Category Archives: ORIGINAL ARTICLE

Halo‐hydromorphism alters nitrogen fertilization responses of tall wheatgrass pastures: Capture and use of resources, tiller dynamics and forage production

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Abstract

Halo-hydromorphism limits productivity in approximately 100 million hectares worldwide. Tall wheatgrass (Thinopyrum ponticum) is a species widely used in these environments for its seeding potential, being the addition of nitrogen a considered technological tool to increase forage quality and production. The objective of the study was to determine the impact of nitrogen fertilization on the capture and use of resources (radiation, water and nitrogen) in a cool season perennial sward growing in contrasting halo-hydromorphic conditions. Cultivated pastures from three independent sites were used. Sites were described according to the degree of halo-hydromorphism using soil salinity and water table attributes (salinity and depth) as environmental indicators: low HHM site [electrical conductivity (EC1:2.5) 0.97 dS/m; water table salinity 2.03 dS/m; depth 85 cm], intermediate HHM site (EC1:2.5 3.86 dS/m; water table salinity 7.40 dS/m; depth 134 cm) and high HHM site (EC1:2.5 4.49 dS/m; water table salinity 7.85 dS/m; depth 31 cm). At each site, a late spring regrowth (~750°Cd) was studied by applying two treatments (n = 5): without (N0) and nitrogen fertilization (N150; 150 kg/ha of nitrogen in the form of urea). The response of tall wheatgrass to nitrogen fertilization in halo-hydromorphic conditions depends on soil salinity and water table attributes. N150 treatments production was twice as high as in N0 in low HHM and intermediate HHM environments (from 1750 to 3500 kgDM/ha and from 1080 to 1985 kgDM/ha, respectively). Meanwhile, in high HHM conditions, forage production was only 40% higher when nitrogen was added (from 625 to 870 kgDM/ha). In low HHM the higher N150 production was related to tiller density and size, whereas in intermediate HHM and high HHM was linked only to tiller size. In N150 treatments, the nitrogen nutrition index was negatively affected with the increase in HHM conditions (0.77, 0.62 and 0.55 for low HHM, intermediate HHM and high HHM, respectively). Instead, nitrogen nutrition index of N0 was similar in all the environments (~0.42). In N150, forage production capacity analysed in terms of radiation and water use efficiency (RUE and WUE, respectively) was similar in low HHM and intermediate HHM environments (RUE ~0.81 gDM/Mj and WUE ~13 kgDM/mm). These findings emphasize the importance of conducting analyses based on resource use and capture to understand productive responses to the increase in growth-limiting factors. Furthermore, they contribute to the identification of environments suitable for nitrogen fertilization.

Morphology, phylogeny and pathogenicity of fungal species associated with leaf blight and stem canker of Theobroma cacao in Malaysia

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Morphology, phylogeny and pathogenicity of fungal species associated with leaf blight and stem canker of Theobroma cacao in Malaysia

Leaf blight of Theobroma cacao in Malaysia was found to be caused by Diaporthe tulliensis and Neopestalotiopsis clavispora while stem canker was caused by D. tulliensis, Fusarium proliferatum and Fusarium solani.


Abstract

Malaysia stands prominently among Asia's key cocoa-producing countries. In the cocoa season of 2022–2023, Malaysia demonstrated its contribution to the industry, with an estimated production of around 364,000 tonnes of cacao bean grindings. Nonetheless, fungal diseases pose undeniable challenges to the cocoa sector. Extensive sampling conducted between September 2018 and March 2019 across multiple states in Malaysia revealed concerning symptoms of leaf blight and stem canker affecting Theobroma cacao plants. The aim of this study was to identify and characterize fungal species associated with leaf blight and stem canker of T. cacao in Malaysia through morphological, molecular and pathogenicity analyses. Morphological and molecular phylogenetic analyses using multiple DNA regions (rDNA internal transcribed spacer [ITS], TEF1 and TUB2) were performed and identified 40 fungal isolates found in this study as Diaporthe tulliensis (17 isolates), Fusarium solani (seven isolates), Fusarium proliferatum (six isolates) and Neopestalotiopsis clavispora (10 isolates). Pathogenicity tests with mycelial plugs and wound treatments showed that D. tulliensis and N. clavispora were responsible for causing leaf blight whereas D. tulliensis, F. solani and F. proliferatum caused stem canker of T. cacao. The present study provides insights into disease aetiology and symptomatology that may be useful in planning effective disease management for the host plant.

