Genotype dependent variation in native and inoculated soil microorganisms of FCV tobacco (Nicotiana tabacum) rhizosphere in vertisols and alfisols

Present study conducted during 2008-09 addresses the acquisition of nutrients from soil by tobacco (Nicotiana tabacum L.) plants with specific emphasis on the genotype and soil type with reference to structural and functional characteristics of roots that influence the availability and uptake of P and N. Objective is to explore the impact of tobacco genotypes VT-1158 and Siri in vertisols whereas 16/108, and Kanchan in alfisols on the activity of beneficial microorganisms such as Azotobacter, Azospirillum and Pseudomonas along with native microflora of the rhizosphere. After 45 DAT, the bacterial population was highest in number and it ranged from 7.02 to 10.90 in tobacco rhizosphere of vertisols and alfisols, while fungi were lowest in number which ranged from 3.92 × 103 to 5.30 × 103 cfu/g soil in the rhizosphere soil of vertisols var VT-1158 and Siri respectively. At 90 DAT microbial population declined in vertisols and alfisols of all the varieties. Inoculation of Azospirillum and Pseudomonas along with application of RDF resulted in maximum viable cell number of 5.89 × 106 cfu/g and 5.90 × 106 cfu/g soil in case of vertisols rhizoshpere of var VT-1158, while 5.95 × 106 cfu/ g and 6.47 × 106 cfu/g soil in the rhizosphere of alfisols tobacco respectively after 45 DAT. Inoculation of bacteria either as monoculture or mixed biofertilizer resulted in almost 10-30 times increase in microbial population of the inoculated bacteria; however, their population decreased after 90 DAT. Mixed biofertilizer (Azotobacter, Azospirillum and Pseudomonas) had a prolonged effect on plant parameters tested and showed a higher nutrient (N and P) content.