Banana is the ‘queen of tropical fruits’ and is one of the oldest fruits known to mankind from pre-historic times. Today, it is the leading tropical fruit in the world market with a highly organized and developed industry. It is the fourth largest fruit crop in the world after grapes, citrus fruits and apples. Drought is an insidious hazard of nature. Although it has scores of definitions, it originates from a deficiency of precipitation over an extended period of time, usually a season or more. This deficiency results in a water shortage for some activity, group, or environmental sector. Water deficit occurs when water potentials in the rhizosphere are sufficiently negative to reduce water availability to sub-optimal levels for plant growth and development. On a global basis, it is a major cause limiting productivity of agricultural systems and food production (Bray et al., 2000). Banana plant productivity is greatly affected by environmental stresses such as drought, water and cold. Plants respond and adopt to these stresses to survive under stress condition at the molecular and cellular levels as well as at the physiological and biochemical levels. Physiological responses to soil water deficit are the feature that is most likely to determine the response of the crop to irrigation. The banana plants are sensitivity to soil moisture stress is reflected in changes in reduced growth through reduced stomatal conductance and leaf size (Kallarackal et al., 1990) increased leaf senescence (Turner, 1998). Bananas (Musa spp.) rarely attain their full genetic potential for yield due to limitations imposed by water ultimately limiting the plants photosynthesis. Turner and Thomas (1998) reported that, the banana is sensitive to soil water deficits, expanding tissues such as emerging leaves and growing fruit are among the first to be affected. As soil begins to dry, stomata close and leaves remain highly hydrated, probably through root pressure. Productivity is affected because of the early closure of stomata. Turner and Thomas (1998) who showed measurements of leaf water potential using either the exuding xylem or relative leaf water content could not be reliably linked to plant functions such as stomatal movement, net photosynthesis or leaf folding. Water potential measured by the exuding latex method appeared the best for determining leaf water status, but even this shows a small change in plants experiencing soil water deficit (Thomas and Turner, 1998) supporting the hydrated status of banana leaves although the soil is dry. Understanding banana plant response to soil moisture deficit and expression of physiological, biochemical traits are of basic scientific interest and have potential application bananas (Musa spp.). With a view to elicit information on these aspects, field and laboratory investigations were undertaken.
Result and Discussion
Plant height
The time trend of plant height of banana cultivars revealed a progressive increase from 3rd MAP to harvest stage (Table 1). Comparison of two treatments at main plot level revealed that M1 recorded significantly higher plant height than M2. Among the sub plot treatments, S1 observed to be the tallest plant with the height of 431.7 cm followed by S2 (322.7 cm) and S3 (250.7 cm). The other sub plot treatments like S4, S6, S7, S8, S11 and S12 showed medium height in the range of 201.7 cm to 245.8 cm and S5, S9 and S10 found to be the dwarfed plants with height ranging from 168.7 cm to 198.8 cm at harvest stage.
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Table 1 Effect of water stress on plant height (cm) at different growth stages of banana cultivars and hybrids
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The interaction effects of M at S and S at M were significant at all growth stages. Among the interaction treatments, M1S1 recorded taller plants of 438.0cm. This was very closely followed by M1S2 (329.0 cm). The main plot M2 resulted in 3% to 5% reduction in height of the plants of M2S1, M2S2, M2S3 and M2S4 over the treatments of M1S1, M1S2, M1S3 and M1S4 at 7th MAP. The other treatments, M2S5, M2S6, M2S7 and M2S8 showed9% to 11% reduction over M1S5, M1S6, M1S7 and M1S8. The treatments of M2S9, M2S10,M2S11 and M2S12 showed greater reduction in height of the plant with the range of 16%~22% over the subplot interaction with M1 at 7th MAP stage. Plant height is an important morphological parameter related to growth and development of the crop.Growth involves both cell growth and development. Cell growth and development is a process consisting of cell division, cell enlargement and cell differentiation (Wareing and Phillips, 1970). These processes are very sensitive to water deficit because of their dependence upon turgor. Morphologically, plant growth is perceived as an increase in plant size in terms of plant height and growth rate, while development involves tissue and organ formation. The influence of water deficit on the growth of banana cultivars exhibited significant variations at all the growth stages. Application of irrigation at 80% available soil moisture caused a significant improvement in plant height, irrigation at 50% available soil moisture resulted in a considerable reduction in plant height. The most evident effect of water deficit to the plant growth of banana was growth inhibition. Cell expansion and enlargement is one of the most sensitive processes affected by a change in plant water status (Begg and Turner, 1976).
