NOTE P.P. Singh et al. (1989) Phytoparasitica17(4):323-326 INHIBITION OF MYCELIAL GROWTH AND SPORIDIAL FORMATION IN THE WHEAT PATHOGEN NEOVOSSIA INDICA BY A POLYAMINE BIOSYNTHETIC INHIBITOR P.P. SINGH1, S. SINGH1, AMARJIT S. BASRA2 and P.S. BEDI 1 DL-ot-Difluoromethylornithine (DFMO), a specific suicide inhibitor of the polyamine biosynthetic enzyme ornithine decarboxylase (EC 4.1.1.17), strongly inhibited mycelial growth and sporidial formation of the wheat pathogen, Neovossia indica, in vitro, while DL-ot-difluoromethylarginine (DFMA), the analogous suicide inhibitor of arginine decarboxylase (EC 4.1.1.19), did not. The inhibited mycelial growth and sporidial formation were not only restored by putrescine (polyamine) addition, but were actually enhanced in the pulIescine + DFMO cultures. Besides altering mycelial growth and morphology, DFMO also reduced the cell size drastically. The inhibition of fungal polyamine biosynthesis is discussed in relation to selective control of plant disease. KEY WORDS: Polyamines; putrescine; ornithine decarboxylase; 'Karnal' bunt of wheat (Triticum aestivum L.), caused by the fungus Neovossia indica (Mitra) Mundk. (= Tilletia indica), was first reported from Karnal (Haryana, India) in 1930 (5). The disease has since been reported from many other countries (4) and is considered a major threat to wheat (1). Studies of the chemical control of 'Karnar bunt with seed- or foliar-applied fungicides are few and the results contradictory (11). It is now well documented that polyamines play an important role in the growth and differentiation of microbial, animal and plant cells (3,12,16). The diamine putrescine is produced from arginine and ornithine via the rate-limiting enzymes arginine decarboxylase (ADC) (EC 4.1.1.19) and ornithine decarboxylase (ODC) (EC 4.1.1.17). Bacteria and higher plants have both the ADC and ODC pathways (10,15), while fungi are largely limited to the ODC pathway (6,14,17), with occasional indications of a Received June 16, 1989; received in final form Oct. 4, 1989. lI)ept, of Plant Pathology,and 2Dept. of Botany~ Punjab Agricultural University, Ludhiana 141 004, India. Phytoparasitica 17:4, 1989 323