and deteriorate rapidly with the high susceptibility to fungal infections by a broad range of bacterial phytopathogens, resulting in severe economic losses. Rhizopusstolonifer (Ehrenb. ex Fr.) Vuill. is a representative necrotrophic fungal
Effect of Trichoderma viride T1433 on the pectolytic enzyme activity of Rhizopus stolonifer (= R. artocarpi) during the development of soft rot of jackfruit was studied. Activity of different fractions of pectolytic enzymes like PG, PME and PL was investigated during pathogenesis and correspondingly the associated resistance of the host was assayed. It was noticed that the biocontrol agent, Trichoderma significantly interacts with the pectolytic enzyme activity of the pathogen. It caused an appreciable reduction in enzymatic action. The reduction in the activity of polygalacturonase enzyme (PG) was recorded to be the highest among all the fractions of pectolytic enzymes. Such a trend appeared to be more pronounced in 'Kujja' than in 'Ghula' cultivar of jackfruit. The reduction in pectolytic enzyme activity was found to be coupled with a significant increase in the activity of polyphenol oxidase enzyme of the host tissues and a concomitant increase in host phenol content. Such inter-relationship between these two enzyme systems plays a key role to stimulate the defense mechanism of the host plant against infection. Significant increase in total phenol content of the host tissue during Trichoderma plant pathogen interaction that was recorded may correspond with the host defense response.
Rhizosphere and rhizoplane of fababean (Vicia faba), melochia (Corchorus olitorius), sesame (Sesamum indicum) and soyabean (Glycine max) plants are inhabited with fungi, mostly Aspergillus flavus, A. niger, Fusarium oxysporum, Penicillium corylophilum, P. cyclopium, P. funiculosum and Rhizopus stolonifer. All fungal species have the ability to produce gibberellin (GA) but F. oxysporum was found to produce both GA and indole-acetic acid (IAA). The optimum period for GA and IAA production by F. oxysporum was 10 days in the mycelium and 15 days in the filtrate at 28 °C. The contents of GA, IAA and cytochrome P-450 were increased at 0.5 and 1% NaCl after 5 days, but GA and IAA were lowered at 4% (700 mM) NaCl. Calcium decreased NaCl stress on F. oxysporum by significant elevating GA biosynthesis at 40mM Ca2+/700 mM Na+. GA at 10 mM and Ca2+ at 10 mM enhanced the germination of seeds under 175 mM Na+.
Authors:S. Dutta, A. Kundu, M. R. Chakraborty, S. Ojha, J. Chakrabarti, and N. C. Chatterjee
Siderophores are low molecular weight
(<1000 D) iron chelating compounds produced by microorganisms. Production of
siderophore is a device of antagonism as by virtue of the capacity of
siderophore production, a microorganism competes for Fe (III) with the others.
Production of siderophores by 9 different soil fungi and wood-decay fungi was
studied following CAS - assay and CAS - agar plate assay. Optimization for the production of
siderophores was done by varying the levels of pH and Fe (III) concentrations
in the low nutrient medium. All the test fungi could produce siderophores,
though the degree of production recorded to be very low both in Botryodiplodia
theobromae and in Fusarium spp. On the other hand, all the species of
Trichoderma showed their excellency in siderophore production. The optimum pH
for production of siderophores remained at neutral pH level though the range
varied from pH 6.0-8.0. The optimum range of the
concentration of Fe (III) required for siderophore production was recorded to
be 1.5-21.0 µM. However, the stress condition of
iron might be a decisive factor for siderophore production.
Seed samples of four Egyptian broad bean cultivars were tested for seed-borne fungi. The deep freezing method was used to isolate twelve seed-borne fungi viz., Alternaria alternata, Aspergillus flavus, A. niger, Botrytis fabae, Cladosporium cladosporioides, Fusarium oxysporum, F. solani,, Penicillium italicum, Rhizoctonia solani, Rhizopus stolonifer, Stemphylium globuliferum and Trichothecium roseum from the broad bean cultivars viz., Giza 3, Giza 429, Giza 843 and Misr 1. Aspergillus flavus, Botrytis fabae, Fusarium oxysporum and Penicillium italicum were the most predominant fungal species. Aqueous extracts from five wild medicinal plants (Asclepias sinaica, Farsetia aegyptia, Hypericum sinaicum, Phagnalon sinaicum, and Salvia aegyptiaca) which were collected from the Sinai Peninsula, Egypt were tested against the predominant fungal pathogens. All the aqueous plant extracts significantly inhibited the mycelial growth of these fungi, but the extract of Asclepias sinaica exhibited the strongest antifungal activity. The maximum seed germination rate was observed in infested Giza 843 and minimum in Misr 1. Treating seeds with plant extract of Asclepias sinaica (10%) enhanced the percentage of seed germination of all cultivars in both laboratory and pot experiments. Maximum root and shoot lengths of seedlings were recorded in Giza 843 during fungal infestation or treatment by plant extract. In greenhouse experiment, the aqueous A. sinaica extract reduced disease severity and total pigments but increased total phenolics and fruit yield.
Authors:Á. Csernetics, Zs. Péteri, B. Linka, and M. Takó
Rhizopusstolonifer in strawberry fruits. Phytochemistry 47, 1515-1520.
Characterization and use of essential oil from Thymus vulgaris against Botrytis cinerea and Rhizopusstolonifer in strawberry fruits
Vágvölgyi, Cs., Heinrich, H., Ács, K., Papp, T. (2004) Genetic variability in the species Rhizopusstolonifer , assessed by random amplified polymorphic DNA analysis. Antonie van Leeuwenhoek 86 , 181-188.
Genetic variability in