|Keywords:||甘藍;結球白菜||Issue Date:||Jun-1993||Publisher:||農業試驗所||Start page/Pages:||181-192||Source:||農業試驗所特刊;第41號||Conference:||蔬菜生產與發展研討會專刊||Abstract:||
Cabbage (Brassica oleracea L. var. Capitata. L.), chinese cabbage (Brassica rapa L. pekinensis group), lettuce (lactuca sativa L.)are the important members among the leafy vegetables. Physiologically they are different from others in having the characteristics to form the leafy “head”. The head starts to form at the growth stage when a certain number of outer leaves have developed. The characteristics of outter leaves are different from the inner ones, which compose the head. Outer leaves have the function to perform photosynthesis, while sugars are accumulated in the inner ones as the storage. The growth process of these leafy vegetables with the ¡§head¡¨ tends to resemble to that of fruit vegetables.
There are four growth phases of heading vegetables from sowing to heading and harvesting. The first phase is the initial growth phase or seedling stage, the second is the outer leaves expansion phase, the third is the inner leaves diff erenciation phase, or the head formation stage, and the fourth is the head development phase.
Morphologically changes of leaf shape and leaf area promoth epinasty ofthe leaves and head formation. Anatomic observation also showed morphological changes of meristem at early stage of heading.
There are several factors affecting head formation and development. Such as inorganic nutrient, water consumption, light and temperature. Partial removal of outer leaves result in poor development of the head since they are the photosynthetic organ. Head yield decreases with the decrease of light intensity, and temperature higher than 20℃ results in low rate of head growth.
Large amount of introgen and calcium is required for the growth during the whole life cycle; potassium is required at 1 st and 3rd growth phase; phosphorus, magnesium and sulfur are required during the early growth phases. Excess introgen offect head formation, the content of introgen in outer leaves being 2-3% and the c/v ratio between 5 and 15 are favorable for head development.
Through the understanding of the mechanism in physiology of head formation, technics in the cultivation of heading leafy vegetable may then be improved, and indics of selection for breeding be gotten.
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