Plant growth regulators are those synthetic materials which have similar physical and biological effects with plant hormones, mainly including auxin, gibberellin, cytokinin, abscisic acid, vinyl and brassinolide, etc.
Plant growth regulator in the growth and development of watermelon are used in the following aspects: the nursery stage using gibberellic acid (gibberelin class) as an initiator to improve the germination rate and germination energy (germinating uniformity) of watermelon seed; while the temperature or humidity is not the time using growth inhibitors to avoid "tall seedlings" occurring, prevent leggy seedlings; if the seeds with good quality and environmental conditions are suitable so that it can completely no need the growth regulators. After watermelon transplanting to the field the plant growth regulator which promote watermelon fruit is the most widely used, mainly the cytokinin substances; currently the most widely used in the production is Forchlorfenuron, it belongs to a synthetic cytokinin substance, the chemical name is 1 - (2 - chloro-4 - pyridyl) -3 - phenyl urea, also known as forchlorfenuron, CPPU, KT-30 and so on. Watermelon is a kind of typical cross-pollinated crop, before fructify it must be pollinated. In the early spring cultivation, some areas are because of more rainy days, low temperature, insufficient light, watermelon plants male flowers open less, pollen viability is low, artificial pollination exist pollination difficult, not fructify and other outstanding problems, so that use the growth regulator containing CPPU and other substances to treat, have the advantages of low cost, high fructify, and therefore have some extent applying on watermelon production.
CPPU can effectively promote watermelon fructify, there have been many papers reported the application of CPPU on watermelon's growth and development. CPPU is widely accepted that can induce the parthenocarpic of watermelon, improve watermelon's fruition rate and promote watermelon fruit enlarging, therefore, CPPU also commonly referred fructify drug.
Currently, all countries in the world were carried out the pesticide registration system, only the registered pesticides allowed appearing in the market and use. In the pesticide registration process, the government department rigorous review the environmental safety of pharmacon, get registered agents are proven safe for the environment and human health. The United States in September 2004 approved forchlorfenuron (the trade name CPPU, KT-30) as a new plant growth regulator used on the grapes and kiwi. The United States believe CPPU is a cytokinin, can promote fruit enlarging, improve fruition rate, increase production, extended the storage time of grapes and kiwi, not affecting the number of fruit and maintain fruit quality.
In Japan, CPPU is a chemical widely used in agriculture, to enhance the yield and quality of kiwi, grapes, pears and others, also used to improve the fruition rate of watermelon, melon and pumpkin.
Japanese prescribed maximum residue limits (MRL) for pesticides CPPU value is 0.1mg/kg, Australia, Israel, USA, New Zealand and other countries required the MRL of CPPU is 0.01mg/kg, the European Union, Switzerland, South Korea and so on required the pesticide residue standards of CPPU is 0.05mg/kg. China required the MRL of watermelon CPPU is 0.1mg/kg.
About the residue analysis of CPPU used in watermelon, scientists carried out a systematic study, the results show that Forchlorfenuron dissipated in watermelon is relatively fast, the half-life is 1.2-1.67d; when the watermelon harvest (after using the drug 40d), there is not Forchlorfenuron residue detected in watermelon fruit; soil also not detected out Forchlorfenuron residues, results strongly indicate that use in the recommended dose, CPPU apply in watermelon is safe.
Source:http://www.cospcn.com