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      Bacillus thuringiensis monogenic strains: screening and interactions with insecticides used against rice pests

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          Abstract

          The screening of Bacillus thuringiensis ( Bt) Cry proteins with high potential to control insect pests has been the goal of numerous research groups. In this study, we evaluated six monogenic Bt strains ( Bt dendrolimus HD-37, Bt kurstaki HD-1, Bt kurstaki HD-73, Bt thuringiensis 4412, Bt kurstaki NRD-12 and Bt entomocidus 60.5, which codify the cry1Aa, cry1Ab, cry1Ac, cry1Ba, cry1C, cry2A genes respectively) as potential insecticides for the most important insect pests of irrigated rice: Spodoptera frugiperda, Diatraea saccharalis, Oryzophagus oryzae, Oebalus poecilus and Tibraca limbativentris. We also analyzed their compatibility with chemical insecticides (thiamethoxam, labdacyhalothrin, malathion and fipronil), which are extensively used in rice crops. The bioassay results showed that Bt thuringiensis 4412 and Bt entomocidus 60.5 were the most toxic for the lepidopterans, with a 93% and 82% mortality rate for S. frugiperda and D. saccharalis, respectively. For O. oryzae, the Bt kurstaki NRD-12 (64%) and Bt dendrolimus HD-37 (62%) strains were the most toxic. The Bt dendrolimus HD-37 strain also caused high mortality (82%) to O. poecilus, however the strains assessed to T. limbativentris caused a maximum rate of 5%. The assays for the Bt strains interaction with insecticides revealed the compatibility of the six strains with the four insecticides tested. The results from this study showed the high potential of cry1Aa and cry1Ba genes for genetic engineering of rice plants or the strains to biopesticide formulations.

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          Most cited references80

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          Crop losses to pests

          E-C Oerke (2005)
          The Journal of Agricultural Science, 144(1), 31-43 ["Productivity of crops grown for human consumption is at risk due to the incidence of pests, especially weeds, pathogens and animal pests. Crop losses due to these harmful organisms can be substantial and may be prevented, or reduced, by crop protection measures. An overview is given on different types of crop losses as well as on various methods of pest control developed during the last century.", "Estimates on potential and actual losses despite the current crop protection practices are given for wheat, rice, maize, potatoes, soybeans, and cotton for the period 2001–03 on a regional basis (19 regions) as well as for the global total. Among crops, the total global potential loss due to pests varied from about 50% in wheat to more than 80% in cotton production. The responses are estimated as losses of 26–29% for soybean, wheat and cotton, and 31, 37 and 40% for maize, rice and potatoes, respectively. Overall, weeds produced the highest potential loss (34%), with animal pests and pathogens being less important (losses of 18 and 16%). The efficacy of crop protection was higher in cash crops than in food crops. Weed control can be managed mechanically or chemically, therefore worldwide efficacy was considerably higher than for the control of animal pests or diseases, which rely heavily on synthetic chemicals. Regional differences in efficacy are outlined. Despite a clear increase in pesticide use, crop losses have not significantly decreased during the last 40 years. However, pesticide use has enabled farmers to modify production systems and to increase crop productivity without sustaining the higher losses likely to occur from an increased susceptibility to the damaging effect of pests.", "The concept of integrated pest/crop management includes a threshold concept for the application of pest control measures and reduction in the amount/frequency of pesticides applied to an economically and ecologically acceptable level. Often minor crop losses are economically acceptable; however, an increase in crop productivity without adequate crop protection does not make sense, because an increase in attainable yields is often associated with an increased vulnerability to damage inflicted by pests."]
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            Insecticidal activity of Bacillus thuringiensis crystal proteins.

            Published data on insecticidal activity of crystal proteins from Bacillus thuringiensis are incorporated into the Bt toxin specificity relational database. To date, 125 of the 174 holotype known toxins have been tested in approximately 1700 bioassays against 163 test species; 49 toxins have not been tested at all; 59 were tested against 71 Lepidoptera species in 1182 bioassays; 53 toxins were tested against 23 Diptera species in 233 bioassays; and 47 were tested against 39 Coleoptera species in 190 bioassays. Activity spectra of the tested toxins were summarized for each order. Comparisons of LC(50) values are confounded by high variability of the estimates, mostly due to within-species variation in susceptibility, and errors associated with estimation of toxin protein content. Limited analyses suggest that crystal protein toxicity is not affected by quarternary toxin rank or host used for gene expression, but that pre-ingestion treatment by solubilization or enzymatic processing has a large effect. There is an increasing number of toxin families with cross-order activity, as 15 of the 87 families (secondary rank) that are pesticidal are active against more than one order. Cross-order activity does not threaten environmental safety of B. thuringiensis-based pest control because toxins tend to be much less toxic to taxa outside the family's primary specificity range.
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              Beyond the spore--past and future developments of Bacillus thuringiensis as a biopesticide.

              Formulated and sporulated cultures of Bacillus thuringiensis (Bt) are widely used as foliar sprays as part of integrated pest management strategies against insect pests of agricultural crops. Although in several cases the presence of the spore has been shown to improve the activity of the product, other Bt-based insecticides have been developed in which the spore is absent. The most notable of these are transgenic plants expressing just the insect toxin gene from the bacterium. This paper will discuss these developments, and the advantages and disadvantages of having the spore present.
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                Author and article information

                Journal
                Braz J Microbiol
                Braz. J. Microbiol
                bjm
                bjm
                Brazilian Journal of Microbiology
                Sociedade Brasileira de Microbiologia
                1517-8382
                1678-4405
                Apr-Jun 2012
                1 June 2012
                : 43
                : 2
                : 618-626
                Affiliations
                [1 ]Universidade do Vale do Rio dos Sinos, Programa de Pós-Graduação em Biologia, Laboratório de Microbiologia e Toxicologia , São Leopoldo, RS, Brasil
                [2 ]Instituto Rio Grandense do Arroz, Estação Experimental do Arroz , Cachoerinha, RS, Brasil
                Author notes
                * Corresponding Author. Mailing address: UNISINOS, Programa de Pós-Graduação em Biologia, Laboratório de Microbiologia e Toxicologia. CEP 93001-970, São Leopoldo, RS/Brasil.; E-mail: lauramnp@ 123456yahoo.com.br
                Article
                S1517-83822012000200025
                10.1590/S1517-83822012000200025
                3768848
                24031872
                d0e8d436-7d23-4407-b652-5cf58c30b9bb
                © Sociedade Brasileira de Microbiologia

                All the content of the journal, except where otherwise noted, is licensed under a Creative Commons License

                History
                : 21 January 2011
                : 04 July 2011
                : 16 January 2012
                Categories
                Environmental Microbiology
                Research Paper

                bacillus thuringiensis,cry proteins,insects
                bacillus thuringiensis, cry proteins, insects

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