Microbial populations, fungal species diversity and plant pathogen levels in field plots of potato plants expressing theBacillus thuringiensis var.tenebrionis endotoxin

Abstract

The environmental release of genetically engineered (transgenic) plants may be accompanied by ecological effects including changes in the plant-associated microflora. A field release of transgenic potato plants that produce the insecticidal endotoxin of Bacillus thuringiensis var. tenebrionis (Btt) was monitored for changes in total bacterial and fungal populations, fungal species diversity and abundance, and plant pathogen levels. The microflora on three phenological stages of leaves (green, yellow and brown) were compared over the growing season (sample days 0, 21, 42, 63 and 98) for transgenic potato plants, commercial Russet Burbank potato plants treated with systemic insecticide (Di-Syston)and commercial Russet Burbank potato plants treated with microbial Btt (M-Trak). In addition, plant and soil assays were performed to assess disease incidence of Fusarium spp., Pythium spp., Verticillium dahliae, potato leaf roll virus (PLRV) and potato virus Y (PVY). Few significant differences in phylloplane microflora among the plant types were observed and none of the differences were persistent. Total bacterial populations on brown leaves on sample day 21 and on green leaves on sample day 42 were significantly higher on the transgenic potato plants. Total fungal populations on green leaves on sample day 63 were significantly different among the three plant types; lowest levels were on the commercial potato plants treated with systemic insecticide and highest levels were on the commercial potato plants treated with microbial Btt.Differences in fungal species assemblages and diversity were correlated with sampling dates, but relatively consistent among treatments. Alternaria alternata, a common saprophyte on leaves and in soil and leaf litter, was the most commonly isolated fungus species for all the plant treatments. Rhizosphere populations of the soilborne pathogens Pythium spp., Fusarium spp. and V. dahliae did not differ between the transgenic potato plants and the commercial potato plants treated with systemic insecticide. The incidence of tuber infection at the end of the growing season by the plant pathogen g dahliae was highest for the transgenic potato plants but this difference was related to longer viability of the transgenic potato plants. This difference in longevity between the transgenic potato plants and the commercial + systemic insecticide potato plants also made comparison of the incidence of PVY and PLRV problematic. Our results indicate that under field conditions the microflora of transgenic Btt-producing potato plants differed minimally from that of chemically and microbially treated commercial potato plants.

Molecular characterization of microbial communities in the rhizosphere soils and roots of diseased and healthy Panax notoginseng

“…after the amendments of organic fertilizers contributed to disease suppression. Consequently, microbial diversity was not always effective to independently predict soil health (Donegan et al 1996), while microbial community diversity in combination with community composition, especially for the functional microbial consortia, could be a more meaningful measure.…”

Fate and Effects in Soil of Cry Proteins from Bacillus thuringiensis: Influence of Physicochemical and Biological Characteristics of Soil

“…Most studies have suggested that Bt plants cause only minor changes in the structure of microbial communities in soil, and the changes are often transient [159][160][161][162][163]. Other studies have shown no apparent deleterious effects of Cry proteins released by Bt plants in root exudates or from biomass of Bt plants incorporated into soil on microbial communities or representative enzymes [29,70,72,81,115,117,126,[164][165][166][167][168][169].…”

“…For example, a significant, but transient, increase in the populations of culturable bacteria and fungi was found in soil microcosms amended with leaves of Bt cotton expressing the Cry1Ac protein [161]; minimal differences were observed in the populations of culturable aerobic bacteria and fungi in soil with transgenic Bt potato expressing the Cry3A protein [162]; populations of nematodes were higher in soil with transgenic tobacco expressing protease inhibitor I than with nonmodified tobacco [192]; and significantly higher levels of culturable aerobic spore-forming and cellulose-utilizing bacteria and lower enzymatic activity of dehydrogenases and alkaline phosphatases were found in soils with transgenic alfalfa expressing -amylase or lignin peroxidase [193]. Wu et al [167,168] found that decomposing straw of Bt rice containing the Cry1Ab protein was not toxic under laboratory conditions to a variety of culturable microorganisms in a flooded paddy soil.…”

Genetically modified poplars in context

“…However, the specificity of its toxicity, and the rapid breakdown of proteins in the environment (compared to the ubiquitous anti-herbivore plant secondary compounds, including lignins) should make these effects relatively minor (Donegan et al 1996, National Research Council 2000. The impacts would be likely to be far less than from plantation establishment itself (compared to either a wild forest or agricultural use), or from planting of a different species or clones-as discussed above with respect to WM.…”