The evolutionary and molecular features of the broad-host-range plant pathogen Sclerotinia sclerotiorum

Sclerotinia sclerotiorum is a pathogenic fungus that infects hundreds of plant species, including many of the world's most important crops. Key features of S. sclerotiorum include its extraordinary host range, preference for dicotyledonous plants, relatively slow evolution, and production of protein effectors that are active in multiple host species. Plant resistance to this pathogen is highly complex, typically involving numerous polymorphisms with infinitesimally small effects, which makes resistance breeding a major challenge. Due to its economic significance, S. sclerotiorum has been subjected to a large amount of molecular and evolutionary research. In this updated pathogen profile, we review the evolutionary and molecular features of S. sclerotiorum and discuss avenues for future research into this important species.     

The broad host range pathogen Sclerotinia sclerotiorum produces multiple effector proteins that induce host cell death intracellularly

Sclerotinia sclerotiorum is a broad host range necrotrophic fungal pathogen, which causes disease on many economically important crop species. S. sclerotiorum has been shown to secrete small effector proteins to kill host cells and acquire nutrients. We set out to discover novel necrosis-inducing effectors and characterize their activity using transient expression in Nicotiana benthamiana leaves. Five intracellular necrosis-inducing effectors were identified with differing host subcellular localization patterns, which were named intracellular necrosis-inducing effector 1–5 (SsINE1–5). We show for the first time a broad host range pathogen effector, SsINE1, that uses an RxLR-like motif to enter host cells. Furthermore, we provide preliminary evidence that SsINE5 induces necrosis via an NLR protein. All five of the identified effectors are highly conserved in globally sourced S. sclerotiorum isolates. Taken together, these results advance our understanding of the virulence mechanisms employed by S. sclerotiorum and reveal potential avenues for enhancing genetic resistance to this damaging fungal pathogen.     

Detection of Cymbidium mosaic virus in Protocorm-Like Bodies in Dendrobium Sonia using One-Step RT-PCR

Dendrobium orchids are clonally mass propagated by tissue culture techniques. However, Cymbidium mosaic virus is prevalent in vegetatively propagated Dendrobium spp. Therefore, a sensitive virus detection method is an important requirement for the production of CymMV-free orchid plants and control of virus spreading in the orchid industry. The presence of CymMV was screened in in vitro PLBs of Dendrobium Sonia using a one-step RT-PCR with specific primers to amplify a 858 bp fragment of a CymMV coat protein gene and flanking regions. Results were compared with those obtained from a conventional indirect ELISA. Only 22% samples showed the presence of CymMV in indirect-ELISA as compared to 78% in RT-PCR. Thus, the one-step RT-PCR appears to be a more sensitive method than indirect-ELISA for detecting CymMV in PLBs.