RESEARCH COMMUNICATIONS 8. Pande, P. K., Krishna Negi and Magan Singh, Inter-species variations in wood elements of red meranti group of Shorea of Malay Peninsula. J. Indian Acad. Wood Sci. (NS), 2004, 1, 60–66. 9. Pande, P. K., Krishna Negi and Magan Singh, Wood anatomical variations in red meranti group of Shorea of Malay Peninsula. Ann. For., 2004, 12, 217–232. 10. Pande, P. K., Krishna Negi and Magan Singh, Intra- and interspecies wood anatomical variation in balau group of Shorea of Malay Peninsula. Indian For., 2005, 131, 1041–1048. 11. Pande, P. K. and Magan Singh, Variations in pulp and papermaking wood anatomical properties of the clonal ramets of Eucalyptus tereticornis Sm. J. TDA, 2004, 51, 19–29. 12. Pande, P. K. and Magan Singh, Intraclonal, inter-clonal and single tree variations of wood anatomical properties and specific gravity of clonal ramets of Dalbergia sissoo Roxb. Wood Sci. Technol., 2005, 39, 351–366. 13. Pande, P. K., Identification, taxonomy, properties and uses of different species of Shoreas of Malay Peninsula. Final Technical Report, CSIR, New Delhi, 2006, p. 48. 14. Desch, H. E., Commercial timbers of the Malay Peninsula. 1. The genus Shorea, Malay. For. Rec., 1936, 12, 125–143. 15. Symington, C. F., Forest Manual of Dipterocarps, Malayan Forest Records (Reprint of Symington, 1943), Penerbit Universiti Malaya, Kuala Lumpur, Malaysia, 1974, p. 244. 16. Kamiya, K., Harada, K., Tachida, H. and Ashton, P. S., Phylogeny of PgiC gene in Shorea and its closely related genera (Diptercarpaceae), the dominant trees in South East Asian tropical rain forests. Am. J. Bot., 2005, 92, 775–788. 17. Rath, P., Rajaseger, G., Goh, C. J. and Kumar, P., Phylogentic analysis of dipterocarps using random amplified polymorphic DNA markers. Ann. Bot., 1998, 82, 61–65. 18. Seibert, B., Food from the Dipterocarps: Utilization of the tengkawang species group for nut and fat production. In Dipterocarp Forest Ecosystem: Towards Sustainable Management (eds Schult, A. and Schone, D.), World Scientific, Singapore, 1996, pp. 616– 626. 19. Maury, G., Diptercarpacees du Fruit a La Plantule, Doctoral thesis, Universite paul Sabatier, Toulouse, France, 1978. 20. Kajita, T. K. et al., Molecular phylogeny of Diptercarpaceae in South East Asia based on nucleotide sequences of matK, trnL intron, and trnL–trnF intergenic spacer region in chloroplast DNA. Mol. Phylogenet. Evol., 1998, 10, 202–209. 21. Ashton, P. S., Dipterocarpaceae. Flora Malesiana, 1982, 9, 337– 552.
ACKNOWLEDGEMENTS. We thank the Director, FRI, Dehradun and Head, Botany Division, FRI for providing necessary facilities during the work. We also thank Mr N. P. Ghyldiyal and Mr Prashant Sharma of the Wood Anatomy Discipline, FRI for laboratory assistance and Council of Scientific and Industrial Research, New Delhi for financial support.
