Effect of 2,4-diacetylphloroglucinol-producing and non-producing strains of Pseudomonas fluorescens on root development of pea seedlings in three different soil types and its effect on nodulation by Rhizobium

The effects of seed inoculation with the 2,4-diacetylphloroglucinol (DAPG)-producing Pseudomonas fluorescens strain F113 and a non-DAPG-producing Tn5 mutant of this strain (F113G22) on the growth of pea roots (Pisum sativum) was studied in three different soil types (sand, silty loam and clay) at two different temperatures (14degreesC and 21degreesC). It could be shown that high concentrations of DAPG in the rhizosphere of pea seedlings increased root mass production by >50% in all soil types providing that soil conditions did not limit plant growth. The presence of DAPG was associated with increased root length and root weight and transiently enhanced lateral root formation of pea plants. It is therefore suggested that DAPG can act as a plant hormone-like substance. inducing physiological and morphological changes in the plant that can lead to enhanced infection and nodulation by Rhizobium.