Hydroponic Seedling Bioassay for the Bioherbicides Colletotrichum truncatum and Alternaria cassiae

A rapid bioassay was developed to measure the bioherbicidal efficacy of spore preparations of the pathogens Colletotrichum truncatum (Schwein.) Andrus and W. D. Moore and Alternaria cassiae Jurair and Khan on hemp sesbania (Sesbania exaltata) and sicklepod (Cassia obtusifolia), respectively. The system uses 4-day-old dark-grown seedlings (grown hydroponically in paper towel cylinders) which were sprayed with spore suspensions. Shoot lengths were monitored non-destructively, and recorded over time under conditions of dark growth, 90-100% relative humidity and 25 C. Shoot growth inhibition and stem collapse (mortality) were directly related to the spore concentration applied. Generally, at 10 3 - 10 4 spores ml-1, these pathogens caused significant shoot growth inhibition within 25-30 h and seedling death within 40-50 h. This bioassay has been used to study herbicide-pathogen interactions, and may be extended to determine the bioherbicidal efficacy of different pathogen isolates, pathovars or spore formulations. This technique is more rapid, uses a lower inoculum volume, requires less space and is performed under more controlled conditions than conventional greenhouse bioassay methods. The data obtained are more quantitative than those obtained from bioassays relying on visual rating systems.     

Identification of two Bacillus amyloliquefaciens strains with high suppression to the key fruit pathogens of Chinese jujube

Two bacterial strains (ZJ01 and ZJ02) isolated from the phyllosphere of Chinese jujube were tested for antifungal activities and morphological mechanisms against Phoma destructiva, Alternaria alternata and Fusicoccum spp., three key pathogens of jujube fruits. Based on their physiological characteristics and 16S rDNA gene sequences, both strains were identified as Bacillus amyloliquefaciens. The disease incidence of jujube fruits sprayed with the fermentation liquor of ZJ01 and ZJ02 on the puncture wounds before inoculation with the spores of those three key pathogenic fungi was 10% or 66.7%, significantly lower than that of Nutrient Broth medium treatment (100%). These results suggest that strains ZJ01 may be a potential biological control agent for Chinese jujube fruit diseases. The antagonistic bacteria could cause five kinds of hyphal alterations of the causal agents, the maximum number ever observed. Of them, hyphal swelling and excessive branching were the dominant phenomenon, the other three varied with the pathogens. The diverse morphological malformation might be helpful to understand the broad antifungal activity of Bacillus spp..     

Effect of carbendazim and mancozeb combinationon Alternaria leaf blight and seed yield in sunflower (Helianthus annus L.)

Abstract

Leaf blight caused by Alternaria helianthi (Hansf.) Tubaki & Nishihara, is the major disease of sunflower affecting the successful cultivation across India. Five individual fungicides and two combination fungicides were evaluated against this pathogen in laboratory and in field experiments. Among them, the combination of carbendazim + mancozeb completely (100%) inhibited the mycelial growth of A. helianthi, irrespective of the concentrations tested followed by carbendazim alone and metalaxyl + mancozeb under in vitro condition. In field conditions, the combination of carbendazim + mancozeb was found to be highly effective in reducing the leaf blight disease of sunflower in all the three experiments as compared to other fungicides and unsprayed control. The reduction of Alternaria leaf blight was also directly associated with an increase in seed yield. The economics of the fungicides spray has been worked out and the benefit cost ratio for the combination of carbendazim + mancozeb at 2.0 g/l was 7.1 as compared to unsprayed control. The overall analysis of the results revealed that the combination of carbendazim + mancozeb at 2.0 g/l can be used for the management of foliar diseases such as Alternaria leaf spot/blight in agricultural crops.     

Inhibitory effect of botanical extracts against Alternaria alternata of aloe vera dry rot

Aloe vera dry rot caused by Alternaria alternata, is one of the most serious fungal diseases affecting the commercial cultivation of aloe vera in North India. Control of this disease through chemical is quite expensive and not ecofriendly. The plant extracts as biopesticdes act as a vital components for the management of this disease. Evaluation of some plant extracts was carried out against A. alternata in laboratory conditions. The extracts were prepared at 5% and 10% concentration and were evaluated through inhibition in radial growth (food poison technique) and spores (conidia) germination (hanging drop technique) against A. alternata. Neem leaf extract gave 58.6% inhibition in radial growth and 56.5% in spore germination at 10% concentration followed by Ocimum sanctum which was found effective and gave 54.7% inhibition in radial growth and 50.4% in spore germination over control.     

Dieter Seidel‐65 Jahre

Fruit extract of Solanum xanthocarpum was evaluated for its toxicity against Alternaria brassicae, the causal agent of Alternaria blight of Indian mustard [Brassica juncea (L.) Czern. &; Coss]. The mass obtained after vacuum drying of the crude methanolic extract was utilised for further sequential fractionation using n-hexane, ethyl acetate, n-butanol and methanol. Among the crude and different fractions tested, methanolic fraction was most effective with a minimum inhibitory concentration (MIC) of 62.5 μg/ml. The methanolic fraction was further fractionated using open column liquid chromatography into five subfractions (I–V) to identify the antifungal bioactive compounds. Among the five subfractions (SFs) tested SF IV was most effective at inhibiting A. brassicae conidial germination and thereby inhibited lesion development of Alternaria blight at a concentration of 15.625 μg/ml or higher. Furthermore, bioautography of SF IV with Alternaria alternata and diagnosis with Dragendorff reagent indicated that SF IV contains a mixture of bioactive alkaloids, namely a₁ (R_f = 0.12) and a₂ (R_f = 0.22). The potential of using S. xanthocarpum as a resource for the development of biofungicides is discussed.     

Biological control of onion leaf blight disease by bulb and foliar application of powder formulation of antagonist mixture

Abstract

Three antagonists: Pseudomonas fluorescens (Pf1), Bacillus subtilis and Trichoderma viride, were tested alone and in combination for suppression of onion leaf blight (Alternaria palandui) disease under glasshouse and field conditions. The average mean of disease reduction was 24.81% for single strains and 42.44% for mixtures. In addition to disease suppression, treatment with a mixture of antagonists promoted plant growth in terms of increased plant height and ultimately bulb yield. Though seed treatment of either single strain or strain mixtures alone could reduce the disease, subsequent application to root, leaves or soil further reduced the disease and enhanced the plant growth. The mixture consisting of Pseudomonas fluorescens Pf1 plus Bacillus subtilis plus Trichoderma viride was the most effective in reducing the disease and in promoting plant growth and bulb yield in greenhouse and field tests.     

Screening of phytotoxicity of Alternaria macrospora MKP1 against Parthenium hysterophorus L.

Parthenium hysterophorus L. an exotic, pernicious weed is considered as one of the most troublesome weeds for agricultural sector by virtue of its high ecological amplitude and adaptability. Microbes and their by-products are now proved to be a worthy alternative to toxic chemicals used for weed management. Alternaria macrospora MKPI was isolated from the parthenium leaves infected with leaf blight and found pathogenic to the weed. The herbicidal potential of cell free culture filtrate of A. macrospora MKP1 has been tested against parthenium by employing detached leaf bioassay and seed germination bioassay and a significant damage was exhibited by the cultural filtrate of pathogen to the parthenium leaves and seeds.