K. A. Raveesha

Antifungal potentiality of some plant extracts against Fusarium sp.

Abstract Aqueous extracts of 46 plants belonging to 32 different families of the plant kingdom were screened for antifungal activity against eight important species of Fusarium viz., Fusarium equiseti, F. moniliforme, F. semitectum, F. graminearum, F. oxysporum, F. proliferatum, F. solani and F. lateritium. The test fungi were isolated from maize, paddy and sorghum seeds collected from Mysore district, Mysore, India. Among the several plants screened only 12 plants have recorded significant antifungal activity. The antifungal activity of aqueous extracts varied among the test pathogens and was compared with that of the synthetic fungicides Blitox, Captan, Dithane M-45 and Thiram. F. proliferatum, which showed high susceptibility for the aqueous extracts, was tested using different solvent extracts viz., petroleum ether, benzene, chloroform, methanol and ethanol extracts of all the 12 plants. The results revealed that these plants could be exploited for ecofriendly management of the diseases caused by the test fungal pathogens and seed biodeterioration during storage.

Study of die back disease incidence of neem in Karnataka, India and PCR based identification of the isolates

A disease survey of die back of neem was done in different agroclimatic regions of Karnataka, India using Global Positioning System (GARMIN 12). Twigs of Azadirachta indica (Neem) infected with die back were collected from different regions of Karnataka, India and they were further analysed to determine the pathogen. Phomopsis azadirachtae the causal organism was isolated on malt extract agar from die back infected neem twigs. They were identified by conventional and molecular methods. Phomopsis genus specific primers (5.8S r-DNA) were then used for the detection of P. azadirachtae, the causative agent of die back of neem by polymerase chain reaction (PCR). Studies revealed the amplification of expected 141 bp DNA in P. azadirachtae isolated from the diseased trees of different regions of Karnataka indicating the causal organism of die back disease on neem. Studies revealed a very high incidence of die back in most of the places of Karnataka. This is the first report on disease incidence of die back of neem. Hand held GPS was used in the study which helps in continuous monitoring of the diseased trees.

In vitro screening of systemic fungicides against Phomopsis azadirachtae, the incitant of die-back of neem

Abstract Phomopsis azadirachtae Sateesh, Bhat & Devaki is the causal organism of die-back of neem (Azadirachta indica A.Juss.) which is, presently, a major crippling disease of neem in India. Six systemic fungicides such as Bavistin (carbendazim), Contaf (hexaconazole), Beam (tricyclazole), Fuji-one (isoprothiolane) Roko (thiophanate methyl) and Downymil (metalaxyl) were evaluated against P. azadirachtae under in vitro conditions. Colony diameter, mycelial dry weight, pycnidial formation and the germ tube length of the pathogen were the parameters studied. The results indicated that carbendazim was the most effective in inhibiting the growth followed by thiophanate methyl. Among the different concentrations tested, carbendazim at 0.25 ppm and thiophanate methyl at 0.75 ppm were optimum for controlling the growth of the pathogen. Both these fungicides can be utilized for the control of die-back of neem.

PCR-based detection of Phomopsis azadirachtae in die-back affected neem seeds.

Abstract Phomopsis azadirachtae Sateesh, Bhat & Devaki is the incitant of die-back disease of neem trees. Delayed appearance of conidia and presence of other microorganisms in the neem tissues are the obstacles in the rapid and accurate identification of P. azadirachtae. This work was carried out to develop a methodology for rapid detection of the pathogen in diseased tissues especially in the neem seeds. rDNA sequences of many Phomopsis spp. were retrieved from the database and were subjected for multiple alignment to select a 179 bp conserved sequence. This was used to design Phomopsis specific primer pair (Forward and Reverse) having the potential to produce a 154 bp product in PCR. The primer pair was utilised to detect the presence of P. azadirachtae in diseased neem seeds and other tissues. This is the first report on the PCR-based detection of P. azadirachtae directly in die-back diseased neem tissues. This method can be employed for rapid and reliable detection of P. azadirachtae in die-back affected neem seeds. Hence it will have very good application in seed health testing laboratories.

