Analysis of Cryptic, Systemic Botrytis Infections in Symptomless Hosts

Abstract

Botrytis species are generally considered to be aggressive, necrotrophic plant pathogens. By contrast to this general perception, however, Botrytis species could frequently be isolated from the interior of multiple tissues in apparently healthy hosts of many species. Infection frequencies reached 50% of samples or more, but were commonly less, and cryptic infections were rare or absent in some plant species. Prevalence varied substantially from year to year and from tissue to tissue, but some host species routinely had high prevalence. The same genotype was found to occur throughout a host, representing mycelial spread. Botrytis cinerea and Botrytis pseudocinerea are the species that most commonly occur as cryptic infections, but phylogenetically distant isolates of Botrytis were also detected, one of which does not correspond to previously described species. Sporulation and visible damage occurred only when infected tissues were stressed, or became mature or senescent. There was no evidence of cryptic infection having a deleterious effect on growth of the host, and prevalence was probably greater in plants grown in high light conditions. Isolates from cryptic infections were often capable of causing disease (to varying extents) when spore suspensions were inoculated onto their own host as well as on distinct host species, arguing against co-adaptation between cryptic isolates and their hosts. These data collectively suggest that several Botrytis species, including the most notorious pathogenic species, exist frequently in cryptic form to an extent that has thus far largely been neglected, and do not need to cause disease on healthy hosts in order to complete their life-cycles.

Identification and characterization of Botrytis medusae, a novel cryptic species causing grey mould on wine grapes in Australia

“…Recently, several Botrytis species were shown to exhibit endophytic stages in their lifecycles in a range of flowering plants (Barnes & Shaw, ; Sowley et al ., ; Grant‐Downton et al ., ; Shaw et al ., ). Shaw et al .…”

“…Shaw et al . () found B. cinerea , B. pseudocinerea , B. mali isolates and an undescribed Botrytis sp. existing as cryptic infections in dandelion.…”

Differences in the gene transcription state of Botrytis cinerea between necrotic and symptomless infections of lettuce and Arabidopsis thaliana

“…In general, B. cinerea is considered to be a necrotroph, which draws nourishment from dead host tissue and produces initially local (‘primary’) necrotic lesions, which subsequently expand to actively cause plant tissue decomposition (Horst, ; Jarvis, ; Coertze & Holz, ; Elad et al ., ). In contrast, recent studies have revealed that B. cinerea can also cause symptomless systemic infection in several host plants including Primula spp., lettuce ( Lactuca sativa ), Arabidopsis thaliana and Taraxacum vulgare (Barnes & Shaw, ; Rajaguru & Shaw, ; Sowley et al ., ; Shaw et al ., ). In this type of infection the fungus grows along with the plant and enters newly expanding organs, without producing symptoms, until the plant becomes physiologically susceptible, typically at flowering.…”

RNA ‘Information Warfare’ in Pathogenic and Mutualistic Interactions

“…The latter can lead to secondary siRNA biogenesis through RNA-dependent RNA polymerase (RDR) activity to form double-stranded RNA (dsRNA), which is then sophisticated RNA-based manipulation was surprising as B. cinerea depends on inducing cell death for a successful necrotrophic lifestyle [45], hence such downregulation of host defence transcripts might seem superfluous. However, B. cinerea and other species in the genus can evade cell death induction and host defences, and grow as asymptomatic endophytes [46,47]. It is tempting to speculate that in such interactions, B. cinerea sRNAs might suppress host cell death responses, while plant sRNAs in turn might suppress fungal virulence mechanisms, thereby modulating the pathogenic (necrotic) interaction into an (asymptomatic) symbiosis.…”