Received 24 July 2006; revised accepted 17 January 2007
Phytoliths as indicators of monsoonal variability during mid–late Holocene in mainland Gujarat, western India Vartika Singh*, Vandana Prasad and Supriyo Chakraborty Birbal Sahni Institute of Palaeobotany, 53, University Road, Lucknow 226 007, India
Phytolith studies were carried out on a 7.8 m profile of mid–late Holocene succession located at Itola, Dhadhar river basin that lies in the sub-humid belt bordering the semi-arid zone of western India. The exposed sediment succession consists of alternating sand, silt and clay with thin layers of terrigenous charcoal partings dated to 3960 ± 510 cal yrs BP and pottery pieces at the basal-most part. Since grasses respond readily to precipitation, the ratio of characteristic cool and moist to warm and humid phytolith associations was used to reconstruct the mid–late Holocene monsoonal variability in this region. The study indicates weakning of the SW monsoon during mid–late Holocene. Winter precipitation, known to have commenced during early– mid Holocene, was still persistent around 3960 cal yrs BP, leading to cool and moist climatic conditions. Following a brief phase of dry climatic conditions, winter precipitation also gradually died out resulting in a dry climate. The SW monsoon regained its strength during the later part of late Holocene. The presence of vast archeological sites of the Indus Valley Civilization in Gujarat region during mid Holocene and their subsequent decline from this region during late Holocene raises questions regarding its relationship with the monsoonal variability during that time-span. The phytolith studies of a late Holocene sequence in mainland Gujarat has provided evidence of extremely weak winter as well as SW monsoonal activity resulting into dry climatic conditions during mid Holocene, a possible cause in the decline of the Indus Valley Civilization. Keywords: Late Holocene, mainland Gujarat, phytoliths, SW monsoon, winter precipitation. PHYTOLITHS are microscopic bodies of opaline silica produced in and between the vegetal cells of living plant tissues. They occur in many plant families, but are distinctive and abundant in grasses1–3 . They also have an advantage over the pollen due to their resistance to decay in highly oxidizing environmental conditions. Owing to the morphological distinctiveness and ecological preferences of grasses, grass phytolith assemblages are now being used for identification of crops in archaeobotany4 and palaeoclimatic interpretations. Grasses follow two photosynthetic pathways: C3 (Calvin–Benson cycle) and C4 (Hatch–
*For correspondence. (e-mail:
[email protected]) 1754
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RESEARCH COMMUNICATIONS Slack cycle). C3 grass phytoliths occur dominantly in subfamily Pooideae and in grasses which mainly flourish during cool season where the available soil moisture is high, in contrast to the C4 grass phytoliths belonging to the subfamilies Chloridoideae and Panicoideae. Grasses of subfamily Chloridoideae occur during warm season in areas of low soil moisture and Panicoideae grasses occur in warm and humid conditions. Morphological variability of the phytoliths amongst the various subfamilies of Poaceae makes them reliable proxy tools for characterizing C3 and C4 grasses in fossil assemblages. Thus relative percentage of characteristic phytoliths in the sediments provides evidence of monsoonal fluctuations. The study area lies in mainland Gujarat, which is bordered by the Thar Desert in the north, the Arabian Sea in the west and the trappean highland in the east. High spatial variability in the rainfall pattern in Gujarat region is a characteristic phenomenon. SW monsoonal activity shows a decreasing trend from south to north. The 7.8 m profile of mid–late Holocene succession is located at Itola, Dhadhar river basin (Figure 1). The Dhadhar river originates from the Aravalli range; it flows southwest and joins into the Gulf of Cambay5,6 . Various lakes and pond subenvironments have been developed during early Holocene in the Dhadhar river basin 7 . The exposed 7.8 m fluviolacustrine sediment succession of late Holocene at Itola consists of interbedded sand, silt and clay with thin layers of terrigenous charcoal partings. The 14 C age of basalmost charcoal layer is 3960 ± 510 cal yrs BP. The dated lithological succession and phytolith studies of 2.5 m Kothiyakad section from the adjoining Mahi basin has been considered for the purpose of correlation (Figure 2). For phytolith analysis, deflocculation of sediments was done by placing 5 g of sediment in a 10% calgon solution overnight; suspended clay was siphoned out. The residue was washed with distilled water several times and treated with 10% HCl and heated in a sand bath for 10–20 min to
Figure 1.
Location map of the study area (modified after Raj7 ).
