A high‐throughput analysis of high‐resolution X‐ray CT images of stems of olive and citrus plants resistant and susceptible to Xylella fastidiosa

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A high-throughput analysis of high-resolution X-ray CT images of stems of olive and citrus plants resistant and susceptible to Xylella fastidiosa

Though morphological traits of resistant olives (narrow vessels) and citrus' (connected vessels) are distinct, across both taxa, susceptible cultivars have many more vessels; representing a potentially broader-reaching trend.


Abstract

The bacterial plant pathogen Xylella fastidiosa causes disease in several globally important crops. However, some cultivars harbour reduced bacterial loads and express few symptoms. Evidence considering plant species in isolation suggests xylem structure influences cultivar susceptibility to X. fastidiosa. We test this theory more broadly by analysing high-resolution synchrotron X-ray computed tomography of healthy and infected plant vasculature from two taxonomic groups containing susceptible and resistant varieties: two citrus cultivars (sweet orange cv. Pera, tangor cv. Murcott) and two olive cultivars (Koroneiki, Leccino). Results found the susceptible plants had more vessels than resistant ones, which could promote within-host pathogen spread. However, features associated with resistance were not shared by citrus and olive. While xylem vessels in resistant citrus stems had comparable diameters to those in susceptible plants, resistant olives had narrower vessels that could limit biofilm spread. And while differences among olive cultivars were not detected, results suggest greater vascular connectivity in resistant compared to susceptible citrus plants. We hypothesize that this provides alternate flow paths for sustaining hydraulic functionality under infection. In summary, this work elucidates different physiological resistance mechanisms between two taxonomic groups, while supporting the existence of an intertaxonomical metric that could speed up the identification of candidate-resistant plants.

Phenotype and genotype characterization of Botrytis cinerea isolates from cut roses in Yunnan, China

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Phenotype and genotype characterization of Botrytis cinerea isolates from cut roses in Yunnan, China

One hundred Botrytis cinerea strains from cut roses were classified into phylogenetic Group II based on polymorphisms in Bc-hch; four subpopulations showed significant variation in morphology, pathogenicity and fungicide resistance.


Abstract

Botrytis cinerea is considered to be the second most destructive fungal pathogen worldwide, causing severe pre- and postharvest losses in cut roses. However, to date, no systematic research on its characteristics in cut roses has been reported. In our study, a total of 100 isolates from cut roses from Yunnan, China, were analysed. A combination of morphological characteristics and phylogenetic analysis of RPB2 revealed that 100 isolates were of the species B. cinerea. These isolates were pathogenic on unwounded detached rose petals. Pathogenicity was evaluated according to the size of petal spots and categorized into grades 0–5, from weak to strong. The inhibition rate varied greatly following the addition of procymidone (21.9%–100%) and cyprodinil (25.0%–92.3%). Analysis of Bc-hch sequences revealed all isolates belong to phylogenetic Group II. According to the presence or absence of transposable elements, 87, 5, 4 and 4 isolates were identified as transposa, vacuma, Boty-only and Flipper-only types, respectively. Detection of mating type indicated that all isolates were heterothallic with 45% belonging to MAT1-1 and 55% to MAT1-2. Isolates were divided into four subpopulations when analysing single-nucleotide polymorphisms at the genomic level, with a significant difference in pathogenicity between subpopulations 1 and 4. The evolutionary tree indicated that isolates AN-02, AN-22 and SM-C18 were clustered in the root, suggesting an earlier evolutionary time than other isolates; moreover, they all exhibited low pathogenicity (grade 1). This systematic study of the characteristics of B. cinerea will provide significant support for grey mould control and further research.

Rice resistance against Bipolaris oryzae infection is mediated by lower foliar potassium concentration

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Rice resistance against Bipolaris oryzae infection is mediated by lower foliar potassium concentration

Lower foliar potassium concentration reduced brown spot symptoms and was linked to stronger biochemical defence reactions, a robust antioxidative system and less damage to photosynthesis.


