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As the title indicates the current work aims to identify the inhibitory effect of plant growth regulators on the growth conditions of soybean. The work revealed that, seed yield and yield components were significantly increased by NAA at 20 ppm over other treatments and control. The application of brassinosteroid at 25 ppm, mepiquat chloride 5% AS and chlormequat chloride applied at 187.5g a.i/ha , 162.5g a.i/ha and 137.5g a.i/ha had also resulted in higher seed yield, compared to control and water spray. The study revealed the superiority of NAA (20 ppm) treatment for majority of the morphological, physiological, growth, biochemical, quality and yield parameters at different growth stages, in addition to seed yield, compared to other growth regulator and control treatments. Suggesting the use of NAA will have many positive benefits on yield and yield attributing characters in rabi-soybean.
Soybean, Growth Regulators, Glycine Max L.MerrilL, NAA, Chlormequat chloride, Mepiquat Chloride, Cycocel, Brassinosteroid
Soybean (Glycine max L. Merill) has been called miracle crop of the twentieth century. It is a highly nutritive and energy rich legume with 43 percent of biologically effective protein and 20 per cent of edible oil, besides the presence of good amount of vitamins, minerals, salts and essential amino acids. It serves both as pulse and oil seed crop and gives 2-3 times more protein yield than other pulses (1) and can bridge the increasing gap between demand and supply for edible oils and pulses in the country. Being a legume, it also fixes atmospheric nitrogen and adds about 65-100 kg N ha-1 year-1 to the soil which helps in increase of yields of the subsequent non-legume crop (2). The general constraint for realization of high productivity levels in soybean, its cultivation in marginal lands with either limited soil moisture or rain fed conditions. Further, the indeterminate growth habit, lack of high yielding varieties, apart from specific inherent physiological constraints, like less partitioning of assimilates towards reproductive structures, abscission of flowers or buds, also contribute to low pod set resulting in low yields of the crop. Growth regulators are known to improve the source-sink relationship, translocation of photo-assimilates and thereby photosynthetic ability of the plants and thus play a significant role in realization of high productivity levels and higher crop yields. The use of plant growth regulators has therefore been described as the most important tool of the agriculturist to increase crop yields (3). Among the growth regulators, auxins promote growth along the longitudinal axis, when applied in low concentration to shoot of the plant, while growth retardants are known to reduce the inter nodal length (4), reduce plant height, influence source-sink relationship and stimulate the translocation of photosynthates towards sink. Foliar application of mepiquat chloride (5) was also reported to help in realization of higher assimilatory rates resulting in higher dry matter production. Cycocel, another growth retardant was reported to shorten and strengthen stems of the plants and thereby reduce losses caused by lodging. The application of brassinosteroids was also reported to induce plant growth due to an increase in the metabolic processes like photosynthesis (6) and protein synthesis. Though, the plant growth regulators have great potential, their application and accurate assessment, etc., have to be judiciously planned in terms of optimal concentrations, stage of application, species specificity and the correct season. In view of their wide spectrum of effectiveness on every aspect of plant growth, even a modest increase of 10-15 per cent could bring about an increment in the gross annual productivity by 10-15 million tones (7). The comparative study of growth promoting and retarding compounds in pulses, particularly, soybean is scanty. Hence, the present investigation was undertaken to study the efficacy of chlormequat chloride, mepiquat chloride, NAA and brassinosteroid on the growth, development and yield of the crop.
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