The pathogenic diversity and host range of Colletotrichum spp. causing pepper spot and anthracnose of lychee (Litchi chinensis) in Australia

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The pathogenic diversity and host range of Colletotrichum spp. causing pepper spot and anthracnose of lychee (Litchi chinensis) in Australia

Pathogenicity on lychee and population genomics show that taxa in the gloeosporioides species complex are predominantly clonal, and symptoms and host range are linked to genotype.


Abstract

Lychee pepper spot, a field disease affecting lychee fruit skin, pedicels and petioles, is caused by Colletotrichum siamense, a fungal pathogen within the gloeosporioides species complex. Members of Colletotrichum from the gloeosporioides species complex and occasionally those from the acutatum species complex also cause postharvest anthracnose of lychee. Pepper spot was first described in Australia many years after anthracnose on lychee was first described, giving rise to the hypothesis that a novel species or strain within the gloeosporioides species complex causes pepper spot. In the present study, 19 isolates of Colletotrichum spp., collected from pepper spot and anthracnose symptoms on lychee fruit, representing 13 different genotypes across five species, were inoculated onto lychee fruit in the field or on detached fruit in the laboratory, to understand more about their pathogenic diversity. We found that symptoms were specific to genotype of the pathogen, as three genetically similar isolates of C. siamense consistently caused pepper spot and anthracnose, whilst other isolates caused anthracnose only. Cross-inoculation studies on detached fruit of lychee, banana, avocado and mango also provided some evidence of host specialization in isolates of C. siamense infecting lychee in Australia. Our experiments provided further evidence that detached fruit assays cannot be used as a reliable proxy for field inoculation studies. This research confirms that C. siamense is a causal agent of both lychee pepper spot and lychee anthracnose in Australia, and Colletotrichum alienum and Colletotrichum queenslandicum are reported as causal agents of anthracnose of lychee for the first time.

Genome‐wide mapping in an international isolate collection identifies a transcontinental erg11/CYP51 promoter insertion associated with fungicide resistance in Leptosphaeria maculans

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Genome-wide mapping in an international isolate collection identifies a transcontinental erg11/CYP51 promoter insertion associated with fungicide resistance in Leptosphaeria maculans

Insertion of a remnant transposable element in the promoter region of the erg11/CYP51 demethylase inhibitor (DMI) target gene confers resistance to DMI fungicides worldwide.


Abstract

Fungicide resistance is often conferred through the mutation of genes encoding fungicide targets or proteins that remove fungicides from cells, but mechanisms can vary widely between taxa. Discovering the specific resistance alleles present in pathogen populations is essential for monitoring the evolution and movement of resistant genotypes. In this study, we explored the genomic basis of demethylase inhibitor (DMI) resistance in Leptosphaeria maculans, the main pathogen of the canola crop Brassica napus. Using an international collection of over 200 genome-sequenced isolates, we assayed in vitro sensitivity to the DMI tebuconazole and conducted a genome-wide association study on a variant set including single-nucleotide polymorphisms (SNPs), small indels and structural variants. The main resistance allele identified was a 237 bp remnant transposable element insertion in the promoter of the erg11/CYP51 DMI target gene in a large proportion of isolates from Europe, an allele known to confer DMI resistance in Australia. Several associated loci were identified, none of which are commonly linked to DMI resistance in other phytopathogens. We also found little to no relationship between DMI tolerance and baseline growth rate, suggesting minimal fitness effects of fungicide resistance in these isolates. This study indicates common DMI resistance alleles in L. maculans are shared across continents and erg11/CYP51 coding mutations, which are near-ubiquitous in other fungal pathogens, may not underpin DMI resistance in this species. Furthermore, that resistance occurs frequently in numerous canola-growing regions suggests management is essential for growers.

