Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC Davis Electronic Theses and Dissertations (2023)

Calosphaeria canker caused by Calosphaeria pulchella, Cytospora or Leucostoma canker caused by Cytospora sorbicola, and Eutypa dieback caused by Eutypa lata are the main canker diseases of sweet cherry in California commercial orchards and a limiting factor to orchard productivity and longevity. It was understood that pruning wounds serve as the primary avenue of infection for these fungal canker pathogens; however, very little is known about the other infection courts of Cal. pulchella, Cyt. sorbicola and E. lata. Thus, this present study was undertaken to identify common infection courts other than pruning wounds for fungal canker pathogens affecting sweet cherry. This was determined by assessing the field incidence of canker pathogens in the wood below pruning wounds, in buds, fruiting spurs and unpruned apical shoots exhibiting dieback symptoms. This work was supplemented by assessing the susceptibility of naturally occurring wounds such as leaf scars, bud scale scars, and harvest wounds on fruiting spurs to the three major canker pathogens of sweet cherry. Additionally, little is known about the effects of temperature and season on the biology of these three pathogens (except for E. lata). Therefore, the second objective of this study were to ascertain their optimal temperatures for spore germination and mycelial growth in vitro among temperatures 5, 10, 15, 20, 25, 30, 35, and 40°C. The third objective of this study supplements the second objective by comparing the susceptibility of pruning wounds to infection by Cal. pulchella, Cyt. sorbicola and E. lata made in summer and winter. Our survey revealed disease incidences of Cal. pulchella and Cyt. sorbicola to be as high as 20% and 35%, respectively, in shoot tips and up to 19.4% and 26.7%, respectively, in declining spurs. Additionally, harvest wounds of fruiting spurs were shown to be highly susceptible to canker infection by the three pathogens with 60% recovery for Cyt. sorbicola, and 42.5% for Cal. pulchella and E. lata. The optimal temperatures for spore germination were estimated to be 29.15°C for Cal. pulchella, 26.95°C for Cyt. sorbicola, and 22.85°C for E. lata; and optimal temperatures for mycelial growth were estimated to be 27.2°C, 23.85°C and 22.5°C, respectively. In field experiments, average recovery of Cal. pulchella was significantly greater from pruning wounds made in summer than that of winter with 84.6% and 10.7% recovery, respectively. The average recovery of E. lata from pruning wounds made in winter was 92.8%, which was significantly greater than that of summer with 80% recovery. Overall, our findings demonstrated that summer pruning of sweet cherry in California poses greater risks of infection by Cal. pulchella. In contrast, winter pruning poses greater risks of infection by E. lata. This study represents new knowledge on the seasonal susceptibility of pruning wounds of sweet cherry to canker infection by Cal. pulchella and Cyt. sorbicola. Additionally, this study provided new information on additional infection courts of major canker pathogens of sweet cherry in California. Since distinct cherry canker pathogens vary in their seasonal infectivity, synchronizing maintenance pruning with low periods of inoculum pressure will be critical for canker disease management in sweet cherry orchards.

    Cover page: Biology of Fungal Canker Diseases of Sweet Cherry in California
    • Article
    • Peer Reviewed
    UC Davis Previously Published Works (2020)
    In this study, declining pistachio rootstocks were detected in newly planted commercial pistachio orchards in Kern County, California. Symptoms were characterized by wilted foliage combined with crown rot in the rootstock. From diseased trees, 42 isolates were obtained, and all had similar cultural and morphological characteristics of Macrophominaphaseolina. Analyses of nucleotide sequences of three gene fragments, the internal transcribed spacer region (ITS1-5.8S-ITS2), partial sequences of β-tubulin, and translation elongation factor 1-α (TEF1) confirmed this identification, and 20 representative isolates are presented in the phylogenetic study. Testing of Koch's postulates showed that M.phaseolina, when inoculated to stems and roots of the pistachio rootstocks using mycelial plugs or a microsclerotial suspension, is indeed pathogenic to this host. The widely used clonal University of California Berkeley I (UCBI) rootstock appeared highly susceptible to M. phaseolina, suggesting that this pathogen is an emerging threat to the production of pistachio in California. This study confirmed the association of M.phaseolina with the decline of pistachio trees and represents the first description of this fungus as a crown rot-causing agent of pistachio in California.
      Cover page: Macrophomina Crown and Root Rot of Pistachio in California
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2018)
      Cytospora species are destructive canker and dieback pathogens of woody hosts in natural and agroecosystems around the world. In this genus, molecular identification has been limited due to the paucity of multi-locus sequence typing studies and the lack of sequence data from type specimens in public repositories, stalling robust phylogenetic reconstructions. In most cases a morphological species concept could not be applied due to the plasticity of characters and significant overlap of morphological features such as spore dimensions and fruiting body characters. In this study, we employed a molecular phylogenetic framework with the inclusion of four nuclear loci (ITS, translation elongation factor 1-alpha, actin, and beta-tubulin) to unveil the biodiversity and taxonomy of this understudied important genus of plant pathogens. Phylogenetic inferences based on 150 Californian isolates revealed 15 Cytospora species associated with branch and twig cankers and dieback of almond, apricot, cherry, cottonwood, olive, peach, pistachio, plum, pomegranate, and walnut trees in California. Of the 15 species recovered in this study, 10 are newly described and typified, in addition to one new combination. The pathogenic status of the newly described Cytospora species requires further investigation as most species were associated with severe dieback and decline of diverse and economically important fruit and nut crops in California.
        Cover page: Molecular phylogeny of <i>Cytospora</i> species associated with canker diseases of fruit and nut crops in California, with the descriptions of ten new species and one new combination.
        Top