Relative Water Content (RWC: %)
The data on RWC revealed a progressive increase from 3rd to 7Th MAP with a decline thereafter. The main and sub-plots treatments differed significantly at all the growth stages. The treatment M1 outperformed with better RWC value of 78.2% at 7th MAP stage, whereas M2 recorded significantly lesser RWC value of 68.7%. Among the sub-plot treatment varieties, S1 was found to be effective in maintaining higher RWC value (83.8%) over S12 (63.7%), which was followed by S2 (83.1%) and S3 (80.2%).
All the interaction treatments registered significant differences at all the stages, therefore, M at S and S at M attained differences significantly. Treatment M1S1 registered higher RWC of 86.1 percentage followed by M1S2 (85.4%), M1S3 (82.5%) and M1S4 (82.0%). However, a considerable reduction could also be noticed in RWC due to interaction with M2 and subplot treatments. M2S1, M2S2, M2S3 and M2S4 maintained its superiority (81.5%, 80.8%, 77.9% and 77.4%) with about 5 to 8 per cent reduction, whereas, all the other treatments showed about 12% to 20% reduction than M1 and subplot treatments. Relative Water Content (RWC) is the appropriate measure of plant water status in terms of the physiological consequence of cellular water deficit. It was used instead of plant water potential as RWC referring to its relation with cell volume, which could accurately indicate the balance between absorbed water by plant and lost through transpiration. The banana plants are able to maintain their internal water status during drought by reducing radiation load and closing stomata (Thomas and Turner, 1998).The RWC was estimated in order to find out the plant water status of banana cultivars under water stress situations. Leaf RWC had a significant influence on photosynthesis, by reducing the net photosynthesis by more than 50% when RWC was less than 80 per cent. As observed by Slatyer (1955), a reduction by 5% in RWC led to reduction in photosynthesis by 40% to 50%. The early reduction of stomatal conductance and the minor diminution of leaf RWC could indicate that the banana plants showed a drought avoidance mechanism to maintain a favorable plant water status involving stomatal closure in response to water stress (Turner and Lahav, 1983).
Total chlorophyll content (mg/g)
Thedata on total chlorophyll content reflected similar time trend of chlorophyll ‘a’, chlorophyll ‘b’ (Figure 1). Main plot treatments differed signify- cantly at all growth stages. Among the main plot treatments, M1 out performed with higher total chlorophyll content of 1.03 mg/g than M2 (0.90mg/g) showing a 13 per cent reduction over M1 at 7th MAP stage. With regard to the sub-plot treatment S1 recorded higher total chlorophyll content of 1.31 mg/g closely followed by S2 (1.17 mg/g) and S3 (1.08 mg/g). S12 however, recorded the lowest content of 0.72 mg/g among the subplot treatments at 7th MAP stage. Significant differences among the interaction treatments also revealed the differential responses of M1 and M2 treatments over sub-plot treatments. Among them M1S1 registered higher total chlorophyll content of 1.35 mg/g over M2. Treatments such as M1S2 and M1S3 also performed better than other treatments with 7 to 13 per cent increase over M2 treatment interaction. A considerable reduction in total chlorophyll content could also be observed due to interaction with M2, the percentage however, varies with different sub plots. Among the sub plot treatments, M2S1, M2S2, M2S3 and M2S4 exhibited 6% to 12% reduction in total chlorophyll content, whereas, all the other treatments showed 13% to 17% reduction over M1 and subplot interaction.
