REVIEW OF LITERATURE

Transcription

1 11 CHAPTER - II REVIEW OF LITERATURE Blue green algae have been recognized as one of the first agents to fix nitrogen in flooded rice soil. They are considered to be one of the potential organisms which can be useful to mankind in various ways (Devi et al. 2010). Since De (1939) attributed flooded soils natural fertility to blue green algae, many trails have been conducted to increase rice yield by algal inoculation of the soil. The progress of phycological studies was being reviewed from time to time Iyengar (1929, 1957); Ghose (1933), Agarkar (1938), Bharadwaja (1940), Randhawa (1958), Singh (1974). A large number of contributions on the advancement of phycological research in India were made on algae in North India by Royle (1839) followed by Griffith (1844), Carter (1858) and Wallich (1860). Kirtikar (1886) was the first Indian phycologist who took interest in this group of plants. Indian workers who worked on the Indian blue green algae are Bhardwaja (1940), Biswas (1932b), Desikachary (1946, 1959); Ghose (1933), Gonzalves (1946, 1947); Iyengar (1927), Rao (1937), Singh (1961), Venkataraman (1957), Prasad and Mehrotra (1979), Mahanty and Padhi (1984), Anand (1990), Thajuddin and Sbramanian (1992), Ahmed et al. (1999), Kaushik (1994), Bhakta et al. (2006). More than 2,000 papers have been published by Indian phycologists of which majority are based on taxonomy and systematic studies (Sarma and Khan, 1991). To review such a large volume of work is an uphill task, and therefore, important contributions on certain aspects have been reviewed only. The occurrence and distribution of blue green algae in Indian rice fields has been reported by several workers such as Mitra (1951), Pandey (1965), Venkataraman (1972), Bendra and Kumar (1975), Sinha and Mukherjee (1975a, 1975b), Prasad et al. (1978), Kannaiyan (1979), Bongale and Bharati (1980), Sardeshpandey and Goyal (1981a), Kannaiyan (1993a), Ahmed et al. (1999), Tiwari et al. (2000), Nayak et al. (2001), Kaushik and Prasanna (2002), Mishra and Pabbi (2004), Choudhury and Kennedy (2005), Rai (2006), Nayak and

2 Review of Literature 12 Prasanna (2007), Digambar Rao et al. (2008), Choudhary (2009), Ghadai et al. (2010). Under submerged soil in a tropical condition of the rice fields in many rice growing provinces of India, blue green algae form the most promising biological system. In addition to contributing nitrogen, blue green algae benefit the crop in many other ways (Goyal 1982). The beneficial effect of algal inoculation on the grain yield of rice has been well documented at many locations Venkataraman (1972), Venkataraman et al. (1974), Kannaiyan (1979), Saadatnia and Riahi (2009). The available information show that some algal forms like Nostoc, Anabaena, Calothrix, Aulosira, Plectonema etc. are ubiquitous in Indian soils while others like Haplosiphon, Scytonema, Cylindrospermum etc. have localized distribution (Venkataraman, 1972; Kannaiyan, 1985). Algal inoculation to rice crop was effective in different agro-climatic conditions as well as soil types (Goyal and Venkataraman, 1971; Kannaiyan, 1983). Cyanobacteria have been reported to promote the nitrogen economy of the soil by converting atmospheric nitrogen into soluble form of ammonia with the help of enzyme nitrogenase contained within the specialized structure called heterocyst (Singh, 1961; Ernst et al. 1992). Both fresh water and terrestrial members of Cyanophyceae have been well documented by Desikachary (1959). His monograph includes 81 genera and 493 species from Indian Territory. Quite a good number of workers (Singh and Chaturvedi, 1979; Fatma, 1985; Iqbal and Pandey, 1988; Iqbal et al., 1988; Chaturvedi et al. 1990) have studied distribution of blue green algae in India. So far a total of 85 genera and about 750 species of blue green algae have been reported from India and its neighborhood (Desikachary, 1959). Devi et al (2010) gave a detailed literature on the ecology and biodiversity of blue green algae. Mishra et al. (2005) studied the role of inoculated blue green algae on paddy cultivation. In Pakistan Shah and Chaghtai 1984, Naz et al. 2004, Hussain et al. 2009, worked on blue green algae; in Saudi Arab and Egypt (Fathi and Zaki, 2003), Italy (Santina et al. 2006), considerable work has been done on blue green algae. In South East Asia the presence of species of Tolypothrix, Nostoc, Cylindrospermum, Calothrix, Anabaena, Plectonema, Anabaenopsis and Schizothrix have been reported by Watanabe (1959a) and Kobayashi et al. (1967).