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remove carbonate content from the sediments. The organic content was removed by heating the residue in 30% H2 O2 in a sand bath for 20–30 min. The remaining residue was washed twice with distilled water. Phytolith extraction was done using heavy liquid solution of CdI2 and KI (specific gravity 2.3) and centrifuged at 1000 rpm for 5 min. The residue was washed, dried and weighed. Dried phytoliths were mounted on the slide using Canada balsam. Few slides were also mounted in immersion oil to view the 3D images of phytoliths. Phytolith identification was made in 400 and 1000X (Olympus BX51 microscope). The extracted phytoliths were counted and classified according to Twiss et al.8 and Mulholland and Rapp9. The multiplicity and redundancy of many phytolith morphotypes prevent the attribution of phytoliths to species and genus. Hence, phytolith associations have been used to decipher variability of palaeoprecipitation in this region. Detailed lithology of the Itola section (7.8 m) is given in Figure 2. The basal part shows organic-rich clay followed by silty sand and sand with numerous thin charcoal partings and pottery pieces, upward the organic-rich clay band is followed by silty sand and sand horizon. The 2.5 m thick Kothiyakhad section from the adjoining Mahi river basin is also composed of alternating organic clay, sand and silt layers with a prominent organic-rich clay band (similar to the Itola section) in the middle part (Figure 2). In both the sections the base is not exposed. The Itola section is a sand-dominated sequence with organic-rich clay having fine charcoal partings in the lower part, which indicates
Figure 2.
Lithology of Itola (a) and Kothiyakhad (b) sections. 1755
RESEARCH COMMUNICATIONS its fluviolacustrine nature and hence shows more sediment accumulation rate than the Kothiyakhad section of the estuarine environment in the same time-span. Kusumgar et al. 10 have dated the Kothiyakhad section; the date of the basal clay layer of the Kothiyakhad section is about 3660 ± 90 14 C yrs BP (3865–4090 cal yrs BP), middle clay layer above the silty sand horizon has a date of 3320 ± 90 14 C yrs BP (3460–3640 cal yrs BP) and the topmost clay layer dates to about 2850 ± 90 14 C yrs BP (2850–3080 cal yrs BP; Figure 2). On the basis of the sediment characteristics and phytolith content three units, Units I–III, have been identified in the Itola section.
Figure 3. 1756
Unit I (0–3.5 m) contains basal clay and silty sand with charcoal partings (Figure 2). Phytolith records of this unit show dominance of rondel and trapezoid phytolith morphotype, characteristics of grass families Pooideae and Festucoideae respectively. However, saddle, bilobate and cross-type morphotypes belonging to families Chloridoideae and Panicoideae occur in low proportions (Figure 3). Non-distinctive phytolith morphotypes, i.e. bulliform, rod, rounded and pointed types are present in small numbers. The charcoal layers consist of epidermal long cells of wheat and barley. Low occurrence of wild rice grass phytoliths is characterized by the presence of bulliform cells with undeveloped scales at the margin (Figure 4).
Distribution pattern of phytoliths plotted against the Itola (a) and Kothiyakhad (b) lithocolumns. CURRENT SCIENCE, VOL. 92, NO. 12, 25 JUNE 2007
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Figure 4. Photomicrographs of grass silica short cells. Location no. 6608. Festucoid/pooid phytoliths: a–c, Rondel, a, (13230) 29H4, b, (13231) 38M1, c, (13230) 39N2; d–f, Trapezoid, d, (13231) 34G4, e, (13230) 39M4, f, (13231) 24T3; Chloridoid phytoliths: g–i, Saddle, g, (13232) 47R3, h, (13232) 30M4, i, (13233) 27O1; j–l, Collapsed saddle, j, (13234) 30P1, k, (13234) 46G2, l, (13235) 46G2; Panicoid phytoliths: m, n, Bilobate, m, (13230) 39R2, n, (13235) 43S1; o, Cross-type phytolith, o, (13234) 46X3. Photomicrographs of grass silica long cells: p, q, Wild rice bulliform cells (fan-shaped) showing poorly developed scales, p, (13234) 43S4, q, (13234) 46U4; r, Cultivated rice bulliform cell showing well-developed scales on the upper margin, r, (13234) 20F2; s, t, Wheat phytolith (13230) 39H1. The numbers in parenthesis indicate BSIP museum slide nos, followed by England Finder Position on the slide. All the slides are housed in the BSIP museum.
