AZOSPIRILLUM SPP PARTICIPATION IN DRY-MATTER PARTITIONING IN GRASSES AT THE WHOLE-PLANT LEVEL

Plant growth-promoting rhizobacteria, particularly those from the genu s Azospirillum spp., may affect root functions such as growth and nutr ient/water uptake, which in turn may affect shoot growth. Calculations based on data from literature on shoot and root mass of crop grasses (79 plant/bacteria associations were analyzed) revealed that inoculati on with Azospirillum spp. increased the shoot-to-root (S/R) ratio in a bout half of reported cases and decreased the S/R ratio in the other h alf. In 11 of 35 cases, the S/R ratio increased when the shoot mass in creased more than the root mass. In 23 of 35 cases, the root mass did not increase, yet the S/R ratio still increased. Thus, the increase in the S/R ratio indicated that shoot growth responds to inoculation mor e than root growth. A decrease in the S/R ratio occurred when (a) root growth dominated shoot growth even though both increased (16 of 36 ca ses), or (b) root growth either increased or remained unchanged, and s hoot growth was either unaffected or even decreased (19 of 36 cases). This analysis suggests that: (a) Azospirillum spp. participates in the partitioning of dry matter (both carbon compounds and minerals) at th e whole plant level by affecting root functions, and (b) the bacteria affect crop grass through multiple mechanisms operating during plant d evelopment.