Pests and Genetics Research Unit

Parlier, CA, United States

Pests and Genetics Research Unit

Parlier, CA, United States
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Shi X.,University of California at Riverside | Shi X.,Pests and Genetics Research Unit | Bi J.,University of California Cooperative Extension | Morse J.G.,University of California at Riverside | And 2 more authors.
European Journal of Plant Pathology | Year: 2013

Xylella fastidiosa causes Pierce's disease (PD), a serious disease in grapevines, and grapevine cultivars vary in susceptibility to X. fastidiosa in the field. The mechanism(s) by which this occurs has not been clearly elucidated. To explore possible mechanisms, X. fastidiosa cells from a PD strain were grown in pure xylem fluid of PD-susceptible grapevines, Vitis vinifera and V. labrusca, versus PD-resistant grapevines, V. champinii and V. smalliana. When grown in xylem fluid from the susceptible species, X. fastidiosa cells formed a heavier biofilm compared to those in xylem fluid from the resistant species. Differential expression of selected genes of X. fastidiosa cultured in the xylem fluids of V. vinifera and V. smalliana was analyzed using a DNA macroarray. Compared with xylem fluid of V. smalliana, xylem fluid of V. vinifera stimulated the expression of X. fastidiosa genes involved in virulence regulation, such as rpfC, gacA, xrvA, gcvR, and cysB, and genes involved in biogenesis of pili and twitching motility, such as pilI, pilU, pilE and pilG. Increased expression of virulence genes likely contributes to the expression of PD symptom in the susceptible grapevines, whereas reduced expression of these genes may lead to limitation of symptoms in resistant grapevines. © 2012 KNPV.

Ma W.,South China Agricultural University | Liang M.,South China Agricultural University | Guan L.,South China Agricultural University | Xu M.,South China Agricultural University | And 3 more authors.
Phytopathology | Year: 2014

Huanglongbing (HLB) is a highly detrimental citrus disease associated with 'Candidatus Liberibacter asiaticus', a nonculturable alpha-proteobacterium. Characterization of the bacterial populations is important for development of disease management strategies. In this study, the 'Ca. L. asiaticus' populations in eight provinces in southern China where HLB is endemic were analyzed based on tandem repeat number (TRN) variations in a previously characterized genomic locus CLIBASIA-01645. Of the 224 HLB samples collected, 175 (78.3%) samples yielded single polymerase chain reaction (PCR) amplicons (the single amplicon group, SAG) and 49 (21.7%) samples produced multiple PCR amplicons (the multiple amplicon group, MAG). Variations in SAG are summarized by Nei's diversity index (H) and ratio of TRN ≤ 10/TRN > 10 genotypes (R10). Variations in the MAG are described by the percentage of occurrence (PMAG). At an orchard-level comparison, the 'Ca. L. asiaticus' population from a Guangdong orchard (n = 24) showed H = 0.50, R10 = 23, and PMAG = 0, significantly different from that of the non-Guangdong orchards in Yunnan (n = 23), H = 0.83, R10 = 2.3, and PMAG = 11.5, and in Hainan (n = 35), H = 0.88, R10 = 1.5, and PMAG = 16.7. In a region-level consideration, the Guangdong 'Ca. L. asiaticus' population (n = 78) was H = 0.77, R10 = 25, and PMAG = 1.3, whereas the non-Guangdong population (n = 84) was H = 0.91, R10 = 1.6, and P MAG = 26.9. Overall, significant differences were observed between the 'Ca. L. asiaticus' population from Guangdong Province and those from the other provinces. A strong aggregation of TRN = 6, 7, and 8 genotypes is characteristic to the 'Ca. L. asiaticus' population in Guangdong. Referenced to genome annotation, we propose that rearrangement of tandem repeats at locus CLIBASIA-01645 could be associated with bacterial environmental adaptation.

Lin H.,Pests and Genetics Research Unit | Gudmestad N.C.,North Dakota State University
Phytopathology | Year: 2013

An overview is provided for the aspects of history, biology, genomics, genetics, and epidemiology of zebra chip (ZC), a destructive disease of potato (Solanum tuberosum) that represents a major threat to the potato industries in the United States as well as other potato-production regions in the world. The disease is associated with a gram-negative, phloem-limited, insect-vectored, unculturable prokaryote, 'Candidatus Liberibacter solanacearum', that belongs to the Rhizobiaceae family of α-Proteobacteria. The closest cultivated relatives of 'Ca. L. solanacearum' are members of the group of bacteria known as the α-2 subgroup. In spite of the fact that Koch's postulates sensu stricto have not been fulfilled, a great deal of progress has been made in understanding the ZC disease complex since discovery of the disease. Nevertheless, more research is needed to better understand vector biology, disease mechanisms, host response, and epidemiology in the context of vector-pathogen-plant interactions. Current ZC management strategies focus primarily on psyllid control. The ultimate control of ZC likely relies on host resistance. Unfortunately, all commercial potato cultivars are susceptible to ZC. Elucidation of the 'Ca. L. solanacearum' genome sequence has provided insights into the genetic basis of virulence and physiological and metabolic capability of this organism. Finally, the most effective, sustainable management of ZC is likely to be based on integrated strategies, including removal or reduction of vectors or inocula, improvement of host resistance to the presumptive pathogen and psyllid vectors, and novel gene-based therapeutic treatment. © 2013 The American Phytopathological Society.

Breksa III A.P.,Albany Research Center | Takeoka G.R.,Albany Research Center | Hidalgo M.B.,Albany Research Center | Vilches A.,Albany Research Center | And 2 more authors.
Food Chemistry | Year: 2010

Six raisin grape cultivars and 10 new raisin grape selections were analyzed for antioxidant activity (ABTS assay) and for total and individual phenolic compounds. Samples were freeze-dried and values are reported on a dry weight basis. Antioxidant activity across the 16 samples ranged from 7.7 to 60.9 μmol Trolox/g DW, with A95-27 exhibiting the greatest activity. Total phenolic content, determined in gallic acid equivalents using the Folin-Ciocalteau assay, ranged from 316.3 to 1141.3 mg gallic acid/100 g DW and was strongly correlated (r = 0.990) with antioxidant results. Concentrations of individual phenolics were determined by HPLC. trans-Caftaric acid was the predominant compound in all samples. A95-15 contained the lowest concentration (153.5 μg/g DW) of caftaric acid, while Fiesta contained the highest concentration (598.7 μg/g DW). Selections A56-66, A95-15, and A95-27 had much higher levels of catechin (86.5-209.1 μg/g DW) and epicatechin (126.5-365.7 μg/g DW) than the other samples.

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