A new host for Nigrospora sphaerica causing leaf spots on Glycyrrhiza glabra

Glycyrrhiza glabra is a perennial medicinal plant. Commercially, it is known as liquorice or mulathi consisting of dried roots and rhizomes of the plant. It is used for the preparation of expectorant, and anti-inflammatory drugs as well as demulscent to improve the flavour of various bitter medicinal preparations. Glycyrrhizi is one of the important active constituents of the drug. During survey, a leaf spot disease was noticed in G. glabra plants growing in Udaipur, India.

Symptoms of the disease appear in the form of small (2-5 mm), circular to irregular, red coloured spots on leaflets, covering major area of the leaf. Occasionally, the spots are seen delineated by the midrib. In advanced stages of the disease, some spots cracked at the centre (Fig.1). Eventually, leaves dry and the plant defoliates.

Isolations from infected leaves were made on potato dextrose agar (PDA). The fungus on PDA was identified as Nigrospora sphaerica, on the basis of culture and morphological characters. The fully developed colonies were flat and grey coloured, having dark brown, septate, branched mycelium. Conidia were black, single celled, globose (12.4-18.5μm), borne on a hyaline vesicle at the tip of the conidiophore. The culture was deposited with the Agharkar Research Institute, Pune, India (accession number ARIFCC-1085).

Koch's postulates were satisfied by spraying a conidial suspension (10⁵ conidia/ ml), obtained from 10-day old culture plates, onto the healthy leaves of G. glabra. Inoculated leaves and water-sprayed controls were covered with polythene bags for 48 hours and kept under natural environmental conditions. Disease symptoms started developing on the inoculated leaves after 8-10 days. The fungus was reisolated from the infected plants.

Review of the pertinent literature revealed that Nigrospora sphaerica is known as leaf pathogen for several hosts (Pavgi et al., 1966; Chowdhry, 1969; Mazumdar et al., 2006). However, G. glabra constitutes a new host record for this pathogen in India and worldwide.