Submitted to: Proceedings of Northeastern Weed Science Society
Publication Type: Abstract Only
Publication Acceptance Date: January 1, 2003
Publication Date: January 1, 2003
Citation: ESKANDARI, F., MCMAHON, M.B., BRUCKART, W.L. A PHOMA SP. THAT KILLS COMMON CRUPINA (CRUPINA VULGARIS). PROCEEDINGS OF NORTHEASTERN WEED SCIENCE SOCIETY. 57:120. 2003. Technical Abstract: Recently, a wilt disease was discovered on common crupina in the containment greenhouse at Ft. Detrick. Infected plants had blackened, necrotic stems and were wilting, at first only on half of the top. Because of the damage, it was of interest to isolate, identify, and evaluate this pathogen for biological control of crupina. A fungal causal agent was isolated and Koch's postulates were satisfied using a wound inoculation procedure. The pathogen grows easily on acidified potato dextrose agar (APDA) under room conditions. After 20 days on APDA, dark, ostiolate pycnidia developed that contain one-celled hyaline conidia. DNA sequence analysis of the ribosomal RNA gene Internal Transcribed Spacer regions 1 and 2 (ITS1 and ITS2) demonstrated 100% identity to several P. exigua Desmaze isolates. Several approaches were used in testing pathogenicity, including: 1) wounding plants with a contaminated needle, 2) drenching crupina plants with inoculum (a mixture of conidia and mycelium), 3) spraying foliage of test plants with inoculum in an atomizer, 4) spraying test plants with a mixture of inoculum and abrasives (either silica gel or carborundum), and 5) immersing seedlings in inoculum for one minute before transplanting. All inoculated plants were placed under constant light in a 23 oC dew chamber for 48 hours. Typical symptoms of stem blight and wilting occurred only when plants were wounded on the stem with a contaminated needle, wounded with spray inoculations that included abrasives, or when seedlings were dipped into inoculum before transplanting. From this, we conclude that infection by P. exigua requires a wound. Symptoms usually appeared quickly, often within 2 days, but occasionally as long as 15 days. Wound inoculation of 4-wk-old plants and dipping seedlings resulted in 100% and 85% wilting, respectively, within 48 hours. Plants 6- to 8- wk-old were less susceptible, with 65% wilting between 4 to 10 days after wounding. Use of abrasives for inoculation of 3-5 wk-old plants caused only 20% infection after 10 days. Symptoms of disease developed only above the portion of the plant that was wounded; roots were always white and healthy, except when seedlings were inoculated. The pathogen seems to be host specific, considering that none of the close relatives, two Centaurea sp., Acroptilon repens, Cynara scolymus, Carthamus tinctorius, Carduus acanthoides, or Cirsium vulgaris, developed symptoms after wound inoculations. Phoma exigua remains of interest as a candidate for biological control of crupina, but the requirement of a wound for infection poses major challenges to practical development.