ARI Biennial Review for 2018-2019

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. 50% of these trees were graft-inoculated with CTV and the rest remained 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) Evaluation of five new sour orange hybrid rootstocks for tolerance to citrus viroids Five citrus hybrid rootstocks are evaluated at Zygi Experimental Station for their tolerance to citrus viroids. The five citrus hybrids are the following: (1) Sour orange × Orange ( Citrus aurantium L. × Citrus sinensis , (L.) Osbeck), (2) Sour orange × Satsouma ( Citrus aurantium L. Citrus reticulata blanco ), (3) Sour orange × Citrumelo 1452 × Lemon ( Citrus aurantium L. × P. trifoliata (L.) Raf × Citrus paradisi Macf. × Citrus limon ), (4) Sour orange × Volkameriana ( Citrus aurantium L. × Citrus volkameriana ), and (5) Sour orange × Carrizo ( Citrus aurantium L × Citrus sinensis (L.) × Poncirus trifoliata (L.) Raf ). (T. Kapari-Isaia, L.C. Papayiannis) Production, maintenance and distribution of healthy stone fruit material Virus-free material is maintained in a pre-basic plantation under insect-proof screen at the Zygi and Saittas Experimental Stations. Currently, 52 stone fruit accessions are included in either plantation, kept in sanitary condition by application of strict measures and regular indexing, in conjunction with optical observation for either fungal problems or genetical aberrations. The plantations provide with propagating material for the basic or mother plantations of the Department of Agriculture and for the experimental glasshouses of the ARI. (T. Kapari-Isaia, L.C. Papayiannis) Grapevine pre-basic plantation Efficient control of plant virus, virus-like and prokaryotic diseases starts with the use of healthy propagating material, which is free not only from disease symptoms, but also from latent infections. EU has recently imposed strict directives on distribution of grapevine material that involve phytosanitary testing of plants for several plant pathogens. Utilisation of healthy plant material seems nowadays the most promising tactic that can ensure good results to control these diseases. During the past decades, ARI has established a long-term project on the maintenance of healthy propagative grapevine material under “pre-basic” status. Approximately 70 local or imported varieties are maintained under insect-proof net houses at Zygi experimental station. These plants are annually tested for a number of plant viruses including Grapevine fan leaf virus, Grapevine fleck virus, Arabis mosaic virus and Grapevine leaf roll associated viruses 1 and 3, viroids and several other prokaryotic pathogens. Tests are performed using pathogen-specific serological and molecular-based laboratory techniques. Virus-free grapevine plant cuttings are then given to the Department of Agriculture for further multiplication and distribution to Cypriot farmers. (L.C. Papayiannis, T. Kapari-Isaia) 44 PLANT PROTECTION