The application of plant growth regulator on nursery stock, flower and forestry
Chemical control technology is a new field of forest research, in which plant growth regulator will be used. By influencing the 5 hormone levels and balances of plant, it can influence the genetic expression of plant and regulate the growth and development.
Plant hormone is a kind of micro organic compound that is generated in the plant body and has physiological activity, which can be transferred from synthetic position to action site and can promote, inhibit and change some physiological process of plants. Currently, plant growth regulators mainly include auxin, gibberellin, cytokinin, ethylene, growth retardant (inhibitor) and other kinds of plant growth regulators.
a. The chemical name of auxin is indole-3-acetic acid (IAA). The most obvious effect of IAA is promoting the cell elongation of woods (increase cell plasticity, increase enzyme synthesis, promote the key rupture and the synthesis of new cell wall, improve the plasma membrane transparency and increase the absorption and permeation of water). IAA will have stronger effect on the plant growth when the working concentration is increasing, but it will have obvious inhibiting effect when it reaches to a certain concentration. IAA can also promote cambium activity and adventitious root formation, prevent ageing, promote or delay fruit drop, form apical dominance as well as promote fruit setting and parthenocarpy. For example, by using indole-3-acetic acid (IAA), indolebutyric acid (IBA), naphthylacetic acid (NAA), naphthoxyacetic acid (NOA), dichlorphenoxyacetic acid (2,4-D), 2,4,5-Trichlorophenoxyacetic acid (2,4,5-T), 2-Methyl-4-chlorophenoxyacetic acid (MCPA) and carbaryl (Sevin,Carbaryi and NAC) in forestry production cultivation, they can promote cutting rooting, flower thinning and fruit thinning and flowering as well as prevent fruit drop before picking period and control slip.
b. There are 72 types of gibberellins (GA1-72) that naturally exist in the plant body. Gibberellin can stimulate cell elongation and can obviously promote internode elongation, but it will not influence internode quantity. Besides, it will have stronger effect on promoting plant growth when the concentration is increasing, but will become stable when it reaches a certain concentration and also will have no inhibiting effect. By using gibberellin on fruit trees, it can promote fruit setting, increase fruit size, induce parthenocarpy and prevent ageing. Besides, it will not influence photosynthetic intensity and can obviously improve respiration intensity. By using gibberellin in the fruit growing, it can inhibit flower bud formation, break dormancy, promote seedling growth, increase seedless grape size and improve fruit shape.
c. Cytokinin (Cytokinins and CTK) also can be called kinetin, which is a kind of derivative of purine. It can promote cell division and enlargement, promote bud germination, overcome apical dominance, promote lateral bud germination, delay the degradation of protein and chlorophyll as well as delay ageing, promote fruit setting of grape and orange and promote flower bud germination. For example, 6-Benzylaminopurine (6-BA and BAP), PBA, diphenyl urea (DPU) and benomyl (benlate) can promote fruit setting, improve fruit shape index, promote lateral bud germination and promote cell division.
d. Ethylene can cause triple response (inhibit stem elongation growth and promote stem expansion growth) and epinasty reaction (the upper part of petiole will grow fast and the bottom part will grow slowly, leaf will become nutant and will also lead to contrary flexure of blade surface). Ethephon can promote fruit ripening, promote flower bud formation, promote leaf drop, flower drop and fruit drop as well as inhibit vegetative growth. For example, ethephon (ethrel, trhephon and CEPA), etacelasil (CGA-15281 and Silaid) and AVG can inhibit vegetative growth, promote flower bud germination, assist mechanical harvest, promote maturation and coloring, promote flower thinning and fruit thinning, delay flower season, promote dormancy and improve cold resistance.
e. Growth retardant mainly inhibits cell division and elongation of shoot apical meristem, which can be reversed by gibberellin. While growth inhibitor can completely inhibit the growth of shoot apical meristem, which cannot be reversed by gibberellin. For example, chlormequat chloride (CCC, cycocel and chloyeguat), morphactin (Morphactin, Chlorflurecol and Maintain), maleic hydrazide (MH and maleic hydrazide), triiodobenoic acid (TIBA), fosamine and multi-effect triazole (Paclobutrazol, pp333 and Cultar) can inhibit vegetative growth, promote flower bud formation, increase fruit setting, promote fruit coloring, promote maturation ahead of time, promote timely flowering and anti-season fruit bearing and improve drought resistance.
f. Other plant growth regulators, such as triacontanol (TRIA, TAL and 1-triacontanol), brassin, brassinolide and brassins all have same effect with GA and CTK, besides, they will lose activity when encountering with alkali but will recover the activity after being treated by acid. In addition, plant growth regulator complexing agents, such as promalin (the complexing agent of BA+GA4+7), can increase shape index, thus the five edges on the fruit top will become obvious.