TABLE 4.

“Long-term” bioassay: control of take-all of wheat by DAPG-producing Pseudomonas strains Q2-87, 1M1-96, and Q8r1-96^a

Treatment	Population density of DAPG producers (CFU g of root−1)b	Shoot ht (cm)c	Disease severityd
Quincy virgin	ND	15.5 a	6.0 a
Quincy virgin plus Q2-87	ND*	15.6 a	6.1 a
Quincy virgin plus 1M1-96	ND*	15.0 a	6.4 a
Quincy virgin plus Q8r1-96	1.9 × 105 a	20.9 b	3.3 b
Quincy TAD	6.3 × 107 b	26.2 c	3.8 b

^aStrains were introduced into raw Quincy virgin soil at a final density of approximately 100 CFU g of soil⁻¹ (dry weight). After eight successive growth cycles of wheat of 3 weeks each (see Fig. 3), the soils were amended with 0.2% (wt/wt) of an oat grain inoculum of the take-all fungus. Wheat grown in Quincy virgin and Quincy TAD soils for eight successive growth cycles of 3 weeks each served as controls. Disease severity and rhizosphere population densities of introduced or naturally occurring DAPG-producing Pseudomonas strains were determined after 3 weeks of plant growth. 

^bMean values of three replicates of six plants each are presented. Population densities of introduced strains Q2-87, 1M1-96, and Q8r1-96 were determined by dilution plating onto KMB⁺ Rif. Population densities of DAPG-producing Pseudomonas spp. occurring naturally on roots of wheat grown in the Quincy virgin or TAD soil were determined by colony hybridization followed by PCR. Different lowercase letters indicate a statistically significant difference (Tukey's studentized range test, α = 0.05). ND, not detected (below lower limit of detection of 10⁴ CFU g of root⁻¹); ND*, not detected (below lower limit of detection of 10² CFU g of root⁻¹). 

^cMean values of six replicates of two plants each are presented. The severity of take-all was rated on a 0-to-8 scale (0 = no disease; 8 = dead plant). Differences between treatments in shoot height were analyzed by analysis of variance followed by Tukey's studentized range test, whereas differences in disease severity were analyzed by using the Wilcoxon rank-sum test. Different lowercase letters indicate a statistically significant difference (α = 0.05).