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Figure 1 Effect of water stress on total chlorophyll content (mg/g) of banana cultivars at different growth stages
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The chloroplast in green plants constitutes the photosynthetic apparatus. Chlorophylls and other photosynthetic pigments are found in the form of protein pigment complexes mainly in thylakoid membranes of grana.Photosynthetic pigments play major role in plant productivity, as they are responsible for capturing light energy and using it as a driving force for producing the assimilates. Water deficit induces disintegration of thylakoid membranes and causes degradation of chlorophyll pigments. This could substantially contribute to the overall inhibition of photosynthesis in leaves of water deficit plants (Farquhart et al., 1982). The mechanism of reduction in chlorophyll content due to the enhancement of chlorophyllase activity in water stressed plants could be the cause for chlorophyll degradation. Ghavami (1973) noticed a drastic reduction in the total chlorophyll content under water deficit condition due to the disruption of fine structure of chloroplast and instability of pigment and enhanced chlorophyllase activity. Thomas and Turner (2001) also observed a decrease in chlorophyll content in banana cultivars leading to decrease in photosynthesis.
Osmotic potential (MPa)
The data on osmotic potential revealed a progressive increase upto 9th MAP and declined at harvest. The main and sub-plot treatments differed significantly at all the growth stages (Table 2). Between the two main plot treatments, M2 had significantly higher osmotic potential (0.42 MPa, 0.73 MPa, 0.72 MPa, 0.90 MPa and 0.81 MPa) over M1 at 3rd, 5th, 7th, 9th and at harvest respectively. All the sub-plot treat- ments also significantly differed. Among the sub- plot treatments S1 recorded the higher osmotic potential of 0.49 MPa, 0.86 MPa, 0.75 MPa, 0.92 MPa, and 0.82 MPa at 3rd, 5th, 7th, 9th and harvest stage respectively. This treatment was followed by S2, S3 and S4. The lowest osmotic potential was registered by S12 (0.53 MPa). The interaction effects of M at S and S at M revealed significant difference at all the stages of growth. At 9th MAP, M2S1, M2S2, M2S3 and M2S4 maintained a high osmotic potential of 0.99 MPa, whereas the treatments M2S10, M2S11 and M2S12 recorded the osmotic potential of around 75% to 79%.
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Table 2 Effect of water stress on leaf Osmotic Potential (MPa) at different growth stages of banana cultivars and hybrids
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Osmotic potential is considered as an important physiological mechanism of drought adaptation in banana plants (Turner, 1972). Osmotic Adjustment requires regulation of intracellular levels of several compounds collectively known as osmolytes. In banana, the osmotic potential was determined from xylem sap. Kallarackal et al (1986) stated that the solute potential of exuding latex provided an excellent guide to the water status of the plant during water deficit conditions. Banana latex contains large number of vacuolysosomal organelles called “lutoids” which are capable of actively transporting ions across the membranes with higher osmotic potential activity during stress conditions. In this present investigation, the cultivars like Karpuravalli, Karpuravalli×Pisang jajee, Saba and Sannachenk- athali registered higher osmotic potential with 50% increase over control at 7th MAP. It can be concluded that, higher osmotic adjustment under stress conditions is considered as an important physiological mechanism of drought adaptation in many plants (Subbarao et al., 2000). The cultivars like Matti, Matti× Anaikomban, Matti×cultivar rose and Pisang jajee× Matti showed only 20 per cent increase in osmotic potential than the control. It was also established that the increase in osmotic potential in response to water stress is a behavior which causes a more water stress tolerance (Turner and Lahav, 1983).Correlation studies with yield
The final yield of crop is the cumulative effects of growth attributes and such of those treatments which manipulate the favourable parameters could result in the positive relationship with higher productivity. The relationships of total chlorophyll content and Relative Water Content were correlated with the final yield presented in the Figure 2 and Figure 3 at 7th MAP. Based on the results arrived from the correlation revealed that the correlation between number of leaves, total chlorophyll content and Relative Water Content were correlated were showed significant positive correlation with yield.
