Microbial preparation of herbicide is defined as bioherbicide that can control the weed. In this approach, indigenous plant pathogens isolated from weeds are cultured to produce the large numbers of infective propagules which are applied at a rate that will cause high levels of infection leading to suppression of the target weed. During the present investigation, cell free culture filtrate (CFCF) of Alternaria alternata was evaluated for its phytotoxicity against a noxious weed Lantana camara. The results of cut shoot, seedling and detached leaf bioassays revealed the presence of a toxic metabolite in the CFCF and a significant reduction in chlorophyll and protein content were also noticed. Phytotoxic moiety was further purified and characterized by using solvent partition, thin layer chromatography (TLC), FTIR and 1H NMR analysis. The acetone extract induced maximum phytotoxic damage at a concentration of 100 μg/ml and TLC purified fraction also exhibited herbicidal potential. The toxic compound was identified as tenuazonic acid upon comparison with FTIR and 1H NMR spectra. This is the first evidence that confirmed the herbicidal potential of a biorational, tenuazonic acid was produced by submerged fermentation of A. alternata.
Cabbage (Brassica oleracea Linn.) is one of the important vegetables grown worldwide. Insect pests have been a major constraint to its production with some reported to have developed resistance to commonly available synthetic insecticides. In order to find alternative control for these pests, field experiments were conducted in the early seasons of 2011 and 2012, to evaluate the efficacy of three plant extracts, Tephrosia vogelli Hooks, Zingiber officinales Rosh and Lantana camara Spanish flag, applied at 5, 10 and 25 % w/v concentrations Delthamethrin (a synthethic insecticide) and an unsprayed plot were included as positive and negative controls respectively. Plots were arranged in a Randomized Complete Block Design (RCBD), with three replications. Mean Data over the two planting seasons were subjected to the analysis of variance and significant means were compared using the least significant difference (L.S.D) at P < 0.05. Z. officinales extract effectively control P. xylostella larvae at all concentrations with 25 % w/v gave the best yield of 0.50 kg/ha while T. vogelii and L. camara extracts were as effective as Deltamethrin at different concentrations and hours on diamondback-moth (P. xylostella) adult The present findings indicated that effective botanicals against Diamondback moth adult and larvae of cabbage can be formulated from extract of T. vogelii, L. camara and Z. officinales at 25 % concentration respectively.
Enhanced social concern towards the ill effects of synthetic agrochemicals, their residual toxicity and resistance development in the target pests created a necessity of exploration of alternatives. Fungal biocontrol agents have been used as herbicides over two decades and research continues to enhance their efficacy comparable to synthetic herbicides. Combinations of synthetic herbicides with the fungal biocontrol agents was an approach adopted to enhance mycoherbicidal activity but had limited acceptance due to negative effects of their synthetic components. Hence a necessity for development of the formulations having least toxicity or being benign to non-target organisms was felt. The present study brings forth a new dimension of holistic and ecofriendly bioherbicidal formulations comprising of crude phytotoxins and spores of Alternaria alternata LC# 508 which enhances outstandingly its mycoherbicidal potential. Spent broth of Alternaria alternata (LC#508) exhibited toxic activity to its spores (autotoxicity) at a concentration of 50μg/ml which was used for developing five formulations FN1 to FN5. Formulations No. 5 was the best of all the formulations when evaluated by pot trails compared to control and other formulations. Disease onset and mortality was observed in 3.5 days and 5 days respectively in case of formulation No 5 (50 μg of crude spent broth + 1x 106 spores/ml) when compared to spore spray alone. Thus the formulation of crude spent broth and fungal spores could be developed as a cost effective and efficacious bioherbicide formulation when compared to the spores alone.