Biological control of downy mildew of maize caused by Peronosclerospora sorghi under environmentally controlled conditions

Downy mildew disease, caused by Peronosclerospora sorghi, is one of the most serious diseases of maize. The disease is currently managed by seed treatment with metalaxyl fungicides. However, problems regarding environmental pollution resulting from the use of fungicides and development of fungicide resistance within populations of P. sorghi are of increasing concern. Assuming that biological control by means of using antagonistic microorganisms may be an alternative for the management of this disease, the efficacy of biocontrol agents viz., Bacillus subtilis G1, Bacillus amyloliquefaciens B2, Brevibacillus brevis 57 and Pseudomonas fluorescens Pf1 for the management of downy mildew of maize and for promoting plant growth was evaluated. The results indicated that seed treatment with B. subtilis G1 and B. amyloliquefaciens B2 significantly (P = 0.05) increased the germination percentage and seedling vigour of maize as assessed by roll towel method. Among them, B. subtilis G1 was the most effective and recorded 9% and 31% increases in germination percentage and seedling vigour of maize respectively, as compared to the control. A talc- based powder formulation of B. subtilis G1 when applied through seed at the rate of 10 g/kg reduced the downy mildew incidence up to 54% under greenhouse conditions. Results of this study suggest that B. subtilis G1 is a promising bioagent for the management of downy mildew of maize and for promoting plant growth. This antagonist could be further exploited for commercial scale up for ecofriendly management of downy mildew of maize under localized climatic conditions

Effect of foliar application of Pseudomonas fluoresencens on activities of phenylalanine ammonia-lyase, chitinase and β-1,3–glucanase and accumulation of phenolics in rice

Changes in activities of phenylalanine ammonia-lyase,chitinase,ß-1,3-glucanase and phenolic content in rice leaves were measured at different times after treatment of leaves with Pseudomonas fluorescens strain Pf1.When rice leaves were sprayed with P.fluorescens,substantial increase in the phenylalanine ammonia-lyase activity was observed 1 day after treatment.Following increase of the first enzyme of the phenylpropanoid pathway,phenolic content of rice leaves also increased to a maximum at 4 days after P.fluorescens treatment.Chitinase activity increased in rice leaves in response to application of P.fluorescens and the maximum enzyme activity was observed 3 days after treatment.ß-1,3-Glucanase activity also increased significantly from 1 day after P.fluorescens treatment and continued to increase through 7 days.A five-fold increase in glucanase activity was observed 7 days after P.fluorescens treatment

Rapid detection of Ganoderma lucidum and assessment of inhibition effect of various control measures by immunoassay and PCR

Molecular and immunological methods have been applied for detecting the Ganoderma disease of coconut. Polyclonal antibodies (PAbs) raised against basidiocarp protein of Ganoderma were used for detection. For polymerase chain reaction (PCR) test, the primer generated from the internal transcribed spacer region one (ITS 1) of ribosomal DNA gene of Ganoderma, which produced a PCR product of 167 bp in size is used for early detection. Ganoderma disease in apparently healthy palms in two coconut gardens was tested by ELISA test using basidiocarp protein antiserum. Field trials were laid out in these early-diagnosed palms for the management of the disease. Based on the ELISA results,Pseudomonas fluorescens + Trichoderma viride with chitin amended treatments arrested the multiplication of the pathogen and showed below the infection level of optical density (O.D) within six months. Integrated disease management (IDM) and fungicide tridemorph treated palms showed below infection level (O.D value) within seven months and T. harzianum and P. fluorescens + T. viride treatedpalms showed below infection level (OD value) of the disease in eighth months

Analysis of aflatoxin B1 and aflatoxigenic mold in commercial poultry feeds in Tamil Nadu, India

A total of 48 commercial poultry feed samples collected from different poultry feed manufactures in Tamil Nadu, India were examined for the contamination of aflatoxin B1 (AFB1) and Aspergillus flavus. AFB1 in the samples was estimated by sandwich ELISA and the presence of A. flavus was detected by Real-Time PCR assay. Real-Time PCR analysis using A. flavus- specific omt primers confirmed the presence of A. flavus in all the samples tested. ELISA results indicated that the AFB1 contents in the poultry feeds ranged from 1.0 to18.7 ppb, which were below the permissible safe limits for poultry bird consumption and health. The results suggest adoption of good man-ufacturing practices by the commercial poultry feed manufacturers during procurement of feed ingredients, handling, storage and processing which might have suppressed the growth of A. flavus and aflatoxin contamination

Analysis of defense genes expression in maize upon infection with Peronosclerospora sorghi

