PGPR and entomopathogenic fungus bioformulation for the synchronous management of leaffolder pest and sheath blight disease of rice

BACKGROUND: The biological control of plant pests and diseases using a single organism has been reported to give inconsistent and poor performance. To improve the efficacy, bioformulations were developed possessing mixtures of bioagents. RESULTS: Bioformulations combining Pseudomonas fluorescens Migula strains Pf1 and AH1 and Beauveria bassiana (Balsamo) Vuill. isolate B2 were developed and tested for their efficacy against leaffolder pest and sheath blight disease on rice under glasshouse and field conditions. The combination of Pf1, AH1 and B2 effectively reduced the incidence of leaffolder insect and sheath blight disease on rice compared with other treatments. An in vitro assay of leaffolder preference to rice leaf tissues treated with Pf1 + AH1 + B2 biformulation showed variation from normal growth and development of leaffolder larvae. Plants treated with the Pf1 + AH1 + B2 combination showed a greater accumulation of enzymes, lipoxygenase and chitinase activity against leaffolder insect compared with other treatments. Similarly, the plants showed a higher accumulation of defence enzymes, peroxidase and polyphenol oxidase activity against sheath blight pathogen in Pf1 + AH1 + B2 treatment compared with the untreated control. The bioformulation mixture attracted the natural enemy population of leaffolder under field conditions. In addition, a significant increase in rice grain yield was observed in Pf1 + AH1 + B2 treatment compared with the untreated control. CONCLUSION: The combination of P. fluorescens strains and B. bassiana isolate effectively reduced the incidence of leaffolder insect and sheath blight disease on rice plants and showed the possibility of controlling both pest and disease using a single bioformulation. Copyright © 2010 Society of Chemical Industry     

Investigation on pre-zygotic barriers in the interspecific crosses involving Gossypium barbadense and four diploid wild species

Interspecific hybridisation has played significant role in the improvement of economically useful traits such as productivity, earliness, fibre quality and resistance to pests and diseases in cotton. However, wide crosses are often limited by the operation of either pre or/and post-fertilization barriers. The present study on pollen tube behaviour of four diploid wild species viz., G. triphyllum, G. davidsonii, G. thurberi and G. armourianum in the pistils of G. barbadense was taken up to determine the extent of pre-zygotic barriers operating in these crosses. High rate of pollen germination (∼80%) and normal growth of pollen tubes were observed upon selfing of both G. barbadense and four wild species. Pollen tubes reached the pistils and fertilization was accomplished within 8 HAP in all the five parental species. In the interspecific crosses, pollen germination was normal in the cross involving G. armourianum and drastically inhibited in the crosses involving G. triphyllum, G. davidsonii and G. thurberi. Even though delayed pollen tube growth was a general feature in all the four crosses, successful fertilization was observed only in the cross involving G. armourianum. In crosses involving G. triphyllum, G. davidsonii and G. thurberi, pollen tubes failed to reach the ovary even at 24 HAP due to the presence of strong stylar and ovarian incompatibility. Abnormalities in pollen tubes such as swelling, twisting, intense callose plug formation, breakage, branching and reverse orientation were frequently observed among the incompatible crosses.     

Prefertilization barriers to interspecific hybridization involving Gossypium hirsutum and four diploid wild species

Interspecific hybridization among species of cotton has lead to improvement in productivity, earliness, fibre quality and resistance to pests and diseases. However, wide crosses is often limited by the operation of either pre‐ or/and post‐fertilization barriers. An investigation on pollen tube behaviour of four wild species in the pistils of Gossypium hirsutum was taken up. Pollen germination was normal in crosses involving Gossypium triphyllum and Gossypium armourianum and markedly inhibited in the crosses involving Gossypium davidsonii and Gossypium thurberi. Pollen tubes reached the pistils and fertilization was accomplished within 8 h after pollination (HAP) in control cross. Even though delay in pollen tube was a common phenomenon in all the four crosses successful fertilization was observed in crosses involving G. triphyllum and G. armourianum, as they reached the ovary at 24 HAP. In crosses with G. davidsonii and G. thurberi, pollen tubes failed to reach the ovary even at 24 HAP indicating the presence of strong stylar and ovarian incompatibility. Measures to overcome such barriers to interspecific hybridization in the incompatible crosses are discussed.     

