Growth and Morphogenesis of Citrus Tissue-Cultures Infected with Psorosis, Vein Enation, and Cachexia

Abstract

Stem segments from Pineapple sweet orange (Citrus sinensis) and Etrog citron (C. medica) infected with psorosis, vein enation, and cachexia, as well as uninfected controls, were cultured in vitro. Production of roots and regeneration of shoots and buds were modified as a result of infection. The number of explants showing morphogenesis and the amount of rooting and/or regeneration of shoots and buds were affected as compared with the uninfected explants cultured as controls. The differences on morphogenic patterns depended on the disease and the disease isolate. Explants infected with vein enation and cachexia produced significantly less primary callus than the controls, whereas psorosis did not affect callus induction. The amount and morphology of secondary callus after the first subculture were similar in infected and uninfected tissues. Biological indexing of callus indicated that psorosis- and cachexia-infected callus were good host systems for the replication of the disease-causing agents, whereas vein enation could not be detected after continuous callus cultures. The citrus cachexia viroid was detected from infected callus by nucleic acid extraction and sequential polyacrylamide gel electrophoresis. Electron microscopy studies revealed alterations at the cell level on psorosis-infected callus.