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Figure 2 Correlation of relative water content (RWC) with yield
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Figure 3 Correlation of total chlorophyll content (mg/g) with yield
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Materials and MethodsThe experiment was carried out at at national research centre for banana, Thiruchirapalli, during 2011-2012. The experiment consists of two treatments as considered as main plot and twelve cultivars and hybrids as taken as sub plots were laid out in split plot design with three replications. The main plots are, M1 (control) with the soil pressure maintained from -0.69to -6.00 bar, M2 (water deficit) with the Soil pressure maintained from -0.69 to -14.00 bar. Soil pressure of -14.00 bar was reached at 30 days and measured by using soil moisture release curve and measured the soil moisture by using the pressure plate membrane apparatus (Figure4) .The sub plots are, S1: Karpuravalli (ABB), S2: Karpuravalli× Pisang Jajee, S3: Saba (ABB), S4: Sanna Chenkathali (AA), S5: Poovan (AAB), S6: Ney poovan (AB), S7: Anaikomban (AA),S8: Matti×Cultivar Rose,S9: Matti (AA),S10: Pisang Jajee×Matti,S11: Matti×Anaikomban and S12: Anaikomban×Pisang Jajee. The relative water content were measured as per the procedure of Weatherly (1950) and expressed in percentage, total chlorophyll content was estimated based on the procedure given by Hixcox and Israelstam (1979) and expressed as mg/g fresh weight., osmotic potentialwere recorded by using the VAPRO meter during 3rd, 5th, 7th, 9th month after planting and at harvest stages of the crop. The yield and yield components were assessed at the time of harvesting. The above Parameters procedures are given below:
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Figure 4 Effect of water stress on Relative Water Content (%) of banana cultivars at different growth stages
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Relative water content
Physiologically functional leaf samples of different crops are taken and their fresh weight is recorded immediately after they are excised from the plants. The leaf samples are brought to full turgid by floating the leaves in water and the leaves are then taken out from water and the water adsorbed on the leaf surface is wiped out gently by using filter paper. The turgid weight is recorded at 2 h, 4 h, 6 h and 8 hafter floating. Then the leaf samples are kept in hot air oven at 80oC for 48 hours and the dry weight is recorded. The floating duration or time to obtain full turgidity varies with the crop species.The technique consists essentially in comparing the water content of fresh leaf with the fully turgid leaf and expressing the results on a percentage basis.
RWC=(FW - DW)/(TW - DW)×100
Where, Fw : Fresh weight of leaf sample ; Tw : Turgid weight of leaf sample ; Dw : Dry weight of leaf sample
Total chlorophyll
Total chlorophyll content was estimated in physiologically active leaves as per the procedure of Hixcox and Israelstam (1979) and expressed asmg/g fresh weight. Fully emerged third leaf from the top was taken for the pigment analysis. Leaf disc were made between the veins in the middle portion of leaf. These leaf discs of known weight were homogenized in a pestle andmortor with 80% cold acetone. The homogenate was centrifuged and the supernatant was made upto 25 mL. The optical density of the sample was recorded at 480 nm, 510 nm, 645 nm, 652 nm and 663 nm in spectrophotometer.
Osmotic potential
Third or fourth leaf from the top was selected. The petiole was slantingly cutted by using a knife. The sap was collected in a 2 mL effendortube and immediately kept in ice box. The Vapor Pressure Osmometer (VAPRO 5520 meter) was opened and the instrument was set by using sugar as blank: 100 mmol/kg, 290 mmol/kg, 1000 mmol/kg. The sensor was opened and the sensor paper was placed in a sensor. The sap sample was added on the sensor paper by using a micropipetor. The chamber was closed. The reading was recorded as mmol/kg and it was converted into Mega Pascal (MPa) by using given formula.
Mpa =(2.51793×value of mmol kg)/1000
Acknowledgment
The research have been supported and facilitated by National Research Centre for Banana (ICAR), Trichy. Tamil Nadu. India. I extend my sincere thanks to Dr. M. M. Mustaffa (Director) NRC for banana, Dr. D. Durga Devi (Professor) TNAU and Dr. I. Ravi (Sr. Scientist) NRC for banana for given proper guidance during research.
