41 Pak. J. Phytopathol Vol. 21(1): 41-44, 2009. SCREENING OF RICE GERMPLASM AGAINST PYRICULARIA ORYZAE THE CAUSE OF RICE BLAST DISEASE M. Usman Ghazanfar, Amer Habib, and S. T. Sahi Department of Plant Pathology,University of Agriculture, Faisalabad ABSTRACT A disease screening nursery of rice germplasm consisting of course and fine varieties was established during the kharif 2007 to determine the source of resistance in rice germplasm against Pyricularia oryzae, the cause of rice blast disease at Rice Research Institute Kala Shah Kaku by artificial inoculum with aqueous spore suspension of the pathogen. The screening revealed that none of the test lines was immune or highly resistant. One line IR- 70181-1-1-1 of course type was found to be resistant. Nine lines of the course type displayed moderately resistant response, while none of the fine type lines showed this response. Seventy seven lines of both course (35) and fine (42) rice were found to be moderately susceptible. Twenty four lines of fine rice showed susceptible to highly susceptible response. However, the prevalence of the resistance against rice blast pathogen is more common in the course as compared to the fine germplasm lines of rice Key words: Rice blast, screening, Pyricularia oryzae, resistant, susceptible. INTRODUCTION Rice (Oryza sativa L.) is one of the most important cereals of the world and is consumed by 50% of the world population (Luo et al; 1998). In Pakistan, it is cultivated on an area of 2581 thousand hectares with total production of 5483 million tons (Anonymous, 2007). This yield is very low as compared to other developed countries of the world and this low production is attributed to several biotic and abiotic factors. Among the biotic factors disease is the most important factor which results in crop losses of $ 5 billion every year (Asghar et al., 2007). Rice blast caused by Pyricularia oryzae Cavara [synonym Pyricularia grisea Sacc. the anamorph of Magnaporthe grisea (Herbert) Yaegashi and Udagawa], is one of the most destructive and wide spread diseases (Jia et al., 2000). This disease has caused significant yield losses in many rice growing countries e.g. 75% losses of grains in India (Padmanabhan, 1965), 50% loss in Philippines (Awodera and Esuruoso, 1975) and 40% loss in Nigeria (Ou, 1985). In Brazil rice blast is considered to be one of the major yield constraints in both irrigated and upland ecosystems (Prabhu and Morais, 1986). The disease can be managed by the use of fungicides, resistant cultivars, agronomic practices and biotechnological methods (Ribot et al., 2008). However, the use of resistant cultivars is the most economical and environment friendly method for the management of rice blast (Castano et al., 1990; Saifullah et al., 1995; Khan et al., 2001; Haq et al., 2002) but the resistance is subject to break down due to appearance of new/more virulent races of the pathogen. The present study reports on the screening/evaluation of rice germplasm for sources of resistance against rice blast disease MATERIALS AND METHODS The present studies were carried out at Rice Research Institute Kala Shah Kaku during July-August, 2007 for the screening of rice germplasm against rice blast disease. The plant debris collected from the previous crop was used for isolation of pathogen. 1. Isolation, purification of Pyricularia oryzae and its pathogenecity test: Infected leaves and nodes of rice plant were cut into small pieces (0.5-1.0 cm) and surface sterilized with 2% sodium hypochlorite for two minutes. These cut pieces were then washed with sterilized water and placed on PDA (Difco) plates. These PDA plates were incubated at 25 0 C for 5 days for the isolation of causal agent. The identification of the pathogen was made by studying the colony characteristics of the isolates on the PDA plates by following the method described in a technical bulletin on seed borne disease and seed health testing of rice (Agrawal et al., 1989). The pathogensity of isolates was confirmed by following Koch’s postulates. The agar slants and Petri plates of purified culture were stored at 5 0 C for further use. 2. Screening of rice germplasm for resistance against rice blast disease: The uniform blast nursery method, approved by International Rice Research