Enhanced nodulation and symbiotic effectiveness of Medicago truncatula when co-inoculated with Pseudomonas fluorescens WSM3457 and Ensifer (Sinorhizobium) medicae WSM419

Abstract

Aims Low numbers of rhizobia in soil or inoculants delay nodulation and decrease symbiotic legume productivity. This study investigated the effect of coinoculation with a helper bacterium, Pseudomonas fluorescens WSM3457 on the Medicago truncatulaEnsifer (Sinorhizobium ) medicae WSM419 symbiosis challenged by a low inoculum dose. Methods In a glasshouse experiment the effect of coinoculation with WSM3457 on the kinetics of nodule initiation and development was assessed 5, 7, 10, 14, 17, 21, and 42 days after inoculation of M. truncatula cv. Caliph with 10 3 cells/plant of E. medicae WSM419. Results Co-inoculated plants had enhanced rate of nodule initiation and development, greater numbers of larger crown nodules, and by day 42 accumulated more N than plants inoculated with E. medicae WSM419 alone. Nodule development was altered by co-inoculation. Approximately 25% of nodule initials on co-inoculated plants formed in closely associated pairs, young nodules were larger with multiple meristems and developed into cluster-like multilobed nodules compared to those on WSM419 inoculated plants. Molecular typing showed WSM3457 occupied a significant proportion of root nodules on co-inoculated plants. Conclusion Co-inoculation with P. fluorescens WSM3457 enhanced symbiotic effectiveness of M. truncatula when inoculated with a low inoculum dose of E. medicae WSM419.

Auxin signalling of Arachis hypogaea activated by colonization of mutualistic fungus Phomopsis liquidambari enhances nodulation and N2 -fixation

“…Previous studies have reported positive effects of dual inoculation with IAA‐producing bacteria and rhizobia on leguminous crops nodulation. However, these studies do not necessary reflect the direct involvement of auxin in interactions between IAA‐producing bacteria and nodulation as these bacteria show siderophore production and phosphate solubilization activity simultaneously (Fox, O'Hara, & Bräu, ; Malik & Sindhu, ; Srinivasan, Holl, & Petersen, ). Herein, our experiments demonstrate that auxin is involved in the enhancement of rhizobial symbiosis by the mutualistic fungus P. liquidambari through transcriptional activation of nodulation signalling pathway and promotion of nodule carbon metabolism.…”

Bio-inoculation of yerba mate seedlings (Ilex paraguariensis St. Hill.) with native plant growth-promoting rhizobacteria: a sustainable alternative to improve crop yield

“…Some of them belonged to wellknown plant growth-promoting genera, such as Pseudomonas (Kloepper et al 1989), Kosakonia (Peng et al 2009), Rhizobium (Bertrand et al 2007, and Ensifer (Fox et al 2011). Previously, Collavino et al (2010) isolated phosphate-solubilizing bacterial strains from the roots and rhizosphere of yerba mate, which were assigned to the genera Enterobacter, Pantoea, Pseudomonas, Acinetobacter, Burkholderia, and Exiguobacterium.…”

Potential of Rhizosphere Bacteria for Improving Rhizobium-Legume Symbiosis

“…balustinum Aur9 might have improved rhizobial infection at initial stages by increasing root hair formation and infection sites which in turn might have added to increase the formation of nodule primordia and early nodule development. Similarly, Fox et al ( 2011 ), while reporting enhanced rate of nodule initiation in Medicago truncatula cv. Caliph as a result of co-inoculation of P .…”

“…Hence, any stimulus that causes increase in root growth could result in more colonization sites for rhizobia (Fox et al 2011 ). It has been recognized that growth and yield of leguminous plants could be enhanced by creating additional infection sites through inoculation of rhizobia in combination with benefi cial rhizosphere bacteria (Plazinski and Rolfe 1985 ;Yahalom et al 1987Yahalom et al , 1990.…”

“…Although the potential to enhance nodulation, nitrogen fi xation, and plant growth and yield of legumes by co-inoculation with PGPR and Rhizobium does exist, there is a need to fi ne-tune combinations of PGPR, Rhizobium , and host genotype used under particular environmental conditions (Remans et al , 2008. However, studies have shown that the growth-promoting ability of co-inoculants may be highly specifi c to the inoculant's strain specifi city (Molla et al 2001a ), strain inherent potential (Medina et al 2003 ) to certain plant species, cultivar, and genotype (Remans et al 2008 ), while other studies have emphasized on cell density of applied inocula (Mishra et al 2009a ) or optimal inoculation dose (Bai et al 2002b ;Fox et al 2011 ), strains effectiveness (El-Sawy et al 2006 ) and composition of root exudates of host plant, and temperature variation or interaction of applied inocula with rhizospheric microfl ora predominant in the particular crop . Also, it has been reported that through the use of favorably interacting rhizospheric microorganisms as microbial inoculant, nodulation as well as N and P uptake and hence yield of legumes could be improved (Zaidi et al 2003 ).…”