Some Like It Hot: Differential Photosynthetic Performance and Recovery of English Walnut Accessions Under Emerging California Heat Waves.

Heat waves (HWs) pose a significant threat to California agriculture, with potential adverse effects on crop photosynthetic capacity, quality and yield, all of which contribute to significant economic loss. Lack of heat-resilient cultivars puts perennial crop production under severe threat due to increasing HW frequency, duration and intensity. Currently, available walnut cultivars are highly sensitive to abiotic stress, and germplasm collections provide potential solutions via genotypes native to varied climates.

Transcriptomic Evidence of a Link between Cell Wall Biogenesis, Pathogenesis, and Vigor in Walnut Root and Trunk Diseases.

Crown gall disease (), crown/root rot disease ( spp.), root lesion disease () and tree vigor are key traits affecting the productivity and quality of walnuts in California. Unchallenged hybrid rootstocks were analyzed by RNA-seq to examine pre-formed factors affecting these traits.

Structural and functional leaf diversity lead to variability in photosynthetic capacity across a range of Juglans regia genotypes.

Similar to other cropping systems, few walnut cultivars are used as scion in commercial production. Germplasm collections can be used to diversify cultivar options and hold potential for improving crop productivity, disease resistance and stress tolerance. In this study, we explored the anatomical and biochemical bases of photosynthetic capacity and response to water stress in 11 Juglans regia accessions in the U.

Desiccation of the leaf mesophyll and its implications for CO diffusion and light processing.

Leaves balance CO and radiative absorption while maintaining water transport to maximise photosynthesis. Related species with contrasting leaf anatomy can provide insights into inherent and stress-induced links between structure and function for commonly measured leaf traits for important crops. We used two walnut species with contrasting mesophyll anatomy to evaluate these integrated exchange processes under non-stressed and drought conditions using a combination of light microscopy, X-ray microCT, gas exchange, hydraulic conductance, and chlorophyll distribution profiles through leaves.

Predicting Stomatal Closure and Turgor Loss in Woody Plants Using Predawn and Midday Water Potential.

Knowledge about physiological stress thresholds provides crucial information about plant performance and survival under drought. In this study, we report on the triphasic nature of the relationship between plant water potential (Ψ) at predawn and midday and describe a method that predicts Ψ at stomatal closure and turgor loss exclusively from this water potential curve (WP curve). The method is based on a piecewise linear regression model that was developed to predict the boundaries (termed Θ and Θ) separating the three phases of the curve and corresponding slope values.

Temporal Responses of Microbial Communities to Anaerobic Soil Disinfestation.

Anaerobic soil disinfestation (ASD) is an organic amendment-based management tool for controlling soil-borne plant diseases and is increasingly used in a variety of crops. ASD results in a marked decrease in soil redox potential and other physicochemical changes, and a turnover in the composition of the soil microbiome. Mechanisms of ASD-mediated pathogen control are not fully understood, but appear to depend on the carbon source used to initiate the process and involve a combination of biological (i.

Complete Genome Sequences of Brenneria rubrifaciens Strain 6D370 and Brenneria nigrifluens Strain ATCC 13028, Causative Agents of Bark Cankers in Walnut.

and , respectively, cause deep and shallow bark canker disease in walnut. exhibits quorum sensing-controlled virulence and rubrifacine pigment production. The complete genome sequences of these species will be useful for studying the role of genes regulated by quorum sensing, including pathways mediating pathogenesis.

Sequencing a × hybrid yields high-quality genome assemblies of parental species.

Members of the genus are monecious wind-pollinated trees in the family Juglandaceae with highly heterozygous genomes, which greatly complicates genome sequence assembly. The genomes of interspecific hybrids are usually comprised of haploid genomes of parental species. We exploited this attribute of interspecific hybrids to avoid heterozygosity and sequenced an interspecific hybrid  ×  using a novel combination of single-molecule sequencing and optical genome mapping technologies.

Variations in xylem embolism susceptibility under drought between intact saplings of three walnut species.

