A phytotoxin produced by the sugarcane red rot fungus, Colletotrichum falcatum Went. was partially purified and its effects studied on sugarcane callus development, plantlet differentiation and shoot growth in tissue culture. The findings indicate that all the above attributes were markedly reduced by the fungal toxin. Potential for the possible use of the toxin to produce red rot resistant sugarcane genotypes by pathogen toxin induced somaclonal variation is examined.
A new necrosis viral disease was observed in blackgram, showed brown necrotic rings along with veinal and stem necrosis. The virus was mechanically inoculated on the local lesion host, cowpea cv. 152 and maintained in the local lesion host throughout the study. Yield studies under pot culture experiment showed 10- to 30-day-old plants were highly susceptible and the yield became almost nil. By using Transmission Electron Microscope (TEM) and indirect Direct Antigen Coated-Enzyme Linked Immuno-Sorbent Assay (DAC-ELISA) studies the virus was identified as Tobacco streak virus (TSV). The ultraviolet absorbance of the purified virus was measured and the ratio of A260/A280 was determined as 1.41. Polyclonal antiserum was raised against blackgram necrosis virus in New Zealand white rabbit and the titre value was determined as 1: 200. Direct antigen coating-ELISA was used to detect the virus concentration in various plant parts and stem portion recorded maximum virus concentration. TSV in blackgram was not transmitted through seeds.
Colletotrichum falcatum Went, the
causal agent of red rot of sugarcane produces a specialized infection structure
called appressorium, for penetrating the host. Environmental cues like surface
hydrophobicity and hardness tend to break the dormancy of the conidia and
initiate conidial germination. Conidial attachment is generally stronger on
hydrophobic surfaces, while hydrophilic surfaces do not permit conidial
attachment of C. falcatum. In vitro studies on conidial germination and
appressorium development were made to examine whether the Ca2+/calmodulin
dependent pathways are involved in appressorium formation in C. falcatum.
Effects of calcium chelator (EGTA), calcium channel blocker (methoxy
verampamil), calmodulin antagonists (chloropromazine, phenoxy benzamine and
W-7) and phospholipase C inhibitor (neomycin) were also examined to see whether
they can impair conidial germination and appressorium development. All these
chemicals were found to inhibit conidial germination and or appressorium
formation in C. falcatum. Chloropromazine and W-7 specifically inhibited
appressorium formation at the µM level. Exogenous addition of Ca2+
was found to restore the inhibition of conidial germination and appressorium
development by EGTA. These results suggest that the Ca2+/calmodulin signal
transduction pathway play an important role in the conidial morphogenesis and
appressorium development in C. falcatum.