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Assessment of Microbial Isolates in Date Palm Plantation Soils of Modibbo  Adama University, Yola Adamawa State, Nigeria

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Date palm 
Microbial isolates 
This research assessed the microbial isolates in the soil of the date palm  plantation of Modibbo Adama University, Yola, Adamawa State. Parameters evaluated included; microbial isolates based on the growth performances  of the date palm. The plantation was divided according to growth  variabilities. Fifteen (15) auger points were taken, five (5) in each  performance site based on the corresponding variability as observed. Soil  samples were collected within the same points for analysis of microbial  isolates, Nutrient agar medium at 105 dilutions was inoculated in a petri dishes and incubated at 300C±10°C for 2-5 days for bacteria colonies, while  for fungi and actinomycetes, sabaurond dextrose agar was used at 25°C for  5-7 days and afterward microorganisms per colony forming units (Cfu) were  counted. Results from the study area showed that the area is highly rich in  microorganisms. A total of 5096 colonies were scattered within 10 families  in the study area. Some microorganisms identified were Actinomyces crime,  Aspergillus niger, Staphylococcus aurus, Streptococcus species,  Pseudomonas auroginosa, Escherichia coli, Bacillus subtilis, and  Lactobacillus species among others. The finding of this study revealed that  there was no significant difference among the microorganism across the  study site leading to the conclusion that soil microorganisms were present  in the study area. However, the microorganisms were very active in the date  palm plantation soil. This is an indication that a strong relationship exists  between, microorganisms and the date palm trees.


Soil contains many micro flora and fauna as long as there  is a carbon source for energy. A large number of bacteria  in the soil exist, but because of their small size, they have  a smaller biomass. Actinomyces are 10 times smaller in  number but are larger in size so they are similar in  biomass to bacteria in soil (Bhattarai, et al. 2015;  Roohallah et al. 2022). 

and often critical roles in these ecosystem services. The  vast metabolic diversity of soil microbes means their  activities drive or contribute to the cycling of all major  elements (e.g. C, N, P), and this cycling affects the  structure and the functions of soil ecosystems as well as  the ability of soils to provide services to people provisioning and regulating ecosystem services (Suzanne  ,2017).

Plant and animal detritus and root exudates  represent essential sources of energy and nutrients for  soil microbial and faunal communities. Bacteria and fungi  represent 95% of the biomass present in most soils,  where they interact with a combination of micro-fauna  (nematodes, protozoa), Meso-fauna (acari, Collembola,  mites) and macro-fauna (earthworms, termites,  molluscs) in complex soil food-web systems that  determine the turnover of organic matter and associated  nutrients in the soil environment ( Moghimian and Kooch,  2013; Duran et al. 2019). 

Decomposition of organic carbon in soil is driven  primarily by the activities of bacteria and fungi, while only  10–15% of soil carbon flux can be directly attributed to  the actions of fauna (Shang et al. 2017). The vast majority  of soil microorganisms are heterotrophs that rely on  organic matter for energy and nutrients.

These can be  divided into microorganisms that respond primarily to  the addition of fresh carbon substrates (zymogenous or r selected biomass) and those that derive their energy  mainly from the decomposition of older, more  recalcitrant forms of organic carbon (autochthonous or K selected biomass) (Shang et al. 2017). 

The date palm (Phoenix dactylifera L.) tree belongs to the  family Arecaceae and is considered a symbol of life in the  desert, as it tolerates high temperatures, water stress,  and salinity more than many other fruit crops (Effi, et al.  2011). Date palms can be planted in a wide range of soils  with varying amounts of organic and mineral nutrients. 

Many parts of the world where date palm is grown still  follow the traditional mixed planting of dates of various  ages at irregular spacing. Moreover, inadequate fertilizer  application and lack of proper tree and bunch  management, such as pruning and fruit thinning, lead to  the production of low fruit quality and thus lower market  values (Elamin et al. 2017). 

In the five years of the establishment of the date palm  plantation of Modibbo Adama University of Yola, studies  have not been done on biological constituents of the soil.  The growth of the individual date palm plants have not  been uniform, while some are performing very well,  others have indication of stunted growth.

Since the  growth of every plant depends largely on the nutrient  status which is in turn affected by the activities of soil  microorganism, information on the soil biological  components in the date palm plantation becomes a pre  requisite to understanding the differences in the  performances of individual plants. The aim of this study is  to assess the microbial isolates in the study area. The specific objectives are to identify and evaluate the  microbial isolates in the study area. At the end of the study the biological component of the  date palm plantation has been ascertained.

