Australasian Plant Pathology最新文献

Citrus orchards in the North-East regions (NER) of India have been experiencing significant declines in yield and production over the past few decades. Recent surveys conducted during 2020–2022 revealed symptoms of little leaf, leaf yellowing, interveinal chlorosis, fruit malformation, stunting and decline in 12 citrus varieties across seven NER states and Kalimpong (West Bengal), India. Phytoplasmas, ‘Candidatus Liberibacter asiaticus’/ Huanglongbing (HLB), and citrus tristeza virus (CTV) have been identified as the primary causal agents of citrus decline in the region. In the present study, a rapid and efficient duplex and multiplex PCR/RT-PCR diagnostic assays were developed and optimized for the simultaneous detection of ‘Candidatus Phytoplasma species’ (16SrI, II, V, and XIV), ‘Ca. Liberibacter asiaticus’, and CTV genotypes (VT, T68/B165, T3/K10, HA16-5/Kpg3, and B2) associated with citrus decline samples in the study. The optimized primers amplified the phytoplasma 16S rRNA gene fragments (~ 1.25 kb), the omp gene fragments of HLB (~ 809 bp), and/or the coat protein gene fragment of CTV (~ 672 bp) in simplex, duplex and multiplex PCR assays in all symptomatic citrus varieties. We validated the developed protocols using 38 citrus Declining isolates of 12 varieties, which revealed mixed infections either of phytoplasma + HLB (12/38), phytoplasma + CTV (2/38), CTV + HLB (7/38), and all the three pathogens (17/38). The duplex and multiplex PCR/RT-PCR assays developed in this study provided a rapid and sensitive tool for simultaneous detection of single, double, or mixed infections of these pathogens in citrus decline-affected orchards. This protocol would be helpful in the rapid indexing of old citrus orchards and newly established citrus nurseries across India, enabling the development of effective management strategies for the citrus decline malady.

Citrus production in Australia is a significant economic activity occurring in disparate regions. The crop is affected by a range of graft-transmissible pathogens including viroids, which are small, circular, non-coding RNA molecules. To ascertain the levels of infection with viroids in Australian citrus orchards, a survey was undertaken using samples collected between 2020 and 2024. To facilitate diagnosis, an RT-qPCR assay was designed and tested that detects all known citrus-infecting apscaviroids including citrus bent leaf viroid (CBLVd), citrus dwarfing viroid (CDVd), citrus viroid V (CVd-V), citrus viroid VI (CVd-VI), and citrus viroid VII (CVd-VII). Almost 700 samples from throughout the growing areas of Australia were tested using two assays, one newly developed citrus-infecting apscaviroid targeting assay and another targeting non-apscaviroids of citrus. Viroids were detected in ~ 20% of samples as individual or mixed infections. CDVd was the most prevalent viroid and was detected in 14% of samples - both citrus exocortis viroid (CEVd) and hop stunt viroid (HSVd) were found in ~ 5% of samples. citrus bark cracking viroid (CBCVd) was not detected and the remaining citrus-infecting apscaviroids, CBLVd, CVd-V, CVd-VI, CVd-VII, were each found at levels of less than 1%. This new multiplex RT-qPCR assay will allow the Auscitrus budwood scheme and similar schemes elsewhere in the world to more efficiently test propagation material to ensure high health status material is provided to citrus industries.

Yam (Dioscorea spp.) is used not only as food in the world but also as an important traditional medicinal herb in East Asia. However, its yield and quality are severely affected by leaf spot disease. Isolating and identifying the novel pathogens will be very helpful for controlling yam leaf spot disease. In 2023, leaf spot disease occurred in about 40% yam from germplasm resource nursery in Wen County (N34°94′68′′, E112°98′22′′), Jiaozuo City, Henan province, China. In the present study, morphological and molecular analysis methods were used to screen for novel pathogens from diseased leaves. Based on morphological characteristics, the isolates from diseased yam leaves mainly belonged into reported pathogenic fungi genera causing leaf spot. Notably, the HSD-JZ8 displayed Schizophyllum-like morphology features. The phylogenetic analysis of phylogenetic analyses of multi-loci (internal transcribed spacers (ITS) and nuclear ribosomal small subunit (SSU)) confirmed HSD-JZ8 as Schizophyllum commune. The pathogenicity of S. commune is confirmed by Koch’s postulates. To our knowledge, this is first report of wood-rot fungus S. commune as the pathogen causing leaf spot on yam worldwide, suggesting that herbs might be new hosts for S. commune in the world.

