Concentration Dependency, Mode of Action and Characterization of Compounds Involved in Alfalfa Autotoxicity PDF Download

Author: Ramesh Satyanarayan Hegde
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ISBN:
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Languages : en
Pages : 164

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Book Description
Greenhouse experiments on allelopathy and autotoxicity of 'WL-316' alfalfa (Medicago sativa L.) indicated that plant height and fresh weight of alfalfa, and fresh weight of 'DK-38' sorghum (Sorghum bicolor (L.) Moench) were lower on soil previously cropped to alfalfa, 'alfalfa-soil', than on that previously cropped to sorghum. Allelopathic and/or autotoxic compounds in alfalfa-soil were implicated in the growth inhibition of the two crops. Incorporation of fresh alfalfa residue--roots only or roots and shoots both--reduced alfalfa emergence, plant height and dry weight. Primary effect of water-soluble inhibitory compounds from alfalfa shoot appeared to be on germination and radicle elongation, the latter being more sensitive than the former. Alfalfa allelopathy is a more severe problem than autotoxicity. Bioassay of the alfalfa shoot aqueous extract at 0, 20, 40, 60, and 80 g.L$sp{-1}$ (on a fresh weight basis) under laboratory conditions showed that alfalfa germination, radicle elongation, and shoot elongation were inhibited by the extract in a concentration dependent manner. Shoot extract from reproductive stage was more inhibitory than from vegetative stage. Under greenhouse conditions, alfalfa seedling emergence was adversely affected following incorporation of fresh alfalfa herbage from the vegetative stage at 97 and 146 shoots.m$sp{-2}$ into soil. Among the several phenolic compounds assayed, coumarin and trans-cinnamic acid were highly inhibitory to alfalfa root growth and shoot growth. The mixtures of phenolics were generally more phytotoxic than their respective individual components except in the case of coumarin and trans-cinnamic acid. Scanning electron microscopy techniques, used to study the root morphology and anatomy of the shoot-aqueous-extract-inhibited alfalfa roots showed a 46% reduction in density and 54% reduction in length of root hairs compared to the control. Thin layer chromatography (TLC) of the acid-hydrolysed, ethyl-ether-extracted alfalfa shoot aqueous extract followed by the gas-liquid chromatography of the TLC fractions indicated that some of the compounds present in the sample had characteristics of chalcones and flavones. Medicarpin was not found in the extract.