Genetic Improvement of Citrus Limon (L. Burm f.) for Resistance to Mal Secco Disease

Among citrus species, lemon (C. limon, L. Burm. f.) is one of the most important and the most susceptible to the severe vascular disease called mal secco, which means 'dry disease' in Italian. The etiological agent of mal secco disease is the imperfect fungus Plenodomus tracheiphilus. This tracheomycosis consists in vein chlorosis of young shoots, leaves, phylloptosis, wood discolouration and the progressive desiccation of the entire plant. Mal secco represents the most limiting factor for lemonculture in the Mediterranean and Black Sea area, where the 48% of worldwide lemon production takes place. To date, agronomical and chemical measures have not been effective in limiting the spread of the pathogen and breeding research have not still reached the goal of the obtainment of novel lemon varieties coupling resistance to mal secco disease and good fruit quality production. In this chapter, breeding strategies ever pursued for unlocking the genetic bases of host resistance and obtaining improved lemon plants, such as traditional breeding, in vitro selection, protoplast hybridization, genetic transformation, are briefly described. Moreover, the application of high-throughput genotyping platforms in marker-trait association studies seems to be the most promising approach for understanding the genetic determinism of mal secco resistance in citrus. In fact, through this strategy, it would be possible discover molecular markers linked to the trait of interest and applicable in Marker Assisted Selection for the identification of novel varieties with improved tolerance to mal secco disease.