PHYSICOCHEMICAL ANALYSIS OF SOIL IN RELATION TO PANAMA DISEASE (FUSARIUM WILT) IN BANANA

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1 IJP, Vol. 5, No. 1, January-June 2012 pp PHYSICOCHEMICAL ANALYSIS OF SOIL IN RELATION TO PANAMA DISEASE (FUSARIUM WILT) IN BANANA Felcy Navajothy A. 1, Narayanaswamy R. 2, Danis Ponniah 3 and Irudayaraj V. 4 1 Department of Physics, St. John s College, Palayamkottai 2 Engineering Physics Section, Annamalai University, Annamalainagar, India Department of Physics, St. Xavier s College (Autonomous), Palayamkottai, India Department of Plant Biology & Plant Biotechnology, St. Xavier s College (Autonomous), Palayamkottai, India Abstract: One of the major problems in banana cultivation is the pathogenic wilt disease caused by the soil borne fungus Fusarium oxysporum. In order to understand the various factors of soil in the development of Fusarium wilt disease in banana, physicochemical analysis of soils of five different resistant varieties and five different susceptible varieties of banana have been done. In susceptible varieties, soil samples of both healthy and infected plants have been compared. It has been observed that all the physicochemical characteristics of soil play a major role, directly or indirectly, in the development of Fusarium-wilt disease in banana. The sandy loam or sandy clay loam type of soil with alkaline ph, low (< 1.4 gm/cm 3 ) bulk density and low ( Dsm -1 ) Electrical Conductivity is more suppressive to Fusarium wilt in banana. In contrast, clay soil type with acidic ph, high bulk density (above 1.4 gm/cm 3 ) and high EC (above 0.3 Dsm -1 ) is more conducive to Fusarium wilt in banana. 1. INTRODUCTION India has first position in the world in banana production. Banana has occupied a top position in India s booming fruit industry with an annual production of 13.5 mt from an area of 4.0 lakh ha. But India has a vision for increasing the production to 25 mt by the end of 2020 AD and has been addressed systematically during the last decade. But still there is a long way to go to achieve target yield potential, which is being threatened from time to time by various biotic and abiotic stresses associated with banana production (Sathiamoorthy et al., 2001). Panama disease, also known as Fusarium wilt of banana (Musa spp.), is one of the most notorious of all plant diseases (Stover, 1962). Fusarium wilt caused by Fusarium oxysporum f. sp. cubense continues to pose threat among commercial Indian cultivars. Twenty-two per cent of total banana production remains at the mercy of this pathogen (Sathiamoorthy et al., 2001). Since Fusarium is a soil borne fungus, the physico-chemical

2 16 IJP, 5(1), 2012 factors of the soil play an important role in the development of the wilt disease in banana. Hence, soil fertility management should best be combined with pest management in order to increase the yield of banana. Although disease suppression has been associated with chemical and physical edaphic factors, reasons for the phenomenon differ in various locations. It has been found that the potential banana-producing life of soils planted with wilt-susceptible bananas can be predicted on the basis of their clay mineral composition (Stotzky & Martin, 1963). A close relationship between suppression of disease and clay (montmorillonoid type) soils was found in tropical America, but in the Canary Islands suppression was associated with host mineral nutrition. Unfortunately, no reports have been made on the transfer of suppression to a disease-conducive soil (Ploetz, 2000). There is a need for better understanding the causes and interrelations of the climate-soil-root complex in banana production. The level of knowledge of such a complex problem has increased significantly in the last thirteen years as a consequence of past experiences and the advent of new and pro-mising technologies (Gauggel et al., 2005). From the above background it is clear that since the physicochemical factors play an important role in the development of wilt disease in banana, it is essential to develop soil management program by analyzing the soil characteristics. Evaluation of soil fertility is now becoming a routine work for soil management and crop production. In order to know the difference in physicochemical characteristics between conducive soils and suppressive soils, soils of five different susceptible varieties (both healthy and diseased) along with five different resistant varieties from different localities of Tirunelveli district, Tamilnadu have been selected and compared. 