FIRST REPORT OF PENICILLIUM GRISEOFULVUM CAUSING LEAF BLIGHT ON RHEUM AUSTRALE

Abstract

Rheum (Rheum australe, family Polygonaceae), a rhizomatous perennial herb with medicinal properties, is a rare and endangered species distributed in the Himalayas at an elevation of 2000- 4500 m above sea level (asl). In November 2011, a disease observed during domestication at Palampur, India (ca.1300 m asl), was characterized by irregular light-brown lesions on the leaves that gradually coalesced into larger blotches affecting the entire blade, which turned dark-brown and withered. Disease symptoms were oustanding during November–February, when the climate is cool (15-20°C) and were less prominent towards the end of March. A Penicillium sp. was consistently isolated when fragments from diseased leaves were surface-sterilised (2% sodium hypochlorite), and plated on potato dextrose agar (PDA). Colonies of single-spore isolates reached up to 8.0 cm diameter in 5 days at 28±2°C, were radially sulcate, often umbonate with usually deep margins, had terverticillate penicillia, with 4-7 phialides per verticil, bearing smooth-walled, ellipsoidal to subsphaeroidal conidia (Frisvad and Samson, 2004). The rDNA ITS was sequenced (GenBank accession No. KJ175262) and found identical (99%) to sequences of Penicillium griseofulvum isolates. Pathogenicity tests were done twice in a screenhouse by spraying a conidial suspension (1×106 conidia ml−1 in sterile tap water), obtained from 7-day-old cultures onto the healthy leaves of 10-month-old Rheum plants. Inoculated plants and water-sprayed controls were kept in a growth chamber at 20°C for 48-72 h. Symptoms appeared 8-10 days post inoculation on the leaves, from which the pathogen was reisolated, fulfilling Koch’s postulates. Control plants did not exhibit symptoms. P. griseofulvum has been reported as post-harvest pathogen (Spadaro et al., 2011). To our knowledge, this is the first record of P. griseofulvum on R. australe worldwide.