Abstract
Stem pitting has been found by the authors in such species of citrus as sweet lime (Citrus limettioides TANAKA), Hassaku (C. hassaku HORT ex TANAKA), Banpeiyu (C. grandis OSBECK), Matopeiyu (C. grandis OSBECK), Tanigawabuntan (C. grandis OSBECK), Matobuntan (C. grandis OSBECK), grapefruit (C. paradisi MACF.), Kotokan (C. kotokan HAYATA), Parson Brown (C. sinensis OSBECK), Wasington Navel orange (C. sinensis OSBECK, var. brasilliensis TANAKA), Funadoko (C. funadoko HORT. ex Y. TANAKA), Kikudaidai (C. canaliculata HORT. ex Y. TANAKA), and Yuzu (C. junos SIEB. ex TANAKA). In these species, stem pititng of Hassaku trees has been known as one of the symptoms of Hassaku dwarf disease, and it is closely associated with stuntiog of tree in the fields. But, stem pitting of other species has not so awared, because of the less cultivation of these species in Japan.
To see whether a certain factor involved in stem pitting initiation of citrus can be transmitted by tissue graft to healthy trees of other citrus or not, the following experiments of transmission of stem pitting were carried out. 1) Budwood from 11 species of citrus (Sweet lime, Banpeiyu, grapefruit, Hassaku, Kotokan and Washington Navel orange) which showed stem pitting in the fields, were inoculated to seedlings of Mexican lime (Citrus aurantifolia SWINGLE) by means of tissue graft. 2) Budwood from Hassaku tree affected by Hassaku dwarf disease, was inoculated to seedlings of sweet lime. 3) Budwood from Hassaku tree affected by Hassaku dwarf disease, was inoculated to two-year old Mediterranean sweet orange trees (Citrus sinensis OSBECK) grafted on Kabusu daidai rootstock (Citrus aurantium LINN.).
The results show that within one or two years after inoculation, stem pitting was formed in Mexican lime (Fig. 3, B, C) and sweet lime seedlings (Fig. 4, B), however, no stem pitting was observed in the wood surface of sweet orange trees. But, in the case of sweet orange trees, abnormal parenchymatous tissue was recongnized in the wood differentiated after inoculations (Fig. 5, B. the arrow).