2. MATERIALS AND METHODS The soil samples of five susceptible (healthy and diseased plants) varieties and five resistant varieties of banana are collected from various localities of Tirunelveli District, Tamil Nadu during the months of November and December, The plants are about 6 months old. The soil samples are collected from the study area from the depth of 30cm as per standard procedure of IARI (Indian Agricultural Research Institute) New Delhi (Tripathy et al., 1990). The sampling sites are randomized to avoid biasing in results. For classical analysis, samples are dried overnight in a cabinet equipped with a heating element and an exhaust fan to remove moisture-laden air. The physical parameters of soils such as bulk density and pore space and the relative amounts of sand, silt, and clay are estimated by standard method. 3. RESULTS AND DISCUSSION In the present study the physicochemical characteristics (soil texture, bulk density, pore space, ph and electrical conductivity of soil samples of susceptible (healthy and infected plants) and resistant varieties of banana have been analysed. The percentage of sand, silt and clay, textural class, bulk density and pore space of the soil samples of susceptible

3 Physicochemical Analysis of Soil in Relation to Panama Disease 17 (Healthy and infected) and resistant varieties of banana have been given in the tables 1 and 2. Based on the results, the physicochemical factors of the disease conducive and disease suppressive soils are discussed Soil Texture Soil texture is an important parameter. With the help of it, mineralogical and chemical composition is defined. It indicates the relative percentage of sand, clay and silt fraction of soil. The percentage of sand, silt and clay in soil samples of susceptible (healthy plants and infected plants) varieties and resistant varieties has been given in Tables 1 and 2. In general, soil texture classes are sand, loamy sands, sandy loams, loam, silt loam, silt, sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay, and clay. Subclasses of sand are subdivided into coarse sand, sand, fine sand, and very fine sand. Subclasses of loamy sands and sandy loams that are based on sand size are named similarly. The soil samples of resistant varieties fall under two types. The soil samples of Kathali and Red banana are of sandy loam type while the soil samples of Chakkai, Robusta and Nendran are of sandy clay loam type. In contrast the each soil sample of susceptible varieties has its own type of soil. Thus five susceptible varieties have five different types of soils as follows: Rasthali Clay, Rasakathali- Sandy clay, Monthan-Loamy sand, Nadu-Sandy loam and Karpooravalli- Sandy clay loam. It is to be noted that the soil samples of both healthy and infected plants of susceptible varieties are of the same type. In general, more amount of sand is present in all the samples except the susceptible variety Rasthali in which more amount of clay is present. Soil samples of healthy plants of susceptible varieties contain 32.6% (Rasthali) to 83.3% (Monthan-Least susceptible variety) sand. While the soil samples of infected plants of susceptible varieties contain 34.7% (Rasthali) to 86.8% (Monthan-Least susceptible variety) of sand. In contrast, the range of sand content in the soil samples of resistant varieties is narrow from 49.4% in the least resistant variety Nendran to 75.2% in highly resistant variety Kathali. In the highly susceptible variety Rasakathali, the soil sample of healthy and infected plants contains 66.7% and 49.6% sand respectively. From the data obtained in the present study, it is noted that moderate amount (60-70%) of sand in the soil is more suppressive to Fusarium wilt disease of banana. In general clay is in moderate amount in all the soil samples except in the susceptible variety Rasthali in which both healthy and infected plants have maximum amount of clay (55.1% -soil of healthy plant, 57.9% - soil of infected plant). Minimum amount of clay (5.0%) is present in the soil sample of healthy plant of least susceptible variety Monthan. Maximum amount (38.4%) of clay is present in the soil sample of the least resistant variety Nendran. It is found that the soil samples of diseased plants have more amount of clay when compared with the soil samples of healthy plants of susceptible varieties and in all the resistant varieties. The clay content of the soils from healthy plants of susceptible varieties varies from 5% (Monthan-Least susceptible variety) to 55.1% (Rasthali) and it is from 16.7% (Kathali - Highly resistant variety) to 38.4% (Nendran Least resistant variety)