Begg J.E and N.C. Turner, 1976, Crop water deficits. Adv. Agron., 28: 161-217
Besset J., M. Genard T. Girard V., Serra and C. Bussi, 2001, Effects of water stress applied during the final stage of rapid growth on peach trees. Scientia Horticulturae, 91: 289-303
Blum A., Mayer J., and Andgolan G, 1989, Agronomical and Physiological assessments of genotypic variation for drought resistance in sorghum, Australian Journal of Agricultural Research,16(1) : 49-61
Bray E.A., Bailey-Serres J., and Weretilnyk E., 2000, Responses to abiotic stresses. In Biochemistry and Molecular Biology of Plants, B.B. Buchanan, W. Gruissem, and R.L. Jones, eds (Rockville, MD: American Society of Plant Physiologists), pp. 1158–1203
Daniells J.W., Watson B.J., O’Farrell P.J and Mulder J.C., 1984, Soil water stress at bunch emergence increases maturity bronzing of banana fruits, Qld. J. Agric. Anim. Sci., 44: 97-100
David, W. (2002). Limitation to photosynthesis in water stressed leaves: stomata vs. metabolism and the role of ATP, Annals of Botany, 89: 871-885
De Silva, J. V., Naylor A. W., and Krammer P. J., 1979, Some ultra structural and enzymatic effects of water stress in cotton leaves, oceedings of National Academy Science, USA, 71: 3243-247
Deshmuukh, P.S., Sairam, R.K. & Shukla, D.S. (1991). Measurement of ion leakage as a screening technique for drought resistance in wheat genotypes. Indian Journal of Plant Physiology, 34, 89-91
Diethelm R., and R. Shibles, 1989, Relationship of enhanced sink demand with photosynthesis and amount and activity of Ribulose-1,5 biphosphate carboxylase in soybean leaves, J. Plant Physiol., 134: 70-74
FarquhartG.D., S.O. Wong, T.R.Evans, and K.T.Hubiok. 1982, Photosynthesis and gas exchange, In H.G.Jones, T.J.Flowers, and M.B.Jones (eds.), Plant Under Stress, Cambridge Univ. Press. Cambridge, pp. 47-67
Flore J.A., A.N. Lakso, and J.W. Moon, 1985, The effect of water stress and vapor pressure gradient on stomatal conductance, water use efficiency, and photosynthesis of fruit crops, Acta Hort. , 207-218
Ghavami M., 1973, Determining water needs of the banana plant. Transactions of the American Society of Agricultural Engineers 16:598-600
Gomez M.S. and P.Rangasamy, 2002, Correlation and path analysis of yield and physiological characters in drought resistance rice. Int. J. Mendel, 19: 33-34
Hiscox J.D. and Israelstam G.F., 1979, A method for the extraction of chlorophyll from leaf tissue without maceration, Can. J. Bot. 57: 1332-1334
Hsiao T.C., 1973, Plant responses to water deficit. Ann. Rev. Plant Physiol., 24: 519, 570
Hsiao J.C. and E. Acevedo, 1974, Plant responses to water deficit and drought resistance. Agric. Meteorol., 14: 59-84.
