Search

Simple Summary: Cassava witches' broom disease (CWBD) is a major threat to cassava production, and it is believed to be caused by phytoplasma, an unculturable bacterial pathogen. However, recent findings suggest that other pathogens, such as viruses or fungi, may cause witches' broom disease in other crops. This study aims to investigate CWBD in the Philippines, specifically its status, and identify its potential pathogen(s). Currently, CWBD has spread nationwide and causes severe symptoms, such as leaf clustering and drying, as well as the browning of stems and roots. Polymerase chain reaction (PCR) and next-generation sequencing (NGS) showed consistent detection and a high abundance of Ceratobasidium sp., but an inconsistent and low detection rate of phytoplasma (Candidatus Phytoplasma luffae) in Philippine cassava samples. These findings challenge existing notions about CWBD and its causal agent. Confirming the causality and understanding Ceratobasidium sp. involvement can lead to better disease diagnosis and control strategies for ensuring food security. Cassava witches' broom disease (CWBD) is one of the most devastating diseases of cassava (Manihot esculenta Crantz), and it threatens global production of the crop. In 2017, a phytoplasma, Candidatus Phytoplasma luffae (Ca. P. luffae), was reported in the Philippines, and it has been considered as the causal agent, despite unknown etiology and transmission of CWBD. In this study, the nationwide occurrence of CWBD was assessed, and detection of CWBD's pathogen was attempted using polymerase chain reaction (PCR) and next-generation sequencing (NGS) techniques. The results showed that CWBD has spread and become severe, exhibiting symptoms such as small leaf proliferation, shortened internodes, and vascular necrosis. PCR analysis revealed a low phytoplasma detection rate, possibly due to low titer, uneven distribution, or absence in the CWBD-symptomatic cassava. In addition, NGS techniques confirm the PCR results, revealing the absence or extremely low phytoplasma read counts, but a surprisingly high abundance of fastidious and xylem-limited fungus, Ceratobasidium sp. in CWBD-symptomatic plants. These findings cast doubt over the involvement of phytoplasma in CWBD and instead highlight the potential association of Ceratobasidium sp., strongly supporting the recent findings in mainland Southeast Asia. Further investigations are needed to verify the etiology of CWBD and identify infection mechanisms of Ceratobasidium sp. to develop effective diagnostic and control methods for disease management. [ABSTRACT FROM AUTHOR]

Basal plant immune responses are activated by the recognition of conserved microbe‐associated molecular patterns (MAMPs), or breakdown molecules released from the plants after damage by pathogen penetration, so‐called damage‐associated molecular patterns (DAMPs). While chitin‐oligosaccharide (CHOS), a primary component of fungal cell walls, is most known as MAMP, plant cell wall‐derived oligosaccharides, cello‐oligosaccharides (COS) from cellulose, and xylo‐oligosaccharide (XOS) from hemicellulose are representative DAMPs. In this study, elicitor activities of COS prepared from cotton linters, XOS prepared from corn cobs, and chitin‐oligosaccharide (CHOS) from crustacean shells were comparatively investigated. In Arabidopsis, COS, XOS, or CHOS treatment triggered typical defense responses such as reactive oxygen species (ROS) production, phosphorylation of MAP kinases, callose deposition, and activation of the defense‐related transcription factor WRKY33 promoter. When COS, XOS, and CHOS were used at concentrations with similar activity in inducing ROS production and callose depositions, CHOS was particularly potent in activating the MAPK kinases and WRKY33 promoters. Among the COS and XOS with different degrees of polymerization, cellotriose and xylotetraose showed the highest activity for the activation of WRKY33 promoter. Gene ontology enrichment analysis of RNAseq data revealed that simultaneous treatment of COS, XOS, and CHOS (oligo‐mix) effectively activates plant disease resistance. In practice, treatment with the oligo‐mix enhanced the resistance of tomato to powdery mildew, but plant growth was not inhibited but rather tended to be promoted, providing evidence that treatment with the oligo‐mix has beneficial effects on improving disease resistance in plants, making them a promising class of compounds for practical application. [ABSTRACT FROM AUTHOR]

Plants recognize a variety of environmental molecules, thereby triggering appropriate responses to biotic or abiotic stresses. Substances containing microbes-associated molecular patterns (MAMPs) and damage-associated molecular patterns (DAMPs) are representative inducers of pathogen resistance and damage repair, thus treatment of healthy plants with such substances can pre-activate plant immunity and cell repair functions. In this study, the effects of DAMP/MAMP oligosaccharides mixture (Oligo-Mix) derived from plant cell wall (cello-oligosaccharide and xylo-oligosaccharide), and fungal cell wall (chitin-oligosaccharide) were examined in cucumber. Treatment of cucumber with Oligo-Mix promoted root germination and plant growth, along with increased chlorophyll contents in the leaves. Oligo-Mix treatment also induced typical defense responses such as MAP kinase activation and callose deposition in leaves. Pretreatment of Oligo-Mix enhanced disease resistance of cucumber leaves against pathogenic fungi Podosphaera xanthii (powdery mildew) and Colletotrichum orbiculare (anthracnose). Oligo-Mix treatment increased the induction of hypersensitive cell death around the infection site of pathogens, which inhibited further infection and the conidial formation of pathogens on the cucumber leaves. RNA-seq analysis revealed that Oligo-Mix treatment upregulated genes associated with plant structural reinforcement, responses to abiotic stresses and plant defense. These results suggested that Oligo-Mix has beneficial effects on growth and disease resistance in cucumber, making it a promising biostimulant for agricultural application.

Epichloë species are endophytic fungi that systemically colonize grass species. Here, we report the genome sequences of Epichloë bromicola strains HS and DP isolated for the first time from Elymus ciliaris in Nagoya, Japan., Competing Interests: The authors declare no conflict of interest.