(29(1):13-19)Studies on the relation of Mycoplasma-like organism with the decline of wentan pummelo in Taiwan

自麻豆地區五處及嘉義一處文旦園採回文旦立枯植株之接穗，除一處外，其餘果園採回之病穗，芽接於椪柑或椪柑與酸桔之穗砧組合幼苗上，經4~6個月後，可發現椪柑新生葉片呈現黃化之病徵，此病徵與一般之柑橘立枯病病原所引起者相同。自麻豆鎮近郊所採回之柳橙及椪柑立枯植株之接穗，嫁接後所得結果與文旦病穗相同。唯文旦穗嫁接後發病比椪柑或柳橙低。另部份由文旦穗生長之葉片亦有黃化及硬化現象。據此，麻豆地區不論文旦、柳橙或椪柑立枯植株，已普遍存在與柑橘立枯病相同或相似病原且此種病原可能為文旦植株葉片黃化、硬化之主因。 比較柑橘立枯病複合病原（Mycoplasma-like orgoism 與Tristeza virus）、立枯病單獨病原（Mycoplasma -like organism）及麻豆文旦立枯之分離株在葡萄柚苗、白柚／廣東檸檬及白柚／墨西哥雷木之穗砧組合苗上之反應，則文旦分離株與立枯病單獨病原相同，經進一步利用墨西哥雷木檢定，該分離株確無Tristeza 病毒之反應。四處採回之文旦枝條，尚未發現Tristeza，但椪柑及柳橙則有。 將文旦及柳橙病穗浸於100 ppm 之抗生素四環素溶液三或六小時，嫁接後幼苗新生葉片尚有部份呈現立枯病病徵，顯示浸藥六小時無法將病組織內之病原完全不活化。 This paper deals with Wentan Pummelo decline by indexing on indicator plants. Symptoms incited by disease sources from declined Wentan Pummelo and likubin-affected citrus trees were compared. The effect of dip treatment with tetracycline on the symptom expression of diseased scions was also studied. From 1977-1978, diseased scions of Wentan Pummelo were collected from five orchards in the Matou area and one orchard in Chiayi. Budsticks were also collected from Matou from Liuchen orange and Ponkan trees showing likubin symptoms. When all of the diseased budwood sources, except from one orchard, were graft-inoculated onto Ponkan seedlings or Ponkan on Sunki plants, likubin symptoms were shown 4-6 months after inculation. Paiyau Pummelo seedlings inoculated with scions from diseased Wentan Pummelo produced leaf yellowing and hardening. They also developed vein-swelling in some leaves in the later stage. These results indicated that leaf yellowing and hardening symptoms on declined Wentan Pummelo trees as well as on orange and Ponkan trees in Matou area could have been induced by a pathogen resembling citrus likubin MLO. Comparsion of likubin complex (tristeza virus and mycoplasma-like organism, MLO), likubin MLO and pathogen from declined Wentan Pummelo was made on such citrus plants as grapefruit seedlings, Paiyau Pummelo on Mexican lime or Rangpur lime stocks. The likubin complex induced severe stunting and small leaves in inoculated plants 1-2 months after inoculation, but the likubin MLO and the pathogen from declined Wentan Pummelo tree excerted little influence on the growth of inoculated plants in early stages. However, they later produced yellowing leaves. Indexing of disease samples from Wentan Pummelo trees on Mexican lime seedlings actually yielded no tristeza reaction. The results suggest that the declined Wentan Pummelo trees with leaf yellowing and hardening symptoms were probably infected with a single pathogen which was likubin MLO. Diseased scions of Wentan Pummelo and Liuchen orange were dipped in 100 ppm of tetracycline solution for 3 and 6 hrs. less than half of the treated scions produced yellowing symptoms in new growth after 4-6 months. In comparing with the growth of no treated scions, the trtracycline treatment seemed somewhat to have suppressed symptom development, but it did not inactivate the pathogen completely