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 areas
which 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 are
the 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 microorganisms.
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 bioenhancer.
The aim of this study is to isolate and characterize phyloplane and rhizosphere microorganisms
from Kenyan rice with growth promoting habits. In this study whole plant rice samples were
collected 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.
