Biocontrol of Parthenium for regenerating lost biodiversity
- Part 2 -

Prof N Irabanta Singh *

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.

Seed germination inhibition of 88% under the influence of 9 day leaf leachate of Cassia tora was reported (Singh and Riti, 2002). Leachates of the selected plants of different immersion period and concentration showed variable seedling growth response of Parthenium.

At 100% concentration leaf leachate of Cassia tora, 76.19% and 71.41% reduction in shoot and root length in 4 day old leachates; 78.26% and 79.31% reduction in shoot and root length in 8 day old leachates and 80% and 79.31% reduction in shoot and root length in 12 day old leachates respectively has been recorded. Thus, the study revealed that the Cassia tora phytoextract could be used as a possible bioherbicides for the control of Parthenium.

Control of Parthenium by Cassia tora in microplot field condition

The effective botanical agents against Parthenium were selected from the above experimented result and trials were made in microplot field condition. The experiment was conducted in the Life Sciences Department, Manipur University in controlled field condition in 2x2 m microplots size in randomized complete block design.

Parthenium and Cassia tora were grown in five combinations i.e. 50:25, 50:50, 50:75, 50:100 and 50:125 ratio plants. Plot of Parthenium alone was maintained as control. Observations were recorded after 3 months from DAS on average plant height, number of branches and number of flowers per plant during the flowering stage of Parthenium and dry plant biomass.

The experimental finding shows that the height of the Parthenium was found decreased as the ratio of Cassia tora to Parthenium increase. In 50:25 Parthenium to cassia tora ratio plot, the height of the Parthenium was not much effected but as the population ratio of Cassia tora increase the reduction percent of Parthenium height were 25.22%, 54%,71.92%, 82.01% and 90.25% at 50:25, 50:50, 50:75,50:100, 50:125 respectively as compared to control plot.

Cassia fora reduced the number of branch of Parthenium in the entire treated plot. Maximum number of main branch was observed in control plot with 8.6 in number and minimum was observed in 50:125 ratio plots with 1.4 in number in Cassia tora treated plot respectively.

The reduction percent of number of branch per parthenium plant was 26.92%, 42.31% ,53.85%, 57.69% and 73.08% in Cassia tora treated plot at 50:25, 50:50, 50:75,50:100, 50:125 ratio respectively as compared to control plot.

The number of flower per Parthenium plant was very much affected with Cassia tora treatment. In 50:25 ratio treatments the number of flower per Parthenium plant was reduced to 94.41% in Cassia tora treated plot respectively as compared to control plot. Cent percent inhibition of flower production per Parthenium plant was observed in 50:125 ratio Cassia tora plot.

As compared to control plot the number of flower per plant kept on reducing as the population ratio of Cassia tora to Parthenium plant increased. The dry biomass of per Parthenium plant was significantly reduced in the entire treated plot as compared to control plot. The maximum dry biomass per Parthenium was observed in control plot with 8.79 g.

The reduction percentage of dry biomass per Parthenium plant were 55.4%, 74.18%, 86.46%, 91.35% and 96.36% in Cassia tora treated plot at 50:25, 50:50, 50:75, 50:100, 50:125 ratio respectively as compared to control plot.

After the initial rain both Parthenium and Cassia tora germinate but the young seedlings of Cassia tora were found larger than Parthenium due to which Ctora grows faster and takes over Parthenium. Due to shade and competition effects, Parthenium remains suppressed amidst the Ctora stand.

Rehabilitation of Parthenium hystero-phorus L. growing fields by Cassia tora

Sites were selected along the road sides where Parthenium were found to be infested luxuriantly. Parthenium plants were cut down before the flowering stage or before the maturation of the seed. The seeds of Cassia tora were broadcasted in different sites before the monsoon. One site was kept as control where seeds of none of Cassia tora were sown the gross plot size was 1m x 5m.

Observation on density (plants/m"), dry matter production (g/plant) and Parthenium control efficiency (%) were recorded at 30 and 60 day respectively after broadcasting. Population of Parthenium was recorded in one square meter area by taking three samples from each of the locations.

The observation at 30 DAS (day after sowing) on density showed the least presence of Parthenium in Cassia tora plot (5.60 per m2) and reduced Parthenium population by up to 69.5% of the control. However, the density of Parthenium increased at 60 DAS to 7.71 plants per m2 in Cassia tora plot and reduced up to 61.45% of the control.

The lowest density of Parthenium in Cassia tora plot might be due to the effect of leachates or exudations of allelochemicals from Cassia tora. Highest density of Parthenium was observed in control plots with 18.34 plants per m2 and 20.0 plants per m2 at 30 and 60 DAS respectively where none of the plant species were sown.

This might be due to the availability of abundant Parthenium seed from the previous season. The biomass of Parthenium was 3.85 g and 6.50 g at 30 DAS and 60 DAS respectively in Cassia tora seeds broadcasted plot and reduced up to 61.2% and 57.7% of the control at 30 and 60 DAS. Cassia tora effectively suppressed the population and biomass of Parthenium as compared to control.

Conclusion

Parthenium has slowly become a serious weed threatening the ecological biodiversity of Manipur infesting many agricultural lands, roadsides, no man lands, pastures etc.


Concluded.....