Species And Variation Of Chinese Collections Of Elsino(e|¨) Spp. Causing Scab Diseases Of Citrus

Two scab diseases are currently recognized on citrus:citrus scab, caused by Elsinoe fawcettii Bitancourt and Jenkins (anamorph Sphaceloma fawcettii Jenkins), and sweet orange scab, caused by E. australis Bitancourt (anamorph S. australis Bitancourt and Jenkins). E. fawcettii mainly affects species of citrus such as tangerines and lemons, but raely affects stweet orange, while E. australis mainly affects fruits of sweet orange, but rarely affects tangerines.China is the world’s largest citrus producing countries with a long history of citrus-growing, and a large number of citrus species and varieties. Citrus scab is a common problem in the citrus industry, affecting tangerines, pomelos and lemons Although, scab disease is economically important in China, but experimental study on the species and intraspecific variation of the pathogenic fungi is lack. Especially, there is no information to show if sweet orange scab is present in China. In addition, the Elsinoe species causing pomelo (Citrus grandis) scab has not yet been identifiedabroad so far. Based on the above facts, the following works were carried out in this study:1. Samples of citrus fruits and leaves with scab or scab-like symptoms were collected from cultivated Citrus species in the main citrus-producing areas of China. Eighty three Elsinoe strains were isolated from these samples and46representative strains were selected for ITS sequence analysis. The results indicated that Elsinoe fawcettii appears to be the sole species in our country and E. australis has not been discovered at present.2. Based on the methods of morphological and molecular characteristics, we demonstrated for the first time that the causal agent of pomelo scab is also E. fawcetti.3. Pathogenicity testing on9Citrus species and Inter-Simple Sequence Repeat (ISSR) analysis indicated that a rich intraspecific variation is present in E. fawcettii population. The46selected strains could be divided into11pathotypes and10ISSR groups. A high consistency is present between the genetic differentiation and pathogenicity differentiation, indicating ISSR could be used for the forcasting or intial identification of the pathotypes of E. fawcettii. 4. Symptoms of citrus scab are often indistinguishable from those caused by other pathogenic fungi, mechanical injuries or insects. In this study, a rapid and reliable real-time PCR technique for the diagnosis of citrus scab was established. By using this technique, a citrus scab-suspected sample could be diagnosed within four hours.