Characterization of Macrophomina phaseolina associated with leaf blight disease on Chlorophytum borivilianum Santapau & R.R. Fern. and its fungicidal susceptibility

Abstract

Safed musli, Chlorophytum borivilianum Santapau & R.R. Fern. is an important medicinal plant due to aphrodisiac and immuno-modulatory properties. Leaf blight disease showing characteristic symptom of necrosis spots on tips and outer margin of leaves, which gradually progressed and cover large portion of leaf lamina. Severe infection causes premature drying of leaves, which give blighted appearance as observed on safed musli growing field of ICAR-Directorate of Medicinal and Aromatic Plants Research, Anand, Gujarat (India). Associated putative fungus was isolated from single microsclerotia and characterized through cultural, morphological and microscopic studies. The association of putative fungus confirmed by pathogenicity test on potted safed musli plants. Mycelium of the causative organism showed dark olive black colonies that ultimately turns black and were found embedded with abundant of microsclerotia. Morphologically microsclerotia were black, smooth, round to oblong, 49.88 - 99.74 ± 5.62 μm in diameter. Pycnidia were exclusively observed on the infected leaves of C. borivilianum, were dark to greyish, globose, membranous and 83.62- 123.88 ± 3.77 μm in diameter. Conidia were single celled, hyaline, aseptate, obovoid and measuring 13.83 - 17.28 ± 0.37 μm × 5.39 - 7.28 ± 0.28 μm. By comparing with available relevant literature, the fungus was tentative identified as Macrophomina phaseolina. The identity of associated pathogen was further confirmed by molecular sequencing of internal transcribed spacer (ITS) of rDNA region and actin gene. In vitro efficacy test showed that among the tested fungicides, metalaxyl 4.0% + mancozeb 64% causes highest mycelial growth inhibition (90.00%) at both, 0.1 and 0.2% concentration and of Pseudomonas fluorescence (PF7) showed 51.72% mycelial growth inhibition.