Isolation and biochemical characterizations of the bacteria (Acidovorax avenae subsp. avenae) associated with red stripe disease of sugarcane

Studies on Acidovorax avenae subsp. avenae, associated with red stripe disease of sugarcane was conducted in the Department of Plant Pathology, Pir Mehr Ali Shah Arid Agriculture University Rawalpindi during 2009 to 2010, in collaboration with Shakarganj Sugar Research Institute (SSRI), Jhang, Pakistan. Red stripe of sugarcane were recently observed on promising clones of sugarcane planted in autumn 2009 at Ashaba Research Farm of SSRI. Bacteria were isolated from diseased plants. These isolates yielded off white convex colonies on potato dextrose agar (PDA) media at 29°C with 1.7 to 1.9 mm diameter and were yellow on yeast extract dextrose chalk agar (YDC) media at 27°C with 1.8 to 2.0 mm diameter. The bacteria were rod shape measuring 0.5 to 0.6 × 1.4 to 1.6 μm on PDA and 0.6 to 0.7 × 1.5 to 1.7 μm on YDC. Bacterial culture was stored at different temperature levels for 150 days. Reisolation of bacterial culture which was stored at 4°C showed best result on YDC at 27°C after 150 days, whereas it showed positive result after 120 days on PDA at 29°C. Bacteria were gram negative, citrate utilization was positive, oxidase was negative, catalase was positive and urease was negative. Morphological appearance and biochemical characterizations identified the bacteria as A. avenae subsp. Avenae. In vitro screening for the efficacy of various antibiotics to inhibit the growth of A. avenae subsp. avenae on YDC media showed that ampicillin and vancomycin were most effective. Artificial inoculation on sugarcane against red stripe disease was observed. Observations were made upto six weeks for disease development. Out of 27 varieties, 16 were found resistant, four moderately resistant, five moderately susceptible and two susceptible.Key words: Sugarcane, yeast extract dextrose chalk agar (YDC), potato dextrose agar (PDA), Acidovorax avenae subsp. avenae, biochemical characterization, antibiotics

Bacteria-inducing legume nodules involved in the improvement of plant growth, health and nutrition

Bacteria-inducing legume nodules are known as rhizobia and belong to the class Alphaproteobacteria and Betaproteobacteria. They promote the growth and nutrition of their respective legume hosts through atmospheric nitrogen fixation which takes place in the nodules induced in their roots or stems. In addition, rhizobia have other plant growth-promoting mechanisms, mainly solubilization of phosphate and production of indoleacetic acid, ACC deaminase and siderophores. Some of these mechanisms have been reported for strains of rhizobia which are also able to promote the growth of several nonlegumes, such as cereals, oilseeds and vegetables. Less studied are the mechanisms that have the rhizobia to promote the plant health; however, these bacteria are able to exert biocontrol of some phytopathogens and to induce the plant resistance. In this chapter, we revised the available data about the ability of the legume nodule-inducing bacteria for improving the plant growth, health and nutrition of both legumes and nonlegumes. These data showed that rhizobia meet all the requirements of sustainable agriculture to be used as bio-inoculants allowing the total or partial replacement of chemicals used for fertilization or protection of crops