ARI Biennial Review for 2018-2019

usually the intensity of field symptoms related well to the severity of CTV symptoms on Mexican lime in the greenhouse. No seedling yellows symptoms on sour orange or grapefruit were observed. (L.C. Papayiannis, T. Kapari-Isaia) Molecular characterisation of Citrus tristeza virus isolates Several isolates collected from different areas of Cyprus causing a wide diversity of symptoms were tested and characterised. Symptoms on field trees ranged from inconspicuous to twig die-back, decline and death of sweet orange or grapefruit trees on sour orange rootstock. Similarly, on Mexican lime, symptoms ranged from barely noticeable leaf-vein clearing to vein corking, stem pitting and plant stunting. Coat protein gene (CPG) amplicons were digested by a selection of restriction enzymes and characterised with single-strand conformational polymorphism. The nucleotide sequence of the CPG was determined and phylogenetic analysis was performed. Results showed that most symptomless isolates from Cyprus clustered among the mild strains reported from Spain, Portugal and Africa. In addition, isolates that were responsible for decline of sweet orange, grapefruit and mandarin trees showed high similarity with strains reported in Africa (B249), whereas four other isolates that caused stem pitting symptoms clustered with T36, an American severe strain from Florida. The RFLP and SSCP techniques and the subsequent nucleotide analysis of the Cypriot CTV isolates enabled their clear distinction in mild and severe, their comparison to universal isolates/strains. The molecular techniques used in the present work enabled, in addition to the differentiation of mild and severe isolates, the establishment of relationships of Cypriot isolates to universal isolates, including the severe isolates T36 and T3 from Florida, B246 from South Africa, B-CTV from India and the mild isolate 28C from Portugal. These results substantiate our belief that CTV was introduced in Cyprus with imported budwood from South Africa in the 1930’s when there was not much knowledge about viruses, and, more recently, from other countries, as travelling became easier during the last three decades. (L.C. Papayiannis, T. Kapari-Isaia) Citrus rootstock evaluation for tolerance to Cypriot isolates of Citrus tristeza virus The main goal of this project was to investigate tolerant rootstock for replacement of the CTV-sensitive sour orange, which is commercially used in Cyprus. Twenty-four plants of the following citrus rootstocks were grafted with Washington Navel sweet orange and are being evaluated for their tolerance to CTV in a replicated complete block design, at Xylotymbou experimental Station of the Institute: Carrizo citrange, Swingle citrumelo, Volkameriana lemon, Gou Tou, Cleopatra mandarin and Sour Orange. Half of these trees were graft-inoculated with CTV and the rest kept healthy. Infected and healthy trees are being evaluated and compared with regard to their performance in the field, fruit production and quality. Most of the trees grafted on citrumelo rootstock showed severe stunting and chlorosis. (T. Kapari-Isaia, L.C. Papayiannis) 41 PLANT PROTECTION