Systemic infections of pome and stone fruit trees by newly emerging virus pathogens and phytoplasmas and possibilities of reducing their economic damage

Fruit crops are often simultaneously infected by several systemic pathogens of viral or phytoplasma nature, resulting in a negative synergistic effect. As a result, the fertility of agricultural crops is reduced and the quality of production is also negatively affected. This weakens the position and competitiveness of farmers worldwide. A comprehensive solution to this problem is the innovation in pathogen diagnostics and the use of new generation high-throughput sequencing methods, as well as the application of new sanitation procedures such as the use of promising antiviral substances or cryotherapy. As a part of the screening of fruit propagating material, orchards and commercial plantations in the Czech Republic were visited and the level of infection with novel viruses and virus-like diseases was assessed. On the basis of this screening, apple hammerhead viroid (AHVd), citrus concave gum-associated virus (CCGaV) and apple luteovirus 1 (ALV-1) were identified as newly emerging apple pathogens. Members of the genus Luteovirus are the major new pathogens of concern infecting Prunus trees. In addition, sequences of other tentatively new viruses are the subject of further studies. ‘Candidatus Phytoplasma mali’, ‘Ca. P. pyri’ and ‘Ca. P. prunorum’ as the causal agents of apple proliferation (AP), pear decline (PD) and European stone fruit yellows (ESFY) are reported as the most economically important phytoplasmas of temperate fruit tree species in Europe. Biotechnological sanitation methods, based on chemotherapy using antiviral agents and antibiotics or cryotherapy in liquid nitrogen, are currently being applied to test the possibilities of obtaining healthy virus- and phytoplasma-free starting material of commercially important fruit crops for certification system.