• Evaluating the Potential Threat to Citrus Plantings from Phytophthora Parasitica Originating from Noncitrus Hosts

      Matheron, M.; Matejka, J.; Butler, Marvin (College of Agriculture, University of Arizona (Tucson, AZ), 1991-01)
      The relative virulence of Phytophthora parasitica recovered from citrus and other plants to rough lemon was investigated Isolates of Phytophthora parasitica from citrus were highly virulent to rough lemon seedlings, causing crown rot and significant reduction of root weight. Isolates of the pathogen from noncitrus hosts caused slight damage to rough lemon, with no crown rot and only minor reduction of root weight. Evidently, isolates of P. parasitica from several noncitrus hosts do not pose a serious threat to citrus groves.
    • Phytophthora Gummosis and Root Rot of Citrus-Effect of Temperature on Disease Development

      Matheron, M.; Matejka, J.; Butler, Marvin (College of Agriculture, University of Arizona (Tucson, AZ), 1991-01)
      Experiments were conducted to examine the effect of temperature on development of Phytophthora gummosis and root rot of citrus as well as the influence of temperature on sporulation of Phytophthora citrophthora and P. parasitica. Maximum production of sporangia by each fungus occurred at 25 C, while slight or no sporangia production occurred at 10, 15, and 35 C. Minimal growth of lesions was observed when stems of rough lemon were inoculated with P. citrophthora or P. parasitica and incubated at 5 and 30 C or 10 and 30 C, respectively. The inhibitory and stimulating effect of certain temperatures on sporulation and disease development could be useful for determination of optimum times for application of fungicides or other disease control measures.
    • Report on the Salt River Valley Citrus Experiment Station

      True, Lowell; Bacon, Dean; Butler, Marvin (College of Agriculture, University of Arizona (Tucson, AZ), 1991-01)
    • Seasonal Changes in Extent of Colonization of Citrus Root Tissue by Phytophthora citrophthora and P. parasitica

      Matheron, M.; Matejka, J.; Butler, Marvin (College of Agriculture, University of Arizona (Tucson, AZ), 1991-01)
      For 24 consecutive months, root pieces were collected from field -grown Lisbon lemon trees established on Citrus aurantium (sour orange), C. jambhiri (rough lemon), and C. volkameriana rootstocks. Root segments were wounded, inoculated with Phytophthora citrophthora or P. parasitica, and incubated for 96 hr in moist chambers. Smaller lesions developed during Jan -Feb than during Jul-Oct on root pieces of all tested rootstocks inoculated with P. citrophthora as well as root pieces of C aurantium inoculated with P. parasitica. Apparently there is a seasonal variation in the susceptibility of citrus rootstocks to colonization by Phytophthora. This information could be useful for more effective timing of fungicide applications.