4 18 IJP, 5(1), 2012 in soils of resistant varieties. The clay content range is comparatively high (9.2% %) in soils from infected plants of susceptible varieties. From the present observation it is clear that soil with more clay content is more conducive for the development of wilt disease. It may be due to more compactness of the soil with the presence of more amount of clay. It results in more water logging and less aeration. Table 1 The Physical Parameters of Soils of Susceptible (Healthy/Infected) Varieties of Banana Variety Sand% Silt% Clay% Textural Bulk Bulk Pore class density density space (gm/cm 3 ) (gm/cm 3 ) (%) (Observed) (Ideal)* Rasthali Healthy/ 32.6/ / /57.9 Clay 1.14/1.16 < /52.8 Infected Rasakathali Healthy/ 66.7/ / /41.7 Sandy Clay 1.24//1.45 < /48.5 Infected Monthan Healthy/ 83.3/ / /9.2 Loamy Sand 1.70/1.72 < /43.0 Infected Nadu Healthy/ 77.5/ / /24.2 Sandy Loam 1.48/1.62 < /45.4 Infected Karpooravalli Healthy/ 64.5/ / /34.2 Sandy Clay 1.52/1.53 < /48.5 Infected Loam (*Based on Table 2 The Physical Parameters of Soils of Resistant Varieties of Banana Variety Sand% Silt% Clay% Textural Bulk Bulk Pore class density density space (gm/cm 3 ) (gm/cm 3 ) (%) (Observed) (Ideal)* Kathali Sandy Loam 1.13 < Red Banana Sandy Loam 1.28 < Chakai Sandy Clay Loam 1.52 < Robusta Sandy Clay Loam 1.43 < Nendran Sandy Clay Loam 1.61 < (*Based on The amount of silt is generally low with the range % and % in soil samples of healthy and infected plants of susceptible varieties respectively and with the range of % in resistant varieties (Table 1 & 2). The presence of silt in higher percentage (12.2%) in least resistant variety Nendran and highly susceptible variety (infected 8.7%) and in lower percentage in highly resistant variety Kathali (8.1%) and least susceptible variety Monthan (4.0%), it may be concluded that soil with higher amount of silt is conducive while the soil with lower amount of silt is suppressive for Fusarium wilt in banana.

5 Physicochemical Analysis of Soil in Relation to Panama Disease 19 From the present observation, it is clear that the compositions of soil particles such as sand, silt and clay which determine the soil type play an important role directly or indirectly, in the development of Fusarium wilt disease in banana. It is to be noted that the soil type of resistant varieties is sandy loam or sandy clay loam in contrast to the soil type of susceptible varieties in which sandy loam, sandy clay loam, loamy sand, clay and sandy clay soil types are found. Since all the resistant varieties grow either in sandy loam or sandy clay loam, sandy type of soil is suppressive to Fusarium wilt of banana. Since the highly resistant variety Kathali grows in sandy loam soil and highly susceptible variety Rasakathali grows in sandy clay, it is concluded that sandy loam soil is more suppressive and sandy clay soil is more conducive to Fusarium wilt disease in banana. Numerous soil properties are influenced by texture including drainage, water holding capacity, aeration, susceptibility to erosion, organic matter content, cation exchange capacity (CEC), ph buffering capacity and soil tilth (how easily or difficult a field is tilled). Soil texture determines the rate at which water drains through a saturated soil; water moves more freely through sandy soils than it does through clayey soils. Once field capacity is reached, soil texture also influences how much water is available to the plant; clay soils have a greater water holding capacity than sandy soils. In addition, well drained soils typically have good soil aeration meaning that the soil contains air that is similar to atmospheric air, which is conducive to healthy root growth, and thus a healthy crop. Soils also differ in their