Intraspecific variability in Phomopsis azadirachtae infecting neem.

Abstract Phomopsis azadirachtae Sateesh, Bhat and Devaki is the causal agent of die-back disease of neem. Six isolates of P. azadirachtae collected from different geographical regions of Tamilnadu were subjected to SDS-PAGE to study the variation among the isolates. Mycelial soluble proteins extracted from the six isolates exhibited marked variations in their electrophoretic protein profile. A few bands were common to all the isolates and each isolate also had a few specific bands. Soluble proteins were resolved into 42 bands of different molecular weights. Similarity index obtained ranged from 29.63% to 59.26%. Above findings indicate the existence of variability in P. azadirachtae isolates and its heterogeneous nature, revealing the genetic diversity of the pathogen.

Potential of seeds of Psoralea corylifolia L. for the management of phytopathogenic spp.

Aqueous and solvent extracts of seeds of P. corylifolia were evaluated for antifungal activity by poisoned food technique against eight important phytopathogenic species of Fusarium commonly associated with maize seeds. Antifungal activity was observed in both aqueous and solvent extracts. Petroleum ether extract showed highly significant activity against all the Fusarium species. F. graminearum was highly susceptible, while F. lateritium was least susceptible. The antifungal activity increased with increasing concentration of the extract. The minimal inhibitory concentration (MIC) value of the aqueous extract for F. graminearum was 15% and for F. equiseti, F. moniliforme, F. semitectum and F. solani it was 40%. Total inhibition was not observed in the case of F. lareritium, F. oxysporum and F. proliferatum. The results of the study are of immense value in the management of seed borne phytopathogenic species of Fusarium known to cause significant yield loss in maize.

Antifumonisin Efficacy of 2-Hydroxy-4-Methoxybenzaldehyde Isolated from Decalepis hamiltonii

Fumonisins are mycotoxins primarily produced by Fusarium verticillioides that grow on food and feedstuffs. In the present investigation, the antifumonisin activity of 2-hydroxy-4-methoxybenzaldehyde isolated from Decalepis hamiltonii was evaluated. The results demonstrated that the compound 2-hydroxy-4-methoxybenzaldehyde exhibited dose-dependent antifungal activity with the zone of inhibition, minimum inhibitory concentration and minimum fungicidal concentration values 14.8 mm (at 500 μg/disc), 100 and 500 μg/mL, respectively. The fumonisin B1 production was completely inhibited at 400 mg/L under in vitro and 750 mg/kg under in vivo. There were no adverse effects observed in treated seed samples. The present findings indicate the possible use of 2-hydroxy-4-methoxybenzaldehyde as an alternative agent for management of fusarial growth and mycotoxins contamination.

Synergistic effect of combinations of fungicides and bacterial extracts against Phomopsis azadirachtae causing die-back of neem

Phomopsis azadirachtae causes die-back of neem and this disease is presently a major devastating disease of neem in India, resulting in the reduction of life expectancy and flower production. Development of effective, eco-friendly management strategies against this disease is most important. Two systemic fungicides carbendazim and thiophanate- methyl were combined with ethyl acetate extract of antagonistic bacteria Pseudomonas aeruginosa culture filtrate at different concentrations viz., 100F: 0E, 80F: 20E, 60F: 40E, 50F: 50E, 40F: 60E, 20F: 80E, 0F: 100E and evaluated against P. azadirachtae under in vitro conditions. The parameters studied were colony diameter, mycelial dry weight, pycnidial formation and the germ tube growth of the pathogen. The effect of these combinations on neem seed germination and seed-borne pathogen was also tested. The results indicated that the combinations tested were effective in inhibiting the growth of the pathogen in vitro. The combinations also inhibited the growth of P. azadirachtae from die-back infected neem seeds and had no significant negative effect on neem seed germination. These combinations could be utilized for the integrated control of die-back of neem.