Genome‐wide association mapping for field spot blotch resistance in South Asian spring wheat genotypes

Posted on by

Abstract

Spot blotch caused by Bipolaris sorokiniana ((Sacc.) Shoemaker) (teleomorph: Cochliobolus sativus [Ito and Kuribayashi] Drechsler ex Dastur) is an economically important disease of warm and humid regions. The present study focused on identifying resistant genotypes and single-nucleotide polymorphism (SNP) markers associated with spot blotch resistance in a panel of 174 bread spring wheat lines using field screening and genome-wide association mapping strategies. Field experiments were conducted in Agua Fria, Mexico, during the 2019–2020 and 2020–2021 cropping seasons. A wide range of phenotypic variation was observed among genotypes tested during both years. Twenty SNP markers showed significant association with spot blotch resistance on 15 chromosomes, namely, 1A, 1B, 2A, 2B, 2D, 3A, 3B, 4B, 4D, 5A, 5B, 6A, 6B, 7A, and 7B. Of these, two consistently significant SNPs on 5A, TA003225-0566 and TA003225-1427, may represent a new resistance quantitative trait loci. Further, in the proximity of Tsn1 on 5B, AX-94435238 was the most stable and consistent in both years. The identified genomic regions could be deployed to develop spot blotch-resistant genotypes, particularly in the spot blotch-vulnerable wheat growing areas.

Assessment of genetic diversity of latent bacteria in coconut leaves associated with lethal yellowing disease symptoms in Kenya

Posted on by
Assessment of genetic diversity of latent bacteria in coconut leaves associated with lethal yellowing disease symptoms in Kenya

Coconut plants with yellowing disease are infected with bacterial species of economic importance. NGS analysis of samples found 285 OTUs with Actinobacteria as the predominant phylum and Streptomyces as the most abundant genus.


Abstract

Coconut (Cocos nucifera) is an economically important palm tree with diverse applications. However, limited scientific research exists on coconut diseases in the Kenyan coastal region. This cross-sectional study aimed to investigate the genetic diversity of latent bacteria associated with yellowing symptoms in coconut plants along the Kenyan coast. Sixty-two samples with symptoms were collected and their bacterial diversity assessed using culture-independent methods. DNA was extracted from controls and symptomatic samples using the cetyl trimethyl ammonium bromide (CTAB) method. Next-generation sequencing with Illumina MiSeq was used to profile the bacterial communities using amplicons of 16S ribosomal RNA sequences (V4 region). Sequence data were analysed using the Quantitative Insights Into Microbial Ecology 2 (QIIME 2) pipeline. A total of 113,330 reads were obtained, which clustered into 285 Operational Taxonomic Units. Bacterial diversity was highest in Kilifi, followed by Kwale and Lamu, while control samples exhibited low bacterial diversity. Actinobacteria was the predominant phylum across all counties, and Streptomyces was the most abundant genus. Kilifi and Kwale counties were more affected than Lamu. This is a pioneer study that provides insight into the bacterial diversity associated with yellowing disease symptoms in coconut plants in Kenya and will help with future elucidation of the agents causing or exacerbating coconut disease symptoms.

Physiological and hormonal responses of drought‐stressed Eucalyptus seedlings infected with Neofusicoccum kwambonambiense

Posted on by
Physiological and hormonal responses of drought-stressed Eucalyptus seedlings infected with Neofusicoccum kwambonambiense

Water stress increased Eucalyptus globulus predisposition to Neofusicoccum kwambonambiense infection and may also have promoted a change in the lifestyle of the fungus.


Abstract

The contribution of Eucalyptus globulus plantations to timber production for pulp, paper and energy production may be hampered by climate change. It is expected that Eucalyptus productivity may be affected through drought stress and changes to both pathogen distribution/pathogenicity and host–pathogen interactions. The impact of the fungal pathogen Neofusicoccum kwambonambiense on E. globulus, causing cankers and dieback, is well known but the impact of drought on disease development is still understudied. Our aim was to study the effect of drought on N. kwambonambiense infection by inoculating E. globulus plants under well-watered conditions or with water limitation. Non-infected plants for both water regimes were also analysed. Morphophysiological, biochemical and hormonal parameters were assessed 65 days post-inoculation. Inoculation under conditions of water stress decreased water potential and photosynthetic efficiency and increased abscisic acid, jasmonic acid and lipid peroxidation. Water-stressed infected plants also showed higher fungal colonization and external lesion length in comparison with well-watered inoculated plants. Our results indicate that drought increased E. globulus predisposition to N. kwambonambiense infection and may also have promoted a change in the lifestyle of the fungus. Identifying host–pathogen interaction responses under different stress conditions is necessary to provide knowledge for decision-making in the management of forest systems in general and of Eucalyptus production in particular.

Uncovering the hidden hosts: Identifying inoculum reservoirs for Phytophthora pseudosyringae in Nothofagus forests in Chile

Posted on by
Uncovering the hidden hosts: Identifying inoculum reservoirs for Phytophthora pseudosyringae in Nothofagus forests in Chile

First study in the Southern Hemisphere on Phytophthora pseudosyringae life cycle in Nothofagus forests and its first detection in Persea lingue leaves.


