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Rhizobium besides its nodule formation characteristic with members of Fabaceae family has been recognized for its great root colonizing ability and growth hormone production potential. In addition to nitrogen fixation in legume plants, rhizobia considered as beneficial tools and act as plant growth promoting rhizobacteria (PGPR) with many non-legumes. Present study was elucidated to determine the comparative role of Rhizbium sp for growth promotion of sunflower. Rhizobia were isolated from five different legumes (mungbean, barseem, lentil, chickpea, and vegetable pea) and checked for their auxin production efficiency. Rhizobial isolates Cp-4 showed maximum auxin potential (5.37 µg mL-1 IAA equivalents).Results showed that inoculation of all rhizobial isolates caused significant increase in growth and physiological parameters of sunflower plants. While prominent results were found with inoculation of mungbean rhizobial isolate Mb-2 which increases the chlorophyll a, N, P, fresh and dry matter of sunflower significantly by 8.34, 4.9, 36, 31, and 34%, respectively in comparison to uninoculated control plants. Hence, present study concluded that Rhizobium sp can be successfully used as PGPR in non-legumes after thorough investigations.

a institute of Soil and environmental Sciences, university of agriculture, Faisalabad, Pakistan; b Physiology/chemistry Section, central cotton research institute, Multan, Pakistan; c department of agronomy, university of agriculture, Faisalabad, Pakistan ABSTRACT Transgenic Bt-cotton produces Bt-toxins (Cry proteins) which may accumulate and persist in soil due to their binding ability on soil components. In the present study, the potential impacts of Btand non-Bt genotypes of cotton on soil microbial activity, substrate use efficiency, viable microbial population counts, and nutrient dynamics were studied. Two transgenic Bt-cotton genotypes (CIM-602 CIM-599) expressing cry1 Ac gene and two non-Bt cotton genotypes (CIM-573 and CIM-591) were used to evaluate their impact on biological and chemical properties of soil across the four locations in Punjab. Field trials were conducted at four locations (Central Cotton Research Institute-Multan, Naseer Pur, Kot Lal Shah, and Cotton Research Station-Bahawalpur) of different agro-ecological zones of Punjab. Rhizosphere soil samples were collected by following standard procedure from these selected locations. Results reveled that Bt-cotton had no adverse effect on microbial population (viable counts) and enzymatic activity of rhizosphere soil. Bacterial population was more in Bt-cotton rhizosphere than that of non-Bt cotton rhizosphere at all locations. Phosphatase, dehydrogenase, and oxidative metabolism of rhizosphere soil were more in Bt-cotton genotypes compared with non-Bt cotton genotypes. Cation exchange capacity, total nitrogen, extractable phosphorous, extractable potassium, active carbon, Fe and Zn contents were higher in rhizosphere of Bt-cotton genotypes compared with non-Bt cotton genotypes. It can be concluded from present study that the cultivation of Bt-cotton expressing cry1 Ac had apparently no negative effect on metabolic, microbiological activities, and nutrient dynamics of soils. Further work is needed to investigate the potential impacts of Bt-cotton on ecology of soil-dwelling insects and invertebrates before its recommendation for extensive cultivation.

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