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Abstract
A 50% increase in total radiation by extending the photoperiod from 16 to 24 hr doubled the weight of all cultivars of loose-leaf lettuce (Lactuca sativa L.) ‘Grand Rapids Forcing’, ‘Waldmanns Green’, ‘Salad Bowl’, and ‘RubyConn’, but not a Butterhead cultivar, ‘Salina’. When total daily radiation (moles of photons) was the same, plants under continuous radiation weighed 30% to 50% more than plants under a 16 hr photoperiod. By using continuous radiation on loose-leaf lettuce, fewer lamp fixtures were required and yield was increased.
Abstract
Radiation from high-pressure sodium (HPS) lamps provided more than a 50% increased yield (fresh and dry weight of tops) of loose-leaf lettuce cultivars Grand Rapids Forcing and Ruby Conn, compared to that obtained by radiation from cool-white fluorescent (CWF) lamps at equal photosynthetic photon flux; yet, input wattage was ≈36% less. It was postulated that the considerable output of 700 to 850 nm radiation from the HPS lamp was a significant factor of the increased yield. Under HPS lamps, the leaves of both cultivars were slightly less green with very little red pigmentation (‘RubyConn’) and slightly elongated, compared to CWF, but plant productivity per unit electrical energy input was vastly superior with HPS.
A wheat (Triticum aestivum cv. Yecora Rojo) stand was grown using nutrient film culture in the closed conditions of NASA's Biomass Production Chamber. Rates of photosynthesis and respiration of the entire stand (about 20 m2) were determined daily using a regime of 20 hr light/4 hr dark, 20 C light/16 C dark an average PPF of 600 μmol/m2/s from HPS lamps, and a CO2 cone of 1000 ppm. Fractional interception of PPF by the stand reached a maximum of 0.96 at 24 days from planting. Rates of photosynthesis were constant throughout the photoperiod as determined by short term drawdowns of CO2 throughout the photoperiod. Drawdown rates of CO2 were correlated with rates determined by logging of mass flow of CO2 injected during chamber closure. Photosynthetic drawdowns of CO2 indicated that photosynthesis was not saturated at 1000 ppm CO2 and that the CO2 compensation point was about 50 ppm. Whole stand light compensation points were 200 to 250 μmol/m2/s between days 13 and 70 and then increased rapidly during senescence.
The isolation of genomic DNA from Capsicum spp. (pepper) of the quality and quantity required for analyses based on nucleic acid hybridization and/or the polymerase chain reaction (PCR) has proven difficult. We report here a procedure that reliably yields sufficient quantities of good-quality pepper genomic DNA from a variety of Capsicum genotypes.