Bacterial halo blight of coffee crop: aggressiveness and genetic diversity of strains

ABSTRACT Bacterial halo blight, caused by Pseudomonas syringae pv. garcae, is an important disease of coffee crop occurring in Brazil and other countries. In recent years, outbreaks of this disease have damaged several coffee crops in Brazil. Aggressiveness and genetic diversity of 25 strains of P. s. pv. garcae, obtained between the years 1958 and 2011, in 23 cities of São Paulo and Minas Gerais states, as well as three strains from Kenya were evaluated in this study. The strains were inoculated on coffee seedlings cultivar Mundo Novo, and their genetic diversity was evaluated by ERIC-PCR, REP-PCR, and their combination. All the strains were pathogenic to the coffee seedlings; the results of pathogenicity tests, in both experiments, could be divided in four aggressiviness classes (highly aggressive; aggressive; moderately aggressive and less aggressive). The Kenyan strains grouped separately from the Brazilian strains with ERIC-PCR and the combination of ERIC- and REP-PCR. The Brazilian strains could be grouped in two sub-clusters, the first including the older strains, obtained from 1958 to 1978, and the other comprising the remaining strains. With a few exceptions, strains isolated from 1997 to 2011, grouped mainly by their region of origin, were predominantly isolated from higher altitude regions, above 800 m. This probably occurred because the climatic conditions that prevail in these regions, characterized by milder temperatures and regular rainfall, are favorable for the coffee crop and for the production of high quality coffee beverage, but can be also favorable to bacterial halo blight.

摘要：由丁香假单胞菌咖啡致变型（Pseudomonas syringae pv. garcae）引发的细菌性晕枯病，是巴西及其他国家咖啡种植中的重要病害。近年来，该病的暴发已对巴西多片咖啡种植园造成严重经济损失。本研究针对1958年至2011年间从巴西圣保罗州与米纳斯吉拉斯州23座城市分离得到的25株丁香假单胞菌咖啡致变型，以及3株来自肯尼亚的该病菌菌株，开展了致病力与遗传多样性分析。将供试菌株接种于咖啡品种蒙都诺沃（Mundo Novo）的幼苗中，并通过肠杆菌基因间重复共有序列聚合酶链式反应（ERIC-PCR）、重复基因外回文序列聚合酶链式反应（REP-PCR）及其联合扩增对菌株的遗传多样性进行检测。所有供试菌株均对咖啡幼苗具有致病性；两次致病性试验结果均可将菌株划分为4个致病力等级：强致病、致病、中等致病、弱致病。通过ERIC-PCR以及ERIC-PCR与REP-PCR联合扩增分析发现，肯尼亚菌株与巴西菌株各自聚为独立的类群。巴西菌株可进一步划分为两个亚类群：第一亚类包含1958年至1978年分离的早期菌株，第二亚类涵盖其余供试菌株。除少数例外情况外，1997年至2011年分离的菌株主要按照其分离地域聚群，且这些菌株大多分离自海拔800米以上的高海拔区域。出现这一现象的原因可能在于：该类区域的主流气候条件以温和气温与均匀降雨为特征，既适宜咖啡种植与高品质咖啡饮品的生产，同时也利于细菌性晕枯病的发生。