**1. Introduction**

128 Antimicrobial Agents

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Sorghum (*Sorghum vulgare* L.) belongs to the tribe Andropogonae of the grass family Poaceae. The genus Sorghum is characterized by spikelet's borne in pairs. Sorghum is treated as an annual, although it is a perennial grass and in the tropics it can be harvested many times. Sorghum crop production has considerably increased in several countries during the past few years. Sorghum is the fifth important cereals after wheat, rice and maize and are significant dietary food for one-third of the world population, these crops are the principal sources of energy, protein, vitamins and minerals for millions of the poorest people in these regions and sustain the lives of the poorest rural people and will continue to do so in the foreseeable future. India is the world's second largest producer of Sorghum. Like all crops, grain Sorghum is subject to infectious diseases which can sometimes limit production. Sorghum is susceptible to fungal and bacterial micro flora under certain environmental conditions. These mycoflora not only threaten plant growth but also affect food quality, causing huge economic losses. Every year, seed and seedling diseases of grain Sorghum are common in India. Grain Sorghum root rot can be a considerable problem in Sorghum production.

Synthetic pesticides are nowadays widely used for the control of plant diseases throughout the world because of their higher effectiveness in controlling disease causing organisms. However, excessive and unsystematic application of these chemicals has created several environmental and health hazards and also some phytopathogens have been developed resistance (Rhouma et al., 2009**)**. Therefore, there is an urgent need to search for effective, safe and biodegradable alternative pesticides. Diseases of cultivated crops remain the major limitation to increased agricultural production. Therefore, protection of plants from pathogens remains a primary concern of agricultural scientists. Despite serious environmental implications associated with the increased use, chemical fungicides remain the first line of defense against bacterial and fungal pathogens.

<sup>\*</sup> Corresponding Author

An Alternative Approaches for the Control of

**2.4 Preparation of plant extracts** 

in a freezer at 20°c until bioassay.

**2.5 Antibacterial activity** 

**2.5.2 Procedure** 

Nutrient Agar (NA) and Potato Dextrose Agar (PDA) for fungi.

extracts and stored in a freezer at -20°c until assayed.

plated in triplicates and average zone diameter was noted.

media to demonstrate inhibition of bacteria and fungi.

Peptone : 5grams Meat extract : 10 grams Sodium chloride : 5grams Agar agar : 15grams Distilled water to make : 1000ml pH adjusted to : 7.2 to 7.4

**2.5.1 Composition of nutrient agar medium** 

Sorghum Pathogens Using Selected Medicinal Plants Extracts 131

microbes as required for bioassay. The bacterial strains are maintained and tested on

The collected plant materials were chopped into small pieces shade dried and coarsely powdered in Willy mill. The coarsely powdered material weighed and extracted with hexane, chloroform, methanol and water in sequential order of polarity using a soxhlet extractor for five to six hours at temperature not exceeding the boiling point of the solvent. For each gram of dry material 2ml of solvent was used. The extracted solvents were filtered through Whatman no-1 filter paper and subsequently concentrated under reduced pressure (in vacuo at 40°c) using a rotary evaporator. The residue obtained were designated as crude

The dried plant extract residues obtained were redissolved in 0.1% Dimethyl Sulfoxide (DMSO) to get different concentrations (100mg/ml, 300mg/ml and 500mg/ml) of crude extracts and filtration through a 0.45μm membrane filter and stored in sterile brown bottles

The prepared hexane, chloroform, methanol and water extracts samples were tested for antimicrobial activity against the test organism's the plant pathogens using the agar cup plate method. Streptomycin (5µg) was placed as a positive control in all plates and inoculated with bacteria and for the bacterial cultures used that was incubated at 37°C for 18-24 hours. Bavistin (5µg) was placed as a positive control in all plates inoculated with fungi and for the fungal cultures that were incubated at 26°C for 36-48 h. The microbes were

The antimicrobial activity of the chloroform, methanol and water extracts of each sample was evaluated by using well diffusion method or cup plate method of Murray *et al.,* (1995) modified by Olurinola, (1996). Which is the most widely used type for identifying the antimicrobial activity, which exploit diffusion of antimicrobial compounds through agar

This assay performed by two methods agar disc diffusion and agar well diffusion. In these two methods the agar well diffusion essay was used to screen for antimicrobial activity of the hexane, chloroform, methanol and water extracts of different plant species. In agar well

Natural plant products and their analogues are an important source of new agricultural chemicals (Cardellina, 1988, Gulter, 1988). Medicinal plants as a group comprise approximately 8000 species and account for around 50% of all the higher flowering plant species of India. Over one and a half million practitioners of the Indian System of Medicine use medicinal plants in preventive, promotive and curative applications. In recent years, secondary plant metabolites (Phytochemicals), previously with unknown pharmacological activities, have been extensively investigated as a source of medicinal agents (Krisharaju et al, 2005). Plants have been formed the basis of natural pesticides, that make excellent leads for new pesticide development (Newman et al., 2000). The potential of higher plants as a source of new drugs is still largely unexplored. Hence, last decade witnessed an increase in the investigation on plants as a source of new biomolecules for human disease management (Grierson and Afolayan, 1999). Green plants are found to be an effective reservoir for the bioactive molecules and can provide valuable sources for the discovery of natural pesticides (Akhtar *et al.,* 1997). Therefore in recent years medicinal plant extracts are intensively analyzed with an aim of isolating novel bioactive compounds.