Applying unoccupied aerial systems to assess genetic gain from mass selection for tembotrione tolerance in sorghum (Sorghum bicolor)

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Abstract

The post-emergent herbicide options to control grasses in sorghum have historically been limited. Therefore, a mass selection program was implemented to increase the tolerance of sorghum to the broad-spectrum herbicide tembotrione. The objectives of this study are to determine (i) which observation timing and vegetative indices are most effective in assessing sorghum injury to tembotrione using unoccupied aerial system imagery and (ii) if mass selection can be used to increase the tolerance of sorghum to tembotrione. Using an unoccupied aerial system, several vegetative indices, collected at either 14 or 21 days after tembotrione application, accurately measured sorghum injury. Over four cycles of selection, tembotrione tolerance increased in a linear and consistent manner. This demonstrates that mass selection can be used as a strategy for developing herbicide tolerance in crops. The modest, but steady genetic gain indicates both the quantitative nature of the trait and sufficient heritability to improve it. Given further development, tembotrione-resistant sorghum hybrids could provide an effective means of post-emergent weed control for a range of common weeds.

Evolution of decreased sensitivity to azole fungicides in western European populations of Plenodomus lingam (Phoma stem canker on oilseed rape)

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Evolution of decreased sensitivity to azole fungicides in western European populations of Plenodomus lingam (Phoma stem canker on oilseed rape)

Plenodomus lingam (Phoma leaf spot/stem canker) populations in western Europe (Germany, Ireland and the United Kingdom) predominantly contain CYP51 promoter inserts leading to deceased azole (DMI) fungicide sensitivity.


Abstract

Plenodomus lingam (Leptosphaeria maculans) and P. biglobosus (L. biglobosa) are fungi causing Phoma leaf spot/stem canker, an international damaging disease of oilseed rape (Brassica napus) and other brassicas. In Europe, fungicides used for disease management are mainly sterol 14α-demethylase (CYP51) inhibitors (DMIs/azoles); quinone-outside inhibitors (QoIs) and succinate dehydrogenase inhibitors (SDHIs) are also used. Decreased DMI sensitivity has emerged in Australian and eastern European P. lingam populations and is mediated by CYP51 promoter inserts resulting in target site overexpression. In this study using in vitro sensitivity testing, we report decreased DMI (prothioconazole-desthio, mefentrifluconazole) sensitivity in modern western European P. lingam isolates (collected 2022–2023) compared to older baseline (1992–2005) isolates. Around 85% of modern western European P. lingam isolates collected, for which the CYP51 promoter region was sequenced, carried a promoter insert, but target site alterations were not detected. Six different CYP51 promoter inserts were identified, most commonly a 237 bp fragment of the Sahana transposable element. Inserts were associated with an approximately 3- to 10-fold decrease in sensitivity to the DMIs tested. In contrast to P. lingam, PCR screening revealed CYP51 promoter inserts were absent in modern western European P. biglobosus isolates (2021–2023). Combined data indicate P. lingam isolates lacking an insert were similarly (or slightly more) sensitive to the DMIs tested for P. biglobosus, whereas those carrying an insert were slightly less sensitive than P. biglobosus. No evidence for substantive sensitivity shifts to the QoI (pyraclostrobin) or SDHI (boscalid) fungicides tested was obtained for either Plenodomus species.

Botryosphaeria dothidea causes stem canker of Idesia polycarpa in China

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Botryosphaeria dothidea causes stem canker of Idesia polycarpa in China

This is the first report of Botryosphaeria dothidea as the pathogen of stem canker of Idesia polycarpa based on morphological and molecular characterization and pathogenicity identification.


Abstract

Idesia polycarpa is a woody oil plant with great development and application prospects. However, stem canker disease of I. polycarpa was frequently observed in Henan and Hubei provinces of China in 2020–2022. The seriousness of the disease caused a large number of trees deaths, which affected seedling production and fruit yield, restricting the development of the I. polycarpa industry. We performed isolation, purification and pathogenicity analysis of canker samples. Pathogenicity tests reproduced typical canker disease symptoms on detached branches of I. polycarpa. Based on morphological observations, conidial morphology and phylogenetic analysis of isolates with high similarity to the rDNA internal transcribed spacer (ITS), EF-1α and TUB2 sequences screened in GenBank by BLAST, the pathogen of canker disease on I. polycarpa was identified as Botryosphaeria dothidea. This is the first report of B. dothidea as the pathogen of stem canker of I. polycarpa.

Identification of candidate RXLR effectors from downy mildew of foxtail millet pathogen Sclerospora graminicola and functional analysis of SG_RXLR41

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Identification of candidate RXLR effectors from downy mildew of foxtail millet pathogen Sclerospora graminicola and functional analysis of SG_RXLR41

Sixty-two RXLR effectors were identified from Sclerospora graminicola. The screening revealed that SG_RXLR41 suppresses INF1-induced cell death and promotes Phytophthora capsici infection by inhibiting host immune responses.