A germplasm collection containing varied Juglans genotypes holds potential to improve drought resistance of plant materials for commercial production. We used X-ray computed microtomography to evaluate stem xylem embolism susceptibility/repair in relation to vessel anatomical features (size, arrangement, connectivity and pit characteristics) in 2-year-old saplings of three Juglans species. In vivo analysis revealed interspecific variations in embolism susceptibility among Juglans microcarpa, J.

Genomic Variation Among and Within Six Species.

Genomic analysis in (walnuts) is expected to transform the breeding and agricultural production of both nuts and lumber. To that end, we report here the determination of reference sequences for six additional relatives of : (also from section ), , , (from section ), (from section ), and the closely related While these are 'draft' genomes, ranging in size between 640Mbp and 990Mbp, their contiguities and accuracies can support powerful annotations of genomic variation that are often the foundation of new avenues of research and breeding. We annotated nucleotide divergence and synteny by creating complete pairwise alignments of each reference genome to the remaining six.

Draft Genome Sequence of Biovar 1 Strain 186, Isolated from Walnut.

biovar 1 strain 186 was isolated from a walnut tree expressing crown gall symptoms. The draft genome sequence of this strain harbored genes for crown gall formation and will be useful for understanding its virulence on Paradox, the predominant hybrid rootstock used for the cultivation of English walnut in California.

Patterns of drought-induced embolism formation and spread in living walnut saplings visualized using X-ray microtomography.

Embolism formation and spread are dependent on conduit structure and xylem network connectivity. Detailed spatial analysis has been limited due to a lack of non-destructive methods to visualize these processes in living plants. We used synchrotron X-ray computed tomography (microCT) to visualize these processes in vivo for Juglans microcarpa Berl.

Comparative genomics of plant-associated Pseudomonas spp.: insights into diversity and inheritance of traits involved in multitrophic interactions.

We provide here a comparative genome analysis of ten strains within the Pseudomonas fluorescens group including seven new genomic sequences. These strains exhibit a diverse spectrum of traits involved in biological control and other multitrophic interactions with plants, microbes, and insects. Multilocus sequence analysis placed the strains in three sub-clades, which was reinforced by high levels of synteny, size of core genomes, and relatedness of orthologous genes between strains within a sub-clade.

AHL signals induce rubrifacine production in a bruI mutant of Brenneria rubrifaciens.

Several members of the bacterial genus Brenneria are pathogenic on different tree species. Cell-free extracts from the bacterial phytopathogens Brenneria rubrifaciens, B. salicis, and B.

The role of tyloses in crown hydraulic failure of mature walnut trees afflicted by apoplexy disorder.

In the Central Valley of California, mature walnut trees afflicted with apoplexy disorder exhibit rapid and complete crown defoliation within a few weeks of symptom initiation. Symptoms are typically found throughout the entire crown and are initially expressed as wilting and chlorosis followed by scorching of leaves. Since the cause of apoplexy disorder is unknown, we set out to elucidate the water relations physiology underlying this condition.

Genetic loci involved in rubrifacine production in the walnut pathogen Brenneria rubrifaciens.

Brenneria rubrifaciens produces a unique red pigment known as rubrifacine that has been hypothesized to play a role in pathogenesis on walnut. Analysis of DNA flanking the Tn5 insertion site in 20 rubrifacine minus (pig(-)) mutants identified three regions required for rubrifacine production. The first region was homologous to nonribosomal peptide synthetases (NRPS), the second was homologous to autoinducer synthase genes (expI homologs), and the third region was homologous to the slyA gene of Candidatus blochmania and Escherichia coli.

Relationship between avirulence gene (avrA) diversity in Ralstonia solanacearum and bacterial wilt incidence.

Bacterial wilt, caused by Ralstonia solanacearum, is a serious disease of tobacco in North and South Carolina. In contrast, the disease rarely occurs on tobacco in Georgia and Florida, although bacterial wilt is a common problem on tomato. We investigated whether this difference in disease incidence could be explained by qualitative characteristics of avirulence gene avrA in the R.