Phytolith morphotypes belonging to subfamilies Pooideae and Festucoideae that dominate during this interval are also indicative of cool climatic condition, probably as a result of frequent winter precipitation. However, extremely low occurrences of phytolith morphotypes belonging to sub-families Panicoideae and Chloridoideae may indicate weak SW monsoonal activity during this phase. CURRENT SCIENCE, VOL. 92, NO. 12, 25 JUNE 2007
Unit II (3.5–4.2 m) is represented by organic-rich clay horizon overlying the sand bed. Phytolith data of this unit show sudden increase in saddle, bilobate and cross morphotypes. However, trapezoids and rondel morphotypes occur in low proportion (Figure 3). The phytolith assemblage shows dominance of morphotypes belonging to sub-families Panicoideae and Chloridoideae, indicating warm and humid 1757
RESEARCH COMMUNICATIONS conditions probably due to increase in SW monsoonal activity during this phase. Unit III (4.2–7.8 m) is made up of silty clay and sand horizon and forms the upper part of the Itola section. Phytolith data of this unit show great fluctuation. Amongst the various phytolith morphotypes, short saddle-type dominates in the phytolith assemblages. However, bilobate and cross-type occur in moderate numbers. Trapezoid and rondel phytolith morphotypes are completely absent in this unit (Figure 3). The large proportion of phytolith morphotypes belonging to sub-family Chloridoideae and moderate numbers of subfamily Panicoideae, indicate fluctuating humid/arid climatic conditions. Warm and humid climate with considerably warm summer conditions due to fluctuating SW monsoon activity is envisaged for this unit. The present-day climatic conditions, particularly the monthly precipitation record of this region show maximum precipitation during summer months (June–September), with almost no rains during winter months (December– February). The semi-arid climate favours shrubs and grasses over woodland type of vegetation, wherein the phytolith study becomes a more promising palaeoecological tool for continental climate reconstruction. Phytolith study carried out on Itola section shows considerable fluctuations in the SW monsoonal activity. The grass phytolith data indicate weak SW monsoon but enhanced winter precipitation leading to cool climatic conditions in this region during mid–late Holocene (3960 cal yrs BP). It is likely that the increased relative proportion of phytolith morphotypes of cool season (C3 ) grasses compared to warm season (C4 ) grasses is possibly due to greater winter precipitation during this phase. Previous studies on salt lakes, Didwana and Lunkaransar in the Thar Desert, Rajasthan area show greatest winter precipitation between 5500 and 3500 yrs BP. The possibility of winter precipitation in the Thar Desert was further confirmed by Enzel et al. 13 , indicating a high water table and improved hydrological conditions of Lunkaransar lake after 5500 yrs BP due to increased winter rainfall. Many studies show that the NE monsoon was stronger than the SW monsoon during LGM in India14. The sudden dominance of phytolith morphotypes belonging to C3 grasses over C4 has been interpreted as a result of increased winter rainfall during the LGM in tropical southern Africa15 . The presence of pottery pieces, and wheat and barley phytoliths in the basal-most part of the Itola section indicates human settlement in this region around 3960 cal yrs 16 BP. Archaeological records of this region show that the Indus Valley Civilization flourished between 5500 and 4500 cal yrs BP. This implies that the climatic conditions were favourable during that period; though it is known that during this time the SW monsoon was on the decline. The apparent unfavourable climatic situation during summer monsoon was greatly compensated by enhanced winter precipitation activity during this phase13 . This is also sup1758
ported by our phytolith studies, which show increased abundance of cool-season grass phytoliths (festucoid and pooid) over warm season phytoliths (panicoid and chloridioid). An increased proportion of wheat and barley phytoliths in the charcoal layer further points to domination of cool-season crops in the assemblage. Presence of large proportion of warm-season grass phytoliths along with cultivated rice phytoliths and paddy field diatoms in the organic-rich clay band of Unit II in the later part of Itola section, is indicative of domination of warm-season crop, probably as a result of increased SW monsoonal activity. It is interpreted that during the early part of late Holocene around 3960 cal yrs BP, Rabi season crops were grown preferentially in this region because of greater precipitation during winter season. Rice (Kharif crop) was grown in this region much later in the late Holocene after the SW monsoon regained its strength. It is speculated13 that the coupled effect of both SW monsoon and winter precipitation made critical difference between early and middle Holocene hydrologic conditions and minimized the drought conditions during the mature phase of the Indus Valley Civilization 5500–4500 yrs BP13 . However, during the late phase of the Indus Valley Civilization, the winter precipitation and SW monsoonal activity both declined considerably, which resulted into severe drought conditions. Extremely low occurrence of phytolith morphotypes in the Kothiyakhad and Itola sections at the top of Unit I from the sand horizon, is indicative of low precipitation and dry climatic conditions during that phase. This could be the time of decline of the Indus Valley Civilization in this region. After a brief pulse of dry climatic conditions the SW monsoon regained its strength. Palaeoclimatic data from various parts of the Indian peninsula14,17,18 show increase in SW monsoonal activity around 3200 yrs BP. This is also supported by the distribution of benthic foraminifera off the central west coast of India, as reported by Nigam and Khare19 . It is interpreted that the organic-rich clay zone of Unit-II in Itola and Kothiyakhad sections 3460 cal yrs 14 BP (3320 ± 90 C yrs) corresponds to this phase. The SW monsoon shows greater fluctuation after this interval, as is evident by variability in the phytolith morphotypes belonging to Panicoideae and Chloridioideae subfamilies in both Itola and Kothiakhad sections. Further studies in the adjoining areas are currently in progress for comparison as well as for the establishment of complete records of mid Holocene monsoonal variability in the region.
