Use of Plant Growth-Promoting Bacteria for Biocontrol of Plant Diseases: Principles, Mechanisms of Action, and Future Prospects

Abstract

3Pathogenic microorganisms affecting plant health are a major and chronic threat to food production and ecosystem stability worldwide. As agricultural production intensified over the past few decades, producers became more and more dependent on agrochemicals as a relatively reliable method of crop protection helping with economic stability of their operations. However, increasing use of chemical inputs causes several negative effects, i.e., development of pathogen resistance to the applied agents and their nontarget environmental impacts (44, 62). Furthermore, the growing cost of pesticides, particularly in less-affluent regions of the world, and consumer demand for pesticide-free food has led to a search for substitutes for these products. There are also a number of fastidious diseases for which chemical solutions are few, ineffective, or nonexistent (62). Biological control is thus being considered as an alternative or a supplemental way of reducing the use of chemicals in agriculture (44,62,136,188).There has been a large body of literature describing potential uses of plant associated bacteria as agents stimulating plant growth and managing soil and plant health (reviewed in references 63, 70, 143, 165, and 188). Plant growth-promoting bacteria (PGPB) (8) are associated with many, if not all, plant species and are commonly present in many environments. The most widely studied group of PGPB are plant growth-promoting rhizobacteria (PGPR) (82) colonizing the root surfaces and the closely adhering soil interface, the rhizosphere (82, 84). As reviewed by Kloepper et al. (84) or, more recently, by Gray and Smith (65), some of these PGPR can also enter root interior and establish endophytic populations. Many of them are able to transcend the endodermis barrier, crossing from the root cortex to the vascular system, and subsequently thrive as endophytes in stem, leaves, tubers, and other organs (10, 28,65,70). The extent of endophytic colonization of host plant organs and tissues reflects the ability of bacteria to selectively adapt to these specific ecological niches (65, 70). Consequently, intimate associations between bacteria and host plants can be formed (28, 70, 84) without harming the plant (70,83,84,92,191). Although, it is generally assumed that many bacterial endophyte communities are the product of a colonizing process initiated in the root zone (102, 165, 177, 188), they may also originate from other source than the rhizosphere, such as the phyllosphere, the anthosphere, or the spermosphere (70).Despite their different ecological niches, free-living rhizobacteria and endophytic bacteria use some of the same mechanisms to promote plant growth and control phytopathogens (15, 46,63,70,92,165). The widely recognized mechanisms of biocontrol mediated by PGPB are competition for an ecological niche or a substrate, production of inhibitory allelochemicals, and induction of systemic resistance (ISR) in host plants to a broad spectrum of pathogens (15,63,66,67,97,146) and/or abiotic stresses (reviewed in referen...

Assessment of Rice Associated Bacterial Ability to Enhance Rice Seed Germination and Rice Growth Promotion

“…In Iran, most rice farms are in the Northern provinces including Guilan and Mazandaran. Due to the growing demand for rice, one of the increasing concern about rice production in the world especially in Iran is the extra use of chemical fertilizers, which have negative effects on human health and environment 9 . So, there is an urgent need to use the substitutes without or with less harmful side effects.…”

New advances in plant growth-promoting rhizobacteria for bioremediation

“…PGPR can be divided into two groups according to their relationship with the plants: symbiotic bacteria and free-living rhizobacteria (Khan, 2005). As reviewed by Compant et al (2005), Glick (1995Glick ( , 2001, Hall (2002), Hallman et al (1997), Lucy et al (2004), Sturz et al (2000), and Welbaum et al (2004), a lot of work have been done on the mechanisms and principles of the PGPR-plant relationship, which was accepted widely as rhizosphere effect. Generally, PGPR function in three different ways (Glick, 1995(Glick, , 2001): synthesizing particular compounds for the plants, facilitating the uptake of certain nutrients from the environment (Çakmakçi et al, 2006;Lucas García et al, 2004a,b;Siddiqui and Mahmood, 2001), and lessening or preventing the plants from diseases (Guo et al, 2004;Jetiyanon and Kloepper, 2002;Raj et al, 2003;Saravanakumar et al, in press).…”

Plant responses to plant growth-promoting rhizobacteria

“…However, in reality they were the result of disease suppression. Many bacteria in soil have similar properties (Compant et al 2005;Haas and Défago 2005), but in a number of cases rhizobacteria can enhance plant growth in the absence of potentially pathogenic microorganisms, as has been shown in e.g. gnotobiotic systems .…”