![]() ![]() Phytoplasma-infected plants often show characteristic symptoms, including witches’ brooms (stem proliferations from a single point), virescence (colored flower parts that remain green), phyllody (development of vegetative tissues instead of flowers), big buds (bulbous enlarged flower buds), sterility, chlorosis, stunting, changes in leaf morphology, and general decline of the plant ( Bertaccini et al. Phytoplasma infect a wide variety of vascular plant species and occur worldwide ( Bertaccini 2007 Hogenhout et al. 2003), and parasitic plants, including dodder ( Cascuta species Garnier et al. Phytoplasma are introduced into the sieve cells during feeding by phytoplasma-carrying sap-feeding insects of the order Hemiptera ( Weintraub and Beanland 2006), grafts of phytoplasma-infected scions ( Aryan et al. All phytoplasmas characterized so far are intracellular pathogens of plants these bacteria colonize the cytoplasm of phloem sieve cells of the plant vasculature and move systemically throughout the plant via migration through sieve plate pores ( Bové and Garnier 2002). ![]() Phytoplasmas form a monophyletic group that has common ancestry with Acholeplasma species ( Harrison et al. Within the Class Mollicutes, members of Ca. The majority of mollicutes live in close association with eukaryotic hosts as symbionts or pathogens and have undergone severe genome reductions. Phytoplasmas (genus ‘ Candidatus phytoplasma’) and other members of the Class Mollicutes are small bacteria with single cell membranes and no cell wall and are thought to have evolved from a Gram-positive Clostridium-like ancestor ( Bertaccini 2007 Hogenhout et al. These findings suggest that witches’ broom-affected parts of the trees contribute to WBDL epidemics by supporting higher phytoplasma titers and attracting insect vectors. Defense genes that have a role in plant defense responses to bacteria and insects are more downregulated in witches’ brooms compared with asymptomatic sections of trees. Moreover, the witches’ brooms were found to attract the vector leafhopper. Sampling of WBDLp-infected lime trees revealed that WBDLp titers and SAP11 WBDL expression levels were higher in symptomatic leaves compared with asymptomatic sections of the same trees. SAP11 WBDL interacts with acid lime ( Citrus aurantifolia) TCP transcription factors, specifically members of the TB1/CYC class that have a role in suppressing axillary branching in plants. Here we show that the gene encoding SAP11 of WBDLp ( SAP11 WBDL) is present in all WBDLp isolates collected from diseased trees. However, it is unclear how WBDL phytoplasma (WBDLp) induces witches’ broom symptoms and if these symptoms contribute to the spread of phytoplasma. ![]() We’ll keep you posted.An insect-transmitted phytoplasma causing Witches’ Broom Disease of Lime (WBDL) is responsible for the drastic decline in lime production in several countries. We made many, many cuttings from the witches’ broom and hope that some will root, grow, and thrive as a new and interesting cultivar of Pinus sylvestris. Until now, it was too high up in the tree to easily access. We would love to name it for Garden and Nursery co-founder, Mareen Kruckeberg. We’ve had our eye on the witches’ broom for years, hoping that we could create our very own cultivar. Many dwarf conifer cultivars are propagated from witches’ broom, as the abnormal growth form often continues in plants grown from cuttings or grafted cuttings. This is very exciting for our horticultural staff. Exploration inside the mass of contorted twigs found a large amount of moss happily growing, along with what looked like an old bird’s nest. The spindly branch that held it was obviously outmatched. No surprise there – I put it on a scale and it weighed almost 30 pounds!įrankly, I was surprised it stayed in the tree as long as it did. Well, ours hit the ground this week when its branch snapped. Witches’ brooms are abnormally dense growth in a woody plant triggered by physical damage, insect infestation, a parasite, or disease. Garden visitors in past years may have noticed the witches’ broom growing in the Scots pine ( Pinus sylvestris) near the Garden’s entrance. ![]()
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