The sensitivity of shoots and roots to end-of-day (EOD) red (R) or far-red (FR) light on growth of `Sugar Baby' watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] was investigated. Plants were grown in full-strength Hoagland solution and treated for 14 days to 15 minutes EOD light in trial 1 and in half-strength Hoagland solution and treated for 10 days to EOD light in trial 2. Exposing shoots to EOD FR resulted in elongated petioles of leaves 1 to 3 (as counted from the cotyledons), internodes 1 to 3, and total stem length in both trials. Exposure to EOD FR resulted in increased stem and petiole dry mass in trial 1, whereas EOD FR resulted in increased root and leaf dry mass in trial 2. EOD FR exposure of roots increased the length of petiole 4 in trial 1. In general, shoots were more responsive than roots to the growth-regulating effects of EOD FR.
The effect of planting population density (as a function of in-row plant spacing and number of rows per bed) on the growth, yield, and pod distribution of cayenne pepper (Capsicum annuum var. annuum L. cv. Carolina Cayenne) was investigated in a 2-year study. In 1988, 15 -, 30-, 45-, and 60-cm in-row spacings in a single row were evaluated, and in 198915 -,30-, and 60-cm in-row spacings in single and double rows were evaluated. Plant population densities at these respective spacings ranged from≈ 11,100 to 44,400 and 11,100 to 88,900 plants/ha. In 1988, pepper plants grown at the highest density (15-cm in-row spacing, 44,400 plant/ha) produced less fruit per plant but more fruit per hectare than those grown in lower densities. In 1989, yields with either a 15-cm in-row spacing in a single row or a 30-cm in-row spacing in double rows (both with 44,400 plants/ha) were higher than in the others. In general, less fruit were located in the lower part of the plant canopy when planted in higher plant population densities.
The influence of end-of-day (EOD), supplemental, cool-white fluorescent light on pepper (Capsicum annuum L. cv. Keystone Resistant Giant No. 3) seedling growth and fruit production after transplanting to the field was investigated. Seedlings were exposed to this light source, which is high in the red wavebands, from one (1988) or two bulbs (1989) for 1 hour before the end of the natural photoperiod. Each year control plants were exposed to ambient light and received no supplemental fluorescent light. Before transplanting to the field, seedlings exposed to two bulbs were shorter and had smaller leaves than plants in the control treatment. Supplemental fluorescent light treatment, regardless of number of bulbs, reduced plant height, leaf area, fruit weight, and fruit count at the first harvest. Total fruit production was not affected by supplemental light, suggesting no residual effect of the light treatment during transplant production on total subsequent fruit production.
The sensitivity of watermelon [Citrullus lanatus (Thumb.) Matsum & Naki `Sugar Baby'] plant growth to day-long alterations in light quality was determined by exposing plants to light transmitted through broad band wavelength selective filters. Of the three acetate filters analyzed (nos. 19, 27, and 74), filter no. 74 transmitted the least amount of photosynthetic photon flux (PPF) (400 to 700 nm), the smallest red light: far-red light ratio (R:FR) (645:735 nm), and the greatest amount of blue light (400 to 500 nm) radiation from metal halide lamps. Plants grown under filter no. 74 were taller, had elongated petioles, and had a greater amount of petiole and stem biomass than plants grown under the other filters. Spectral transmission properties of commercially available rowcover materials were evaluated for variation of PPF, R:FR, and blue light. Clear polyethylene rowcovers were completely permeable to all measured (330 to 850 nm) wavelengths of radiation from metal halide lamps. White polyethylene rowcovers were the least permeable of the rowcover materials to wavelengths of radiation with decreases in the PPF, R:FR, and blue light. Spunbonded polyester materials slightly reduced PPF, R:FR, and blue light. Plants grown under white polyethylene and spunbonded materials grew taller (longer stems) than plants grown under the clear polyethylene rowcover. Petiole lengths were generally longer for plants grown under white polyethylene. Our results suggests that alterations in the R:FR and blue light due to selected wavelength transmission through commercially available rowcover material alter early watermelon growth.
A polyethylene mulch system that changes its predominant surface color from black to white in the field has been developed and used to grow tomatoes (Lycopersicon esculentum Mill. cv. Mountain Pride) and squash [Cucurbita pepo var. melopepo (L.) Alef. cv. Dixie Hybrid]. The system uses a black photodegradable polyethylene mulch placed on top of a white nondegradable polyethylene mulch (photodegradable mulch overlay system). As the black photodegradable mulch degrades with increasing exposure to radiation, the white mulch surface is exposed. Differences among plastic systems in the percentage that breaks down may be explained by differential shading of the mulch by the vegetative growth of the crops. None of the formulations of the Plastigone brand photodegradable mulches in the photodegradable mulch overlay system had an effect on tomato or squash production. As the color of the system changed from black to white, soil temperatures under the mulch decreased. Tomato production remained unaffected in one of the two years as long as the mulch remained black for at least the first 20 days during that season. In year 2, the controlled mulch system color change affected neither tomato nor squash production relative to nondegradable white and black mulches used as controls.