Preliminary field test to assess the performance of the azospirillum-sorgum association in different crop management conditions.

In view of the release of 3 GM strains characterised for their ability to synthesize Indol-3- Acetic Acid (IAA-, IAAn, IAA+++) an alternative experirnent with WT strains with different ability in the synthesis of IAA was carried auto The evaluation of the effects of "natura!" strains, somehow similar in this aspect to the GM to be tested would be helpull even consideringt that A. brasilensSep 245, used in this study, is the base system to construct the genetically modified strains. The 3 WT strains provided, A. irakenseK BC1 (low IAA-producer), A. brasilenseS p245 (medium-IAA producer) and A. brasilense Sp7 (high-IAA producer) were compared to an untreated contrai, under three different levels of nitrogen fertilisation (0,90 and 180 kg ha-l). In order to evaluate the effect of IAA on the performance of the Azospirillum/plant association multiple fiela' trial including different conditions or water supply and soil managemen were also considered. The experirnental scheme included a comparison between irrigation at 100% of restitution of root system in the first soillayer could have no beneficial effects, especially in very drought conditions, such as thbse occurred this year. These results could be related to the effect of IAA over-producer strains on root system, as previously described for A. brasilense Sp6 I AA over-produce mutant, which affects the root length density particularly in the first 0-30 cm soil layer. When water is a limiting factor (not irrigated soil) the association with IAA producer azospirillum improves drought resistance while when water is available (irrigated soil) a further development of the root system would not provide benefits. Minimum tillage causes a greater development of the root system in the upper soillayer compared to conventional tillage (ploughing)