1. Perasall, D. M., Palaeoethnobotany – A Handbook of Procedures, Academic Press, San Diego, 2000. 2. Piperno, D. R. and Pearsall, D. M., The silica bodies of tropical American grasses: Morphology, taxonomy and implications for grass systematics and fossil phytoliths identification. Smithson. Contrib. Bot., 1998, 85, 1–40. CURRENT SCIENCE, VOL. 92, NO. 12, 25 JUNE 2007
RESEARCH COMMUNICATIONS 3. Twiss, P. C., Predicted world distribution of C3 and C4 grass phytoliths. In Phytolith Systematics. Emerging Issues: Advances in Archaeological and Museum Science (eds Mulholland, S. C. and Rapp Jr., G.), 1992, vol. 1, pp. 113–128. 4. Kajale, M. D. and Eksambekar, S. P., Phytolith approach for investigating ancient occupations at Balathal, Rajasthan, India. Part 1: Evidence of crops exploited by initial farmers. In Applications in Earth Sciences and Human History (eds Meunier, J. D. and Colin, F.), A. A. Balkema, Lisse, 2001, pp. 199–204. 5. Chamyal, L. S., Maurya, D. M. and Raj, R., Fluvial systems of the drylands of western India: A synthesis of Late Quaternary environmental and tectonic changes. Quat. Int., 2003, 104, 69–86. 6. Chamyal, L. S. and Merh, S. S., The Quaternary formations of Gujarat. Mem. Geol. Soc. India, 1995, 32, 246–257. 7. Raj, R., Fluvial response to Late Quaternary tectonic changes in the Dhadhar river basin, mainland Gujarat. J. Geol. Soc. India, 2004, 64, 656–666. 8. Twiss, P. C., Suess, E. and Smith, R. M., Morphological classification of grass phytoliths. Soil Sci. Soc. Am. Proc., 1969, 33, 109– 115. 9. Mulholland, S. C. and Rapp Jr., G. (eds), A morphological classification of grass silica bodies. In Phytolith Systematics. Emerging Issues: Advances in Archaeological and Museum Science, 1992, vol. 1, pp. 65–90. 10. Kusumgar, S., Rachna, R., Chamyal, L. S. and Yadav, M. G., Holocene paaleoenvironmental changes in the lower Mahi basin, western India. Radiocarbon, 1998, 40, 819–823. 11. Singh, G., The Indus Valley culture seen in the context of postglacial climatic and ecological studies in Northwest India. Archaeol. Phys. Anthropol. Oceania, 1971, 6, 177–189. 12. Swain, A. M., Kutzbach, J. E. and Hastenrath, S., Estimates of Holocene precipitation for Rajasthan, India, based on pollen and lake-level data. Quat. Res., 1983, 19, 1–17. 13. Enzel, Y. et al., High-resolution Holocene environmental changes in the Thar Desert, northwestern India. Science, 1999, 284, 125– 128. 14. Sarkar, A., Ramesh, S., Bhattacharya, S. K. and Rajagopalan, G., Oxygen isotope evidence for a stronger winter monsoon current during the last glaciation. Nature, 1990, 343, 549–551. 15. Scott, L., Grass development under glacial and interglacial conditions in southern Africa: Review of pollen, phytolith and isotope evidence. Palaeogeogeogr. Palaeoclimatol. Palaeoecol., 2002, 177, 47–57. 16. Possehl, G. L., Climate and eclipse of the ancient cities of the Indus. In Third Millennium BC Climate Change and Old World Collapse (eds Dalfis, H. N., Kukla, G. and Weiss, H.), NATO ASI Series I, Springer, New York, 1997, vol. 49, pp. 193–244. 17. Sarkar, A., Ramesh, R., Somayajulu, B. L. K., Agnihotri, R., Jull, A. J. T. and Burr, G. S., High resolution Holocene monsoon record from the Eastern Arabian Sea. Earth Planet. Sci. Lett., 2000, 177, 209–218. 18. Yadava, M. G. and Ramesh, R., Monsoon reconstruction from radiocarbon dated tropical Indian speleothems. Holocene, 2005, 15, 48–59. 