Jagtap V., and Bhargava, S., 1995, Variation in the antioxidant metabolism of drought tolerant and drought susceptible varieties of sorghum. Moench exposed to high light, low water and high temperature stress. J. Plant Physiol. 145: 195-197
Jones H.G., A.N. Lakso, and J.P. Syvertsen, 1985, Physiological control of water status in temperate and subtropical fruit trees. p. 301-344. In: J. Janick (ed.). Hort.Rev. AVI Publ., Westport, Conn
Joseph M.C., D.D. Randall and C.J. Nelson, 1981, Photosynthesis in polyploid tall fescue, II. Photosynthesis and RUBP case of polyploid tall fescue, Plant Physiol., 68: 894-898
Kallarackal J., Milburn J.A and Baker D.A., 1990, Water relations of the banana. III effects of controlled water stress on water potential, transpiration, photosynthesis and leaf growth, Australian Journal of Plant Physiology, (17) : 79-90
Kallarackal J., Milburn J.A. and Baker D.A., 1986, Transpiration characteristics of banana leaves inresponse to progressive depletion of available soil moisture. Sci. Hortic., 30: 289-300
Kaloyereas S.A., 1958, A new method of determining drought resistance, Plant physiol, 33: 232-233
Levitt J., 1972, Responses of plants to environmental stress. Academic press. New York
Manica L., Simao S., Koller O.C., Peres F.P.Z. and Conde A.R., 1975, Influence of the time of selecting suckers on the growth and productivity of the first ratoon of banana. Nanico. Rev. Ceres, 22: 359-366
Martignone R.A., J.J. Guiamot and F. Nakayama, 1987, Nitrogen partitioning and leaf senescence in soybean as related to nitrogen supply. Field Crops Res., 17: 17-20
Martin U., Alladru, S.G. &Bahari, Z.A., 1987, Dehydration tolerance of leaf tissues of six woody angiosperm species. Physiologia Plantarum,69, 182-186
Murthy K.S. and S.K. Majumdar, 1962, Modification of the techniques for determination of chlorophyll stability index in relation to studies of drought resistance in rice, Curr. Sci., 31: 470-471
Pallar J.E., J.R. Stansel and M. Koske. 1979. Effect of drought on flour runner peanut. Agron. J., 71: 853-858
Robinson J.C., 1984, Bananas and Plantains, Wallingford, CAB International
Senaratana T. & Kersi B.D., 1983, Characterization of solute efflux from dehydration injured soybean (Glycine max Merr.) seeds. Plant Physiology, 72, 911-914
Siddique, M.R.B., A. Hamid and M.S. Islam, 2000, Drought stress effects on water relation of wheat. Bot. Bull. Acad. Sin., 41(1): 35-39
Singh K., Verma H.D., Singh P.P., Jasmini D.K., (1985). Effect of sowing dates and nitrogen on growth and yield of some new wheat varieties. Indian J. Agron, 30: 72-74
Slatyer R.O., 1955, Australian Journal of Agriculture Research, 61: 365-377
Stover R.H., 1972, Banana,Plantain and abaca diseases. Common wealth mycological institute, Kew England.
Stover R.H., and N.W. Simmonds, 1987, Bananas (3rd edition) Longman, London, United Kingdom.
Tezara W., Mitchell V., Driscoll S.P and Lawlor D.W., 2002, Effects of water deficits and its interaction with CO2 supply on the biochemistry and physiology of photosynthesis in sunflower. J. Expt. Bot. 53, 1781-1791
Thomas D.S., and Turner D.W., 2001, Banana leaf gas exchange and chlorophyll fluorescence in response to soil drought, shading and lamina folding, Scientia horticulturae, 90: 93-108
Turner D.W., 1993, Bananas and plantains. In Handbook of Environmental Physiology of Fruit Crops Volume II : Sub-tropical and Tropical Crops, 37-64 (Eds. B. Schaffer and P. C. Andersen), Boca Raton, CRC Press
Turner D.W., 1998, The impact of environmental factors on the development and productivity of bananas and plantains. In Proceedings of the 13th ACORBAT meeting, Guayaquil, Ecuador, 635-663 (Ed. L. H. Arizaga). Ecuador, CONABAN
Turner D. W. and Lahav E., 1983, The growth of banana plants in relation to temperature. Australian Journal of Plant Physiology 10: 43-53
Turner D.W. and Thomas D.S., 1998, Measurements of plant and soil water status and their association with leaf gas exchange in banana (Musa spp.): a laticiferous plant. Scientia Horticulturae, 77: 177-193
Turner D.W., 1972, Banana plant growth. 1. Groeth. 1. Gross morphology. Aust, J. Expt, Agric. Animal Husband, 12: 216-224
Wahad Z., Zulkifli Hj and S. Suzita, 2000, Proceedings of the first national banana seminar at Awana Genting and country resort. UPM: Serdang (mys), P.343
Wareing P.F., and I.D.J. Phillips, 1970, The control and development in plants. Pergamon Press, Oxford, 1-21
Weatherly P.E., 1950, Studies in the water relations of cotton. 1. The field measurement of water deficits in leaves, New Phytol., 49: 81-97
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D. Durga Devi1 
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I. Ravi2 