susceptibility to erosion (erodibility) based on texture; a soil with a high percentage of silt and clay particles has a greater erodibility than a sandy soil under the same conditions. Differences in soil texture also impacts organic matter levels; organic matter breaks down faster in sandy soils than in fine-textured soils, given similar environmental conditions, tillage and fertility management, because of a higher amount of oxygen available for decomposition in the light-textured sandy soils. The cation exchange capacity of the soil increases with per cent clay and organic matter and the ph buffering capacity of a soil is also largely based on clay and organic matter content. Soil tilth is influenced by texture, soil moisture, aeration, and organic matter as well (Nutrient Management Spear Program Thus the present study along with previous studies shows that for the successful cultivation of banana, proper soil management is necessary. By testing the soil type, proper soil management is possible to convert Fusarium wilt conducive soil into Fusarium wilt suppressive soil as proved by Scher and Baker (1980). Metz fine sandy loam soil from the Salinas Valley in California was suppressive to the Fusarium spp. which induces wilts of flax and carnation. Suppressiveness to Fusarium oxysporum f. sp. dianthi was transferred to conducive soil when the Metz fine sandy loam was added in small amounts to steamed greenhouse soil (Scher & Baker, 1980) Bulk Density of the Soil Bulk density is an indicator of soil compaction. It is calculated as the dry weight of soil divided by its volume (g/cm 3 ). This volume includes the volume of soil particles and the

6 20 IJP, 5(1), 2012 volume of pores among soil particles. Bulk density reflects the soil s ability to function for structural support, water and solute movement, and soil aeration. Bulk densities above thresholds indicate impaired function. Bulk density of soil samples of all the susceptible (healthy / infected) and resistant varieties has been given in Tables 1 and 2. The bulk density of the soil samples of susceptible varieties varies from 1.24 gm /cm 3 (Rasthali Healthy) to 1.72 gm /cm 3 (Monthan Infected). It ranges from 1.13 gm /cm 3 (Kathali) to 1.61 gm /cm 3 (Nendran) in soil samples of resistant varieties. All the resistant varieties grow in sandy loam soil or sandy clay loam soil. Ideal bulk density for sandy loam soil and sandy clay loam soil is below 1.4 gm /cm 3. The bulk density of the varieties Kathali (Highly resistant variety) and Red banana which grow on sandy loam soil falls in the ideal range i.e 1.13 and 1.28 gm /cm 3. But the bulk density in other three resistant varieties Chakkai, Robusta and Nendran (Least resistant variety) with sandy clay loam type of soil deviates from the ideal value (< 1.4 gm /cm 3 ) of bulk density. The bulk density in the least resistant variety Nendran is 1.61 gm / cm 3. In the case of sandy clay loam soil, the bulk density above 1.6 gm /cm 3 affects the root growth. In the case of susceptible varieties, the bulk density of the soil ranges from 1.14 to 1.7 gm/cm 3 in healthy plants and it is from gm/cm 3 in infected plants. As seen in the table 1, in all the cases the bulk density values deviate from the ideal values. More deviation is seen in soil samples of infected plants when compared to the soil samples of healthy plants of susceptible varieties. It is interesting to note that the deviation in the least susceptible variety Monthan is only 0.1 (healthy) and 0.12 (infected). But in the case of highly susceptible variety Rasakathali, the deviation is more with 0.14 (healthy) and 0.35 (infected). In agricultural terms the bulk density of the soil can be used to give an indication of the porosity and structure of the soil which will govern O 2 and H 2 O movement in the soil. It is also a measurement of the degree of compaction of the soil, which gives a comparative basis to indicate the strength of similar materials. One of the most important factors agriculturally in terms of bulk density is plant growth; if the soil has a high bulk density (compaction) the seed will be restricted in emergence and root growth which will affect the total plant growth and yield. It has been observed that in the case of tomato and maize soil with a low bulk density had a