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The effect of Candidatus Phytoplasma pruni infection on sweet cherry fruit

Published in Phytopathology Journal online on May 7, 2021, by Wright AA, Shires MK, Beaver C, Bishop G, Dupont ST, Naranjo R, Harper S. 

Summarized by Corina Serban, August, 2021


Candidatus (Ca.) Phytoplasma (P.) pruni is the causal agent for the X-disease phytoplasma. In sweet cherries the symptoms are small and distorted fruit, with poor color and taste that results in unmarketable fruit. X-disease phytoplasma can spread by infected bud wood, root grafting between neighboring trees, and leafhopper vectors. The disease pathology is not well understood, especially at the cultivar level.

The Wright et al. 2021 study looked at the visual symptoms of X-disease across different sweet cherry cultivars and locations within eastern Washington. The sweet cherries evaluated in this study were four mahogany cultivars, ‘Bing’, ‘Benton’ ‘Cristalina’, and ‘Santina’, and two blush cultivars, ‘Rainier’ and ‘Early Robin’. Fruit color and size, as well as biochemical changes such sugar and acid content, and total phenolics were evaluated in this study. All those measured parameters were related to the titer of Ca. P. pruni present. The main findings from this study are that infection stage and symptom severity correlates with Ca. P. pruni titer (Figure 1.) Wright et al. 2021 observed this effect on fruit color and shape, where changes in color development are cultivar specific (Figure 2.). Importantly, infection could be divided into two stages of infection such as early and established stages based on pathogen titer. Also, the assessment of sugar and metabolites showed little difference in sugar content between healthy trees and early stage of infection. However, for trees that were in established stage of infection, fructose, glucose, and sorbitol showed a decrease concentration across most cultivars and locations. This study also showed that ‘Cristalina’ and ‘Santina’ cultivars had a decrease in citric acid content in established infections compared with early infections.

The Wright et al. 2021 study is the first comprehensive evaluation of X-disease phytoplasma and biochemical content of fruit from different commercially grown sweet cherry cultivars known to be infected with Ca. P pruni. This study provides pathways for future research to better understand how X-disease is caused in sweet cherries and in other stone fruit.

Box plot with higher RQ values of Ca P. Pruni in severe and moderate symptoms
Figure 1. Comparison of Ca. P. pruni titer RQ values against symptom severity on commercial sweet cherry cultivars


Asymptomatic, mild to moderate, and severe symptoms of Ca P. pruni in different cherry cultivars

Wright AA, Shires MK, Beaver C, Bishop G, Dupont ST, Naranjo R, Harper S. The effect of Candidatus Phytoplasma pruni infection on sweet cherry fruit. Phytopathology. 2021 May 7. doi: 10.1094/PHYTO-03-21-0106-R. Epub ahead of print. PMID: 33961495




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