3 Review of Literature 13 In temperate soils blue green algae are less abundant than in tropical and subtropical regions. They are found to occur in Russia (Shtima, 1969), Northern and Western Europe (Granhall, 1975; Henriksson, 1971; Henriksson et al., 1972) and North America (Jurgenson and Davey, 1968; Mayland and McIntosh, 1966; Shields and Durrell, 1964). In Sweden the Cyanophycean algae were present in over 80 percent of the clay soil and over 90 percent of the lime soils (Granhall and Henriksson, 1969). Blue green algae helps in the nitrogen nutrition of crops. In Bangladesh, a good number of works have been reported on the nitrogen fixation Bhuiya et al. (1984), Rother et al., (1988), Begum and Mandal (1997), Mandal et al. (1993), Begum et al.(2008) studied the nitrogen fixing potential of some isolated distribution and nitrogen fixing capacity of blue green algae in soils of cyanobacteria in the rice field soils of Bangladesh. Aziz et al. (1992) worked on taxonomy and ecology of rice field soil algae of Bangladesh. Hussain et al (2009) reported 28 species of blue green algae in 14 genera from rice field soils of Asota Saharif district in Pakistan. Gafur and Parvin (2008) studied distribution and nitrogen fixation of soil cyanobacteria in the Chittagong University campus of Bangladesh. Begum and Islam (1982) studied the role of blue green algae and rice yield. The blue green algal flora of Indian rice field soil has been studied by Tiwari (1972); Laloraya and Mira (1974); Sarma and Kanta (1978a, 1978b); Saha and Mandal (1980); Sardeshpande and Goyal (1981a, 1981b); Bongale (1984). Over 800 taxa belonging to 70 genera of blue green algae have so far been reported from Indian rice soils. Nayak and Prasanna (2007) studied on abundance and diversity of heterocystous cyanobacteria in rice field soils of India. In the processes of biological nitrogen fixation in rice field ecosystem, the inherent nitrogen fixing capacity of indigenous cyanobacterial is one of the most important factors (Kaushik, 2002). Watanabe and Yamamoto (1971) in India found that in controlled growth Tolypothrix tenuis could fix nitrogen at the annual rate of 2000 lb per acre, thus potentially increasing the rice production by about 20 percent. The production of rice has, therefore, considerably been increased in recent years due to the artificial inoculation of blue green algae in the rice fields. The International Rice Research Institute (IRRI), Philippines, in 1978, stressed on the

