NEMATODES FROM WEST BENGAL ( INPlr \ ) . XXV . QUALITATIVE AND QUANTITATIVE STUDIES OF PLANT AND SOIL INHABITING NEMATODES ASSOCIATED WITH PADDY CROP IN MALDA AND JALPAIGURI DISTRICTS

Baqri and his co-workers (1980-91) have published a series of papers on plant and soil nematodes collected during the surveys of paddy crop in different districts of West Bengal. These papers also report, besides taxonomical work, the results of qualitative and quantitative studies identifying the potential/serious nematode pests of paddy crop in the districts of the state (Baqri et. 01. 1983, 19? 1 a, 1991 b). Such information becomes more us«ful in chalking out any strategy on the management of phytophagous nematodes.


INTRODUCTION
Baqri and his co-workers (1980-91) have published a series of papers on plant and soil nematodes collected during the surveys of paddy crop in different districts of West Bengal.These papers also report, besides taxonomical work, the results of qualitative and quantitative studies identifying the potential/serious nematode pests of paddy crop in the districts of the state (Baqri et.01.1983, 19? 1 a, 1991 b).Such information becomes more us«ful in chalking out any strategy on the management of phytophagous nematodes.
The present paper reports the results of qualitative and quantitative estimation of plant and soil nematodes associated with paddy crop in MaIda and Jalpaiguri districts of West Bengal.These studies were conducted under the All India Coordinated Research Project on Nematode Pests (sponsored by ICAR, New Delhi) during the years 1978-85.The data on the information furnished herewith is the unpublished part of the final report of the Coordinated project submitted to the ICAR, New Delhi.

MATERIAL AND METHODS
The sampling was made at random.For the quantitative estimation, the methodology described by Baqri et 01.(1983) was followed.The nematode population per 200 ml (beaker) soil was counted from each sample under stereoscopic binocular microscope.From each root sample, 10 gm roots were processed through blender and phytophagous nematode population (genera wise) was also estimated.

I. District Maida
The results of the quantitative estimation of important parasitic genera and other nematodes (saprophagous and predaceous) from the surveyed localities of MaIda district have been furnished I in Table-I and III.Table-I provides information about the surveyed localities, number of samples collected,.range with average and percent of frequency of ocurrence and dominance of important nematode genera estimated in the soil of paddy fields.The information about frequency of ocurrence and degree dominance (average) of key nematode pests from soil and roots of paddy crop has been furnished in Table-III.
Upon analysis (Table-III), it was noted that Hirschmanniella gracilis, Meloidogyne graminicola (larvae) and Tylenchorhynchus mashhoodi were most abundant species because their frequency of ocurrence was observed in 97.5%,80% and 72.5% in soil samples respectively.Hirschmanniella gracilis was found dominating in 77.50/0 samples while the dominance of TylenchorMynchus mashoodi and Meloidogyne graminico/a has been noted in 15% and 7.5% soil respectively.The results of the quantitative estimation of nematodes from roots 110 gm reveal that the number of Meloidogyne graminicola (2nd stage juveniles) ranges from 2-664 with an average of 119, which is considered to be very high.The frequency of occurrence of this species has been noted in 70% root samples.The range of Hirschmanniella gracilis (adults and juveniles) was counted from 4-82 with an average of 18 in 97.5% root samples.On the basis of all these results, this can easily be concluded that M. graminicola and H. gracilis are serious pests.Besides, rylenchorhynchus mashhoodi is a potential pest in district Maida.

II. District Jalpaiguri
The results of quantitative estimation of nematodes from 42 soil and root samples collected from 10 villages near Jalpaiguri have been furnished in Table-II.The information on average of soil and root populations has been"incorporated in Table-III.The analysis in Table-II reveals that Hirschmanniella spp.(mostly H. gracilis), Meloidogyne graminicola and Tylenchorhynchus mashhoodi are also abundant in Jalpaiguri district.Hirschmanniella spp.were noted in 90.5% and found dominating in 73% soil samples over other parasitic nematodes (Table-III).The occurrence of Meloidogyne graminicola and Tylenchorhynchus mashhoodi was noted in 66% and 26% samples whereas they dominated in 20% and 7% samples respe,ctively.The occurrence of Helicotylenchus spp.(H.retusus & H. dihystera) and Pratylenchus thornei and other parasitic nematodes was not significant.The results of estimation of nematQde populations/IOgm roots conclude that the 2nd stage juveniles of Meloidogyne graminicola are abundant and found in high number, i.e. from 2-128 with an average of97 and frequency of occurrence 66.3%.The Hirschmanniella spp.(mainly H. gracillis) were estimated from 01-40 with an average of 06 and frequency of occurrence 90.50/0.All these results confirm that M. graminicola and Hirschmanniella spp.are the key pests of paddy crop in J alpaiguri district.

SUMMARY
The present paper reports the results of qual itative and quantitative studies of plant and soil nematodes associated with paddy crop in Maida and Jalpaiguri districts of West Bengal.In Maida district, 34' species were identified, of which 13 belong to phytophagous group of the Order Tylenchida.The remaining 21 species were either predaceous or saprophagous belonging to the orders Aphelenchida and Dorylaimida.The frequency of occurrence of Hirschmanniella gracilis was observed in 97.S% but dominated in 77.5% samples.Meloidogyne graminico/a and Tylenchorhynchus mashhoodi were the other two important nematode pests in district Maida.Though they were encountered in 80% and 72.5% soil samples, but were found dominant only in ISO/o and 7.S% samples, respectively.The estimation of nematodes/l Ogm roots of paddy from the same fields also confirm the above results.
In all, 31 species of the orders Tylenchida, Aphelenchida, Dorylaimida and Monon~hida have been identified fr9m Jalpaiguri district.Of these, 13 species of the order Tylenchida are phytophagous and the remaining are either saprophagous or predaceous.The quantitative estimation of the phytophagous nematodes from soil and root samples reveal that Hirschmanniella spp.mainly H. gracilis, Meloidogyne graminicola and Tylenchorhynchus mashhood;' are the most important pests of rice crop in Jalpaiguri district because their frequency of occurrence has been calculated in 90.S%, 66% and 26% soil samples, respectively.Hirschmanniella spp.and M. graminicola (both endoparasites) have also been recorded from 90.S% and 66% root samples.Hence, our study reveals that these species are the key pests of paddy crop in Jalpaiguri district.the manuscript of this paper.The financial assistance from ICAR, New Delhi to conduct the study is also acknowledged        -> RESULTS AND DISCUSSIONS A. QUALITATIVE STUDY I. District Maida During November, 1983, 40 soil and root samples were collected from nine localities of district MaIda.In all, 13 species of the established/suspected phytophagous nematodes of Order

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Figures in parenthesis indicatepercent frequency of occurrence.

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Results of the survey of Paddy crop in MaIda district, West Bengal.Range of nematode number with its avarage per 200 ml of soil. ~

Table I
contd.Results of the survey of Paddy crop in MaIda district, West Bengal.
Results of the survey of Paddy crop in J alpaiguri district, West Bengal.