• Volume 82, Issue 5

      November 1975,   pages  167-203

    • Leaf variation due to 2, 4-D influence inTrigonella foenum-graecum L

      K Unnikrishnan Molly Hariharan

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      Pretreatment of seeds ofTrigonella foenum-graecum L. with 2 ppm 2, 4-D induced seven patterns of abnormalities resulting from fusion and proliferation of leaflets. Vascular nature of abnormal leaf primordia and petioles are correlated to the morphological abnormalities. The size of leaf buttress or primordium at the time of pretreatment is critical in bringing about the abnormalities. Whenever the external stimulus (applied 2, 4-D) prevails upon the internal stimulus, leaf abnormalities result.

    • Weed-crop behaviour in pure and mixed stands of maize andEchinochloa colona Link

      Promila Kapoor P S Ramakrishnan

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      The interference between maize andEchinochloa colona was studied by growing the two species in pure and mixed stands under varied nutritional levels in the soil. Both the species responded to density stress in pure stands by mortality and plasticity. Density dependent mortality was comparatively higher for maize than forE. colona. The higher mortality rate of maize was related to the higher growth rate in this species. The dry matter production was also more sensitive to density stress for maize than forE. colona. The generally higher mortality in the more fertile soil was explained as due to the better expression of genotypic individual differences and the consequent elimination of the weaker individuals by more vigorous ones.

      In mixed stands, whilst the reciprocal effects of the weed and the crop were brought out due to suitable experimental design, the effect of the weed on the crop was less marked as compared to the reverse effect. This was due to differences in size and growth habit of the two competing species. Whilst the effect of the weed on the crop may be purely a competition by roots for nutrients from the soil the reverse effect could be primarily due to shading of the weed by the crop. The plasticity and mortality responses of the two competing species are discussed and it was shown that: (i) the effect of the weed on the crop was enhanced due to an early start that the former may receive in the mixture and the adverse effect was realized in cob characters and (ii) the interference from the weed to the crop is a continued risk throughout the life cycle and that longer the period of association between the two, greater the damage done to crop yield.

    • Bioassay of nuclear polyhedrosis virus against larval stages ofSpodoptera litura (Fabricius) and the effect of protectants against ultraviolet light

      Udom Komolpith N Ramakrishanan

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      The LC50 values for 4, 5 and 7 day old larvae ofSpodoptera litura were respectively, 4·677, 13·740 and 37·240×106 polyhedral inclusion bodies (PIB)/ml. The adjusted relative susceptibility on the basis of relative amounts of food consumed by the various age group of larvae was found to be 1, 10·8 and 88·5 for 7, 5 and 4 day old larvae. The LT50 values ranged from 5·32 to 9·50 days for the various concentrations of poly-hedra/ml. Activated charcoal and camel special water proof black drawing ink protected the virus to a certain extent against ultraviolet light.

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