P. Hariprasad

Mass multiplication and formulations of biocontrol agents for use against fusarium wilt of pigeonpea through seed treatment

Trichoderma harzianum and Pseudomonas fluorescens are the two major fungal biocontrol agents found in the soil and the rhizosphere of various crop systems. We used different agricultural waste bases such as wheat bran, rice bran, paddy straw and neem cake for mass-multiplying T. harzianum and P. fluorescens. Ten isolates each of T. harzianum and P. fluorescens were isolated from rhizosphere soil samples collected from various pigeonpea-growing fields. We evaluated the efficacy of these isolates, both in increasing seed quality variables of pigeonpea and in inhibiting the mycelial growth of Fusarium udum Butler. Trichoderma harzianum isolate 4 and Pseudomonas fluorescens isolate 3 were selected and mass-multiplied using different agricultural waste products as bases. Among the latter, boiled rice bran was found to increase the growth of both biocontrol agents. Talc and sodium alginate formulations of mass-multiplied biocontrol agents were prepared and evaluated for their affects against fusarium wilt under greenhouse conditions. Fresh cultures of both biocontrol agents were found to increase seedling emergence and reduce fusarium wilt disease incidence when compared to the control and the formulations.

Mechanisms of plant growth promotion and disease suppression by Pseudomonas aeruginosa strain 2apa.

A new Pseudomonas strain, designated as 2apa was isolated from tomato rhizosphere and identified as a member of species Pseudomonas aeruginosa based on its morphology, conventional, biochemical, cell wall fatty acid methyl ester analysis, and 16S rRNA gene sequence analysis. The strain 2apa was positive for root colonization, indole acetic acid (IAA), salicylic acid and siderophore production and inhibited the growth of wide range of microorganisms. Antimicrobial substances produced by this strain with further purification and structure elucidation proved to be phenazine. Under laboratory and greenhouse conditions the strain promoted plant growth and suppressed a wide range of foliar and root pathogens in tomato. The protection offered by strain 2apa to foliar pathogens is considered as induced systemic resistance and was further confirmed by enhanced accumulation of phenolics, elicitation of lipoxygenas activity, and jasmonic acid levels. The broad‐spectrum antimicrobial and induced systemic resistance exhibiting strain P. aeruginosa 2apa can be used as an effective biological control candidate against devastating fungal and bacterial pathogens, which attack both root and foliar portions of tomato plant. Production of other functional traits such as IAA and siderophore may enhance its potential as biofertilizer.

Cerebroside mediated elicitation of defense response in chilli (Capsicum annuum L.) against Colletotrichum capsici infection

Abstract Enhancing the host resistance by using naturally occurring elicitors derived from pathogenic organisms is emerging as an ecofriendly approach in plant disease management. Cerebrosides, categorized as glycosphingolipids, were isolated and partially purified from the wilt causing fungus (Fusarium oxysporum f. sp. lycopersici). Cerebroside treatment significantly reduced the anthracnose disease incidence under greenhouse conditions. Cerebroside elicitors were found to stimulate the early H2O2 accumulation followed by the production of plant defense-related enzymes such as Phenylalanine ammonia lyase (PAL), Peroxidase (POX), Polyphenol oxidase (PPO), and Lipoxygenase (LOX) when applied to chilli (Capsicum annuum L.) plants by spray treatment and also induced the accumulation of capsidiol. Defense-related enzyme activities were increased by the elicitor treatment and an high level in activity was maintained during the experimental period. Under greenhouse conditions, the cerebroside elicitors effectively protected chilli plants against infection by anthracnose causing organism, Colletotrichum capsici.

Elicitation of resistance in pearl millet by oligosaccharides of Trichoderma spp. against downy mildew disease.

Abstract In this study, we made an attempt to develop an ecofriendly management strategy against pearl millet (PM) downy mildew (DM) disease through seed priming with cell wall oligosaccharide of Trichoderma spp. Oligosaccharide treatment with mannitol significantly enhanced the seedling vigor when compared with the other controls. Significant reduction in DM disease was recorded in seeds treated with oligosaccharides extracted from Trichoderma virens and its efficacy was further increased when treated along with mannitol. At the biochemical level, increased activity of defense-related enzymes such as peroxidase and lipoxygenase was recorded followed by accumulation of signaling molecule Jasmonic acid in seedlings raised from seed treated with oligosaccharide (with or without mannitol) from T. virens. Under field conditions, oligosaccharide with mannitol provided a significant protection against the DM disease over other treatments. The possible utilization of oligosaccharide in inducing the systemic resistance against DM disease in PM is discussed.

Involvement of catalase in bacterial blight disease development of rice caused by Xanthomonas oryzae pv. oryzae.

We investigated the role of catalase in determining the virulence of Xanthomonas oryzae pv. oryzae isolates and the reaction of different rice cultivars to virulent isolates. Catalase, being an antioxidant enzyme, plays a major role in combating the toxic effect of reactive oxygen species (ROS) in plant cells. Among the 11 isolates studied, a variable level of catalase activity and differential expression of isoforms in different isolates was recorded. The maximum level of catalase activity was found in isolate XOO2 followed by XOO4, and the minimum level of activity was recorded in isolate XOO3. A virulence assay conducted on the susceptible rice cultivar Jaya revealed that the bacterial isolate with the highest level of catalase activity caused the maximum lesion length and vice versa. Among 31 cultivars screened, cv. CTH-1 showed the lowest incidence of disease, and lesion length was almost nil. The cultivars Thanu, Rasi and CTH-3 were found to be highly susceptible to X. oryzae pv. oryzae infection. We discuss the possible use of catalase enzyme as a biochemical marker in studying the virulence of X. oryzae pv. oryzae isolates.

Bacterial blight pathogen concentration in cotton seeds; its role in seed quality parameters of fuzzy and acid delinted seeds

Abstract The adverse effects of increasing concentration of Xanthomonas axonopodis pv. malvacearum on cotton seed quality parameters, seedling dry weight and on defense-related enzyme, Phenylalanine Ammonia Lyase (PAL) were studied. Different concentrations of pathogen (1×102 to 1×108 CFU/ml) were treated on both fuzzy and acid delinted seeds and subjected to the standard blotter method to study the effect of the pathogen on seed quality parameters. The seedling symptom test following the roll towel method, the modified germination test to study the blight incidence and the field emergence test were carried out to discover the field planting value and disease incidence under laboratory and field conditions. From these experiments, it was found that the decrease in the seed quality parameters like seed germination, seedling vigour, and the dry weight of seedlings when X. axonopodis pv. malvacearum concentration was increased. Whereas the bacterial blight incidence increased with an increase in pathogen concentration, in both greenhouse and field conditions. Phenylalanine ammonia lyase activity was found to increase along with the pathogen concentrations, but total phenol content decreased as pathogen concentration increased. The effect of X. axonopodis pv. malvacearum load on seed quality parameters, PAL enzyme activity of fuzzy and acid delinted cotton seeds are discussed in the present study.