Microbial inoculant

Microbial inoculants also known as soil inoculants or bioinoculants are agricultural amendments that use beneficial rhizospheric or endophytic microbes to promote plant health. Many of the microbes involved form symbiotic relationships with the target crops where both parties benefit (mutualism). While microbial inoculants are applied to improve plant nutrition, they can also be used to promote plant growth by stimulating plant hormone production (Bashan & Holguin, 1997; Sullivan, 2001). Microbial inoculants also known as soil inoculants or bioinoculants are agricultural amendments that use beneficial rhizospheric or endophytic microbes to promote plant health. Many of the microbes involved form symbiotic relationships with the target crops where both parties benefit (mutualism). While microbial inoculants are applied to improve plant nutrition, they can also be used to promote plant growth by stimulating plant hormone production (Bashan & Holguin, 1997; Sullivan, 2001). Research into the benefits of inoculants in agriculture extends beyond their capacity as biofertilizers. Microbial inoculants can induce systemic acquired resistance (SAR) of crop species to several common crop diseases (provides resistance against pathogens). So far SAR has been demonstrated for powdery mildew (Blumeria graminis f. sp. hordei, Heitefuss, 2001), take-all (Gaeumannomyces graminis var. tritici, Khaosaad et al., 2007), leaf spot (Pseudomonas syringae, Ramos Solano et al., 2008) and root rot (Fusarium culmorum, Waller et al. 2005). The rhizobacteria commonly applied as inoculants include nitrogen-fixers, phosphate-solubilisers and other root-associated beneficial bacteria which enhance the availability of the macronutrients nitrogen and phosphorus to the host plant. Such bacteria are commonly referred to as plant growth promoting rhizobacteria (PGPR). The most commonly applied rhizobacteria are Rhizobium and closely related genera. Rhizobium are nitrogen-fixing bacteria that form symbiotic associations within nodules on the roots of legumes. This increases host nitrogen nutrition and is important to the cultivation of soybeans, chickpeas and many other leguminous crops. For non-leguminous crops, Azospirillum has been demonstrated to be beneficial in some cases for nitrogen fixation and plant nutrition (Bashan & Holguin, 1997). For cereal crops, diazotrophic rhizobacteria have increased plant growth, grain yield (Caballero-Mellado et al., 1992), nitrogen and phosphorus uptake, and nitrogen (Caballero-Mellado et al., 1992), phosphorus (Caballero-Mellado et al., 1992; Belimov et al., 1995) and potassium content (Caballero-Mellado et al., 1992). Rhizobacteria live in root nodes, and are associated with legumes. To improve phosphorus nutrition, the use of phosphate-solubilising bacteria (PSB) such as Agrobacterium radiobacter has also received attention (Belimov et al., 1995a; 1995b; Singh & Kapoor, 1999). As the name suggests, PSB are free-living bacteria that break down inorganic soil phosphates to simpler forms that enable uptake by plants. Several different fungal inoculants (typically referred to as mycorrhizae) have been explored for their benefits to plant nutrition. Fungal inoculation has been observed tobenefit plant success and improve soil quality. The most commonly investigated fungi for this purpose are the arbuscular mycorrhizae (AM or AMF). Ectomycorrhizae are often symbiotic with coniferous species. Other endophytic fungi, such as Piriformis indica can also be beneficial. Fungal inoculation alone can benefit hostplants. Inoculation paired with other amendments can further improveconditions. Arbuscular mycorrhizal inoculation combined with compost is acommon household amendment for personal gardens, agriculture, and nurseries. Ithas been observed that this pairing can also promote microbial functions insoils that have been affected by mining. Certain fungal partners do best in specificecotones or with certain crops. Arbuscular mycorrhizal inoculation paired with plantgrowth promoting bacteria resulted in a higher yield and quicker maturation inupland rice paddys.