28S RDNA GROUP-I INTRONS - A POWERFUL TOOL FOR IDENTIFYING STRAINS OFBEAUVERIA-BRONGNIARTII

The nuclear ribosomal DNA of the entomopathogenic fungus Beauveria bro ngniartii is polymorphic in terms of both restriction site and length. Insertions of 350-450 bp long, identified as group-I introns, were de tected in the 288 rDNA. A panel of 47 strains of B. brongniartii, two B. bassiana and one Metarhizium anisopliae of various geographical and biological origins were found to contain 14 variant forms of intron d iffering in size and restriction pattern, at four different positions. Twelve types of ribosomal large subunit were defined on the basis of variant distribution and compared with strain clustering based on inte rnal transcribed spacers analysis. There was a correlation between the characteristic introns and isolates collected from the sugar cane pes t Hoplochelus marginalis. Primers for polymerase chain reaction amplif ication were chosen from these variants, and used to develop a specifi c method for detecting strains pathogenic towards Hoplochelus.