4 Review of Literature 14 use of blue green algae and Azolla as a biofertilizer for rice cultivation. The Central Rice Research Institute of India (CRRI), Cuttack and the National Facility for Blue Green Algal Collection, Indian Agricultural Research Institute (IARI), New Delhi are currently conducting collaborative research and training activities to demonstrate knowledge of blue green algae and Azolla and to encourage their uses as a source of nitrogen fertilizer for rice cropping throughout south and South East Asia. Singh (1942, 1961) made detailed studies on periodicity of blue green algae in rice fields of Uttar Pradesh and Bihar and reported abundant growth of Aulosira fertilissima, Anabaena ambigua, Anabaena fertilissima and Cylindrospermum gorakhaporense. An analysis of 2,213 soil samples from 15 rice growing states in India revealed the presence of blue green algae in only 33 percent samples dominated by Aulosira fertilissima and different species of Nostoc (Venkataraman, 1975). A survey was conducted by the Central Rice Research Institute (CRRI), India, to evaluate the distribution of N 2 fixing blue green algae at different water regime (2-4 cm, 5-10 cm, more than 10 cm) in paddy flood water and it was found that species of Aphanothece, Aulosira, Cylindrospermum, Anabaena, Nostoc, and Gloeotrichia were more abundant in moist soil than in habitats with stagnant water (Singh and Singh, 1986). In Gujarat, Mahajan and Patel (1983) made systematic account of 12 taxa belonging to Scytonema and Tolypothrix which were collected from paddy fields of three localities viz. Limpsai, Matar and Naragam of Koira district of the state. They also dealt with the systematic account of 48 taxa from the same district. The well known phycologists of the state are Dixit (1936), Pingale (1988), Mahajan and Patel (1986), Vasistha (1960), Barhate and Tarar (1983b) and Marathe (1967). Chaporkar and Gangawane (1984) studied on the blue green algal flora of Marathowada, from the cultivated soils. Sardespande and Goyal (1981a) reported the distribution of nitrogen fixing blue green algal flora from rice field soils of Konkan region. The other prominent workers who worked on the blue green algae of Maharastra are Mahajan and Patel (1986), Marathe (1967, 1969). Koltze and Goyal (1985) studied on the blue green algal flora from Vidarabha region of Maharastra. Mahajan and Mahajan (1994) reported a total of 112 taxa of blue

5 Review of Literature 15 green algal belonging to 19 genera from different types of cultivated crop field soils of Jalgaon district, Maharastra. Bongale (1981) studied on the soil algae from paddy fields of Panjim (Goa). In Orissa, Chatterjee and Mahanty (1990) dealt with the study of phytoplankton from the lakes of Bhubaneswar. The blue green algae of rice fields of the state have been studied and many interesting species of blue green algae were observed from various water bodies of Bhubaneswar by Mahanty (1984). Satapathy and Adhikary (1993) made a survey on the occurrence of various algal forms on the rock surfaces of various temples and caves of Bhubaneswar, Puri and Konark. Sahu et al. (1996) studied on the distributional pattern of blue green algae in different agroclimatic zone of rice fields of Orissa and reported about 120 heterocystous blue green algae from 9 genera and 23 nonheterocystous forms belonging to 3 genera. Padhy et al., (1992) Pandey et al., (1998) made a study on the blue green algae of rice field soils of Ganjam district of Orissa. Dey et al., (2010) worked on the occurrence and nitrogen fixation In Andhra Pradesh, a report on the crop field soils belonging to four major cereal crop have been presented by Shakuntala (1990). She gave taxonomic enumeration of 59 different taxa of blue green algae which were collected from the field soils of these crops. Dikshit and Pandey (1986) studied the blue green algal flora of paddy field of Andhra Pradesh. There are a few reports of occurrence of blue green algae in Rajasthan. Goyal (1964) presented the algal flora of Jodhpur. Gupta and Kumar (1968, 1972), Vaidya and Patel (1968), Soni and Bharadwaja (1980) presented the algal flora of Udaipur, Parvateesam and Misra (1993) made a survey of algal composition along with physicochemical characteristics of fresh water in man made Pushkar lake of the temple town, Ajmer of Rajasthan. A total of 88 algal forms were recorded out of which 29 belong to Cyanophyceae. Other workers of the state of Rajasthan are Dadheech et al., (1992), Chaturvedi and Habib (1993). In Bihar, Kumar and Saha (1993) worked on the algal taxa in different sources of drinking water of Bhagalpur and give a systematic account of 32 taxa belonging to Cyanophyceae. Verma et al. (1990) reported 27 species of blue

