First Report of the Blast Single-celled Spore Pathogen, Pyricularia oryzae, on Rice in the India

Rice (Oryza sativa L.) is one of the most important cereal crops of the world and a prime staple food for half of the world’s human population (Singh and Singh, 2019). Among biological factors, diseases are of prime importance. Major diseases like a blast, brown spot, false smut, sheath blight, bacterial blight, sheath rot, etc. cause significant damage to the rice crop all over the world (Sahu et al., 2018). Among diseases, rice blast, caused by Pyricularia grisea (Cooke) Sacc. (Perfect stage – Magnaporthe oryzae) is one of the most important fungal diseases causing significant yield losses in rice (Panda et al., 2017). Rice Blast disease has been observed in almost all rice production regions in the world (Ou, 1985). The disease is the most explosive and potentially deadliest disease of the rice (Oryza sativa) crop and is a model system for research on the molecular mechanisms that fungi use to cause plant disease (Valent, 2021). In August 2019, leaf lesions, 2 to 5 mm in diameter, with light-colored centers and brown spindle-shaped symptoms were observed on leaves of paddy at the University of Birsa Agricultural University Research Farm in Ranchi, Jharkhand. Diseased plants were collected, and infected leaves from five plants were placed overnight on a tissue paper towel in a Petri dish at 28°C. Conidiophores bearing pyriform, hyaline, uniseptate conidia (16.75 to 22.4 × 7.4 to 8.1 µm) erupted from the lesions single-celled spore was bearing along with double-celled spore (Fig.1) of the conidiophore which is of the length of cell 6.5 to 9.8 µm. The single-celled spore (Fig.2) is hyaline and circular. Single-spore cultures RB-1 were established and grown on oatmeal agar medium at 28°C under constant fluorescent light, producing regular blackish-white colonies with mid- to dark gray pigmentation and profuse sporulation were identified under the compound microscope then 20-day-old plants of commercial CO39 seeds were spray inoculated with 8 ml of conidial suspension (10⁶ conidia/ml in distilled water) in four pots to test for general susceptibility to Pyricularia oryzae. Controls were sprayed with a water suspension. Treated plants were incubated under 14 h of light at 28°C and 10 h of the dark at 25°C for up to 7 days. Leaves inoculated with RB-1showed rapid symptom development and shriveled within 5 days post-inoculation. Characteristic teardrop-shaped, pale-bordered lesions were observed nest to the dead tissues. Abundant conidia were reisolated from all leaf lesions and a double-celled spore was found, thereby fulfilling Koch’s postulates. The experiment results signify that formation of double-celled single septa, triple-celled double septa are common and reported in nature and the formation of single-celled spore P.oryzae occurs in rare chances in nature, and the existence of a single cell was observed. Control plants in pots show no infection whatsoever after 10 days. The isolate RB-1was preserved in the Ranchi Agriculture College Department of Plant Pathology Laboratory.