Relationship of Tristeza and Incidence of Lime Root Rot Disease

Abstract

Observations were made on eighty five lime trees (Citrus aurantifolia christm., Swing.) variety PAN, infected with tristeza virus. the degree of disease infection varied from tree to tree. Most of heavily inforted trees were more susceptible to root rot disease, whereas, root rot disease incidence was rarely observed on theless infected trees. It has been indicated that such an occurrence reflected a synergistic reaction between tristeza virus and some soil-borne parthogenic fungi in the lime tree.
Two fungi, Diplodia sp. and Fusarium sp., were consistently inolated from infected roots of tristeza disease trees. The parthogenicity of these fungi was tested. Wound inocultation with either Diplodia sp. or Fusarium sp. was done on roots of both tristeza infected and healthy lime trees. The incidence of root rot diseasewas obscrved only on lime trees that were healthy lime trees. The incidence of root rot disease was obscrvedonly on lime trees that were heavily intected with tristeza. these trees were so predisposed as to enhance the severity or damage caused by the subsequent infection with either Diplodia or Fusarium root rot. However, Phytophthora sp. has never been inolated from diseased roots even by using selective media. An attempt was made to induce root rot by Phytophthora parasitica isolated from damping-off lime seedling in the nursery but the attempt was not successful.