Initiation of root growth stimulation by Azospirillum lipoferum CRT1 during maize seed germination

Abstract

Maize seeds were inoculated with a commercial inoculant containing 1.3 × 107 Azospirillum lipoferum CRT1 cells. After 24 or 48 h, bacteria were washed from the seed surface. Washed and unwashed seeds were then planted in pots containing perlite and grown for 28 days under greenhouse conditions. Whatever the density of Azospirillum at planting, the number of these bacteria at the end of the experiment was similar (1.9-8.0 × 107 bacteria·plant-1). However, comparison of root surface areas of the plants were different depending on the period of contact between seeds and the density of the inoculum. Twenty-four hours of contact was not sufficient to increase root growth surface areas. Contact for 48 h permitted us to obtain root surface areas comparable with those measured after a continuous contact. These results showed that in order to promote maize root surface areas, an optimal density of Azospirillum is not required during the whole cultural cycle. This optimal density is indispensable only up to the emergence of the radicle.Key words: Azospirillum, maize, inoculation, PGPR.