Department of Plant Pathology, Punjab Agricultural University, Ludhiana, 141 004, India

Background and objectives
Kernel smut of rice caused by Tilletia barclayana has become an important disease of rice because of its consistently increasing incidence in major rice growing areas of the world [1]. The disease is soil- seed- and air-borne. Teliospores of the pathogen germinate and produce primary sporidia of filiform shape which further produce allantoid secondary and tertiary sporidia. The allantoid sporidia become air-borne and cause infection in the flowering spikelets of rice. Production and multiplication of sporidia and their infectivity have been studied and the results are reported here.

Materials and methods
The cultures of T. barclayana were obtained and maintained on PDA at 29 +/- 1C. Five basal media, i.e. PDA, host-extract, Richard's, Czapeck's and glucose-nitrate, were tested for growth and sporulation of the pathogen. Observations in terms of average colony diameter and number of sporidia per ml were studied on bits of fresh leaves of Cyprus rotundus, Echinocloa crusgalli, Euchiena maxicana, Sorghum vulgare, Oryza sativa and Zea mays. Aqueous suspension containing filiform and allantoid sporidia were prepared as described by Warham and Burnett [2] and panicles of two varieties PR 106 and PR 110 were inoculated. Severity of the disease was calculated. Relative incubation period, disease severity and teliospore production were studied in varieties PR 103, PR 106 and PR 108.

Results and conclusions
Potato dextrose agar and the host-extract media supported maximum radial growth of T. barclayana, followed in sequence, by Richard's, Czapeck's and glucose-nitrate agar media. Production of both filiform and allantoid sporidia was more on PDA and host-extract media. It was least on Czapeck's medium whereas nil on Richard's and glucose-nitrate media. The sporidia of the pathogen were capable of germination on the host (0. sativa) and non host plants like C. rotundus, E. crusgaili, E. maxicana, S. vulgare and Z. mays. Maximum tertiary sporidia production was on 0. sativa closely followed by E. crusgaili under glasshouse conditions, whereas Z. mays, S. vulgare and E. crusgaili supported maximum sporidia production which was slightly more than that on 0. sativa.
The production of infected grains was always much higher with inoculations by allantoid type of sporidia than that of filiform sporidia. There was significant interaction between sporidia type and sporidia concentration for producing the disease. However, there was decrease in production of infected grains between allantoid and filiform sporidia with an increase in sporidia concentration. The incubation period and production of teliospores was different in different varieties of the host.
These studies revealed that the type of growth of the pathogen and production of allantoid sporidia are nutrient dependant. In nature, the sporidia can multiply on leaves of the host and non host plants. Mainly the infection is caused by the allantoid type of sporidia and the incubation period and teliospore production varies in different varieties of the host.

1. Chahal SS, Mathur SB, 1993. J. Phytopathology 137, 301-308.
2. Warham EJ , Burnett PA, 1990. Plant Disease 199, 525-527.