Botrytis species: relentless necrotrophic thugs or endophytes gone rogue?

Abstract

Plant pathology has a long-standing tradition of classifying microbes as pathogens, endophytes or saprophytes. Lifestyles of pathogens are categorized as biotrophic, necrotrophic or hemibiotrophic. Botrytis species are considered by many to be archetypal examples of necrotrophic fungi, with B. cinerea being the most extensively studied species because of its broad host range and economic impact. In this review, we discuss recent work which illustrates that B. cinerea is capable of colonizing plants internally, presumably as an endophyte, without causing any disease or stress symptoms. The extent of the facultative endophytic behaviour of B. cinerea and its relevance in the ecology and disease epidemiology may be vastly underestimated. Moreover, we discuss the recent discovery of a novel Botrytis species, B. deweyae, which normally grows as an endophyte in ornamental daylilies (Hemerocallis), but displays facultative pathogenic behaviour, and is increasingly causing economic damage. We propose that the emergence of endophytes 'gone rogue' as novel diseases may be related to increased inbreeding of hybrid lines and reduced genetic diversity. These observations lead us to argue that the sometimes inflexible classification of pathogenic microbes by their lifestyles requires serious reconsideration. There is much more variety to the interactions of Botrytis with its hosts than the eye (or the plant pathologist) can see, and this may be true for other microbes interacting with plants.

Reduced susceptibility of tomato stem to the necrotrophic fungusBotrytis cinereais associated with a specific adjustment of fructose content in the host sugar pool

“…An intermediate lifestyle, hemibiotrophy, entails the succession of a biotrophic and a necrotrophic phase in the infection process. Although this classification might appear an oversimplification of virulence strategies of pathogenic fungi (Oliver and Solomon, 2010; Van Kan et al , 2014), it coincides with the prominent antagonism between hormonal signalling of salicylic acid (SA) and jasmonate (JA), which trigger systemic responses against biotrophic and necrotrophic fungi, respectively. Beside these two major pathways, the fine tuning of signalization in the plant’s immune system relies on a complex network involving most plant hormones, including abscissic acid (ABA), ethylene (ET) and gibberellic acid (GA), presumably to allocate resources for growth, reproduction and defence in a cost-efficient manner (Pieterse et al , 2012; Yang et al , 2012; Huot et al , 2014).…”

Characterization of Egyptian <i>Botrytis cinerea</i> Isolates from Different Host Plants

“…The composition of such medium consists of the following components (gL −1 distilled water): glucose, 20 g; NaNO 3 , 1 g; KH 2 PO 4 , 1.2 g; MgSO 4 •7H 2 O, 0.2 g; KCl, 0.15 g; agar, 25 g. This medium was autoclaved at 121˚C for 20 min. After cooling to 65˚C, the following ingredients were added: chloramphenicol, 0.05 g; tannic acid, 5 g; CuSO 4 , 2.2 g; Cabrio Top fungicide (Pyraclostrobin), 0.1 g. Different organs from strawberry (cv.…”

“…(teleomorph: Botryotinia fuckeliana (de Bary) Whetzel) is a necrotrophic fungus responsible for gray mold on hundreds of dicot plants [1] and a notorious pathogen of a variety of crops which are affected in temperate and subtropical regions, causing soft rotting of all aerial plant parts, and rotting of vegetables, fruits and flowers post-harvest worldwide [2]. B. cinerea has become an important model for molecular study of necrotrophic fungi [3] and is also capable of colonizing plants internally as an endophyte without causing any disease or stress symptoms [4]. Generally, one of the fungal genomic variability sources is the existence of transposable elements (TEs) [5] [6].…”

Spore Density Determines Infection Strategy by the Plant Pathogenic Fungus Plectosphaerella cucumerina

“…For instance, the fungal genus Botrytis is often labeled as an archetypal necrotroph, even though there is evidence that it can behave as an endophytic fungus with a biotrophic lifestyle (van Kan et al, 2014). The rice blast fungus Magnaporthe oryzae, which is often classified as a hemibiotrophic leaf pathogen (Perfect and Green, 2001;Koeck et al, 2011), can adopt a purely biotrophic lifestyle when infecting root tissues (Marcel et al, 2010).…”

“…The pathogenic fungi Magnaporthe grisea, Sclerotinia sclerotiorum, and Mycosphaerella graminicola, the oomycete Phytophthora infestans, and the bacterial pathogen Pseudomonas syringae are examples of hemibiotrophic plant pathogens (Perfect and Green, 2001;Koeck et al, 2011;van Kan et al, 2014;Kabbage et al, 2015).…”