19. Nigam, R. and Khare, N., Spatial and temporal distribution of foraminifera in sediments off the central west coast of India and use of their test morphologies for the reconstruction of palaeomonsoonal precipitation. Micropalaeontology, 1999, 45, 285–303. ACKNOWLEDGEMENTS. We thank Dr N. C. Mehrotra, Director, BSIP, Lucknow for providing facilities and Dr Rahul Garg for help and encouragement during the study. Thanks are due to Prof. L. S. Chamyal and his research group for rendering help during field work. This work was supported in-part under grant-in-aid from the Department of Science and Technology, New Delhi. Received 28 July 2006; revised accepted 20 February 2007 CURRENT SCIENCE, VOL. 92, NO. 12, 25 JUNE 2007
Presence of citrus greening (Huanglongbing) disease and its psyllid vector in the North-Eastern region of India confirmed by PCR technique A. K. Das*, C. N. Rao and Shyam Singh National Research Centre for Citrus, Amravati Road, Nagpur 440 010, India
Citrus greening or Huanglongbing disease caused by a nonculturable, phloem-limited bacterium, Candidatus Liberibacter asiaticus, is one of the most serious and destructive citrus diseases in the world. The presence of this disease in citrus orchards in the North-Eastern region of India has been confirmed through polymerase chain reaction (PCR)-based molecular detection. Samples of DNA extracted from leaves of putatively infected different citrus cultivars and from the vector of the disease, Diaphorina citri, were subjected to analysis using PCR and produced DNA amplicons characteristic of Ca. L. asiaticus. This is the first molecular evidence confirming the presence of greening disease and its psyllid vector in NE India. Keywords: Candidatus Liberibacter asiaticus, citrus, greening disease, PCR detection, psyllid vector. T HE nutritional value of citrus fruits is well known in our dietary requirements. Presently, it is the third largest fruit industry after mango and banana in India. The NorthEastern (NE) region of India offers favourable climatic conditions for cultivation of various citrus species. Submountain and hilly tracts of states like Meghalaya, Assam, Manipur, Arunachal Pradesh, Mizoram, Nagaland, Tripura, Sikkim and Darjeeling District, West Bengal grow excellent quality citrus fruits. Different citrus species, viz. mandarin, sweet orange, lemon and other limes are cultivated in all the states of the NE region covering 57.2 thousand hectares, with a total production of 306 thousand tonnes1. The entire citrus orchards in NE India are of seedling origin, with few budded or grafted plants at some experimental research stations. Like many other crops, citrus in this region is plagued with a host of diseases caused by different etiological agents such as fungi, bacteria, viruses and phytoplasmas. Among all the diseases of citrus described to date, citrus greening disease (CGD) is considered to be probably the most destructive and lethal2 . The disease infects citrus trees of almost all cultivars and causes substantial economic losses to the citrus industry by shortening the lifespan of infected trees. It is estimated that globally more than 60 million trees had been destroyed by the disease2,3 . The name of the disease has been *For correspondence. (e-mail:
[email protected]) 1759
