A Check List of Weeds in Rice Fields of Coastal Orissa , India

A survey was undertaken to different rice ecologies to collect, identify and conserve the weed species as herbarium specimens in coastal districts of Orissa. In this programme, 201 angiosperm taxa and 3 pteridophytes under 146 genera belonging to 56 families were collected, identified and documented. Poaceae was the dominant family followed by Fabaceae and Cyperaceae. Families are arranged according to modified Bentham and Hooker’s system of classification in the enumeration. Genus and species were arranged alphabetically under each family and genus. The number of weed species was more in upland followed by irrigated, semi deep water and deep water.Conservation strategies are also highlighted in this paper. Keywards: exploration, weeds rice fields, Orissa, conservation


Introduction
Rice is widely grown cereal crop that feeds millions of people in world (Kumar et al., 2008).It is the most important cereal crop cultivated in wide range of habitat under varying temperature and water regime.Rice fields are one of the large and extensive fresh water ecosystem on earth.The total rice areas is about 44.6 Mha in India.These act as a ideal habitat for numerous species of aquatic, amphibious and terrestrial weeds that compete with rice crop for space and nutrients.With the dominance of rice crop, grasses, sedges and broad leaves plants are referred as weeds.Biodiversity is the key component for sustainable environment.Currently rice fields are under serious threat owing to rapid increase in human population and urbanization.This phenomenon sets the biodiversity of rice fields at stake making it necessary to take immediate step for conservation.Application of agrochemical and inorganic fertilizer is the major concern for biodiversity loss.Rice fields are the transitional ecosystem that acts as both aquatic for one part of the year and terrestrial the rest.This unique ecosystem acts as potential habitat for numerous species of biota that have adapted to the highly disturbed environment.In Orissa most of the rice fields are rainfed which means it depends on rainwater only.
During rainy season, the rice fields are full of rain water but in Rabi season the fields are completely dry, so the floral succession differs in both the season due to different water regime.Most of the aquatic plants did not appear during dry season.Rice fields are colonized by terrestrial, semiaquatic and aquatic species (Moody & Drost, 1983).Moody (1989) reported 2049 species of weeds from 15 south-east Asian countries.Till now, no systematic survey of weed species was made in Orissa in particular and eastern India in general except some sporadic reports.For effective weed management practice, study of weed phenology and their biology is highly essential.Some sporadic reports regarding the occurrence of weeds in Orissa were made by Patnaik (1956), Tripathy and Mishra (1988), Maiti et al. (1983).Mishra and Choudhury (1996) made extensive survey of aquatic plants in different areas of Bhubaneswar in Orissa state.Subudhi et al. (2002) and Subudhi and Choudhury (2000) reported deep water weed flora and floristic diversity of weeds in Cuttack district of Orissa.Besides these, Bahar and Bhat (2012) reported rice weeds of Kashmir.Pragada andMalliboyana (2010, 2012) and Singh and Rao (1973) reported the phytosociological study rice weeds of Andhra Pradesh respectively.Realizing these, extensive survey were undertaken in seven districts of coastal Orissa in different seasons.A total 201 Angiosperm taxa and three pteridophytes were collected identified and housed in as herbarium specimen in P. G. Department of Botany, Utkal University Bhubaneswar.In the enumeration, families are arranged according to modified Bentham andHooker's system of classification (1882-1883).
Figure 1.Distribution of weed species

Material and Methods
Field trips were undertaken regularly to different rice growing areas during Kharif and Rabi season.Weeds in upland are different from irrigated and lowlands.In irrigated, usually marshy plant are metwith.In lowlands, aquatic and submerged plants are commonly grown, in bunds, terrestrial plant are grown.The plant samples were collected with flowering and kept inside polythene bag.The detailed information regarding associate, ecology, other field characters are recorded in note book.After collection, the specimens were dried, poisoned and fixed in herbarium sheets (Jain & Rao, 1977).The samples are identified in consultation with regional and modern flora.Information regarding utility were collected from local people.Some unidentified specimen were confirmed after matching with the herbarium at CentralNational Herbarium, Calcutta and regional herbarium at Regional Research Laboratory, Bhubaneswar.Correct name was given to each plant in consultation with the flora of British India (Bentham & Hooker, 1882-1883;Saxena & Brahmam, 1994;Haines, 1921Haines, -1925) ) and modern floras.

Study Area
Orissa is one of the coastal district lies in coast of Bay of Bengal.It is situated in 17 o 49′ to 22 o 34′ N latitudes and 81 o 27′ to 87 o 29′ E longitudes.The coastal districts are Cuttack, Puri, Bhadrak, Balasore, kendrapara, Jagatsinghpur and khurda etc. (Figure 2).These districts are having maximum rainfed areas.High rainfall occurs due to south west monsoon during the month of July and August (Figure 3).

