Multigene characterization of phytoplasmas associated with flat branch disease in sweet cherry and their effects on some fruit properties

Cherry trees occupy a prime position among temperate fruit crops all over the world with a high nutritional value and abundant phenolic compounds contributing greatly to health benefits. Symptoms of flat branching characterized by flat, highly compressed branches with a rough corrugated surface, twisted at the tip, were observed in some cherry cultivars at ICAR-CITH experimental field. The phytoplasma presence was confirmed through multigenic approach which shows presence of Candidat us Phytoplasma asteris’ and ‘Ca. P. trifolii’ strains. The incidence of flat branch and witches’ broom symptoms associated with ‘Ca. P. trifolii’ varied from 5.8 to 25% in cultivars Bigarreau Nepoleon (Double), Bigarreau Noir Grossa and CITH-Cherry- 9. However, incidence of leaf rolling, swollen nodes and bud proliferation associated with ‘Ca. P. asteris’ was 7.5% in cultivar Stella and 10% in Sunburst, respectively. The multigene characterization of sweet cherry phytoplasma strains confirmed the validity of these molecular markers for identification of phytoplasmas that are enclosed in 16SrI and 16SrVI groups, respectively. During the study it was observed that flattened branches produce very little annual growth and subsequently affected spur production during next year. The negative effect of branch flattening was observed on set, growth, and retention of fruits. It delayed phenological events related to fruit development and maturity. Moreover, compared to normal branches, the flat branches produce low quality fruits in terms of size, weight, color, and biochemical properties.