significantly lower penetration resistance than the high bulk density soil. Soil strength affected shoot and root systems of both species but had no significant effect on shoot height. In both species, roots were thicker and closer to the stem base in strong soil compared to those in weaker soil (Goodman & Ennos, 1999). Careful management on the land is required to create an ideal bulk density for optimum plant growth and healthy soil (Grossman & Reinsch, 2002) Soil Pore Space Soil pores play a major role in water and air movement. Also, soil microorganisms reside in pores. Pore space is largely determined by size and arrangement of aggregates and affects the movement of water, air, and organisms in soil. The percentage of pore space in a given volume of soil is an important physical parameter of soil. The pore space is present

7 Physicochemical Analysis of Soil in Relation to Panama Disease 21 between the soil particles. So pore space will be more in coarse soils such as sandy type than in fine soils such as silt or clay. Another interrelating factor of the soil with pore space is the bulk density. When there is more pore space the bulk density is low and low per cent pore space will be seen in soil with high bulk density. In the present study the pore space percentage in soil samples of susceptible (healthy and infected) and resistant varieties has been given in Tables 1 2. The percentage of pore space ranges in soil samples of susceptible and resistant varieties of banana are: % in healthy susceptible varieties, % in infected susceptible varieties and % in resistant varieties. In the case of susceptible varieties, the pore space percentage is slightly lower in soils of infected plants when compared to soils of healthy plants. The pore space is 52.5% in highly resistant variety Kathali in contrast to 48.5 % in highly susceptible variety Rasakathali. The pore space percentage is inversely proportional to the bulk density of the soil. Thus the bulk density in the resistant varieties increases in the order of Kathali (1.13), Red banana (1.28), Robusta (1.52), Chakkai (1.43) and Nendran (1.61). While the pore space percentage decreases in the same order as follows: Kathali (52.5%), Red banana (49.8%), Robusta (48.7%), Chakkai (45.8%) and Nendran (45.6%). More or less the same kind of trend is also seen in susceptible varieties also PH and Electrical Conductivity PH plays an important role in the survival of all the organisms, from microorganisms to higher plants and animals. Soil ph is the most important value in soil report. Soil ph is the measure of the hydrogen ion activity or concentration in the soil solution. Roots grow in this soil solution and take up nutrients from these layers of water around the soil particles. Soil ph or rather the ph of the soil water determines the solubility and therefore the availability of nutrients found in soil water. ph also has a profound effect on soil microbiology and alters the nutrient cycling that takes place based on the biological activity. It plays a major role in the survival of the pathogen Fusarium in banana field. By knowing the soil ph for the suppressiveness of Fusarium pathogen, proper soil amendments can be made by altering the ph of the conducive soil. In the present study, the ph range in the soils samples of resistant varieties is from 7.82 (Robusta) to 8.22 (Kathali Highly resistant variety). The ph in healthy and infected susceptible varieties varies from 6.71 (Monthan) to 7.98 (Karpooravalli) and 6.0 (Rasthali, Monthan) to 7.2 (Karpooravalli) respectively (Table 3 ). It has been found that when the soil ph increases, the suppressiveness to wilt also increases. From the present observation, it is concluded that soils with ph above 7 are more suppressive to Fusarium and the soils with ph below 7 are more conducive to Fusarium wilt in banana field. Bananas can grow well in slightly alkaline soils. In alkaline soil wilt disease is less prevalent. It has also been proved that under the laboratory condition, the most suitable ph level for the growth of fungus the Fusarium oxysporum f. sp. vanillae isolates is Maintaining soil ph in the optimum range is part of a holistic approach that will create a healthy root environment

