Agriculture Reference
In-Depth Information
Antibiotic Synthesis
Production of antimicrobial compounds has been documented in several plant growth
promoting microorganisms (O'Sullivan & O'Gara 1992; Haansuu et al. , 1999) and this is the
mechanism most commonly associated with the ability of biofertilizers to inhibit
phytopathogens (Keel et al. , 1992; Chet & Inbar, 1994; Whipps, 1997). The ability of some
bacteria to suppress fungal pathogens depends on their ability to produce antibiotics such as
pioluteorina, pirronitrina, fenacin-1-carboxylic acid and 2,4-diacetylphloroglucinol (Picard, et
al. , 2000). Other compounds with pathogen-inhibiting capacities released by bacteria include
hydrogen cyanide (HCN) and/or lytic enzymes such as chitinase, -1,3 glucanase, proteases
and lipases (Friedlender et al., 1993; Chet & Inbar, 1994). Though pectinolytic activities are
commonly associated with pathogenic bacteria, some species of non-pathogenic bacteria such
as Rhizobium (Angle, 1986), Azospirillum (Umali-Garcia et al. , 1980; Tien et al., 1981),
Klebsiella pneumoniae , Yersinia (Chatterjee et al. , 1978) and Frankia (Séguin & Lalonde,
1989) are also capable of degrading pectins. In general terms, pectinolytic enzymes play a
role in the invasion of the roots by bacteria.
Induction of Systemic Resistance
Research on the benefits of microbial inoculants extends beyond their capacities to
improve plant nutrition, since microbial inoculants can also trigger the mechanism of
systemic acquired resistance (SAR) of plants to different phytopathogenic agents such as
Blumeria graminis, Gaeumannomyces graminis, Fusarium culmorum and Pseudomonas
syringae (Heitefuss, 2001; Waller et al. , 2005; Khaosaad et al. , 2007; Ramos-Solano et al. ,
2008). In plants, the SAR is a global resistance response that occurs after plants have contact
with a pathogen or a product derived from it. In a broad sense, the systemic acquired
resistance in plants is equivalent to the response of the immune system of animals to the
attack by pathogens. After an early and localized exposure to certain infectious organisms,
SAR actives the resistance mechanisms at the whole plant level against a wide variety of
pathogens, (including to that initiating the response), so it is considered as a wide-spectrum
response. It has been shown that endophytic colonization of cocoa seedlings by Trichoderma
activates the plant defense signaling cascades (Bailey et al. , 2006). SAR is associated with the
induction of a great variety of genes (genes PR's or pathogenesis related) and requires the
accumulation of endogenous salicylic acid.
SAR is associated with the ability to induce cellular defense responses more rapidly and
to a greater degree than in non-induced plants, a process called "priming." The phenylalanine
ammonia lyase (PAL) gene activation and callose deposition are among the main cellular
defense responses induced by SAR.
Plant growth-promoting rhizobacteria can effectively induce pathogen resistance by
triggering the expression of the hypersensitive response (HR) of plants, enhance lignification
and callose deposition, increase hydrogen peroxide production and expression of the defense
enzymes β-1,3-glucanase,
chitinase,
phenylalanine
ammonia
lyase,
peroxidase
and
polyphenol oxidase (Niranjan-Raj et al., 2006).
Search WWH ::




Custom Search