SCREENING OF BACTERIAL AND FUNGAL ISOLATES FOR THEIR PLANT GROWTH PROMOTING ACTIVITIES

Abstract

Rice (Oryza sativa  L.) is the most important staple food crop in several developing countries, and is ranked third in Kenya after maize and wheat. Most of the rice is grown in Central Kenya; other areaswhich produce small quantities include Western, Nyanza and Coastal Kenya. Declining soil fertility as a result of continuous cropping without replenishing soil nutrients is a major problem in Kenya.  Low soil fertility problem can be minimized by using fertilizers. However the use of chemical fertilizer is currently limited due  to rising costs and environmental concerns. This situation can be altered  by exploring alternative sources which are cost effective and environmental friendly. Phosphorus and nitrogen arethe two most limiting nutrients in rice soils while IAA is an essential natural growth promoter that extensively affects plant growth and development. Many soil micro-organisms are able to solubilize the unavailable phosphorus, increase uptake of nitrogen and also synthesize growth promoting hormones. The phylloplane and  the rhizosphere of the rice plants provides conducive habitat for various micro-organisms. It has been documented that inoculation of rice with plant growth promoting bacteria (PGPB) resulted in an increased plant/crop growth and yield. The PGPB acts as bio-fertilizer and bio-enhancer. The aim of this study is to isolate and characterize phyloplane and rhizosphere micro-organisms from Kenyan rice with growth promoting habits. In this study whole plant rice samples werecollected from different rice growing regions of Kenya out of which a total of 130 pure bacterial and 120 pure fungal isolates were obtained. These isolates were screened for production of plant growth promoting factors such as phosphate solubilization, nitrogen fixation and IAA production. Out of the 130 bacterial isolates, 99 (76.2 %) were positive for phosphate solubilization, over 80 % for nitrogenase activity and 50 (38.5%) for IAA production. Out of the 121 fungal isolates, 21 (17.5 %) were positive for phosphate solubilization, none for  nitrogenase activity and 6 (5 %) for IAA production. This clearly indicates the potential that these micro-organisms have for utilization as bio-fertilizers in rice production.