Cultural Practices
In Orissa, most of the lands are rainfed because there is no irrigation facility and direct seeded in rainfed areas is the usually practice of the farmers.It is also economical and better suited for lowlands.After summer plough, in the month May/June, fields are broadcasted.Germination occurs after onset South west monsoon along with weeds.In July, there is heavy rainfall, which encourages the growth of weed species of different category much quicker than rice.After one month of germination, beusaning followed by laddering are the usually practices in Orissa which destroyed most of weed species.Water remains in fields up to October in lowlands, most of the hydrophytes grow in lowland as weeds, it remains up to December, there after, weed species dies.During Rabi season, other weed species appear and diversity is very less due to non availability of water.In irrigated field, the species richness is low but some dominant species occur very luxuriantly.

Results and Discussion
During exploration, 201 numbers of species under 145 genera belonging to 56 families were collected, identified and documented.The weed species are categorized 1) upland, 2) irrigated, 3) lowland, 4) saline ecology.The species are different from ecology to ecology.The number of weed species are more in upland (65) followed by irrigated (61), semi deep water (54) and deep water (21) (Figure 4).It is interesting to note that upland weeds can not beavailable in lowland/irrigated conditions.Upland weeds are having xeric adaptation due less water and flowers in August and September, whereas lowland weeds are hydrophytic adaption.These plants flower in October-December, the vegetative growth starts with onset of rainfall.It is interesting to note that out of 78 species of monocots 48 species are sedges and grasses, which constitute 64.97% of the total monocots.The approximate ratio of monocot and dicots species is 1:2.8.So it indicates that dicots are represented by nearly about three times than the monocots, which is represented in the Table 1.Out of 56 families, 20 families are represented by single species.Poaceae is the first dominant family where as it is in the 2 nd and 3 rd position in the flora of Bihar and Orissa and flora of British India respectively (Figure 5).On the other hand, Fabaceae and Cyperaceae are the 2 nd and 3 rd largest family respectively.erosion (Oudhia, 2001).So awareness should be given to the farmers/common people to conserve the species in general and weeds in particular for future use.There are four rice ecologies namely upland, irrigated, semideep water and deep water.

Upland Weeds
Rice fields, where there is no standing water are called as Uplands.The plant species in uplands are having some xeric adaptation and tolerance for drought.The species germinate immediately after rain in the month of June.

Semi-Deep Water Ecology
In this ecology, the standing water remain up to 50 cm throughout the crop season.So only aquatic/semiaquatic plants occur in this ecology.In this ecology, the paddy seeds were broadcasted before onset of monsoon, so after rain, weed seeds germinate quickly and grows faster than rice plants.But  Similarly Wolffia globosa is used as feed of duck and fishes.The species like Cynodon dactylon is used in every ritual of local people.Rice ecologies have been destroyed due to habitat destruction, construction of houses and conversion of rice field for other purposes so the flora in general and economic plants in particular are on the verge of extinction.It is high time to conserve all the useful weed species as species cafeteria/weed garden so that awareness will be developed among the common people about the utilitarian value of weed species.

Figure 4 .
Figure 4. Weeds of different ecology

Table 1 .
Percentage of families, genera and species of dicots and monocots are represented below Due to population growth, operation of biotic factors like conversion of agriculture land to residential complexes, application chemical, pesticide and inorganic fertilizer, the biodiversity both flora and fauna in rice fields are declining at alarming rate.Again many weed species are having potential value for food, medicine and check soil Oudhia (2001) of species is very less.The common species in this ecology are Bergia capensis, Oxalis corniculata, Hydrocera triflora, Aeshynomene aspera, In deep water ecology, standing water remains above 50 cm.throughoutcropseason.After the field was dried, boro rice crop was grown.The species diversity was still less than semi deepwater.The floating plant and emergent types were met with in this ecology.The common species are Nymphaea nouchali, Nymphaea stellata, Nelumbo nucifera, Neptunia oleracea, Nymphoides indica, Nymphoides hydrophylla, Utricularia stellaris, Blyxa echinosperma, Ceratophyllum demersum, Nechamandra alternifolia, Vallisnaria spiralis.Pistia stratiotes, Spirodela polyrrhiza, Wolffia globosa, Azolla pinnata, Oryza rufipogon, Eichhornia crassipes, Leersia hexandra, Utricularia inflexavar stellaris.Every plant has theraptical value so weeds are not exception.Weeds have many utilitarian values such as medicinal, food, fodder, ritual purpose and soil conservation, etc.The species viz., Enydra fluctuans, Hydrolea zeylanica, Monochoria vaginalis, Limnophila indica, Nelumbo nucifera, Neptunia oleracea, Nymphaea nouchali, Pistia stratiotes, Trapa natans var.bispinosa, etc. are having medicinal properties for different diseases.Oudhia (2001)reported many medicinal weeds from Chhatisgarh.The species such as Alternanthera sessilis, Centella asiatica, Commelina benghalensis, Ipomoea aquatic, Portulaca oleracea, Mollugo pentaphylla and Marsilia minuta, etc. are used as leafy vegetable but the rhizome of Nelumbo nucifera, Trapa bispinosa var.bispinosa, etc. are used as food.The grasses like Panicum repens, Cynodon dactylon, Paspalum flavidum, Digitaria cliaris, Eriochloa procera, Chloris barbata, etc. are used as fodder.Azolla pinnata is very good fodder for cattle.