Downy mildew, caused by Peronosclerospora sorghi is one of the important diseases affecting maize (Zea mays L.) production worldwide. Several downy mildew resistant maize lines have been identified. However, variability in the degree of resistance among maize genotypes to P. sorghi has been reported. In the present study the molecular basis of resistance of maize to P. sorghi was studied by using differential-display reverse transcription PCR (DDRT-PCR) technique. Maize seedlings of downy mildew resistant (MAI 756) and susceptible (CM 500) cultivars at two-leaf stage were inoculated with P. sorghi and leaf samples were collected at 0, 3 and 5 days after inoculation and analyzed for differentially expressed cDNAs using cDNA-RAPD approach. A total of 17 cDNA fragments corresponding to transcripts that showed alterations during the defence response of maize to P. sorghi were identified. Genes involved in signal transduction and several genes with unknown functions were found to be upregulated in maize after infection by P. sorghi. Among 35 random primers tested, OPD-05 has identified a differentially expressed cDNA coding for serine/threonine kinase protein in resistant maize genotype. Constitutive and high level expression of serine/threonine kinase gene was observed in the uninoculated plants of resistant genotype, whereas no expression of this gene was observed in uninoculated plants of susceptible genotype. However, the transcript level was induced 3 days after inoculation in the susceptible genotype and slightly reduced 5 days after inoculation. This study represents the first identification of maize serine/threonine kinase gene that is upregulated following infection by P. sorghi

Mass multiplication of Trichodermaharzianum using biodegradable banana waste for the control of Fusarium wilt of banana.

Fusarium wilt caused by Fusarium oxysporum f. sp. cubense (E.F. Smith) Snyd. and Hans. is one of the most destructive diseases of banana worldwide (Moore et al., 2001). The pathogen is soil-borne and remains viable up to 30 years (Moore et al., 1995). Breeding banana for resistance against fusarium wilt is diffi- cult because of the sterile and polyploid nature of the plant and the saprophytic and pathogenic habits of the pathogen (Novak, 1992). Several disease managementTrichoderma spp. isolated from rhizosphere of banana (Musa sp.) from different areas of Tamil Nadu, India were evaluated under in vitro condition for their antagonistic potential against Fusarium oxysporum, the banana fusarium wilt pathogen. Trichoderma harzianum isolate Th-10 was the most effective in inhibiting the mycelial growth of fusarium in vitro. Out of five different organic substrates (rice bran, rice chaffy grain, farmyard manure, banana pseudostem and dried banana leaf) tested, dried banana leaf was the best carrier material to support T. harzianum growth. Strain Th-10 colonized the dried banana leaves within few days and produced high density of propagules (4.6×1032 cfu/g of leaf). Addition of jaggery (10% w/v) to the dried banana leaves increased the multiplication of T. harzianum which survived for >6 months on the stored substrate. When applied as dried formulation, the population of T. harzianum Th-10 increased from 104 to 1013 cfu/g of soil within 60 days. In two field trials, soil application of T. harzianum Th-10 as dried formulation effectively controlled fusarium wilt with an efficacy comparable to that of the fungicide carbendazi

Differential Induction of Chitinase and β-1,3-Glucanase in Rice in Response to Inoculation with a Pathogen (Rhizoctonia solani) and a Non-Pathogen (Pestalotia palmarum)

Rice leaf sheaths were inoculated with R. solani (pathogen) and P. palmarum (non-pathogen) and were analyzed for the accumulation of pathogenesis-related (PR) proteins. Inoculation of rice plants with R. solani and P. palmarum resulted in a marked increase in activities of chitinase and b-1,3-glucanase. The levels of both enzymes were higher in incompatible interactions than in compatible interactions. Western blot analysis indicated that two proteins with molecular weights of 33 and 35 kDa cross-reacting with barley chitinase antibody were induced in rice in response to inoculation with R. solani. The appearance of these chitinases was correlated with increase in enzyme activity

Inhibition of fungal plant pathogens by seed proteins of Harpullia cupanioides (Roxb.)

Seed extracts of 50 plant species belonging to different families were evaluated for their ability to inhibit growth of Trichoderma viride in vitro. Of the various seed extracts, the seed extracts of Harpullia cupanioides (Roxb) belonging to Sapindaceae family exhibited very high antifungal activity. The seed extract of H. cupanioides strongly inhibited the growth of Rhizoctonia solani, Curvularia lunata, Colletotrichum musae and Alter­naria alternata. Seed extract of H. cupanioides retained its antifungal acti­vity even after heating at 100 °C for 10 min or autoclaving at 121 °C for 20 min. For partial purification of antifungal proteins, H. cupanioides seed extract was subjected to ammonium sulphate fractionation followed by gel filtration on Sephadex G-200 column. The fractions from sephadex G-200 were individually tested for their antifungal activity against T. viride. SDS-PAGE analysis of the fractions from Sephadex-G200 column indi­cat­ed that the fractions with antifungal activity contained a 68-kDa band as well as other low molecular weight protein bands. The N-terminal amino acid sequence of the 68-kDa protein (13 residues) was determined by Edman degradation. However, comparison with sequences in the GenBank database (Swiss Prot) did not reveal any homology with known protein sequences