MORPHOLOGICAL AND MOLECULAR CHARACTERIZATION OF Magnaporthe oryzae CAUSING RICE BLAST AND ITS REACTION TO RESISTANT ADVANCED BREEDING LINES

Abstract

Experiments were conducted for identification and characterization to study pathogenic variation among Magnaporthe oryzae isolates. Eight blast resistant advanced lines of rice developed by BRRI were tested phenotypically and at molecular level for the presence of Pi9 gene and their yield and yield attributes were studied. The experiments were carried out at Bangladesh Rice Research Institute (BRRI). The three isolates of Gazipur, Rangpur and Khulna were morphologically confirmed on the basis of three celled (2 septate) and pyriform hyaline conidia. Cultural characteristics on PDA, PSA and OMA media and mycelial growth as well as sporulation of the isolates were considered for determination of morphological variation. Cultural characteristics of three isolates showed different color (olivaceous, brownish or greyish to black), margin (filamentous, entire or undulate), surface texture (velvety or wrinkled) and colony form (regular or irregular) but same in case of elevation (flat) in different media. Sporulation of Khulna isolate was higher compared to others. Molecular detection of M. oryzae was confirmed using four specific primers namely; Bt1a/Bt1b, CAL-228/CAL-737, ACT-512/ACT-783, ITS1/ITS4 by amplifying fungal targeted region; beta tubulin (515 bp), calmodulin (510 bp), actin (260 bp), Internal Transcribed Spacer (520 bp), respectively in expected position. Eight Pi9 gene introgressed blast resistant lines were evaluated along with donor parent (IRBL9-W) as resistant check and recurrent parent (BRRI dhan28) as susceptible check variety. Phenotypic reaction for blast resistance indicated that six lines (PL-6, PL-17, PL-21, PL22, PL-26, PL-35) showed resistant reaction (score 0-2) and only one line (PL-34) showed

susceptible

reaction (score 4). BRRI dhan28 gave average score 3.75 (highest score 5) which was susceptible and IRBL9-W gave average score 0.5 (highest score 1) which was resistant to blast. These resistant lines were amplified with two linked markers RM8225 (172 bp) and NMSMPi9-1(168 bp) and all the phenotypically resistant lines gave the band at similar position with the linked markers. PL-21 gave maximum yield (4.47 t/ha) among the tested lines which was similar to BRRI dhan28 (4.94 t/ha). Therefore, it could be concluded that except PL-34, all the developed lines have Pi9 gene and resistant to rice blast disease. The line PL-21 could be advanced for releasing as variety.