INTRODUCTION:-
Rice is the second largest crop grown in the world in
terms of both area and production. Rice is the staple
food for more than half of world's population. However
over 90 percent of the rice in the world is produced
and consumed in Asian countries. Rice is
known to be attacked by many diseases and some of
them are seed borne. Brown leaf spot of rice caused by
Drechslera oryzae (Breda de Haan) (Subram. and
Jain) is one of the major fungal disease of rice which
occurs in almost all the rice growing areas of the country
(R.S. Singh., 2005).
This disease was responsible for the famous Great
Bengal famine in India which led to death and migration
of many people. This is also known as the disease
of the poor farmers who are not able to provide all the
required package of practices which a crop needs due
to paucity of money. Most conspicuous symptoms of
this disease occurs on leaves and glumes of maturing
plants. Symptoms also appear on young seedlings
and the panicle branches in older plants. Leaf spots
may be evident shortly after seedling emergence and
continue to develop until maturity. Leaf spots vary in
size, are typically 1/8 inch in diameter, and are circular
to oval in shape. The smaller spots are dark brown
to reddish brown, and the larger spots have a dark
brown margin and reddish brown to gray centers.
Bipolaris oryzae is a seed borne pathogen ( Bedi and
Dhaliwal, 1970; Fakir and Ahmed et. al. 1976 and
Mian et. al. 1989). It can survive within the seed for
four years.
Bipolaris oryzac was found to be the most predominant
seed borne fungi by Mishra et.al (1988) when
they studied samples collected from a different agroclimatic
region of Bihar, Jammu, Andhra Pradesh
and Orissa. Ali and Deka (1996) also reported the
prevalence of B. oryzae from Assam. Diversity and
pathogenicity of the rice brown spot pathogen has
been investigated in Bangladesh by M M Kamal and
M.A.T. Mia in 2009 using genetic fingerprint analy