Take-All Suppressive Properties of Bacterial Mutants Affected in Antibiosis

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Abstract
Ten Tn5-induced mutants of bacterial strains I11 and N R R L B-15135 with altered inhibition (antibiosis) of Gaeumannomyces graminis var. [Pseudomonas fluorescens] tritici on agar medium were added to fungal inoculum by vacuum infiltration and tested for their ability to suppress take-all disease. Eight mutants were antibodies-negative and two mutants gave increased antibodies. Suppression was evaluated by measuring the weight of plant [wheat] tops and estimating the level of root infection. In all experiments, all four N R R L B-15135 antibiosis-negative mutants showed lower levels of disease suppression when compared with the parent strain. This was also true with three of the four I11 antibodies-negative mutants, except in one experiment where, although two of these mutants induced significantly lower plant top weights than those induced by the parent, root infection was not significantly greater. The suppressive properties of the fourth I11 mutant were not significantly different from the parent. The two N R R L B-15135 mutants with increased antibodies towards the pathogen did not give increased levels of disease suppression.