6 Review of Literature 16 green algae from the paddy field of North Bihar. Jha et al. (1986) reported 21 genera of cyanobacteria with 60 species from rice fields of Pusa and adjoining area. Sinha and Srivastava (1980) recorded several members of Cyanophyceae, Bacilliriophyceae, Chlorophyceae and Xanthophyceae from Balmikinagar. Choudhury (2009) studied the periodical occurrence of the members of Chroococcaceae in the rice fields of North Bihar and identified 28 species of cyanobacteria belonging to 9 genera during rice cultivation and growing season. Taxonomic enumeration of algal flora of Madhya Pradesh was done by Sen et al., (1992). They gave an account of a total a 52 genera of fresh water algae from Bilaspur district of which 10 belong to Cyanophyceae. Sarma and Naik (1996) reported on 32 species of blue green algae from Raipur district. Singh et al. (2000) enumerated 33 species of rice field blue green algae belonging to 15 genera from Jabalpur and Kanti district. Mahajan (1986, 1987, and 1992) studied the algal flora of Pawagiri, Oon and Khargone area in Madhya Pradesh. In Tamil Nadu extensive collection of blue green algae were made from different fresh water bodies, moist soils and paddy fields (Rao, 1938); Ramakrishnan and Kannan (1992). Venkataraman (1979) demonstrated the significance of application of algal biofertilizer in the rice fields and their usefulness. Venkataraman (1961, 1964, 1972, 1975, and 1979) is a pioneer in algal research and country s foremost scientist in the field of biological nitrogen fixation by blue green algae. His scientific contribution covers wide range of basic and applied aspects of biological nitrogen fixation by blue green algae. Nedumaran and Manokaram (2009) reported 25 cyanobacterial species from some salt pans of Pudukkottai, Tamil Nadu, members of Oscillatoriaceae, Chroococcaceae, Nostocaceae, Scytonemataceae, Rivulariacaeae and Stigonemataceae were found to occur. Anand and Verappan (1980) studied the effect of fungicides on blue green algae. Anand and Revathi (1987) reported 16 heterocystous, 12 nonheterocystous and 7 coccoid forms of blue green algae from rice fields of Tamil Nadu. Nirmala et al. (1990) made an extensive study on the species of Stigeoclonium from Madras.

7 Review of Literature 17 From Karnataka blue green algae are known mainly through the work of Hedge and Somania (1992). Bharati and Bongale (1975) and Bharati 1990) recorded 48 genera and 388 species of cyanophycean algae from 8 districts of Karnataka. Bongale and Bharati (1980) recorded 244 members of Cyanophyceae from cultivated soil of Karnataka. Bongale (1981) worked on the soil algae from paddy field of Chikkamanchali (Raichur district, Karnataka) and Panjim (Goa). A checklist of heterocystous blue green algae from the paddy soils of Couvery basin was presented by Shivaram and Sivappa Shetty (1988) which includes 16 blue green algal isolates belonging to 6 different genera. Singh and Bongale (1990) studied the algal flora of paddy fields in Siris, Karnataka. Shivaprakasha and Shivappa Shetty (1983) studied the distribution of N 2 fixing blue green algae in paddy field soils of Shimoga district. In West Bengal, the blue green algal flora rests mainly upon the works of Prain (1905), Bruhl and Biswas (1922), Biswas (1926), De (1939), Cartner (1926), Gupta (1965, 1975), Sinha and Mukherjee (1975a, 1975b), Saha and Mandal (1980) etc. Mukhopadhya and Chatterjee (1981) made a checklist of blue green algae from the paddy fields of 24 Parganas and Howrah district. Santra (1987a, 1987b, 1991) and Pal and Santra (1982, 1985), with a view to study the distribution pattern of algae in varied environment, reported 40 species of blue green algae from Midnapore. A checklist of algal flora of Sunderban delta of West Bengal was also presented by Pal et al., (1988); Sinha and Mukherjee (1984) recorded 40 forms of blue green algae belonging to 20 genera from paddy fields of Bankura district. Santra (1993) reported 240 algal taxa from West Bengal. In Madhya Pradesh, Mahajan has made a series of work on the algal flora of this state from 1986 to The algae and the planktonic forms from different water bodies of Madhya Pradesh have also been described by various workers like Agarkar (1975), Kaushik (1987), Srivastava and Sen (1987), Kaushik et al.(1991), Dikshit and Agarkar (1974) etc. Sarma and Naik (1996) identified 32 species of cyanobacteria from the rice fields of Raipur district. Singh et al. (2000) reported 33 species of blue green algae from 15 genera in the rice field soil of Jabalpur and Kanti districts.