Abstract

Downy mildew caused by Sclerospora graminicola is a systemic disease that affects the yield and quality of foxtail millet. This obligate biotrophic oomycete manipulates host physiology and immune processes through numerous effectors. A thorough comprehension of effector biology is crucial to unravel disease mechanisms and understand host plant resistance. In this study, bioinformatic analyses revealed 498 potentially secreted proteins in S. graminicola, of which 62 were identified as RXLR effectors; 46 RXLR-encoding genes exhibited upregulated expression during the early stages of infection. To elucidate the functions of these secreted proteins, a heterogeneous expression system was developed using Nicotiana benthamiana. Twenty-one RXLR effectors secreted by S. graminicola were transiently expressed in N. benthamiana, of which four could suppress INF1-triggered cell death. Various defence responses in N. benthamiana were attenuated, including inhibition of defence gene expression, reduction of reactive oxygen species (ROS) accumulation and diminished callose deposition. The expression of SG_RXLR41 also enhanced the growth of Phytophthora capsici on N. benthamiana leaves. These findings indicate that S. graminicola facilitates infection and expansion through the secretion of multiple RXLR effectors, and SG_RXLR41 is an important virulence-related effector that is involved in manipulating plant immunity by suppressing cell death.

Identifying quantitative trait locus and candidate genes for maize (Zea mays L.) plant architecture traits based on segregating populations constructed by high‐generation sister lines

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Abstract

Leaf length, width and angle are important traits in the architecture of maize plants. Delving into the genetic mechanisms of these traits is of utmost significance for promoting population yield. In this study, we employed the high-generation sister lines PCU and PCM, which have significant differences in leaf morphological traits, as parental entities for the creation of F2 and F2:3 populations. Through quantitative trait locus (QTL) mapping of the traits in the three ear leaves by ICIM, 55 QTL were obtained, with six stable QTL selected across divergent populations. These QTL had physical spans ranging from 0.34 to 44.8 Mbp. Through gene annotation and qRT-PCR, Zm00001d007382, Zm00001d035965, Zm00001d042777 and Zm00001d020641 were predicted as potential candidates for regulating maize plant architecture. The results of this study lay a foundation for analysing the genetic mechanisms of maize plant architecture traits and cloning-related genes.

Estimating the frequency of virulence against an Stb gene in Zymoseptoria tritici populations by bulk phenotyping on checkerboard microcanopies of wheat near‐isogenic lines

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Estimating the frequency of virulence against an Stb gene in Zymoseptoria tritici populations by bulk phenotyping on checkerboard microcanopies of wheat near-isogenic lines

The BCP method leverages the relationship between the ratio of Zymoseptoria tritici lesions on wheat near-isogenic lines differing by one resistance gene (Stb16q) and the frequency of virulent strains in the inoculated population.


Abstract

Monitoring virulent strains within pathogen populations is crucial to improve host resistance deployment strategies. Such monitoring increasingly involves field pathogenomics studies of molecular polymorphisms in pathogen genomes based on high-throughput screening technologies. However, it is not always straightforward to predict virulence phenotypes from these polymorphisms, and in planta phenotyping remains necessary. We developed a method for ‘bulk phenotyping on checkerboard microcanopies of wheat near-isogenic lines’ (BPC) for estimating the frequency of virulence against a resistance gene in mixed populations of the fungal pathogen Zymoseptoria tritici, the causal agent of Septoria tritici blotch (STB) in wheat, without the need for strain-by-strain pathogen phenotyping. Our method involves the uniform inoculation of a microcanopy of two wheat lines—one with the target resistance gene and the other without it—with a multistrain mixture of isolates representative of the population to be characterized, followed by the differential quantification of infection points (lesions). Using Stb16q, a wheat resistance gene that has recently broken down in Europe, we found a robust correlation between the ratio of the mean number of lesions on each wheat line and the frequency of virulent strains in the inoculum. Using pairs of virulent and avirulent strains, as well as synthetic populations consisting of 10 virulent strains and 10 avirulent strains mixed in different proportions, we validated the principle of the method and established standard curves at virulence frequencies close to those observed in natural conditions. We discuss the potential of this method for virulence monitoring in combination with molecular methods.