Pyricularia oryzae and Bipolaris spare the most devastating phytopathogens having multiple hosts. P. oryzae causes blast disease on rice and wheat while Bipolaris oryzaepv oryzae causes brown spot disease on rice.The pathogens cause yield losses up to50% depending upon strain and environmental conditions. In present study, 03 strains of P. oryzaeand 05 strains of Bipolaris sp were tested for their virulence potential on rice and wheat .The P. oryzae strains were found to be pathogenic on both crops causing disease severity 72-84-% while Bipolaris sp66-68% caused virulence on rice only. Under laborotary conditions, the fungal strains showed variable growth rate on different media. Growth rate of P. oryzae was found to be 1.3-1.4 cm/day on Potato dextrose agar (PDA), 1.2-1.6 cm/day1.2-1.6 cm/day onrice agar (RA) and1.6-1.7 cm/day on Wheat agar (WA). While that of Bipolaris sp was observed as 1.5-1.3cm/day1-1.2 cm/day… and 0.8-1.5 cm/day on PDA, RA and WA respectively.
In plant assays, maximum area under disease progressive curve (AUDPC) of rice plants was observed in P. oryzae P6 84-76 U2 and Bipolaris sp 81-76 U2 treated plants. In wheat, P. oryzae P6 treatment caused highest AUDPC 84-72U2 on all wheat varieties i.e.Pak-2013, Galaxy-2013 and Morocco. The virulent strains significantly enhanced the activities of oxidative stress markers such as Superoxide dismutase SOD.112.7-150.6.-min g-1Peroxides(POD)(1.8-4.8)U/g F.W, Polyphenol oxidases (PPO) 0.1-1.08 U/g F.W and Phenylalanine ammonia lyase (PAL) 0.1-0.8 U/g F.WCarnitineacyltransferase (CAT)0.01-0.2mM/gF.W, Ascorbate peroxides (APX),0.01-0.8 mM/gF.WMalondialdehyde (MDA) 0.001-0.7mM/gF.W and Hydrogen peroxide (H2O2)0.01-0.9on rice and wheat. These findings show the pathogenic variability and host range of different fungi prevailing in rice-wheat cropping system of Pakistan.
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