ECOTYPES OF THE FUNGUS BIPOLARIS-ORYZAE WITH VARIOUS RESPONSES OF THEMYCOCHROME SYSTEM

Two types of fungi based on the light required for induction of conidi ophore formation are known as 'photo-induced' and 'non-photo-induced' sporulators. Conidial development in a 'photo-induced' strain of Bipol aris oryzae (formerly, Helminthosporium oryzae) is controlled by antag onistic action of blue and near-UV radiation mediated through the 'myc ochrome' system al two developmental stages: conidiophore induction an d conidiophore maturation. Otherwise, conidial development in a 'nonph oto-induced' strain of B. oryzae, unlike that in the 'photo-induced' s train, is controlled by antagonistic action of blue and near-UV radiat ion at the conidiophore maturation stage alone. In this study, we coll ected fungi, B. oryze, from brown lesion spots on rice leaves cultivat ed in paddy fields, and investigated the possible existence of a new e cotype different from known 'photo-induced' and 'non-photo-induced' sp orulators, We also investigated the sensitivity of conidial developmen t of each isolate to blue and near-UV radiation. The isolates were ide ntified as B. oryzae by morphology of hyphae and conidia and the sympt omatic brown lesion spots on rice leaves caused by each isolate. There was no distinction between 'photo-induced' and 'non-photo-induced' st rains on rDNA base. Moreover, the existence of a new type of 'non-phot o-induced' sporulator different from the one presently known was confi rmed. In this newly identified sporulator, conidial development was no t affected by light irradiation. Among 153 isolates, one isolate belon ged to a previously known 'non-photo-induced' sporulator, five isolate s belonged to a new 'non-photo-induced' sporulator ecotype, and over 9 5% of the isolates were 'photo-induced' sporulators. Among 'photo-indu ced' strains, there were several subtypes having different sensitiviti es to near-UV radiation required for inducing conidiophore formation.