Pathogenicity and cytological examination of adapted and non-adapted Bipolaris species on resistant and susceptible cultivars of rice and corn

Date

7-2015

Degree

Bachelor of Science in Agriculture

Major Course

Major in Plant Pathology

College

College of Agriculture and Food Science (CAFS)

Adviser/Committee Chair

Christian Joseph R. Cumagun

Abstract

The genus Bipolaris causes two important cereal diseases: brown spot of rice (Bipolaris oryzae) and leaf spot of corn (Bipolaris maydis). This study examined the morphology of the two Bipolaris species and its pathogenicity and cytology on resistant and susceptible rice and corn cultivars. B. oryzae has curved to straight conidium (length, 35-170 µm; width, 11-17µm) with papillate hilum, 6-13 distoseptate and flexuous solitary conidiophore. B. maydis has slightly curved conidium (length, 70-160µm; width, 15-20 µm) with rounded to pointed hilum, 7-11 distoseptate and flexuous to straight, solitary conidiophore. Resistant (CH-45) and susceptible (IR-72) rice cultivars were inoculated with B. oryzae (adapted) and B. maydis (non-adapted) isolates. B. oryzae was pathogenic on both rice cultivars producing higher lesion density and size on the susceptible cultivar at 3 to 5 days after inoculation which is significantly different from the resistant cultivar (P=0.05). B. maydis was non-pathogenic on both rice cultivars. Resistant (Sweet Grande) and susceptible (SuperSweet) corn cultivars were also inoculated with two Bipolaris species. B. maydis was pathogenic on both corn cultivars producing higher lesion density and size on the susceptible cultivar at 7 days after inoculation which is significantly different from the resistant cultivar (P=0.05). B. oryzae was non-pathogenic on both corn cultivars. At the cytological level, conidia of both Bipolaris species germinated on two hosts but only B. maydis produced appressoria on resistant and susceptible corn cultivars. H2O2 accumulation around the hyphal tips is due to the turgor pressure exerted by the hyphae which forces DAB stain to accumulate in the immediate surrounding of the swollen hyphae at 24 h after inoculation. In contrast, death cells, which is a form of defense response were formed around the attempted penetration site on resistant rice cultivar inoculated with B. maydis at 24 h after inoculation. This study suggests that in rice-corn cropping system, B. oryzae is not a potential source of inoculum for leaf spot of corn. Likewise, B. maydis is not a potential source of inoculum for brown spot of rice.

Language

English

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

LG 993.5 2015 A3 A46

Document Type

Thesis

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