8 Review of Literature 18 Anand and Hooper (1995) reported 158 taxa of blue green algae in 33 genera which were recorded from rice fields of Kerela state. Shaji and Panikkar (1994) also studied the Cyanophyceae of Kerela. In Punjab, systematic enumeration of blue green algae was made by Ghose (1919, 1920, 1923), Vasistha (1960) and others. Sarma and Kanta (1978a, 1978b) gave a systematic account of algal flora of Patiala and its environs. There are a good number of reports of blue green algae from the state of Uttar Pradesh also. Those who are associated with the works of Cyanophyceae of the state are Pandey (1965), Singh (1961), Pandey and Tripathi (1988), Chaturvedi and Pandey (1976), Pandey and Chaturvedi (1979) and Singh and Chaturvedi (1979). It is evident from the recorded literature that tremendous works on blue green algae have been done in India. However, in Northeast India the information on distribution of blue green algal study is very scanty. A survey of blue green algae present in North East India has been carried out with a view to study their distributional pattern in various habitats by Reddy et al. (1985) and reported 552 species from 3 orders. Alfred (1978), Changkakaty (1989), worked on the taxonomical study of blue green algae of Meghalaya. Changkakati (1989) gave a detailed account of algae of Meghalaya on their altitudinal pattern wherein she reported a total of 102 species of Cyanophyceae belong to 31 genera. Singh (1996) studied the blue green algae from rice field soils of Mizoram. Devi et al. (1999) reported 110 blue green algal species from 34 genera found in the rice field soils in Manipur. Singh et al. (1997a) studied 224 rice field soil samples from 7 districts of Nagaland and isolated 64 blue green algal species under 31 genera. Singh et al. (1997b) reported 83 species of blue green algae belonging to 25 genera in 450 soil samples collected from 7 districts of Arunachal Pradesh. Singh et al. (1997c) identified 79 species of blue green algae from 30 genera in his 213 rice field soil samples collected from Tripura state. Singh (2001) isolated 462 cyanobacteria belonging to 13 families and 5 orders from 2023 rice field soil samples collected from different rice growing areas of north eastern states of India.

9 Review of Literature 19 Assam is almost a virgin ground where very little information of blue green algae is available. Brahul and Biswas (1922), Parukutty (1939), Bordoloi (1974) have given only preliminary information about the algal flora of this state. Devi (1981) put forwarded detailed information of Darrang district of Assam. Ramakant and Pandey (1984) made a preliminary survey on blue green algae of the paddy field soils of Assam. Hazarika (1988) studied the distribution of blue green algae of rice field of Golaghat subdivision and reported the presence of 81 species of blue green algae belonging to 21 genera from the rice field as well as other habitats including hot spring of Nambar. Deka and Bordoloi (1991) published a research article on the studies of blue green algae from rice fields of Assam and reported 82 species, out of which 47 were nonheterocystous and the rest 35, were heterocystous. Saikia and Bordoloi (1994) have recorded a total of 28 species of blue green algae belonging to 12 genera from the rice fields of Barpeta, Nalbari and Kamrup district of Assam. Talukdar (1997) reported 152 species of blue green algae belonging to 43 genera and 14 families from Kamrup district of Assam. Bhuyan (1996) conducted taxonomical and ecological studies on Myxophycean algae from Nagaon district of Assam. Ahmed et al. (1999) reported 15 genera of blue green algae with 64 species from rice field of Nagaon subdivision; Raut and Dey (1999) reported some blue green algal flora from Irongmara (Barak valley), Assam. Nandi and Raut (2000) reported 66 algal species from different habitats of Dargakona area, Silchar, Assam, Yasmin (2003) studied on a few blue green algal species of Morigaon, and Hazarika (2004) reported the Myxophyceae algae of Lakhimpur district of Assam. Das (2009) worked on the blue green algae of Bongaigaon, Assam, Deka and Sarma (2011) made a preliminary survey work on Oscillatoriaceae of Goalpara district, Assam. Pesticides are considered as one of the main tools for increasing agricultural production beside the use of chemical fertilizers, high-tech agricultural equipments and high yielding varieties. At present these pesticides have made great impact in agricultural practices in India wherein large quantities of chemicals are used for green revolution to accelerate food production and control vectors of diseases (Krishnamurthy, 1987).

