Trevor V. Suslow

Transgenic tobacco plants which express the chiA gene from Serratia marcescens have enhanced tolerance to Rhizoctonia solani

We have prepared independent lines of transgenic tobacco plants which express high levels of theSerratia marcescens ChiA protein intracellulary or extracellularly (in glycosylated or unglycosylated forms). We have measured the susceptibility, of these plants toRhizoctonia solani infection in greenhouse trials and in the field. Transgenic tobacco plants which constitutively express theS. marcescens ChiA protein exhibit tolerance to the fungal pathogenR. solani. Disease tolerance is observed in transgenic tobacco plants which express the bacterial chitinase intra-or extracellulary. This is the first report to document disease reduction in the field in transgenic plants engineered for fungal disease tolerance.

Resistance to Rhizoctonia Solani in Transgenic Tobacco

We are attempting to develop significant resistance to fungal disease through the expression of novel activities in genetically engineered plants. Transgenic tobacco plants which express high levels of the Serratia marcescens chitinase gene (chiA) have been shown to have significant resistance to Rhizoctonia solani in greenhouse trials. These genetically engineered tobacco lines have been demonstrated to also have significant resistance to R.solani in two seasons of field trials.

Osmotolerance-minus mutants of pseudomonas putida strain mk280 are not impaired in cotton spermosphere and rhizosphere colonization

Strain MK280 of Pseudomonas putida was treated with N-methyl-(N′-nitro-N-nitroso-guanidine) to obtain mutants sensitive to an osmotic potential of −1.0 MPa (selected by supplementing a minimal medium with NaCl, Na2SO4, KCl or sorbitol). There were no significant differences between the populations of MK280 applied onto seeds and its osmosensitive mutant (NP179) after bacterial suspensions were dried onto cotton seeds. Likewise, osmotolerance did not correlate with short-term rhizosphere colonization since population density of strain NP179 on roots were not significantly different from strain MK280 when cotton was grown in non-autoclavcd or autoclaved soil at a low matric potential (−0.18 MPa). Strain B10-13b (a Pseudomonas fluorescens strain for which low rhizosphere colonization potential had been previously correlated with osmosensitivity) colonized the spermosphere and rhizosphere as well as strain MK280 and NP179 when cotton was grown in autoclaved soil. However, in the same non-autoclaved soil, its population density in the rhizosphere was significantly lower than MK280 and NP179. This suggests that the inability of strain B10-13b to colonize is influenced by other factors of plant-microbe dynamics than osmotolerance.