Search Results
Abstract
‘GL 659’ and ‘Vanguard’ lettuce seed lots germinated almost completely at 30°C when treated with ethephon (100 mg/liter). Similar treatment at 35°C failed to release seeds from dormancy. Kinetin treatment (10 mg/liter) at 35°C was only moderately effective in breaking heat dormancy, but when ethephon and kinetin were combined at this temperature, the interaction was synergistic and germination was almost complete. The preincubation time requirement at 25°C before maximum germination could occur after transferring to 35°C was nearly eliminated by treating seeds with the ethephon-kinetin mixture. ‘Calmar’ seeds, which had a lower heat tolerance, could not be induced to germinate completely at high temperature by any treatment.
Abstract
Lettuce (Lactuca sativa L.) seed coatings containing a granular activated carbon layer adjacent to the seed and overcoated with standard coating materials gave faster, more complete and more uniform seedling emergence than did simple coatings with standard materials. Evidence suggests the granular carbon layer acts to speed O2 diffusion into and adsorb endogenous growth inhibitors excreted from the germinating seeds. Variability of seedling emergence was found to be inversely related to the mean emergence rate.
Abstract
Lettuce (Lactuca sativa L.) seedlings emerged from vermiculite tablets but did not survive in warm weather plantings (maximum daytime air temperature >32°C) under irrigated desert conditions. Final plant stands of 90% were obtained with modified seed tablets containing activated carbon and nutrient P in cool weather (maximum daytime air temperature <26°C).
Abstract
Lettuce (Lactuca sativa L.) seed weight and size were unrelated to rate of germination and germination percentage at 25°C. In 4 cultivars tested, all seed physical parameters, except density index were highly significant predictors of radicle elongation (weight>thickness>iength = width>density index). However, more than 62% of the growth variation remained unexplained. Seed weight did not influence the uniformity of 7-day-old seedlings.
Abstract
Surveys were made of Li in leaves, irrigation water and soil in groves of 37 to 43 year old ‘Marsh’ grapefruit on sour orange rootstock. Lithium in leaves increased during the late summer. Leaves with 50 to 60 ppm Li in September generally developed necrotic lesions on margins below the tip in November when they contained 60 to 90 ppm Li and abscissed within 1 to 4 months. Lithium varied widely between spring-cycle leaves on the same tree and within the leaf where it accumulated in the lesions. Severe Li toxicity symptoms were associated with 0.18 to 0.25 ppm Li in the irrigation water, 0.7 to 1.0 ppm in the soil and from 68 to 232 ppm in spring-cycle leaves in November. Vigorous growth and high yields occurred with 24 to 34 ppm Li in the leaves, 0.07 to 0.11 ppm Li in the irrigation water and 0.3 to 0.4 ppm in the soil. Severe leaf symptoms with Li content as high as 175 ppm were induced by soil applications of LiCl under field conditions.