Synergetic effect of rhamnolipid from Pseudomonas aeruginosa C1501 and phytotoxic metabolite from Lasiodiplodia pseudotheobromae C1136 on Amaranthus hybridus L. and Echinochloa crus-galli weeds.

Rhamnolipid (Rh) is a biosurfactant produced by the bacterial Pseudomonas aeruginosa. This present study investigates rhizospheric strain C1501 of P. aeruginosa with an accession number KF976394 with the best production of rhamnolipid: a biosurfactant. The partially purified rhamnolipid from strain C1501 and Tween 80 was tested on mycelial growth of wild strain C1136. The enzyme activities involved in biodegradation, as well as necrosis induction on the tested weeds, were performed using scanning electron microscopy. It was observed that the different concentrations of rhamnolipid tested enhanced the dry mycelia weight yield of Lasiodiplodia pseudotheobromae which has been established to be producing a phytotoxic metabolite for killing weeds. It was observed that strain C1136 had a high level of cellulase and xylanase enzyme activities during this study. The scanning electron microscopy showed that the mutant strain of C1136 combined with 0.003% v/v of rhamnolipid enhances biodegradability and a high level of necrosis on the tested weeds compared with that on the untreated weeds. The highest CMCase activities and xylanase activities were obtained on the fourth day from the phytotoxic metabolite produced from the mutant strain of L. pseudotheobromae when combined with 0.003% v/v of rhamnolipid. This study has shown that rhamnolipid can serve as an adjuvant in order to enhance the penetrability of bioherbicide active ingredient for controlling weeds.