Important plant diseases, a review of the causal fastidious prokaryotes and their insect vectors

Abstract

Phytopathogenic fastidious prokaryotes are plant pathogens that either resist to grow in any available bacterial culture mediums or require specific or enriched mediums to grow. They include Xylella fastidiosa, Leifsonia xyli subsp. xyli, L. xyli subsp. cynodontis and Clavibacter michiganensis subsp. sepedonicus and C. michiganensis subsp. michiganensis that reside in xylem and spiroplasmas,phytoplasmas and Candidatus Liberibacter spp. that reside in phloem. X. fastidiosa is the causal agent of more than 19 diseases; among them Pierce’s disease of grape and citrus variegated chlorosis are two major maladies that cause serious economic loss on wine and citrus juice industry. L. xyli subsp. xyli, and L. xyli subsp. cynodontis are associated with ratoon stunting disease of sugarcane and Bermuda grass stunting respectively and C. michiganensis subsp. sepedonicus with bacterial ring rot in potato and C. michiganensis subsp. michiganensis with bacterial tomato canker. Spiroplasmas are the causal agents of citrus stubborn, corn stunt and periwinkle diseases. Phytoplasmas are associated with more than 500 diseases worldwide. Ca. Liberibacter spp., are the causal agents of citrus Huanglongbing or citrus greening, zebra chip disease of potato and others. General characteristics of X. fastidiosa including its scientific classification, host ranges and diseases incited, and cell shape and size; specific and enriched media for X. fastidiosa; symptoms induced by X. fastidiosa; geographic distribution of X. fastidiosa; and the insect vectors that transmit the diseases will be discussed. Pierce’s disease is the limiting factor for the establishment of wine industry for the entire southeastern United States from Texas to the Carolinas along the gulf coast of Mexico. Recent introduction of the glassy-winged sharpshooter leafhoppers in California has threatened the winery ndustry of California. The significance of the isolation of X. fastidiosa from the tissues with citrus variegated chlorosis symptoms followed by the identification of the major insect vectors will be addressed. The biological characteristics of the three phloem-limited prokaryotes, namely spiroplasmas, phytoplasmas and Ca. Liberibacter spp., and the diseases they induce and their vectors will be discussed. Most plant pathogenic prokaryotes do not require an active insect vector to spread them from plants to plants, while X. fastidiosa, Ralstonia syzygii, Ca. Liberibacter spp., phytoplasmas, and spiroplasmas do. To date among all known vectors, the single most successful insects vectoring the diseases belong to the Order of Hemiptera. In the past three decades, researches have emphatically addressed the biology, ecology, vector relationships and epidemiology of crop diseases caused by plant pathogenic prokaryotes which were well documented in numerous review articles. Herein a review of the significance of the insect vectors of fastidious prokaryotes that cause important plant diseases is to be addressed. 植物病原微生物中有一群營養苛求原核生物，此群病原細菌無法在一般細菌性培養基生長或者需在含特殊成份或豐富複合配方之培養基才能生長，專一棲息於植物導管組織內之細菌包括 Xylella fastidiosa, Leifsonia xyli subsp. xyli, L. xyli subsp. cynodontis, Clavibacter michiganensis subsp. sepedonicus,及C. michiganensis subsp. michiganensis，另專一棲息於植物篩管組織內細菌包括螺旋菌質體(spiroplasmas)、植物菌質體(phytoplasmas)及Candidatus Liberibacter spp.。X. fastidiosa 曾經引起超過19個重要病害之致病因子，其中葡萄皮爾斯病(Pierce’s disease of grape)及柑橘斑駁黃化病 (citrus variegated chlorosis)為二個主要典型病例，曾經造成葡萄釀酒及柑橘果汁加工產業重大損失；L. xyli subsp. xyli, and L. xyli subsp. cynodontis分別被認為引起甘蔗宿根矮化病(ratoon stunting disease of sugarcane)及百慕達草矮化症(Bermuda grass stunting)相關致病因子，C. michiganensis subsp. sepedonicus會引起馬鈴薯細菌性輪腐病(bacterial ring rot in potato)及C. michiganensis subsp. ichiganensis會引起番茄細 菌性腫瘤病(bacterial tomato canker)；螺旋菌質體被認為會引起柑橘停滯生長(citrus stubborn)、玉米矮化(corn stunt)及日日春(periwinkle)等病害之致病因子；植物菌植體在全世界被認為會引起超過500個病害之相關致病因子；Ca. Liberibacter spp. 被認為會引起柑橘黃龍病(citrus Huanglongbing)或別名柑橘綠化症(citrus greening)、馬鈴薯薯片斑紋病(zebra chip disease of potato)及其他被影射病害致病因子。本文將論述X. fastidiosa一般特性包括科學化分類屬性、寄主範圍、如何誘導病害發生、細菌型態及大小、特殊培養基需求性、病徵學、世界地理分佈及媒介昆蟲傳播病害等；美國東南地區墨西哥灣沿岸地區從德克薩斯到卡羅萊納等州建立龐大葡萄釀酒產業體系，葡萄皮爾斯病一直是該地區葡萄產業之主要限制因子，近年來加州地區人為引入媒介昆蟲褐透翅尖頭葉蟬(glassy-winged sharpshooter leafhoppers)已造成該地區葡萄釀酒產業極大衝擊；將會討論從罹病柑橘斑駁黃化病病徵組織分離X. fastidiosa病原生物學意義進一步鑑定主要媒介昆蟲。3種侷限篩管原核生物,螺旋菌質體、植物菌質體及Ca. Liberibacter spp. 之生物學特性、如何引起病害發生及媒介昆蟲將一倂討論。大部份植物病原原核生物並不需要藉由活躍媒介昆蟲從事植物與植物間病原擴散，但是 X. fastidiosa, Ralstonia syzygii, Ca. Liberibacter spp., 螺旋菌質體及植物菌質體等需要藉由媒介昆蟲傳播病原至健康植物。目前所有已知媒介昆蟲中大部份能成功傳播病害皆隸屬於半翅目(Hemiptera)昆蟲，過去30年許多研究學者已在不少回顧專題完整紀錄植物病原原核生物引起作物病害並詳細論述其生物學、生態、媒介昆蟲相關性與流行病學，本文僅就營養苛求原核生物之媒介昆蟲引起重要植物病害之意義作回顧論述。