Abstract

Mortality of Nothofagus trees in native forests in Chile has been observed for more than 30 years. Phytophthora pseudosyringae was identified as the causal agent of partial defoliation and bleeding cankers on Nothofagus obliqua and N. alpina. Nevertheless, to improve the conservation of natural resources it is crucial to determine potential native hosts that may act as inoculum reservoirs. Two N. obliqua stands were visited and all native plant species with symptoms resembling those caused by Phytophthora spp. were examined. Seven isolates from cortical and foliar tissues were isolated and subsequentially identified as P. pseudosyringae. Pathogenicity tests were carried out on eight species from a native forest. P. pseudosyringae caused cankers in N. obliqua, N. dombeyi and Persea lingue. Under natural conditions, no symptoms were detected on leaves of Cryptocarya alba, N. dombeyi, N. obliqua or Peumus boldus, but lesions were formed in inoculation assays under a controlled environment, suggesting that these species may act as hosts. Leaf necrosis in P. lingue was observed in both natural and controlled conditions. P. pseudosyringae can sporulate on lesions of C. alba, N. dombeyi and N. obliqua leaves. In Sophora macrocarpa, sporulation was observed both on asymptomatic tissues and on lesions. The frequent association of S. macrocarpa in the understorey of Nothofagus spp. strengthens the putative role of S. macrocarpa as an inoculum reservoir for epidemic events in Nothofagus. This is the first study carried out in the Southern Hemisphere on the life cycle of P. pseudosyringae in native Nothofagus forests.

Levan differentially primes barley defence against infections by Fusarium graminearum, Rhizoctonia solani and Pyricularia oryzae

Posted on by
Levan differentially primes barley defence against infections by Fusarium graminearum, Rhizoctonia solani and Pyricularia oryzae

Levan could induce distinct pathways in response to different pathogens.


Abstract

The widespread use of pesticides poses significant challenges to the safety of agricultural products and the ecological environment. Levan-type fructans have the ability to act as an induced resistance stimulus, enhancing plant disease resistance, which aligns with the principles of green development. This study showed that levan polysaccharide, produced by Halomonas smyrnnensis levansucrase, could induce the resistance of barley to Fusarium graminearum much better than inulin-type fructans or low-molecular-weight chitosan oligosaccharide. Three different application methods of levan, namely seed soaking, leaf spraying or their combination, all decreased the necrotic areas caused by F. graminearum and Rhizoctonia solani. When inoculated with F. graminearum, the content of hydrogen peroxide, proline or jasmonic acid and the activities of peroxidase and ascorbate peroxidase in levan-treated barley were higher than those in the control. In contrast, when inoculated with R. solani, the hydrogen peroxide content and peroxidase activity in levan-treated leaves showed a faster induction than the control at the early priming and the content of proline and methyl salicylate was higher than that of the control. Thus, levan induces distinct pathways in response to different pathogens.

Phylogeny and taxonomy of five species associated with apricot canker in Beijing, China

Posted on by
Phylogeny and taxonomy of five species associated with apricot canker in Beijing, China

Morphology, phylogeny and pathogenicity analyses on Cytospora leucostoma, Phaeobotryon rhois and Diplodia gallae and two new species (C. huairouensis and C. prunina) from apricots in China identified the first two as pathogens.


Abstract

Apricot (Prunus armeniaca) is an economically important fruit tree in Beijing, China. However, canker diseases have become one of the main threats to apricot production. In the present study, a field survey was conducted in apricot orchards in Beijing and the disease incidence of apricots was surveyed (75.7%). Thirty fungal strains were isolated from branches of apricots. Five species were identified through multilocus phylogenetic (rDNA internal transcribed spacer [ITS], large subunit [LSU] and tef1-a for Botryosphaeriales; ITS, act, rpb2, tef1-a and tub2 for Cytospora) and morphological analyses, including two new species (Cytospora huairouensis and C. prunina) and three known species (C. leucostoma, Diplodia gallae and Phaeobotryon rhois). C. leucostoma and P. rhois were identified as the causal agents of canker of apricot by pathogenicity tests conducted on 3-year-old plants in the greenhouse. The current study contributed to a theoretical basis for predicting the potential risk of apricot canker in Beijing, China.

Wheat stripe mosaic virus from Brazil and South Africa evolved as distinct subpopulations with low genetic variability

Posted on by
Wheat stripe mosaic virus from Brazil and South Africa evolved as distinct subpopulations with low genetic variability

Phenotyping and sequencing reveal that wheat stripe mosaic virus (WhSMV) in Brazil is genetically homogeneous constituting a distinct subpopulation, more variable than the South African population.


Abstract

Wheat stripe mosaic virus (WhSMV) is the causal agent of soilborne wheat mosaic disease (SBWMD) in Brazil, which is a serious threat to wheat production in the southern part of the country. WhSMV also occurs in Paraguay and South Africa. The virus is soilborne, transmitted by Polymyxa graminis, and management strategies are mainly based on genetic resistance. Variation in the reaction (type and severity of symptoms) of cultivars has been reported depending on the region and/or year of cultivation, leading wheat breeding programmes to test their materials in several locations, which increases costs and is time-consuming. One hypothesis is that this variation in symptoms is a result of the genetic variability of WhSMV. We assessed the genetic variability and population structure of WhSMV infecting wheat in Brazil and South Africa. In field experiments conducted in different locations in southern Brazil, a consistent reproducibility of symptoms was observed in a set of cultivars, and molecular analysis showed a low degree of genetic variability of the Brazilian viral population. The hypothesis that the variation in SBWMD symptoms in Brazil is due to genetic variability of the virus was thus rejected. Comparison of the Brazilian and South African WhSMV isolates indicated that they comprise distinct subpopulations and that the Brazilian subpopulation is more variable than the South African subpopulation. The lower genetic variability of the South African subpopulation suggests genetic stability or a recent emergence of WhSMV in that region.