Pathogenic variability of Phaeoisariopsis personata (Berk. and Curt.) V. Arx. in resistant and susceptible peanut (Arachis hypogaea L.) genotypes

The appearance of initial symptoms caused by the isolates ranged from 10 to 12 days in susceptible line ICG-7827. The most virulent isolate produced the highest number of lesions per leaflet, the largest lesion size, the greatest number of spores per lesion, and the highest percentage defoliation among the isolates studied. The least virulent isolate gave the lowest value of the above parameters. Among the isolates tested, isolates 1 and 5 were recorded as the most virulent isolate and the least virulent isolate, respectively. Resistant and susceptible peanut varieties/lines from the Institute of Plant Breeding (IPB), UPLB, Philippines, and from ICRISAT, India, were tested against the most virulent and the least virulent isolates. The resistant variety/line had delayed symptoms appearance for an average of 2.09 days, reduced lesion number per leaflet by 42.41 percent, lesion size by 50 percent, spore per lesion by 88.60 percent, and defoliation by 64.84 percent compared to the susceptible genotypes. Resistant and susceptible varieties/lines delayed symptom appearance for 1.25 days, reduced lesion number per leaflet by 28.84 percent, lesion size 20.96 percent, spore production per lesion 48.12 percent, and defoliation 27.41 percent when inoculated with the least virulent isolate compared to the most virulent isolate. Maximum activities of polygalacturonase (PG) and cellulase were obtained from cultures grown at 25 deg C. PG activity was optimum at pH 7.0 to 8.0 and cellulase at pH 7.0. The optimum temperatures for stability of PG and cellulase were 30 and 40 deg C, respectively. Sodium polypectate concentration for maximum PG activity ranged from 1.50 to 1.75 percent whereas carboxymethyl cellulose for maximum cellulase activity ranged from 1.50 to 2.00 percent. All isolates varied significantly in both their PG and cellulase activities in vitro. Maximum PG and cellulase activities were detected in 10-day-old cultures, after which the activity decreased with increasing age. The most virulent isolate showed 68.75, 60.71 percent higher PG and cellulase activities respectively, compared to the least virulent one. Blended susceptible peanut leaves, when used as carbon source in the medium, induced more PG activity than resistant peanut leaves, citrus pectin, and carboxymethyl cellulose. Carboxymethyl cellulose produced the highest cellulase activity compared to other carbon sources. The most virulent isolate had higher PG and cellulase activities compared to the least virulent one. There was an increase in the in vivo activity of both enzymes from 5th day until the 10th, 15th, and 20th days of infection by P. personata in both susceptible and resistant lines. However, the activity later decreased. For both enzymes, the activity was higher in the susceptible line than in the resistant one. The most virulent isolate showed higher PG and cellulase activities than the least virulent one