‘Candidatus Phytoplasma asteris’ subgroups display distinct disease progression dynamics during the carrot growing season

Abstract

Aster Yellows phytoplasma (AYp; ‘Candidatus Phytoplasma asteris’) is an obligate bacterial pathogen that is the causative agent of multiple diseases in herbaceous plants. While this phytoplasma has been examined in depth for its disease characteristics, knowledge about the spatial and temporal dynamics of pathogen spread is lacking. The phytoplasma is found in plant’s phloem and is vectored by leafhoppers (Cicadellidae: Hemiptera), including the aster leafhopper, Macrosteles quadrilineatus Forbes. The aster leafhopper is a migratory insect pest that overwinters in the southern United States, and historical data suggest these insects migrate from southern overwintering locations to northern latitudes annually, transmitting and driving phytoplasma infection rates as they migrate. A more in-depth understanding of the spatial, temporal and genetic determinants of Aster Yellows disease progress will lead to better integrated pest management strategies for Aster Yellows disease control. Carrot, Daucus carota L., plots were established at two planting densities in central Wisconsin and monitored during the 2018 growing season for Aster Yellows disease progression. Symptomatic carrots were sampled and assayed for the presence of the Aster Yellows phytoplasma. Aster Yellows disease progression was determined to be significantly associated with calendar date, crop density, location within the field, and phytoplasma subgroup.

Divergence within the Taxon ‘Candidatus Phytoplasma asteris’ Confirmed by Comparative Genome Analysis of Carrot Strains

“…These results are consistent with the occurrence of different 16SrI subgroups on individual fields during the season. Furthermore, our research confirms the disparities in the coded effectors of the SAP group within the 16SrI groups, which were illustrated by Clements and colleagues [64]. The phylogenetic analysis did not provide information on a shared geographical origin regarding the introduction into Germany (Figure 4).…”

“…Notably, the genes coding for the effectors SAP11 and SAP54 were not identified for strain M33 whereas M8 encodes both genes. The lack of SAP11 stands in accordance with earlier findings from field studies supporting their absence in the 16SrI-B group [64]. Similar to the multi-copy gene analysis, these results also indicate that the numbers of genes coding for secreted or putative secreted proteins are higher within the larger chromosomes than in the smaller ones.…”

Limited variation in microbial communities across populations ofMacrostelesleafhoppers (Hemiptera: Cicadellidae)

“…Due to their mode of feeding, Auchenorrhyncha may cause feeding damage, but more importantly, vector plant pathogens, such as the agriculturally important genus Candidatus Phytoplasma (Mollicutes) (hereafter Phytoplasma ). These phloem-limited plant parasitic bacteria can cause extensive damage to more than 700 plant species, including maize (Ramos et al ., 2020), carrot (Clements et al ., 2021), grapevine (Moussa et al ., 2023) and many other important crops. Therefore, managing these vector species is of great economic importance even though estimates of economic loss are lacking.…”

Molecular Matchmakers: Phytoplasma Effector SAP54 Targets MADS-Box Factor SVP to Enhance Attraction of Fecund Female Vectors by Modulating Leaf Responses to Male Presence

“…As obligate bacterial parasites, phytoplasmas frequently trigger the emergence of unusual plant structures such as leaf-like floral parts (phyllody) and the excessive growth and clustering of leaves and branches (witch's broom) (Lee et al, 2000;Al-Subhi et al, 2018;Kumari et al, 2019). These alterations not only compromise plant health but also promote attraction and colonization of insect vectors that are primarily responsible for phytoplasma spread and transmission (Sugio et al, 2011a;Frost et al, 2013;MacLean et al, 2014;Orlovskis & Hogenhout, 2016;Clements et al, 2021;Al-Subhi et al, 2021;Huang & Hogenhout, 2022). The responsible phytoplasma genes encode for effector molecules that, once inside the plant cell cytoplasm, target and typically disrupt or degrade essential plant transcription factors involved in growth, development, and defence (review by Wang et al, 2024 and references therein as well as Liu et al, 2023;Suzuki et al, 2024;Correa Marrero et al, 2024;Yan et al, 2024;Zhang et al, 2024).…”