Australasian Plant Pathology最新文献

Gall rust disease caused by Uromycladium falcatarium is a major constraint to the productivity of Falcataria falcata, a fast-growing leguminous tree widely planted in tropical reforestation and agroforestry systems. Despite its ecological and economic importance, the landscape-level environmental and silvicultural drivers of gall rust incidence remain poorly understood. This study examined site-specific factors of disease incidence and severity in 125 plantations spanning five administrative regions and elevation ranges in Mindanao, Philippines. Results showed that both disease incidence and severity increased with elevation, particularly at elevations > 400 m above sea level (ASL), where infection levels frequently exceeded 75% of trees per plot. Stand density emerged as the most consistent structural predictor, with low-density stands (< 1000 trees/ha) having higher incidence and severity. Other contributing factors included insect species richness, high soil water holding capacity, and an interaction between elevation and slope aspect, wherein northeast-facing slopes had higher risk at low elevations. Disease severity was also associated by proximity to roads and an elevation-dependent effect of soil nitrogen. These findings suggest the multifactorial nature of gall rust outbreaks and the need for integrated, site-specific disease management strategies. Maintaining adequate stand density, improving drainage in waterlogged sites, and strategic site planning may reduce disease pressure. The study provides critical baseline information for sustainable F. falcata cultivation and forest health planning in tropical plantation landscapes.

Rice blast disease is present in most rice-growing regions of the world and parts of Australia, however it was not previously known to occur in New South Wales. In February 2024, leaf symptoms characteristic of rice blast were observed on rice in a commercial field near Lismore in northern NSW. The pathogen was isolated and identified based on morphological and molecular features. Isolates were used to inoculate seedlings, resulting in disease symptoms under controlled growth conditions, and the pathogen was re-isolated from leaf lesions. This is the first confirmed report of rice blast disease on cultivated rice in New South Wales.

During 2023 and 2024, surveys across plum orchards in Himachal Pradesh, India, revealed a high disease incidence of 80%, characterized by typical canker symptoms on branches and trunks frequently accompanied by gum exudation. Twenty-seven bacterial isolates were recovered from symptomatic tissues of the plum cultivar ‘Black Amber’, and four representative isolates (P5, P6, P7, and P8) were subjected to morphological, biochemical, and molecular characterization. The isolates were identified as Gram-positive, coccoid, catalase-positive, and urease-positive obligate aerobes. Pathogenicity was confirmed through both the detached twig method and in planta glasshouse inoculations. Of the tested isolates, only P5 consistently induced characteristic necrotic lesions, sunken cankers, and gum exudation 18 to 30 days post-inoculation, with symptoms eventually leading to shoot dieback. Koch’s postulates were satisfied through the successful re-isolation of isolate P5 from symptomatic tissues. Molecular characterization and phylogenetic analysis based on 16S rRNA, gyrB, and leuS gene sequencing (GenBank accessions PV162547.1, PV268675, and PV268676) confirmed the identity of the pathogen as Staphylococcus warneri. While this bacterium has been previously reported on Prunus species in Iran, this study represents the first report of S. warneri causing bacterial canker and gummosis of plum in India, identifying it as a significant emerging threat to the region's stone fruit production.

Gleditsia sinensis is an important economic tree species widely cultivated in China. In June 2019, stem canker symptoms were observed on G. sinensis trees in Zaozhuang City, Shandong Province. Combined with morphological characterization, phylogenetic analysis, and pathogenicity assays, the causal agent of the disease was identified as Aplosporella javeedii. This study represents the first report of A. javeedii infecting G. sinensis to induce stem canker.

Bhindi yellow vein mosaic virus (BYVMV) and okra enation leaf curl virus (OELCV) diseases cause substantial losses in okra production in the tropics. In developing a successful breeding strategy, okra geneticists must understand how BYVMV and OELCV disease resistance is inherited as well as recognise and utilize resistant genotypes. Six generations (P₁, P₂, F₁, F₂, BC₁, and BC₂) of two chosen crosses: Tolerant × Tolerant (T × T) and Tolerant × Susceptible (T × S) among two tolerant and a susceptible genotype for each disease were used to study the genetic control of host tolerance to BYVMV and OELCV diseases of okra. The inheritance study indicated that tolerance to BYVMV and OELCV disease was controlled by duplicate dominant genes in Tolerant × Tolerant (T × T) cross and duplicate recessive genes in Tolerant × Susceptible (T × S) cross. For both the disease reaction features, digenic epistasis was also found in the scaling and joint scaling tests. In addition, the study also indicated that Tolerant × Susceptible crosses for OELCV and BYVMV diseases produced offspring with tolerant genes for both the crosses. The results suggested selection in later generations (F₄ or F₅), or intermating among selected segregates, followed by one or two generations of selfing could break the undesirable linkage and allow accumulation of favourable alleles for improvement of these traits in okra.

Being the third-largest producer of the globe, Bangladesh's food and economic security is intrinsically linked to rice production. Diseases are a major threat to rice production worldwide, including Bangladesh. Rice blast and bacterial blight (BB) pose significant global threats to rice cultivation. We employed marker-assisted backcrossing to successfully introgress four resistance (R) genes, i.e., Pi9, Pb1, Xa4, and Xa21, into the genetic background of a susceptible rice cultivar BRRI dhan28 to increase its resistance. Pi9-US2 and Pb1-US2 were used as donors for Pi9 and Pb1 blast-resistant genes, respectively, while IRBB58 was the source for Xa4 and Xa21 BB-resistant genes. A rigorous breeding program involving successive backcrosses, self-pollination, and marker-assisted selection was implemented to generate F₁ to BC₃F₇ populations. Genotypic and phenotypic analyses of 400 BC₃F₂ populations demonstrated simple Mendelian inheritance patterns of blast and BB resistance. Among the 50 best selected fixed advanced BC₃F₇ lines, 37 exhibited resistances conferred by all four genes. The aAdvanced lines (ALs) exhibited a significantly low disease score (0–1) for rice blast and BB compared to the BRRI dhan28 (7–9). Marker-trait association analysis showed molecular markers negatively correlated with disease susceptibility. The multi-location trial demonstrated the broad-spectrum resistance of the selected ALs against blast and BB with improved yield and quality traits. Among the ALs, BR(Path)13784-BC3-63–6-4-HR6 or G35 gave the maximum average yield (6.74 t ha⁻¹) across the locations. The molecular markers used in this study can be a promising tool for candidate gene identification. Our advanced lines have the potential to be directly released as a commercial variety or used as a genetic stock in rice breeding programs to combine with other genes.

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.