Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/2/2002
Publication Date: 10/20/2002
Citation: BRLANSKY, R.H., HOWD, D.S., BROADBENT, P., DAMSTEEGT, V.D. HISTOLOGY OF SWEET ORANGE STEM PITTING CAUSED BY CITRUS TRISTEZA VIRUS. PLANT DISEASE 86:1169-1174. 2002. Interpretive Summary: One of the most important plant viruses infecting citrus is the citrus tristeza virus (CTV). CTV is transmitted by several different aphids. One of the most efficient carriers of the virus is the brown citrus aphid (BCA) that became established in Florida in 1994. Some strains of the virus cause very severe symptoms in sweet orange trees that leads to tree decline and reduction in fruit size and yield. One of the symptoms of this disease is stem pitting. Infection by the virus causes variously-sized pits or groves in the woody stems, limbs, and twigs of infected trees. The cause of the stem pitting was shown to be associated with overgrowths of the bark tissue and aggregations of virus inclusion bodies. The structure of the overgrowths and stem pits were revealed by light and electron microscopic studies. Understanding the nature of the stem-pitting process helps us devise better control strategies for this serious virus disease and its transmission.
Technical Abstract: Some strains of the Citrus tristeza virus (CTV) cause stem pitting in sweet orange (Citrus sinesis [L.] Osb.). This abnormality causes tree decline and reduction in fruit size and yield of affected citrus trees. Stem pitting symptoms can occur on trunks, on all sizes of limbs and on the twigs where fruit are produced. Variously sized pits or groves in the wood often contain a yellow gum. Irregular growth of the phloem occurs into the area of these xylem pits. The histology of stem pitting caused by an Australian CTV isolate was studied in sweet orange using light and electron microscopy. Using scanning electron microscopy, details of the wood pits containing the gumming material were revealed. In thin sections of bark tissue, outgrowths of the phloem tissue were found at various intervals that corresponded to the pits in the wood. Higher numbers of viral inclusions were detected in the phloem outgrowths than were present in the other sieve elements. Understanding the nature of the stem-pitting process helps us devise better control strategies for this serious virus disease and its transmission.