The  information on microorganism will thus, baseline  information for future management of the date palm  plantation soils and by extension any other date palm that may be grown under similar conditions. The results  of the research will be an invaluable tool to the date palm  plantation managers in the Department of Forestry and  Wildlife Management, Modibbo Adama University of Yola  and indeed many other organizations and individuals that  are involved in date palm research and production. 


The Study Area 

Adamawa State is located in the North Eastern part of  Nigeria. It lies between latitude 7o and 11o N of the  equator and longitude 11o and 14o E (Figure 1) (Adebayo  et al., 2020). The date palm plantation of the Department  of Forestry and Wildlife Management Modibbo Adama  University, Yola, Adamawa State is located between  latitude 8°N and 11°N Longitude 11.5°E and 13.5°E  (Figure 2).

Adamawa state falls under the Sudan,  southern and Guinea savannah types of vegetation and  its experiences distinct dry and wet seasons with  temperature and humidity varying with seasons.

The wet  or rainy season falls between April and November, which  is characterized by a single maximum in August and  September. During this season, the moisture-laden southwest trade wind from the Atlantic Ocean blows over  the area. Seventy percent of the total rainfall in the area  happen to fall within four month of May- September  (Adebayo et al. 2020). 

The area has an average of 62 rainy days, while average  amount of rainfall recorded in the area is 972 mm the dry  season which is the harmattan period between  December March. The period is characterized by dry,  dusty and hazy northern trade wind that blows over the  area from Sahara desert.

Temperature within the area varies with season. Although the temperatures are  relatively high almost all the year round, temperature of  the area ranges from 27°C-40° C. December and January  is the coldest months with the average temperature of  34° C (Adebayo, et al. 2020). The natural vegetation of the  area is Sudan savannah type which is characterized by  thick vegetation around hills and mountain ranges.

The vegetation has a wide variety of savannah trees species among which area are; Acacia spp, Adansonia spp,  Anogeisus spp. (Akosim et al. 2020).

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Assessment of Microbial Isolates in Date Palm Plantation Soils of Modibbo  Adama University, Yola Adamawa State, Nigeria 43
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Assessment of Microbial Isolates in Date Palm Plantation Soils of Modibbo  Adama University, Yola Adamawa State, Nigeria 44

The soils of Adamawa State are classified as ferruginous  tropical soils. These types of soils are defined often  generally as having a marked differentiation of horizons  and an abundance of free iron oxides usually deposited  as red or yellow mottles or concretions. The soils of  Adamawa State as derived from this system include  Luvisols, Legosols, Cambisols, Vertisols and Lithosols  (Adebayo et al. 2020). 

Soil sampling process for microbial isolates 

Soil sample was taken in each auger point in the date palm plantation. A composite sample, after mixing the  sample thoroughly, sterile polythene bags was used to convey samples to the laboratory within 24 hours of  collection for analysis of soil bacteria, fungi, and  Actinomycetes at the department of microbiology of  Modibbo Adama University, Yola. 


Bacteria population was estimated by the method of  Vieira, (2005) using the nutrient agar medium at 105  dilutions. The inoculated petri-dishes was incubated at  300c±10°c for 2-5 days for bacteria colonies. The laboratory analysis involved adding 1g of soil into 9ml of sterile water in a test tube, followed by vigorous shaking,  and then serial dilution was done in four test tubes before transfer into the petri dish.

However, molten agar/media was poured into the petri dish. For isolation and characterizing of fungi and  Actinomycetes dilution plate method was used, sabaurond dextrose agar for fungi and Actinomycetes selected media for Actinomycetes was used as basal medium to isolate species.

The inoculated petri- dish was incubated at 25°c for 5-7 days for growing the fungi and  Actinomycetes colonies. Representative isolates of fungi was identified under the microscope with the help of standard manuals (Naher et al. 2013).

Representative isolates of bacteria were also identified under the microscope. Fungi identification was done under the appearance and pigmentation of spores on agar and Actinomycetes was identified under the appearance on agar plates. 



Soil Microorganisms (cfu-1) in the Study Areas 

The soil micro – organisms ‘colony count result shows the presence of Actinomycetaceae, (Actinomyces cream,  Actinomyces yellow, Actinomyces blue),  Staphylococcaceae; (Staphylococcus aureus),  Streptococcaceae, (Streptococcus spp.),  Pseudomonadaceae, (Pseudomonas auroginosa),  Enterobacteriaceae, (Escherichia coli), Bacillaceae,  (Bacillus subtilis), Trichocomacaceae, (Aspergillus niger,  Aspergillus fumigates), Lactobacillaceae, (Lactobacillus spp.), Aeromonadaceae, (Aeromonas spp.),  Streptomycetaceae, (Streptomyces spp.),  Enterobacteriaceae, (Klebsiilla spp., Proteus spp.,  Citrobacter spp.), and Bacillaceae, (Bacillus copus). The soil micro – organism’s colony where categorized into three (3) basic forms Bacteria, Fungi and Actinomycetes. 

