Parthenium hysterophorus: A noxious weed

Parthenium hysterophorus (Asteraceae family) is regarded as one of the worst weeds because of its invasiveness, fast growing habit and economic and environmental impacts. The vigorous mode of reproduction and the ability to possess of an arsenal of secondary metabolites has given it the status of invasive alien species. This noxious weed possesses large and persistent soil seed bank, high seed germination rate and ability to undergo dormancy under unfavorable periods. It is able to invade all disturbed land including farms, pastures and vacant lots and grows profusely along roadsides and railway tracks. This weed thus colonizes a range of vegetation and soil types and spread easily by water, farm and industrial machinery, animals, vehicles, stock fodder, movement of stock, grains and seeds. It affects each and every part of the ecosystem. It is considered to be a cause of a spectrum of clinical patterns: allergic respiratory problems, contact dermatitis, mutagenicity in human and livestock. During dry season, the mature plant crumble to a fine dust, that is scattered by the wind and becomes the source of "airborne contact dermatitis". Pollen grain of this weed produces hypersensitive disorders in susceptible individuals; the symptoms being watery eyes, swelling and itching of mouth and nose, constant coughing especially at night, continually running nose and sneezing. The plant produces toxic allelochemicals that affects the seed germination and the growth of the plants in its surroundings. Moreover, these substances are potent mitodepressive agents leading to several types of chromosomal abnormalities in dividing cells of plants growing in vicinity of this weed. Hence, it is also a threat to biodiversity of an area. The wide adaptability of the plant, its photo- and thermo-insensitivity and drought tolerance capacity in addition to allelopathic potential makes it a strong competitor in all habitats. There is also a growing concern that this weed will become more competitive and aggressive as concentration of carbon dioxide in the atmosphere increases i.e. due to green house effect. Looking at the harmful effect of the weed, there is an urgent need to control the population of this weed. However, it is a big challenge because of its high regeneration capacity, production of huge amount of seeds, high seed germinability and extreme adaptability to a wide range of ecosystems.