Abstract

Brown spot, caused by Bipolaris oryzae, is a very important disease of rice. This study investigated the effect of potassium (K) on rice resistance to brown spot. The working hypothesis tested was that higher foliar K concentration could allow plants to respond more efficiently against fungal infection. Plants were grown in nutrient solution amended with three K rates (0.5, 1.0 and 2.5 mM) and noninoculated or inoculated with B. oryzae. The photosynthetic performance of plants, activities of defence and antioxidant enzymes and the concentrations of reactive oxygen species, phenolics and lignin were determined. Foliar K concentration was significantly higher by 38% and 91% for plants supplied with 1.0 and 2.5 mM K, respectively, compared to plants supplied with 0.5 mM K. Brown spot severity was significantly higher (≥20%) for plants supplied with 1.0 and 2.5 mM K than those supplied with 0.5 mM K (≤15%). Higher brown spot severity for plants supplied with 2.5 mM K resulted in changes in the photosynthetic apparatus, reduced chlorophyll a + b and carotenoids concentrations, and higher production of hydrogen peroxide and superoxide anion radical. In contrast, higher activities of defence and antioxidant enzymes and more production of phenolics for plants supplied with 0.5 mM K helped them to cope with B. oryzae infection more efficiently. In conclusion, rice resistance against brown spot was achieved by keeping a lower foliar K concentration linked to more active defence reactions, a robust antioxidative system and less damage to the photosynthetic apparatus.

Ceratocystis fimbriata alters root system architecture and causes symptom development only in detached storage roots in Bayou Belle and Beauregard sweet potato

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Ceratocystis fimbriata alters root system architecture and causes symptom development only in detached storage roots in Bayou Belle and Beauregard sweet potato

Ceratocystis fimbriata affected root system architecture of sweet potato even though it did not cause symptoms and was not isolated from roots until swollen storage roots were detached from the plant.


Abstract

Little is known about how the sweet potato (Ipomoea batatas) root system responds to Ceratocystis fimbriata in the growth substrate. Understanding whether the fungus affects the root system before harvest of storage roots (SR) could guide timing of management efforts. Cuttings of cultivars Bayou Belle and Beauregard, both previously considered susceptible to black rot, were in unamended or infested sand. At the onset of SR formation, effects on first- and second-order lateral root (LR) length and number among and within treatments, cultivars and replicate experiments were recorded. First-order LR length in inoculated Bayou Belle plants was 31% greater than in inoculated plants of cultivar Beauregard in Expt 1, but there were no differences in Expt 2. Second-order LR length varied among, and within, cultivars, inoculum treatments and experiments in Expts 1 and 2. At 49 days after planting in Expt 1, only inoculated plants had necrotic lesions on stems in both cultivars, with more than twice as many recorded on Bayou Belle than Beauregard. SR had no lesions at harvest. Detached SR originating from inoculated treatments and stored in sampling bags for 25 days developed black rot lesions at either end of the SR (45% and 31% of total in Expt 1 and Expt 2, respectively) or elsewhere, including those centred on LR emergence sites or lenticels (55% and 69%, respectively). Exposing developing plants to inoculation may reveal differences in SR susceptibility not found when harvested SR are wounded and inoculated.

Plant spectral diversity from high‐resolution multispectral imagery detects functional diversity patterns in coastal dune communities

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Plant spectral diversity from high-resolution multispectral imagery detects functional diversity patterns in coastal dune communities

In this study, we estimated spectral and functional diversity in a common framework encompassing all their multivariate components. Our findings indicate that spectral diversity accurately captures the functional structure of plant communities and approximates species patterns in the functional space. Furthermore, we showed the efficient approximation of functional diversity patterns by spectral diversity across spatial scales and along ecological gradients.


Abstract

Question

Remote sensing is a fundamental tool to monitor biodiversity and spectral diversity may represent a proxy for different biodiversity facets such as taxonomic (TD) and functional diversity (FD). We used fine-resolution multispectral imagery to explore spectral diversity (SD) patterns across spatial scales (i.e., plot, transect, area), and assess SD relationships with TD and FD along an environmental gradient.