Associated bacterial diversity of insecticide-susceptible and -resistant brown planthopper, <Emphasis Type="Italic">Nilaparvata lugens</Emphasis> (Homoptera: Delphacidae) analyzed by culture-dependent and -independent methods

Nilaparvata lugens (Stål) is one of the major pests of rice throughout tropical and temperate Asia. Indiscriminate use of insecticides for suppressing N. lugens has resulted in the development of resistance to multiple insecticide classes, causing frequent control failures in the field. Analysis of gut bacterial diversity within an insect host is the initial step towards understanding the ecological roles of the symbionts. Present study aimed to survey the bacterial diversity associated with laboratory-reared (insecticide-susceptible) and field-collected (insecticide-resistant) populations of N. lugens by culture-dependent and PCR-Denaturing Gradient Gel Electrophoresis (DGGE) methods. Seventeen bacterial isolates were obtained by the culture-dependent method. Molecular characterization using the 16S rRNA gene and phylogenetic analysis revealed that the isolates belonged to Firmicutes and Proteobacteria. Taxonomic assignment placed these isolates into seven families representing 10 genera. Enterobacteriaceae was the most dominant family with its occurrence in four out of the five populations studied. The DGGE profiles indicated a low complex gut bacteria associated with N. lugens with limited number of bands. The Shannon-Wiener index ranged from 0.898 in insecticide-susceptible population to 0.946–1.035 in resistant populations. Sequencing and phylogenetic analysis revealed that the DGGE bands belonged to Firmicutes, Proteobacteria and Bacteriodetes. Results of this study illustrated that gut bacterial community associated with N. lugens is dominated by Proteobacteria and Firmicutes. Present findings could provide the basis for future work on the possible role of the bacterial symbionts in insecticide resistance and to formulate potential resistance management strategies.     

Chitin-based bioformulation of Beauveria bassiana and Pseudomonas fluorescens for improved control of leafminer and collar rot in groundnut

The talc-based formulation of Beauveria bassiana (B2 and B4) and Pseudomonas fluorescens (TDK1 and Pf1) strains and its mixture amended with and without chitin were developed and tested for their efficacy against the leafminer insect pest (Aproaerema modicella) and collar rot (or) seedling blight pathogen (Sclerotium rolfsii) in groundnut under glasshouse and field conditions. Application of talc-based formulation of B2 + TDK1 + Pf1 strains mixture (amended with or without chitin) through seed, soil and foliar spray effectively reduced the incidence of leafminer and collar rot in groundnut compared to individual bioformulation and control treatments both under glasshouse and field conditions. Groundnut leaves when treated with this bioformulation mixture, altered the feeding behavior of leafminer larvae and increased larval mortality under in vitro. Further, a significant increase in growth parameters and yield were observed in groundnut plants treated with B2 + TDK1 + Pf1 compared to individual bioformulation and untreated control. Increased accumulation of chitinase enzyme was observed in groundnut plants treated with mixture of B2 + TDK1 + Pf1 against A. modicella and S. rolfsii when compared to other treatments.     

Biochemical studies on the hepatoprotective effect of Picrorrhiza kurroa on changes in liver mitochondrial respiration and oxidative phosphorylation in -galactosamine-induced hepatitis in rats

Oral pre-treatment with alcoholic extract of Picrorrhiza kurroa rhizomes and roots (50 mg/kg/day for 10 days) significantly prevented the -galactosamine-induced alterations in respiration and oxidative phosphorylation of liver mitochondria.     

