Differential endophytic colonization of sorghum plant by eight entomopathogenic fungal isolates and in vitro evaluation of Conidia virulence.
Studies were conducted to investigate the potentials of three strains of B. bassiana, two strains each of I. farinosa and Metarhizium anisopliae and a strain of I. fumosorosea to colonise sorghum endophytically after application of conidia to rhizosphere and the effect on the plant growth characteristics. Virulence of the conidia before and after endophytic growth phases were assessed using Galleria mellonella larvae mortality bioassay in-vitro. All the strains of the fungi colonised the sorghum plant. The strains of I. farinosa and B. bassiana were detected in the roots, the stem and the leaves while M. anisopliae was detected in the root only after 20 days. The shoot length of the sorghum plants inoculated with the strain of Beauveria, BB 315 were significantly higher than the control while none of the strains significantly affected the length of the root. One strain of I. farinosa (ARSEF 5081) and a strain of B. bassiana (432.99) significantly reduced the plant vigour and the length of the shoot when compared with the control. M. anisopliae strains had no significant impact on the plant growth characteristics. Conidia of 14 days old cultures of the fungal isolates (primary conidia) and that of the first growth on Sabouraud Dextrose Agar (SDA) after the endophytic growth phase in sorghum (Secondary conidia), were tested for virulence using Galleria mellonella bioassay system. The LT of G mellonella larvae increased significantly (P<0.05) when they were 50 inoculated with the secondary conidia of some of the strains, compared to virulence of the primary conidia. However, virulence of the primary and secondary conidia of two strains of B. bassiana, BB 315 and 776.05 were not significantly different. The desirable roles of entomopathogenic endophytes for use under marginal environmental conditions were discussed.
Key words: Virulence, Conidia, Sorghum, Shoot length, Root length