Claviceps africana Discovered in India

Abstract

The African ergot pathogen (Claviceps africana Frederickson, Mantle, & de Milliano) of sorghum (Sorghum bicolor (L.) Moench) was recently discovered in the Americas (4) and Australia, having previously only been recognized outside Africa in Thailand and Japan (3). The fungus provides a striking example of intercontinental epiphytotics of uncertain origins. Another fungus (C. sorghi Kulkarni, Seshadri & Hegde), the anamorph of which (Sphacelia sorghi McRae) is morphologically similar to that of C. africana and also causes ergot disease of sorghum, is considered to be the pathogen endemic to the Indian subcontinent (1,2). Five isolates of endemic ergot pathogen of sorghum from different locations in Southern India were provided as C. sorghi by ICRISAT, Hyderabad. The isolates were morphologically indistinguishable when cultivated on an asparagine-sucrose-salts agar, producing a white mycelium but no spores. Suspensions of hyphal fragments of each isolate were inoculated into gaping florets of a male-sterile sorghum grown at the Chelsea Physic Garden, London, in 1998. Infection of a few florets occurred with difficulty (<0.1% efficiency) by two of the isolates (from Andhra Pradesh and Madhya Pradesh states) to give a pathology typical of C. africana (2), especially with respect to the prominent young sphacelium forcing the glumes apart before first exudation of honeydew, the low concentration of honeydew oligosaccharides, and the white cascade of secondary sporulation on honeydew. This sphacelial fructification functioned as highly infective inoculum in other inflorescences, readily producing similar pathology leading to the formation of persistently small, roughly spherical “sclerotia” that were typical of C. africana in the recent American epiphytotics, but bearing none of the sclerotial characteristics of C. sorghi. Analysis of ergot tissue from near-mature inflorescences revealed dihydroergosine, an alkaloid that differentiates C. africana from C. sorghi, together with festuclavine, the identity of which was shown by GCMS (gas chromatography-mass spectrometry) (2). This evidence from pathogen isolates was complemented by analysis of a sample of small, spherical “sclerotia” from ICRISAT that also had a similar alkaloid composition. It is therefore clear that C. africana is now in India and this influences not only the interpretation of data on sorghum ergot disease published in recent years from that region, where the identity of the pathogen may not have been rigorously monitored, but also future phytopathological strategies for sorghum more widely in Asia. References: (1) R. Bandyopadhyay et al. Plant Dis. 82:356, 1998. (2) D. E. Frederickson et al. Mycol. Res. 95:1101, 1991. (3) P. G. Mantle and H. A.-G. Hassan. Int. Sorghum Millets Newsl. 35:97, 1994. (4) E. M. Reis et al. Plant Dis. 80:463, 1996.