Black root rot of cotton is a serious production constraint for the cotton industry in Australia. It is caused by the ascomycete Berkeleyomyces rouxiae which is a broad host range pathogen. To date there has been minimal genomic surveying in this genus and herein we report two high quality genome assemblies for cotton-derived isolates.

The genus Hirschmanniella comprises economically important plant-parasitic nematodes associated with aquatic and semi-aquatic plants, especially rice. In this study, the occurrence and distribution of Hirschmanniella spp. across six northern provinces of Vietnam were studied. Three species: H. mucronata, H. oryzae, and one unidentified Hirschmanniella sp were recorded. Among them, H. mucronata was the most prevalent, detected in five provinces with a high frequency of occurrence (up to 83.3%) and considerable population densities (up to 159 ± 192 individuals/250 g soil), especially in Vinh Phuc. H. oryzae was mainly detected in Hai Phong, with moderate density and limited distribution. The unidentified Hirschmanniella sp. was restricted to Nam Dinh with low frequency and density. These findings highlight the dominance of H. mucronata in northern Vietnam’s rice ecosystems and suggest potential taxonomic diversity requiring further investigation. Additionally, an updated checklist of valid Hirschmanniella species was provided. To facilitate species identification, a user-friendly browser-based interactive key that integrates morphological characters for distinguishing Hirschmanniella species was also designed. This study provides essential baseline knowledge on rice-associated nematodes, supporting diagnostics, taxonomy, and future research aimed at sustainable management of nematode pests in rice production in Vietnam and beyond.

Chrysanthemum stunt viroid (CSVd) is reported for the first time in trailing verbena in nursery stock in New Zealand. RT-PCR with published Pospiviroid primers detected CSVd in four of seven vegetatively propagated samples from a commercial nursery but not in seed propagated plants from a national retail chain. The isolate had 99% identity with isolates from overseas. Plants were also infected with a number of viruses which may be masking CSVd’s effect on its host. This finding highlights verbena as a previously unrecognised potential reservoir of CSVd in the country’s nursery and horticulture industries.

A new leaf spot disease in Bauhinia purpurea tree was detected in Kerala Agricultural University Campus, Thrissur, Kerala state, India. The foliar pathogen was isolated on Potato Dextrose Agar (PDA) medium after surface sterilizing the leaf bits with 0.1% mercuric chloride. The inoculated plates were incubated at room temperature (25 °C). Koch’s postulates were fulfilled, and the pathogen was identified as Colletotrichum siamense based on morphological and cultural characteristics, along with multi-gene phylogenetic analysis. Ecological and pathological significance of emerging fungal pathogens within tree-pathogen systems deserve research focus.

Bacterial wilt disease in plants, historically attributed primarily to the strains of Ralstonia solanacearum species complex, is undergoing re-evaluation due to recent discoveries. While the strains of R. solanacearum species complex remain major pathogens, emerging evidence reveals a broader spectrum of bacterial pathogens from the Enterobacteriaceae family, including Enterobacter cloacae, Enterobacter mori, Klebsiella oxytoca, Kosakonia cowanii and Serratia marcescens, as well as Providencia vermicola from the Morganellaceae family, all implicated in causing comparable wilt symptoms in plant hosts traditionally associated with R. solanacearum species complex. Although much remains to be understood about their pathogenicity and infection mechanisms, recent advancements through whole-genome sequencing have provided limited but valuable insights into their potential virulence factors.

Phytochemicals from natural sources are increasingly recognized as promising substitutes for synthetic fungicides. The current study assessed the effectiveness of lemongrass extract (LGE) in managing stem-end rot diseases in mango fruit caused by the fungus Lasiodiplodia theobromae. The minimum inhibitory concentration (MIC) for LGE was determined to be 2.00 g/L, indicating its potential use as a preventative, as well as for simultaneous and curative measure for stem-end rot diseases in mango fruit. Moreover, results revealed that LGE at 2.0 g/L concentration outperformed synthetic fungicides (mancozeb 2.5 g/L) in both toxicity and effective volume concentration against L. theobromae. These findings underscore the potential of LGE as a possible substitute to conventional chemical fungicides in agricultural practices.

Twenty-nine chemical compounds were identified in LGE. The four major compounds were as follows: 2-monopalmitin (19.64%), α-citral (16.44%), α-monostearin (13.95%), and β -citral (12.00%).

Red rot compromises sugarcane production, causing severe yield losses. Symptomatic leaf samples were collected from a commercial plantation in Alagoas, Brazil. The isolated pathogen was identified by morphological, cultural, pathogenicity, and phylogeny studies, confirming the occurrence of F. tanahbumbuense causing red rot in sugarcane worldwide.