Co - inoculation of legumes with Azospirillum and symbiotic rhizobia

VICARIO JULIO CESAR; GALLARATO LUCAS ANTONIO; PAULUCCI NATALIA SOLEDAD; PERRIG DIEGO; BUENO MIGUEL A; DARDANELLI MARTA SUSANA

Handbook for Azospirillum

Springer

Lugar: Berlín; Año: 2014;

Azospirillum (α-subclass of proteobacteria) have been known for many years as plant growth promoting rhizobacteria (PGPR). They were isolated from the rhizosphere of grasses and cereals all over the world and so far numerous species have been described Azospirilla are generally regarded as rhizosphere bacteria, but display strainspecific differences in the way they colonize roots. They predominantly colonize the root surface and only a few strains are able to infect plants. Some Azospirillum strains have specific mechanisms to interact with roots and colonize even the root interior, while others colonize the mucigel layer or injured root cortical cells. Under certain environmental and soil conditions, Azospirillum can positively influence plant growth, crop yields and N-content of the plant. This plant stimulatory effect exerted by Azospirillum has been attributed to several mechanisms. The contribution of biological nitrogen fixation in this plant response, however, has been questioned. One of the most pronounced effects of inoculation with azospirilla on root morphology is the proliferation of root hairs as observed in several grasses, cereals, and legumes under controlled conditions in the greenhouse as well as in the field. The factors, such as the production of plant growth-promoting substances and the increase in the rate of mineral uptake by plant roots have been taken into account to explain the plant yield enhancement and could even be more important in establishing the plant response. The positive effects of combined inoculation with Azospirillum and rhizobacteria have been reported for several legumes and cereals. Most Azospirillum?rhizobacteria coinoculation studies have focused on the final effects on plant growth and nodulation parameters; in contrast, few data are available on the simultaneous effect of double inoculation and stressful conditions on the early signalling exchange between the symbiotic partners. The response of dually inoculated plants and the enhanced growth of legume plants may be attributed to early nodulation, an increase in the number of nodules, and a general improvement in root development. The objective of this chapter was to summarize the effects of co?inoculation with Azospirillum and rhizobia on nodulation and growth of legumes.