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Assessment of Microbial Isolates in Date Palm Plantation Soils of Modibbo  Adama University, Yola Adamawa State, Nigeria 46

The result of the soil micro – organism’s colony count (cfu 1) based on high growth performance in the study area is  presented in Table 1. The results of the high growth  performance site indicate that Bacteria count ranged  from 3.0×10-4cfu/ml to 5.0 ×10-4cfu/ml, Fungi count ranged from 3.0 ×10-4cfu/ml to 5.4 ×10-4cfu/ml and  Actinomycetes count also ranged from 9.0 ×10-4cfu/ml to  19.0 ×10-4cfu/ml respectively. 

Results of the medium growth performance site indicate  that Bacteria count ranged from 3.8×10-4cfu/ml to 6.8  ×10-4cfu/ml, Fungi count ranged from 4.6 ×10-4cfu/ml to  6.0 ×10-4cfu/ml and Actinomycetes count also ranged  from 6.0 ×10-4cfu/ml to 21.0 ×10-4cfu/ml respectively. 

From the low-performance site, results indicate that  Bacteria count ranged from 3.0×10-4cfu/ml to 4.5 ×10 4cfu/ml, Fungi count ranged from 3.0 ×10-4cfu/ml to 6.7 respectively. 

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Assessment of Microbial Isolates in Date Palm Plantation Soils of Modibbo  Adama University, Yola Adamawa State, Nigeria 47

1.1 Checklist of Micro-Organisms in the Study Area 

Table 3 shows the checklist of eleven (11) families containing seventeen (17) species of microorganisms identified in the study area. The families encountered were Actinomycetaceae (Actinomyces crime,  Actinomyces yellow, Actinomyces blue),  Aeromonadaceae (Aeromonas spp.), Trichocomacaceae  (Aspergillus niger, Aspergillus fumigatus), 

Staphylococcaceae (Staphylococcus aurus),  Streptococcaceae (Streptococcus spp.),  Pseudomonadaceae (Pseudomonas auroginosa),  Enterobacteriaceae (Escherichia coli, Klebsiilla spp.,`  Citrobacter spp., and Proteus spp.), Bacillaceae (Bacillus subtilis, Bacillus copus), Lactobacillaceae (Lactobacillus spp.), Aeromonadaceae (Aeromonas spp.) and  Streptomycetaceae (Streptomyces spp.) were present in the plantation soils.. 

The result in Table 4 shows the identified gram stained  bacteria from nutrient agar plates which five 5 indicate  gram negative and nineteen (19) show gram positive in  term of shapes the result indicates fifteen (15) Cocci  cluster, five (5) bacilli, and four (4) Cocci in chain  respectively.

Table 5 also shows the morphology of the  bacteria in which four indicated flat and twenty raised  respectively. The result in table 6 indicates the total  fungal diluted in plates of potato dextrose agar, the  pigmentation shows Aspergillus niger, Aspergillus fumigatus, Penicillin, Flavows, Microsponum canisMicrosponum andoumis, Strestomycete and  Actinomycetes respectively. The result in Table 7 shows  the total Actinomycetes counts in diluted plates of starch  casein agar, the pigmentation shows four cream colour,  five cream pseudomonas species and fifteen cream  yellow respectively. 

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Assessment of Microbial Isolates in Date Palm Plantation Soils of Modibbo  Adama University, Yola Adamawa State, Nigeria 48


Soil Microorganisms (cfu-1) in the Study Areas 

Findings of the soil microorganisms showed a wide  diversity in the date palm plantation which were  categorized based on high, medium and low performance sites. 

These microorganisms (bacteria, fungi and  actinomycetes) influence plant diversity and productivity  according to van der Heijden et al. (2008). This is because  they play important roles in the nutrient cycles and  energy flows, providing essential services to the forest  ecosystem. Soil fungi, for example have the function of  catalyzing the turnover of complex organic resources,  which can drive the degradation of organic matter.  Bacteria generally utilize the easily available substrates  decomposed by fungi.