Competitive interactions between Goniozus nephantidis and Bracon brevicornis,parasitoids of the coconut pest Opisina arenosella

Black-headed caterpillar, Opisina arenosella Walker (Lepidoptera: Crytophasidae) is an endemic, frequently outbreaking pest of coconut in India and Sri Lanka. It also occurs in Bangladesh and Myanmar. Two larval parasitoid wasps Goniozus nephantidis (Muesebeck) (Bethylidae) and Bracon brevicornis Wesmael (Braconidae), are widely employed, either singly or in combination, for the biological control of O. arenosella in India. The co-occurrence of G. nephantidis and B. brevicornis in the field indicates the potential for competitive interactions which may interfere with pest suppression. In order to study the outcome of competitive interactions between these parasitoids, host larvae were exposed to the parasitoid species either alone or in combination. Females of G. nephantidis and B. brevicornis did not discriminate between unparasitised hosts and hosts parasitised by the other species. Survival of G. nephantidis and B. brevicornis from eggs to adult eclosion was 89.6 and 81.8%, respectively, when larvae of O. arenosella were exposed to these parasitoids individually. When both species were released simultaneously, the survival of G. nephantidis was 86.8% and females of that species chased B. brevicornis females, attempting to bite and sting them. The mean percentage of progeny obtained was significantly higher for G. nephantidis than for B. brevicornis. G. nephantidis dominated due to its parental care behaviour producing 87.0% of progeny and a sex ratio (proportion of females) of 0.79, whereas B. brevicornis produced 84.0% progeny and a sex ratio of 0.36. Although parental care by G. nephantidis females serves to protect the progeny from intruders, it may be disadvantageous from the standpoint of pest suppression under field conditions especially, when the pest population density is high.     

Enhancement of the productivity of tea (Camellia sinensis) secondary metabolites in cell suspension cultures using pathway inducers

Tea cell suspension culture is an alternative method for the synthesis of secondary metabolites. For the separation of cells, different concentrations of pectinase were used and a concentration of 0.5% was found to be the optimum concentration for the separation of cells (41.7%) in the culture medium than the other two concentrations (33.3 and 25.0%). The separated cells were cultured in liquid MS medium using different PGR combinations. The time taken for the cells to reach stationary phase, under different PGRs, ranged from 17 to 21 d. The maximum cell density was found in IAA and 2, 4-D medium at 21 d followed by 2, 4-D. Results revealed that the amount of secondary metabolites such as catechins were high with stationary phase when compared to other growth phases (lag and log phases). Different concentrations of shikimic acid (10, 20, and 30 mM) were added to the stationary phase of cell culture in the bioreactor and the secondary metabolite content was analyzed. Synthesis of polyphenols, catechins, caffeine, and other secondary components were high (33.87, 22.85, and 4.66%) with 20 mM shikimic acid treatment than the other two concentrations.     

Pseudomonas-induced defence molecules in rice plants against leaffolder (Cnaphalocrocis medinalis) pest

Fluorescent pseudomonad strains Pf1, TDK1 and PY15 individually and in combination were evaluated against leaffolder, Cnaphalocrocis medinalis Guen., in rice under in vitro, glasshouse and field conditions. Among the various treatments used, a combination of Pf1, TDK1 and PY15 strains effectively reduced the incidence of leaffolder pest in rice plants to an extent comparable with chlorpyrifos-methyl. In addition, morphogenesis of the insect pest in all stages, larval, pupal and adult, was greatly affected by a combination of Pseudomonas Pf1, TDK1 and PY15 strains. Further, the induction of defence-related molecules was demonstrated. An increased accumulation of defence molecules such as chitinase and proteinase inhibitors was observed with a combined Pf1, TDK1 and PY15 treatment compared with all other treatments. Western blot analysis of chitinase revealed the extra induction of 18, 28 and 35 kDa isoforms in rice plants treated with a mixture of Pf1, TDK1 and PY15 strains against leaffolder pest. The study revealed that a combination of fluorescent pseudomonad strains affects the development of leaffolder pest by inducing defence molecules in rice plants which in turn enhance resistance to leaffolder attack.