit-peel surface during the first 3 days after anthesis (DM) was due mainly to epidermal cell division. During the following 11 days fruit-peel area increased due to increases in epidermal cell size. At 14 DM no further epidermal cell enlargement occurred, probably due to an increase in cuticle thickness. After this stage fruit peel surface increased due to cracks in the epidermal layer which preceded and probably initiated lenticel development. In leaves adjacent to developing fruit, a reduction in starch occurred during the last week of fruit development, coinciding with sharp increases in glucose, fructose and sucrose levels and an increase in total fruit-flesh sucrose from 50.4 9 to 111.6 9 per fruit, illustrating the importance not to harvest prematurely.'Galia' tipe spanspek is onder beheerde klimaatstoestande verbou en gesnoei sodat daar twee vrugte en 19 blare per plant ontwikkel het. Blare en vrugte is op agt verskillende stadia gemonster en ontleed. Deling en vergroting van peri karp selle het in die eerste week na antese plaasgevind maar daarna was slegs selvergroting vir vruggroei verantwoordelik, 'n Vergroting in vrugskil oppervlak gedurende die eerste 3 dae na antese was hoofsaaklik die gevolg van selc;leling. Gedurende die volgende 11 dae het die vrugskil oppervlak vergroot weens vergrotings in die epidermissef/e. Twee weke na antese het epidermisse//e nie verder vergroot nie, waars~ynlik weens 'n verdikking van die kutikula. Na hierdie stadium het vrugskil oppervlakte vergroot weens barsies in the epidermale sellaag wat lentiselontwikkeling voorafgegaan en waarskynlik ge"inisieer het. In blare naasliggend aan die ontwikkelende vrugte het 'n afname in stysel-inhoud gedurende die laaste week van vrugontwikkeling plaasgevind. Dit het saamgeval met skerp toe names in glukose, fruktose en sukrose konsentrasies in blare en 'n toename in die totale sukrose inhoud van 50.4 9 tot 111.6 9 per vrug. Dit iIIustreer waarom vrugte slef.js op die volryp stadium gepluk behoort te word. . ,
Operational cost of producing lettuce (Lactuca sativa) during the winter in greenhouses is high in the northern regions of the United States due to the addition of supplemental lighting (SL) and heating. Crop productivity in greenhouses should increase to offset high operational costs and maintain profits. Factors including SL composition, heating efficiency, suitability of production systems (PS), and cultivar performance can affect crop productivity. Research-based information on optimizing the above environmental- and production-related factors is limited. This information is critical for growers to make informed decisions and increase profits during winter hydroponic production. We evaluated the interactive effects of SL composition, solution temperature, PS, and cultivar treatments on lettuce shoot dry weight (SDW, g·m−2) and shoot water content (SWC, %) in a greenhouse maintained at suboptimal air temperature (13.7 °C) using a split-plot design. There were three light treatments (sunlight without SL, sunlight + narrow-spectrum SL at nighttime, and sunlight + full-spectrum SL at nighttime), two solution temperature levels [heated (18.8 °C) and unheated (13.2 °C)], two hydroponic PS [constant flood technique (CFT) and nutrient film technique (NFT)], and eight cultivars included in the study. Results indicated that 1) a narrow-spectrum SL at nighttime in combination with heated solution resulted in maximum SDW of lettuce, 2) the SDW and SWC (major determinant of economic yield) increase between the heated and unheated solution temperature treatments was higher in the CFT than in the NFT, and 3) the positive effects of using heated solution were seen mainly in the green-color cultivars. Our research identified the optimal spectral composition of nighttime SL, tested the positive effects of alternate heating methods using heated solution on plant growth under suboptimal air temperature conditions, compared the suitability of two hydroponic PS for lettuce production, and quantified yield potential of several lettuce cultivars in hydroponic production during winter. Growers can use our research findings to make informed decisions about their investment and to maximize hydroponic lettuce productivity and profits during winter.
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