10 Review of Literature 20 The pesticides use to control pests also influence the nontergated micro flora of algae (Reddy et al., 1999). These influences have been shown to bring about morphological, physiological, cytological and mutagenic changes in microorganisms (Das and Singh, 1977; Lal and Saxena, 1980, 1982; Padhy, 1985; Zarger and Dar, 1990). This group of chemicals inhibits growth, photosynthetic activities and enzyme activity and also interferes with synthesis of DNA, RNA and protein in algae (Lal and Saxena, 1980). The inhibition of growth and photosynthesis in Chlorella treated with methyl parathion was studied by Saroj and Bose (1983a, 1983b). Bertangnoli (1974) found that the growth and respiration in Chlorella was retarded when treated with 2, 4-D and Diuron. Many reviews and research reports have appeared on effect of pesticides on algae (Ahmed and Venkataraman, 1973; Tarar and Shewale, 1984; Adhikary, 1989; Anand 1990; Nagpal and Goyal, 1992; Rathi and Adhikary 1994; Kapoor and Arora 1996a, 1996b, 1998, 2000a, 2000b). Venkataraman and Rajyalakshmi (1972) reported that 27 strains of nitrogen fixing blue green algae lose their viability when treated with different concentrations of two fungicides and six pesticides. Singh (1973) studied the effect of BHC, Lindane, Diazine and Endrin on Cylindrospermum, Aulosira fertilissima and Plectonema boryanum. Singh et al. (1979) found that recommended dose of herbicide-alachlor at the rate of µ/ml toxic to Anabaena doliolum, Nostoc muscorum and Aphanothece stagnina. Pachpande and David (1980) studied the effect of some common herbicides like 2-4 D, Malic Hydrozide etc. on the growth and development of soil algae like strains of Chlorococcum infusionum. Gangawane and Saler (1979) investigated the effect of fungicide Brassicol, Methyl Benzimidazole Carbamate (MBC), Difolatum and Hexacap on Westiellopsis, Aulosira, Nostoc, Tolypothrix and Calothrix. Anand and Veerappan (1980) studied the effect of pesticides-demicron 100, Ekalux 25, fungicides Blitox and Dithane on three blue green algae viz. Anabaena variabilis, Cylindrospermum muscicola and Nostoc entophytum. Sardespande and Goyal (1982) noted that Endosulfon induced reduction in growth of Anabaena iyengarii, Haplosiphon intricatus and Calothrix bharadwajae. Sahu et al. (1992) reported the Endosulfon toxicity to several cyanobacteria.

11 Review of Literature 21 Benthiocar has been very widely used in rice cultivation because of its selective effect and persistence. Rajendraprakash et al. (1990) have shown that Benthiocarb reduces porphyrin and chlorophyll biosynthesis in rice and barnyard grass; Kolte and Goyal (1992) studied the effect of four herbicides- Bautachlore, Benthiocarb, Pandemathalin, Oxadiazon and found no adverse effect on growth of Calothrix marchica. But higher concentrations of these herbicides have been shown to effect the growth and nitrogen fixation of cyanobacteria. Mahapatra et al. (1992) studied the effect of Demithoate on Anabaena doliolum and found highly toxic to the algae even at very low concentration. Pabbi and Vaishya (1992) studied the effect of two insecticides BHC and Carbaryl in different concentration on the growth of two strains of Anabaena variabilis and they found that higher concentrations of both the insecticides were lethal for both the strains. Sharma and Gaur (1981) studied the effect of Lindane on Anabaena doliolum, Aulosira fertilissima and Nostoc from paddy fields and found that the level of tolerance of these organisms to Lindane was 9, 15 and 10 ppm respectively. Effect of 2, 4-D was tested on few nitrogen fixing cyanobacteria, and it is reported that concentration of 200 kg per hector application have neither stimulatory nor inhibitory effect on Aulosira fertilissima (Venkataraman and Rajyalaxmi, 1971). Kapoor and Sarma (1980) found the same result on Anabaena doliolum but Tiwari et al (1981) reported different results in the case of some Nostoc sps and Anabaena sps as 2000 micro gm per ml or above concentration. Nath and Sarma (2010) found Lyngbya limnetica and Oscillatoria perornata as more resistant blue green algal species against 2,4-D. Effect of Malathion was studied by Subramanium et al (1994) on 10 stains of Aulosira fertlissima ARM 68 and Nostoc muscorum ARM 221 and found that in absence of inorganic phosphate in the medium phosphate starvation causd increased activity of alkaline phosphate while the pesticide induced acid phosphate activity. According to Vyas (1988) fungicides are a potentially serious

