Biocontrol of Parthenium for regenerating lost biodiversity

Prof N Irabanta Singh
Contd from previous issue
Under these circumstances, the concept of biological control means of controlling Parthenium offers a potential alternative. In Manipur also, it is now seen growing gregariously in wasteland, National and State highways, and is spreading like a wildfire. Due to its prolific cover and hazardous properties to the environment, adequate measures are required for the proper management of this weed. Increasing public concern on environmental issues requires alternative weed management systems which are less herbicide dependent or based on naturally occurring compounds.
In light of the above facts, it is proposed to undertake certain aspects of management of Parthenium hysterophorus L for checking its proliferation and thus control its harmful effects using selected botanical agents.
Control of P. hysterophorus using botanical agents
During the field surveys, the plants were found growing in the habitat with Parthenium but appear to have suppressive activity on the growth of Parthenium were also collected for identification and also for examination of their allelopathic property to Parthenium seed germination or seedling growth.
Ten different herbaceous plants (Table 1) growing nearby with Parthenium growing region were collected for biocontrol study against Parthenium management
Table 1: The botanical agents growing nearby the Parthenium plants collected during the
field surveys in the N.E. region.
SI No. Botanical agent Family
1) Cassia tora Fabaceae
2) Cassia occidentalis Fabaceae
3) Xanthium strumarium Asteraceae
4) Mirabilis jalapa Nyctaginaceae
5) Amaranthus spinosus Amaranthaceae
6) Ipomoea carnea Convolvulaceae
7) Chromolaena sp. Asteraceae
8) Ricinus communis Euphorbiaceae
9) Polygonum orientale Polygonaceae
10) Cassia sericea Fabaceae
The aqueous extract of different concentrations (5%, 10%, 20%, 30%, 50%) of leaf and stem of selected botanical agents were tried against the germination and seedling growth of Parthenium in vitro. The experimental result revealed that the extracts of the selected plants had significant effect on reduction of seed germination, seedling growth, dry matter product and vigour of Parthenium. Among the test plants leaf extract of Ricinus communis, Cassia sericea, Amaranthus spinosus, Polygonum orientale, and Cassia fora L. showed 100% inhibition of Parthenium seed germination at 20% concentration. It is evident from the data that allelochemicals present in Ricinus communis, Cassia fora, Cassia sericea, Amaranthus spinosus and Polygonum orientale might possibly inhibit the process of seed germination. The reduction in germination was higher under leaf extract than stem extract. No seedling growth was observed when reduction in root length of Parthenium was observed at 5% and 10% concentration respectively. In case of leaf extract of Cassia tora, 46.66% & 53.33% reduction in shoot length and 66.66% and 76.19% reduction in root length of Parthenium was observed at 5% and 10% concentration respectively. At 20% concentration of stem extract, maximum inhibition of plumule length was observed in Cassia tora and Xanthium strumarium with a value of 0.44 cm and 0.62 cm respectively whereas maximum plumule length was obtained in Control with 1.48cm. Generally extract of Cassia tora, Amaranthus spinosus and Xanthium strumarium were more inhibitory against root and shoot length than the other extract tested plants.
At higher concentration (20%) significant reduction of 44.8% to 73.1% and 39.9% to 64.64% were observed in leaf and stem extract of Cassia tora, Amaranthus spinosus, Xanthium strumarium and Cassia sericea as compared to control. Increase in concentration of phytoextract of the selected allelopathic plants results in decrease in dry matter accumulation in Parthenium. Amaranthus spinosus exhibited 61.76% and 70.58% reduction in dry matter accumulation whereas in Cassia tora, 61.76% and 67.64% reduction in dry matter accumulation of Parthenium was observed at 5% and 10% concentration respectively.
Leachate of selected botanical agents at different soaking period were prepared and were tested against the seed germination and seedling growth of Parthenium at different concentrations in vitro. Result revealed that the inhibitory effect of the leachate of selected botanical agents on germination of Parthenium was directly proportional to the soaking period and concentration. Among the test plant leaf leachate of Cassia tora (100% concentration) exhibited the most effective plant leachate against Parthenium showing 71.78%, 81.69% and 89.24% seed germination inhibition in 4, 8- and 12-days old leachates respectively.
(To be contd)