Production and optimization of bioherbicide with improved phytotoxicity by regenerated fusant strain of <i>Fusarium oxysporum</i> and <i>Fusarium incarnatum-equiseti</i>

Protoplast fusion, a genetic modification that involves fusion of two microbial protoplasts to form a hybrid cell, has a great potential for obtaining industrially useful microorganisms. However, its potential for bioherbicide production has not been fully utilised. This study investigated the effects of protoplast fusion technique and optimisation on the phytotoxic activity of bioactive compounds (bioherbicides) produced by fungal strains. Protoplast fusion technique was employed to generate fusants of <i>Fusarium oxysporum</i> and <i>Fusarium incarnatum-equiseti</i>. The primary screening for herbicidal activity was conducted on fusant strains usingdetached leaf necrosis assay, followed by extraction of metabolites from both fusant and parent strains. The phytotoxic activity of the metabolites was conducted using <i>Cucumis sativus</i> and <i>Sorghum bicolor</i> assay, followed by post-emergent weed assay on <i>Ageratum conyzoides</i>, <i>Sida acuta</i> and <i>Amaranthus spinosus.</i> Optimisation studies of the fermentation processes were also conducted at different pH and time. The study showed that only one (RFS_07) out of 8 regenerated fusant strains expressed higher herbicidal activity than the parent strains. The study further revealed that metabolite of fusant exhibited significantly (<i>p</i> ≤ 0.05) higher phytotoxicity on post-emergent <i>A. conyzoides</i> (78%), <i>S. acuta</i> (55.0%)and <i>A. spinosus</i> (65%) when compared to parent strains (58-65%, 32 -38% and 45.5-48.5%), respectively. Highest phytotoxic activities of the metabolites were recorded at 14 days of fermentation, and pH 6.0 and 6.5 for parent and fusant strains, respectively. The study revealed the significance of the protoplast fusion technique in improving the efficacy of bioherbicides from fungal strains for effective management of weeds.