12 Review of Literature 22 threat on the overall productivity of soil and interfere with the life processes of cyanobacteria. Tandon et al. (1988) studied the interaction of Malathion and Endosulfon with blue green algae and they found that Malathion has a different toxicity to Anabaena and Aulosira fertilissima and also observed that Endosulphan greatly effects on photosynthesis and nitrogenase activities of both the species. Das and Adhikary (1996) studied the sensitivity of 10 rice field cyanobacteria to Hildan and found that cyanobacterial species which produced abundant mucilage and having a well defined sheath were also sensitive to higher concentration of Hildan. Choudhury and Sarma (2001) studied the effect of Bavistin and Ethion on Aulosira fertilissima, Lyngbya limnetica, Oscillatoria chlorina species from soil and reported that Ethion has more toxic effect than that of Bavistin. Several pesticide resistant mutant strains of blue green algae have been screened by many workers. Singh and Sinha (1994) isolated a mutant strain of Anabaena doliolum from wild population which is resistant to 100 µg DDT ml -1. Yadav and Tiwari (1994) isolated the herbicide resistant mutant variety Anacystis nidulans IU 625. Singh (1987) and Bisen et al. (1996) studied on pesticide resistant mutants of a few Cyanobacteria and isolated some pesticide resistant mutant varieties. Vaishampayan and Prasad (1982) isolated two Blitox resistant mutants Nostoc linckia and Nostoc muscorum. Mishra et al. (1991a, 1991b, 1994) had made a series of works on some herbicide resistant cyanobacteria. Subramanium et al. (1994) studied on biodegradation and utilization of organophosphorus pesticides in cyanobacteria. Kar and Singh (1979), while working on Nostoc muscorum and Wollea bharadwajae, reported that there was a gradual loss in toxicity of hexachlorocyclohexane (HCH) when repeated inoculation and removal of the cells was ensured. This suggests that pesticide was detoxified by some blue green algae. The filamentous cyanobacteria have a natural ability to degrade a highly chlorinated aliphatic pesticide. There are quantitative evidences that this ability of blue green algae can be enhanced by genetic engineering to degrade another chlorinated pollutant (Kutz and Wolk

13 Review of Literature ). Cyanobacteria can readily remove nitrogen and phosphorus from polluted effluents (De la Noue et al., 1984) and offer an alternative for tertiary waste water treatment in Arctic and Anarctic zones (Tang et al. 1997). As blue green provide a substantial form of biomass in several important types of habitats which are of direct practical importance in several aspects, it becomes essential to study their distribution if this natural resource potential is to be explored to the best advantages. There are abundance of diverse algal forms exhibiting seasonal periodicity in different localities of Assam. But no remarkable work has so far been done on the study of algae in general and Cyanophycean algae in particular in this state. Only a few attempts have been made to study the systematic account of algae from the state of Assam (Bruhl and Biswas, 1922; Bordoloi, 1974; Devi, 1981; Hazarika, 1988; Talukdar, 1997). Keeping in view the importance of blue green algae in agriculture and its impact on environment, it is urgent need to study the algae of this region. Dhubri, a district of Assam, is the study area selected for the present work. Review of literature reveals that the Cyanophycean algae of this area were not explored earlier and most of the areas are still lying virgin. Therefore, some information on the occurrence, distribution and effects of pesticides on blue green algae of the district is considered to be of paramount importance.