8 22 IJP, 5(1), 2012 which will help the plants to flourish. Soil amendments and nutrients will be more readily available when the ph is in the proper range and good stewardship practices are followed. Table 3 PH and EC of Soil Samples of Susceptible (Healthy / Infected) and Resistant Varieties of Banana Variety ph ECDsm -1 Rasthali (Healthy) Rasthali (Infected) Rasakathali (Healthy) Rasakathali (Infected) Monthan (Healthy) Monthan (Infected) Nadu (Healthy) Nadu (Infected) Karpooravalli (Healthy) Karpooravalli (Infected) Kathali Red banana Robusta Chakkai Nendran Electrical conductivity (EC) is the ability of a material to transmit (conduct) an electrical current. By knowing the electrical conductivity of the soils, farmers can make more precise management decisions about fertilizer applications, irrigation, use of nematicides, and other pesticide applications. This important physical parameter of the soil is useful both for the researchers and farmers. The EC range of the soil is between 0.11 (Red banana) to 0.21 Dsm -1 (Kathali) in resistant varieties. It s ranges in soil samples of susceptible healthy and susceptible infected varieties are 0.13 (Rasakathali) 0.27 Dsm -1 (Monthan) and 0.39 (Rasakathali) 0.58 Dsm -1 (Monthan) respectively (Table 3). The present observation clearly shows that the soils with EC between Dsm -1 are more suppressive and soils with EC above 0.3 Dsm -1 are more conducive to Fusarium wilt in banana. The EC is inversely proportional to the ph in soil samples of both susceptible and resistant varieties. Clays greatly impact EC because of their exchangeable cations and the water film associated with them (McNeill, 1980). The physicochemical condition of soil is very important, since root development is determined chiefly by the degree of aeration of the soil. In poorly aerated compacted soils, there is a marked decrease in root development. It has been reported that there is a higher root density in loam to silty loam soils, decreasing as the sand content increased to textures like sandy loam. Lower root densities have been observed in soils with higher clay content (clay loam) and a finer texture (silty clay) (Vaquero, 2003). Root distribution, in relation to soil depth, is determined by soil type and drainage conditions and that root growth is

9 Physicochemical Analysis of Soil in Relation to Panama Disease 23 stopped or reduced by hardpans, impermeable layers, high clay content or waterlogged areas (Stover & Simmonds, 1987). 4. CONCLUSION From the present study, it is clear that the texture, bulk density and pore size of the soils play a major role in the healthy growth of banana. The well marked difference in various physical parameters between susceptible (healthy and infected) and resistant varieties shows the important role of soil characteristics in controlling conduciveness or suppressiveness of the soil to Fusarium wilt of banana. The highly resistant variety Kathali grows in sandy loam soil and highly susceptible variety Rasakathali grows in sandy clay. It has been is concluded that sandy loam soil is more suppressive and sandy clay soil is more conducive to Fusarium wilt disease in banana. The bulk density of the varieties Kathali (Highly resistant variety) and Red banana which grow on sandy loam soil falls in the ideal range i.e 1.13 and 1.28 gm /cm 3. But the bulk density in other three resistant varieties Chakkai, Robusta and Nendran with sandy clay loam type of soil deviates from the ideal value (< 1.4 gm /cm 3 ) of bulk density. In all the cases of susceptible varieties, the bulk density values deviate from the ideal values. More deviation is seen in soil samples of infected plants when compared to the soil samples of healthy plants of susceptible varieties. It is interesting to note that the deviation in the least susceptible variety Monthan is only 0.1 (healthy) and 0.12 (infected). But in the case of highly susceptible variety Rasakathali, the deviation is more with 0.14 (healthy) and 0.35 (infected). In the case of susceptible varieties, the pore space percentage is slightly lower in soils of infected plants when compared to soils of healthy plants. The pore space is 52.5% in highly resistant variety Kathali in contrast to 48.5 % in highly susceptible variety Rasakathali. The pore space percentage is inversely proportional to the bulk density of the soil. The ph range in the soils