Biosourcing Endophytes as Biocontrol Agents of Wilt Diseases
Endophytes are the centre of many investigations in the recent years, mainly for their role as biological control agents towards various pathogens. Of the many types of phytopathogens, wilt pathogens are thought to benefit the most from application of end
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Adeline Su Yien Ting
Abstract
Endophytes are the centre of many investigations in the recent years, mainly for their role as biological control agents towards various pathogens. Of the many types of phytopathogens, wilt pathogens are thought to benefit the most from application of endophytes. Wilt pathogens colonize internal plant tissues, especially the vascular tissues, which are also a common colonization niche for endophytes. The pre-colonization of biocontrol endophytes has been shown to render some form of protection to the host plant, resulting in disease suppression when challenged with the pathogen. Investigations to identify potential biocontrol agents are commonly initiated by performing extensive isolation and screening of endophytes from various asymptomatic host plants. This is followed by in vitro assays with selected pathogens, with various mechanisms of their antagonistic interaction established. Isolates with strong biocontrol activities are subsequently tested at the glasshouse and field stage to determine biocontrol efficacy. To date, tremendous progress has been made in understanding the diversity and mechanisms of control of endophytes against wilt pathogens. Their biocontrol efficacies are evident in laboratory screenings and glasshouse trials. In field trials however, poor control efficacy is often observed, attributed to the influence of indigenous microflora in the soil and environmental conditions. To address these limitations, bioformulation of endophytes is explored. This article will discuss the endophytes identified as biocontrol agents against wilt pathogens, the typical methods for biosourcing of these biocontrol endophytes, the challenges in implementing endophytes for wilt control and strategies to address these limitations.
A.S.Y. Ting (*) School of Science, Monash University Sunway Campus, Jalan Lagoon Selatan, 46150 Bandar Sunway, Darul Ehsan, Selangor, Malaysia e-mail: [email protected] V.C. Verma and A.C. Gange (eds.), Advances in Endophytic Research, DOI 10.1007/978-81-322-1575-2_15, © Springer India 2014
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Introduction
The term “endophyte” refers to microorganisms that exist and colonize tissues of its host plant (endon Greek for within; phyton for plant) without causing any visible symptoms (Petrini 1991; Wilson 1995; Stone et al. 2000). The asymptomatic nature of the association is crucial to define endophytes in recent times, as some pathogens (virulent and latent pathogens) and parasites are also endophytic (Freeman and Rodriguez 1993; Marler et al. 1999; Sturz and Nowak 2000; Sieber 2002; Sikora et al. 2008). In most studies, endophytes refer exclusively to fungi (Carroll 1988; Clay 1988) although they constitute of both bacterial and fungal origins. Endophytes have been found to infect cells inter- or intracellularly and can colonize cells locally or systematically (Stone et al. 2000). Figure 15.1 illustrates intracellular growth of endophytes in roots of wild banana. As a result of the different modes of infection and colonizat
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