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Abstract
A preplant acetone permeation of ‘Grand Rapids’ and ‘Mesa 659’ lettuce (Lactuca sativa L.) seeds with either cyclohexanecarboxamide 1-(3-chlorophthalimide) (phthalimide) or gibberellin A 4+7 (GA) in combination with kinetin (KIN) and/or (2-chloroethyl) phosphonic acid (ethephon) markedly relieved the adverse effect of high temperature (20°, 12 hr night/30°C day regime) on seedling emergence from soil. Permeation of GA in ‘Grand Rapids’ seeds increased seedling hypocotyl length by 121% compared to only 25% for phthalimide permeated seeds. In ‘Mesa 659’ seeds, the corresponding increases with GA and phthalimide permeation were 52% and 26%, respectively. Permeation of GA + ethephon + KIN and phthalimide + ethephon + KIN increased seedling hypocotyl elongation over the control by 126% and 60% in ‘Grand Rapids’ and 91% and 21% in ‘Mesa 659’, respectively. Seed permeation with phthalimide tended to increase the leaf chlorophyll content of emerging seedlings. Permeation of GA decreased leaf chlorophyll up to 28% in ‘Mesa 659’ and up to 13% in ‘Grand Rapids’. These findings indicate that phthalimide could be substituted for GA in seed treatments needed to alleviate the adverse effects of high temperatures on germination and seedling establishment and to improve growth characteristics of emerged seedlings.
A high-wire system, in which the plant is trained into a single stem, is gaining popularity in year-round greenhouse cucumber (Cucumis sativus) production, especially with supplemental lighting, as it allows for uniform foliar and light distribution and higher yield and quality. However, this system requires much higher plant densities than the conventional umbrella system, resulting in increased crop start-up costs. A technique for raising twin-head transplants and a twin-head “V” high-wire cucumber system were developed to address this issue. The twin-head transplants were raised by topping the seedlings after the appearance of the fourth true leaf and then two strong lateral shoots were allowed to develop and be trained into a “V” system after planting. The twin-head system achieved similar plant growth and fruit yield as the conventional single-head system on two long English seedless cucumber cultivars (Bodega and Myrthos) and two breeding lines (2005A and 24–119) tested over 2 years. The twin-head system also improved the fruit grades in ‘Bodega’ by increasing the percentage of fruit in medium size while reducing the percentage of fruit in small size. Because the twin-head system achieved the same fruit yield as the conventional single-head system while using only half the number of transplants, we can conclude that the twin-head “V” high-wire system is a more cost-effective high-wire system for year-round greenhouse cucumber production.
The effects of CaCl2, GA3, and H2O2 priming on Isatis indigotica Fort. seed germination characteristics, seedling growth parameters, and antioxidant enzyme activities under salt stress were investigated. NaCl had an adverse effect on the germination and seedling performance of I. indigotica. However, these three priming agents alleviated salt stress by increasing the germination percentage, improving seed vigor, accelerating germination velocity, and establishing strong seedlings. The optimal concentrations were 15 g/L for CaCl2, 0.2 g/L for GA3, and 40 mm for H2O2. Seed priming treatments enhanced the activities of antioxidant enzymes in seedlings, such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), under a salt environment, which reduced the oxidative injury caused by salt. Seed priming is a promising technique that can enhance the ability of I. indigotica seed germination when salt is present.