Microcycle Conidia Production in an Entomopathogenic Fungus Beauveria bassiana: The Role of Chitin Deacetylase in the Conidiation and the Contribution of Nanocoating in Conidial Stability

In the field, substantial quantities of insect pathogenic fungal conidia (5 × 10¹²/ha) are usually applied for the control of pests. In this regard, attempts are being made to obtain higher yields of conidia to make the process viable. One of the approaches is to induce microcycle conidia (MC) production. In a solid-state fermentation on rice, the SYB-grown inoculum with more pseudomycelia of <i>B. bassiana</i> enhanced MC production almost 5 times compared to the aerial conidia (AC) within 10 days. A chitosan (CNP) and alginate-chitosan (ACNP) nanocoating of MC increased the overall temperature and UV stability. The % cumulative mortalities of <i>Spodoptera litura</i> larvae over 10 d were 83 ± 8.0, 90 ± 5.0, 83 ± 5.0, and 90 ± 6 for AC-, MC-, CNP- coated MC and ACNP-coated MC, respectively. Using probit analysis, the LT₅₀ values were 5.8, 6.0, 7.5, and 6.3 d for AC, MC, CNPs-MC, and ACNPs-MC, respectively. It was observed that chitin deacetylase (CDA) plays a significant role in increasing MC formation. The higher relative proportion of total CDA over chitosanase activity (higher CDA: chitosanase activity ratio) was found to be correlated with the microcycle conidiation.