samples of resistant varieties is The ph ranges in healthy and infected susceptible varieties are and respectively. It has been found that when the soil ph increases, the suppressiveness to wilt also increases. From the present observation, it is concluded that soils with ph above 7 are more suppressive to Fusarium and the soils with ph below 7 are more conducive to Fusarium wilt in banana field. Bananas can grow well in slightly alkaline soils. In alkaline soil wilt disease is less prevalent. The EC range of the soil is between Dsm -1 in resistant varieties. Its ranges in soil samples of susceptible healthy and susceptible infected varieties are Dsm -1 and Dsm -1 respectively. The present observation clearly shows that the soils with EC between Dsm -1 are more suppressive and soils with EC above 0.3 Dsm -1 are more conducive to Fusarium wilt in banana. The EC is inversely proportional to the ph in soil samples of both susceptible and resistant varieties. The values of soil parameters like soil texture, soil type, bulk density, pore space, ph and EC significantly differ between the susceptible and resistant varieties and between the

10 24 IJP, 5(1), 2012 healthy and infected plants of susceptible varieties. These results seem to suggest that the absence and/or presence of disease could be controlled partly by the physicochemical characteristics of the different soil areas of the same field plot as suggested by Dominguez et al. (1996) who have also studied the soil chemical characteristics in relation to Fusarium wilts in banana crops of Gran Canaria Island (Spain). References [1] Dominguez, J., Negrin, M. A. & Rodriguez, C. M. (1996), Soil Chemical Characteristics in Relation to Fusarium Wilts in Banana Crops of Gran Canaria Island (Spain). Communications in Soil Science and Plant Analysis, 27: [2] Gauggel C. A., Sierra, F. & Arévalo, G. (2005), The Problem of Banana Root Deterioration and its Impact on Production: Latin America s Experience. In: Turner, D. W. & Rosales, F. E. (Eds.) Banana Root System: Towards a Better Understanding for its Productive Management Proceedings of an International Symposium Held in San José, Costa Rica, 3-5 November International Network for the Improvement of Banana and Plantain, Montpellier, France, pp [3] Goodman, A. M. & Ennos, A. R. (1999), The Effects of Soil Bulk Density on the Morphology and Anchorage Mechanics of the Root Systems of Sunflower and Maize. Annals of Botany, 83: [4] Grossman R. B. & Reinsch T. G. (2002), SSSA Book Series: 5 Methods of Soil Analysis Ch. 2, Ed. Dane J. H, Clarke Topp G. Soil Science Society of America, Inc. Madison, Wisconsin, USA. [5] McNeill, J. D. (1980), Electrical Conductivity of Soils and Rocks. Tech. Note TN-5. Geonics Ltd., Mississauga, ON. [6] Page, A. L. (1982), Methods of Soil Analysis (Part 2), Soil Science Society America Madison, Wisconsion. [7] Ploetz, R. C. (2000), Panama Disease: A Classic and Destructive Disease of Banana. Online. Plant Health Progress doi: /php hm. [8] Sathiamoorthy, S., Uma, S & Selvarajan, R. (2001), Banana Research and Development Programme in India and Highlights of NRCB-INIBAP Collaborative Projects. In: Monila, A. B., Roa, V. N. & Maghuyop, M. A. G. (Eds.) Advancing banana and plantain R & D in Asia and the Pacific. Proceedings of the 10th INIBAP-APNET Regional Advisory Committee Meeting held at Bangkok, 2000/11/10-11, INIBAP-APNET, Los Banos. pp [9] Scher, F. M. & Baker, R. (1980), Mechanism of Biological Control in a Fusarium-Suppressive Soil. Phytopathology, 70 (5): [10] Stotzky, G. & Martin, R. T. (1963), Soil Mineralogy in Relation to the Spread of Fusarium Wilt of Banana in Central America. Plant and Soil, 18 (3): [11] Stover, R. H. & N. W. Simmonds (1987), Bananas. 3rd ed. Tropical Agriculture Series. John Wiley & Sons, Inc. New York, USA. [12] Tripathy, D. P., Gurdeep, S & Panigrahi, D. C. (1990), Proceedings of the 7th National Symposium on Environment, India School of Mines, Dhansand, pp [13] Vaquero M. R. (2003), Soil Physical Properties and Banana Root Growth. In: David W. Turner & Franklin E. Rosales (Eds) Banana Root System: Towards a Better Understanding for its Productive Management, Proceedings of an International Symposium Held in San José, Costa Rica, 3-5 November 2003.

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