Location

Coastal sand dune, Viareggio, Italy (“Migliarino–San Rossore–Massaciuccoli” Regional Park, 43°83′ N, 10°25′ E).

Methods

We measured TD as species richness, while SD and FD were computed using probability density functions based on pixel and species position in multivariate spaces. We compared SD and FD patterns in space occupation, and we tested whether these patterns are coordinated along the sea–inland gradient. We also assessed univariate relationships between SD and biodiversity facets, and we tested how these facets were partitioned across scales.

Results

We found a strong correspondence between functional and spectral patterns in space occupation and along the environmental gradient, with a lack of significance when considering TD. However, TD and SD showed higher variation at broader scale while most FD variation occurred at plot level.

Conclusion

By measuring FD and SD with a common methodological framework, we demonstrate that SD approximates functional patterns in plant communities. Moreover, we show that SD retrieved using high-resolution images can capture different aspects of FD, and that the occupation of the spectral space is analogous to the occupation of the functional space.

Effects of dispersal and geomorphology on riparian seed banks and vegetation in a boreal stream

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Effects of dispersal and geomorphology on riparian seed banks and vegetation in a boreal stream

We studied the effects of hydrology and geomorphology for seed dispersal and environmental filtering on riparian vegetation. Riparian seed bank and vegetation contained different species, but we found no clear effect of hydrochory. Geomorphologically different sections (lakes, slow-flowing and rapid sections) were more similar to each other than expected, and differences in trait composition of seed bank and vegetation were mostly based on seed longevity.


Abstract

Question

Riparian vegetation and seed banks are the foundation of functional riparian zones, yet insight in the processes that explain their composition is limited. We tested three theories fundamental to dispersal and environmental filtering of riparian seed banks and vegetation. Combining these theories, we expected hydrochory to lead to increased species richness downstream in both soil seed bank and vegetation with accumulation restarting after a lake section, and geomorphological filtering to lead to higher similarity of seed bank and vegetation composition locally and within lakes, slow-flowing sections and rapids, respectively, than between them.

Location

Svartån, a free-flowing river in central Sweden.

Methods

We surveyed riparian vegetation and conducted a germination experiment on riparian soil seed bank cores from lakes, slow-flowing sections and rapids. We combined these with trait data on seed dispersal syndromes, floating capacity of seeds and seed longevity. We analysed differences throughout the system with linear models and between process domains with Kruskal–Wallis tests and similarity in community composition with the Horn–Morisita similarity index.

Results

Our results indicated that species richness did not increase downstream and was relatively similar throughout lakes, slow-flowing sections and rapids for both riparian seed banks and vegetation. Seed floating capacity was similar throughout these river sections, too, and seed longevity was higher in seed banks than in vegetation.

Conclusions

Geomorphology and hydrochory were not as important drivers in this area for riparian seed bank and vegetation composition as expected. In the area and on the scale studied here, other local and regional environmental factors and dispersal syndromes are more likely to be determinants of riparian dynamics and composition. Continued studies of riparian seed banks can help improve our understanding of riparian composition and functioning in the future.

A chromosome‐level genome of mango exclusively from long‐read sequence data

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Abstract

Improvements in long-read sequencing techniques have greatly accelerated plant genome sequencing. Current de novo assemblies are routinely achieved by assembling long-read sequence data into contigs that are assembled to chromosome level by chromatin conformation capture. We report here a chromosome-level mango genome using only PacBio high-fidelity (HiFi) long reads. HiFi reads at high coverage (204x) resulted in the assembly of 17 chromosomes, each as a single contig with telomeres at both ends. The remaining three chromosomes were represented each by two contigs, with telomeres at one end and ribosomal repeats at the other end. Analyzing contig ends allowed them to be paired and linked to generate the remaining three complete chromosomes, telomere-to-telomere but with ribosomal repeats of uncertain length. The assembled genome was 365 Mb with 100% completeness as assessed by Benchmarking Universal Single-Copy Orthologs analysis. The haplotypes assembled demonstrated extensive structural differences. This approach using very high genome coverage may be useful for assembling high-quality genomes for many other plants.