SUMMARY
White dust spread on the leaves and stigmatic surface of Crotalaria pellida L. and Desmodium heteracarpon (L.) DC var. strigosum Meeuwen growing in the midst of a Parthenium hysterophorus L. stand was found to be clusters of Parthenium pollen. The fruit set in those species was poor. It was found that Parthenium pollen grains contained growth inhibitors which inhibited fruit set in many test species when artificially dusted on the stigmatic surface. In culture conditions the germination and pollen tube growth of the test species were inhibited in the presence of Parthenium pollen or their extract. The plant produces on an average 3375 million pollen grains per square metre areas of the stand. The pollen grains disperse in dusters of 600 to 800 each and are carried great distances by wind. Pollen grains deposited on leaves in large quantity also reduce the chlorophyll content in these species.
Root or leaf extract of Parthenium hysterophorus L. inhibited the growth of Rhizobium phaseoli and Azotobacter vinelandii. Similar inhibition was caused by parthenin, caffeic acid, and anisic acid, the important inhibitors isolated from the weed. Leghaemoglobin content in the root nodules of the bean plants grown in soil mixed with Parthenium leaf was reduced significantly as compared with the control. Nitrosomonas activity was progressively lowered with decreasing distance from the plant and also in leaf- or root-mixed soil. Leaf and root leachate, parthenin, anisic acid, vanillic acid, and fumaric acid inhibited nitrite production to varying degrees.
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