Phloem Metabolites of Prunus Sp. Rather than Infection with Candidatus Phytoplasma Prunorum Influence Feeding Behavior of Cacopsylla pruni Nymphs

Abstract

Phytoplasmas are specialized small bacteria restricted to the phloem tissue and spread by hemipterans feeding on plant sieve tube elements. As for many other plant pathogens, it is known that phytoplasmas alter the chemistry of their hosts. Most research on phytoplasma-plant interactions focused on the induction of plant volatiles and phytohormones. Little is known about the influence of phytoplasma infections on the nutritional composition of phloem and consequences on vector behavior and development. The plum psyllid Cacopsylla pruni transmits 'Candidatus Phytoplasma prunorum', the causing agent of European Stone Fruit Yellows (ESFY). While several Prunus species are susceptible for psyllid feeding, they show different responses to the pathogen. We studied the possible modulation of plant-insect interactions by bacteria-induced changes in phloem sap chemistry. Therefore, we sampled phloem sap from phytoplasma-infected and non-infected Prunus persica and Prunus insititia plants, which differ in their susceptibility to ESFY and psyllid feeding. Furthermore, the feeding behavior and development of C. pruni nymphs was compared on infected and non-infected P. persica and P. insititia plants. Phytoplasma infection did not affect phloem consumption by C. pruni nymphs nor their development time. In contrast, the study revealed significant differences between P. insititia and P. persica in terms of both phloem chemistry and feeding behavior of C. pruni nymphs. Phloem feeding phases were four times longer on P. insititia than on P. persica, resulting in a decreased development time and higher mortality of vector insects on P. persica plants. These findings explain the low infestation rates of peach cultivars with plum psyllids commonly found in field surveys.

Involvement of SUT1 and SUT2 Sugar Transporters in the Impairment of Sugar Transport and Changes in Phloem Exudate Contents in Phytoplasma-Infected Plants

“…Our metabolomic survey of phloem exudates indicates that the infection triggers very few changes in the overall phloem sap composition, as described in phytoplasma-infected Prunus species [ 35 ] but in contrast to what was described in exudates collected from symptomatic leaves of phytoplasma-infected mulberries [ 25 ]. The novelty of our study compared to previous ones was to study separately the general effect of infection on the sap flow from that on the relative composition of each of the transported metabolites.…”

“…Studies on symptomatic, well-established phytoplasma infections reported disorganization of the vascular tissues [ 4 , 31 ] and the transcriptional reprogramming of genes involved in sugar transport and metabolism [ 16 , 18 , 24 , 28 , 32 , 33 ]. A phytoplasma infection also triggers modifications in the phloem sap composition [ 25 , 34 , 35 , 36 ], with changes in metabolites produced by diverse metabolic pathways. Such effects could be triggered by the phytoplasma for nutrition, plant defense response or physiological adjustments of impaired phloem activity [ 5 ].…”

The phytopathogen ‘Candidatus Phytoplasma mali’ alters apple tree phloem composition and affects oviposition behavior of its vector Cacopsylla picta

“…The phloem sap samples were derivatized with trimethylsilyl (TMS) to focus the GC-MS analysis on sugars and organic acids according to Gallinger and Gross (2020). Ribitol (Sigma-Aldrich Chemie GmbH, Munich, Germany) was used as internal standard.…”

“…P. mali' N = 14). Reference standards and respective suppliers were used according to Gallinger and Gross (2020).…”

“…Phytoplasma infection, however, may alter the phloem composition in infected plants as previous studies have shown (Gai et al 2014;Giorno et al 2013;Lepka 1999;Maust et al 2003). Moreover, behavior and fitness of vector and non-vector species was strongly influenced in correlation with differences in host plant phloem composition and particularly with regard to infected vs. non-infected plants (Gallinger and Gross 2020;Mayer et al 2011;Pradit et al 2019). Some phloem-feeders, like the Asian citrus psyllid (Diaphorina citri), oviposit and develop exclusively on young shoots (Grafton-Cardwell et al 2013).…”