Conversely, they are affected by  the plant communities as they depend on the products of  plant photosynthesis: litter and rhizo-deposits (Wardle,  2006; Qiao et al., 2014; Prescott and Grayston, 2013). The  microorganisms ‘influence on plant diversity and  productivity is in consonance with the findings of Lladó,  et al. (2017) who stated that bacteria commonly harbor  genes encoding plant cell wall-degrading enzymes and  contribute significantly to the decomposition of organic  matter.

In addition, bacteria are the major natural agents  responsible for N fixation in forest ecosystems and for  other ecosystem processes, such as mineral weathering  leading to the release of inorganic nutrients. The roles of  bacteria and fungi, however, should not be viewed as  separate.

The high abundance of fungal biomass in forest soils has multiple consequences for bacteria, including  the creation of specific niches in the soil patches  colonized by mycorrhizal fungi (i.e., the  mycorrhizosphere) and soil mycelial mats, provision of  nutrients via organic matter decomposition, and an  increase in soil connectivity by fungal mycelia that allow  certain bacteria to move across the environment. 

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Assessment of Microbial Isolates in Date Palm Plantation Soils of Modibbo  Adama University, Yola Adamawa State, Nigeria 50
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Assessment of Microbial Isolates in Date Palm Plantation Soils of Modibbo  Adama University, Yola Adamawa State, Nigeria 51
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Assessment of Microbial Isolates in Date Palm Plantation Soils of Modibbo  Adama University, Yola Adamawa State, Nigeria 52

Also, the fining shows that the numbers of bacterial  communities decreases with decrease in depth. This  agrees with the report of Lauber et al. 2009; Rousk et al. (2010) stating that bacterial abundance and diversity  have been reported to decrease with decreasing soil pH.  Similarly, the composition of fungal communities has  been previously shown to differ substantially between  litter and organic horizons, while deeper soil horizons  showed greater similarity (O’Brien et al. 2009; Lindahl et  al. 2007).

In several forest types, this is due to the higher  abundance of saprotrophic fungi in litter and the  dominance of ectomycorrhizal species in deeper soil  (Lindahl et al. 2007; Edwards et al. 2010).. Duran et al.  (2019) stated that date palm can influence the  composition and functioning of the soil bacterial  community by altering the microclimate (via shading and  through fall effects and uptake/transpiration of soil  water), litter production, amount and quality of root  exudates, and interactions with root symbiotic organisms  such as mycorrhizal fungi. 

This is because, in the forest ecosystem, trees can change  the forest microclimate, and they can produce exudation  from roots, litter, and wood debris; meanwhile, they  (trees) interact with soil microbes and micro fauna  through roots, and thus, can influence ecosystem  properties.

Date Palm can selectively attract and maintain rhizosphere microbes by root exudates, and at  the same time, the microbial communities may strongly  affect the growth of date palm by releasing mineral elements. Thus, the interaction between aboveground  vegetation and soil microbial communities can influence  the process of the forest ecosystem.

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Assessment of Microbial Isolates in Date Palm Plantation Soils of Modibbo  Adama University, Yola Adamawa State, Nigeria 54
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Assessment of Microbial Isolates in Date Palm Plantation Soils of Modibbo  Adama University, Yola Adamawa State, Nigeria 56

Findings also show the presence of highly important bacterial  and fungal groups (though in few numbers). In date palm  plantation soils, microbial communities are affected by the  changes in aboveground vegetation communities and soil  environmental properties (such as nutrients, temperature, and  moisture) influenced by human activity. These changes (as a  result of agricultural activities) in the date palm plantation are  believed to be responsible for the relatively low density of  microorganisms in the study area. The loss of important  microorganism as a result of application of pesticides in the  plantation this also agreed with the findings of Mikayla et al. (2017) who stated that plantation could induce significant  shifts in soil microbial community through biotic and abiotic  factors, including species composition, above- and below ground litter, and soil substrate quality and quantity, which are  associated closely with soil microbial community. 


Based on Based on the findings of this study, it can be  concluded that; microorganisms were present in the study  area. However, the numbers of microorganisms were very  active in the date palm plantation soil. This is an indication that  strong relationship exists between microorganisms and the  date palm trees. The organism’s breakdown complex organic  matter, giving fertility to the soil, others like Actinomycetaceae  through the ground, making the soil fertile and nutrients pass  through and absorbed by the date palm trees. The date palm  trees on the other hand produce food for microorganism through litters and exudates. 


The following recommendations are hereby made: 

The Agricultural practices which combine trees and crops  should be encouraged and application of agrochemicals is  deleterious to the interrelationship of microorganisms and date palm plants. It also interferes with the varieties of food  chains and food webs of the ecosystem. 


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