A Microsatellite Analysis Used to Identify Global Pathways of Movement of Phytophthora cinnamomi and the Likely Sources of Wildland Infestations in California and Mexico.

The genetic structure of a sample of isolates of the oomycete plant pathogen Phytophthora cinnamomi from natural and agricultural outbreaks and the long-distance movement of individual genotypes were studied using four microsatellite markers to genotype 159 isolates of Californian, Mexican, and worldwide origins. Allelic profiles identified 75 multilocus genotypes. A STRUCTURE analysis placed them in three groups characterized by different geographic and host ranges, different genic and genotypic diversity, and different reproductive modes. When relationships among genotypes were visualized on a minimum spanning network (MSN), genotypes belonging to the same STRUCTURE group were contiguous, with rare exceptions. A putatively ancestral group 1 had high genic diversity, included all A1 mating type isolates and all Papuan isolates in the sample, was rarely isolated from natural settings in California and Mexico, and was positioned at the center of the MSN. Putatively younger groups 2 and 3 had lower genic diversity, were both neighbors to group 1 but formed two distinct peripherical sectors of the MSN, and were equally present in agricultural commodities and natural settings in Mexico and California. A few genotypes, especially in groups 2 and 3, were isolated multiple times in different locations and settings. The presence of identical genotypes from the same hosts in different continents indicated that long-distance human-mediated movement of P. cinnamomi had occurred. The presence of identical genotypes at high frequencies in neighboring wildlands and agricultural settings suggest that specific commodities may have been the source of recent wild infestations caused by novel invasive genotypes.

Host-induced aneuploidy and phenotypic diversification in the Sudden Oak Death pathogen Phytophthora ramorum.

BACKGROUND: Aneuploidy can result in significant phenotypic changes, which can sometimes be selectively advantageous. For example, aneuploidy confers resistance to antifungal drugs in human pathogenic fungi. Aneuploidy has also been observed in invasive fungal and oomycete plant pathogens in the field. Environments conducive to the generation of aneuploids, the underlying genetic mechanisms, and the contribution of aneuploidy to invasiveness are underexplored. We studied phenotypic diversification and associated genome changes in Phytophthora ramorum, a highly destructive oomycete pathogen with a wide host-range that causes Sudden Oak Death in western North America and Sudden Larch Death in the UK. Introduced populations of the pathogen are exclusively clonal. In California, oak (Quercus spp.) isolates obtained from trunk cankers frequently exhibit host-dependent, atypical phenotypes called non-wild type (nwt), apparently without any host-associated population differentiation. Based on a large survey of genotypes from different hosts, we previously hypothesized that the environment in oak cankers may be responsible for the observed phenotypic diversification in P. ramorum. RESULTS: We show that both normal wild type (wt) and nwt phenotypes were obtained when wt P. ramorum isolates from the foliar host California bay (Umbellularia californica) were re-isolated from cankers of artificially-inoculated canyon live oak (Q. chrysolepis). We also found comparable nwt phenotypes in P. ramorum isolates from a bark canker of Lawson cypress (Chamaecyparis lawsoniana) in the UK; previously nwt was not known to occur in this pathogen population. High-throughput sequencing-based analyses identified major genomic alterations including partial aneuploidy and copy-neutral loss of heterozygosity predominantly in nwt isolates. Chromosomal breakpoints were located at or near transposons. CONCLUSION: This work demonstrates that major genome alterations of a pathogen can be induced by its host species. This is an undocumented type of plant-microbe interaction, and its contribution to pathogen evolution is yet to be investigated, but one of the potential collateral effects of nwt phenotypes may be host survival.

An exploratory study of the nutritional composition of Tanoak (Lithocarpus densiflorus) acorns after potassium phosphonate treatment.

Native American Pomo communities who live in the Northern Coastal range of California and consume acorns from tanoak trees as part of traditional diets are facing the potential loss of many culturally important trees to sudden oak death. Pomo and other Native American communities are reluctant to use the protective fungicide, potassium phosphonate, on trees used for acorn collection without information on how the treatment affects acorn properties. In this study, select macronutrients and polyphenolics were quantified in tanoak acorns to evaluate the influence of potassium phosphonate treatment on the composition and nutritional value of tanoak acorns. Of the fatty acids tested from C14:0 to C20:1, only C17:0 was significantly lower (p < 0.05) in the nontreated and treated acorns after the first year. There were no differences detected in total phenolic content, gallic acid content, or ellagic acid content. Protein, phosphorus, and potassium levels were not significantly affected by fungicide treatment. Soluble glucose and fructose levels were significantly higher (p < 0.05) in both nontreated and treated groups after the first year; soluble sucrose levels did not change. Total glucose, starch, and total nonstructural carbohydrates increased significantly (p < 0.05) in the nontreated group after the first year but not in the treatment group; however, the treatment group values did not differ significantly from the control group values at baseline. The lack of any negative significant differences between acorns from treated and untreated tanoak trees implies that sodium phosphonate application for the prevention of sudden oak death does not impact the predominant polyphenolics or macronutrient quality of tanoak acorns.

Understanding the native Californian diet: Identification of condensed and hydrolyzable tannins in tanoak acorns (Lithocarpus densiflorus).

The tanoak (Lithocarpus densiflorus) acorn was a staple food in the Native American diet and is still used in traditional dishes. Acorns from the genus Quercus have been shown to contain a large range of hydrolyzable tannins. However, neither hydrolyzable nor condensed tannins have been characterized in tanoak acorns. The aim of this study was to identify the full range of hydrolyzable and condensed tannins in extracts of tanoak acorns using liquid chromatography/electrospray ionization-mass spectrometry/mass spectrometry. Condensed tannins were identified as B type oligomers of (epi)-catechin (procyanidins) with a degree of polymerization up to six. Oligomers up to and including tetramers were identified by UV spectra and MS detection whereas pentamers and hexamers were detected only by MS. The total concentration of condensed tannins was 464 mg/100 g acorn pericarp. The concentration of propocyanidin monomers, dimers, trimers, and tetramers in acorn pericarp (mg/100 g acorn pericarp) were 95 +/- 10.9, 148 +/- 35.0, 90 +/- 17.9, and 131 +/- 1.9, respectively. No procyanidins were found in the acorn cotyledon tissue. A total of 22 hydrolyzable tannins were identified in methanolic extracts of acorn cotyledon tissue. Gallic acid derivatives predominated and included galloylated esters of glucose, hexahydrodiphenoyl esters of glucose, and methylated gallates. Galloylated esters of glucose were present as isomers of galloyl glucose, digalloyl glucose, and trigalloyl glucose. Mass spectral fragmentation patterns indicate the presence of one gallic acid-galloyl glucose isomer and two gallic acid-digalloyl-glucose isomers. No isomers of tetragalloyl glucose and pentagalloyl glucose were identified. Ellagic acid and ellagic acid pentoside were also identified.