Five decades of research on phytoplasma-induced witches’ broom diseases

Abstract

Phytoplasmas, prokaryotic wall-less microorganisms, are important pathogens of several plant species in most parts of the world. Phytoplasmas have been reported associated with various symptoms on hundreds of plant species. Witches' broom disease (WBD) is one of the most common disease symptoms, which is caused by phytoplasma strains belonging to different phytoplasma groups. Symptoms of the disease differ from one host to the other as well as from one phytoplasma strain to the other. However, WBD symptoms are usually characterized by the production of a large number of small leaves, accompanied in some host plants by the production of several branches/shoots. Phytoplasma strains belonging to more than 13 groups and 39 subgroups have been reported associated with WBD in more than 116 plant species. Most of the phytoplasma strains causing WBD symptoms in plant species belong to the 16SrII and 16SrI groups, mainly 16SrII-D and 16SrI-B subgroups. The current review provides information on the different types of phytoplasma strains associated with WBD symptoms in ornamental plants, medicinal plants, forest trees, weeds, vegetable crops, field crops, and fruit trees. Emphasis is on WBD on acid limes, almonds, peanuts, jujube, and cassava that have resulted in significant economic losses in different countries. Description of the symptoms, phytoplasma groups, and management options is also provided for some of the diseases.

Molecular identification of ‘Candidatus Phytoplasma palmicola’ associated with coconut lethal yellowing in Equatorial Guinea

“…noviguineense' and 'Ca. P. dypsidis' in Papua New Guinea and Australia, respectively (Bertaccini et al, 2022;Harrison et al, 2014;Jones et al, 2021;Miyazaki et al, 2018) (Gurr et al, 2016;Hemmati et al, 2020;Yankey et al, 2018). Although the transmission of phytoplasmas among palms has been intensively studied, to date the only insect vector identified is Haplaxius crudus, which is known to transmit 'Ca.…”

“…P. wodyetiae’ and ‘ Ca . P. cynodontis’ (Gurr et al, 2016; Hemmati et al, 2020; Yankey et al, 2018). Although the transmission of phytoplasmas among palms has been intensively studied, to date the only insect vector identified is Haplaxius crudus , which is known to transmit ‘ Ca .…”

Cassava Witches’ Broom Disease in Southeast Asia: A Review of Its Distribution and Associated Symptoms

“…In general, the symptoms of witches' broom are associated with phytoplasma infections and have been reported in more than 116 plant species [19], making phytoplasma an emergent group of crop pathogens [20,21]. Nevertheless, phytoplasma detected in cassava in the Americas (ribosomal group 16SrIII) is found in plants with different symptoms such as a frogskin-like appearance of the roots [22][23][24], or a proliferation of shoots starting at the base of the main stem [25,26].…”

History of lethal yellowing with emphasis on the susceptibility of royal palms (Roystonea spp.)

“…To conclude this section, additional diseases of royal palms associated with phytoplasmas not enclosed in group 16SrIV will be mentioned briefly as LY-like diseases -as a whole-negatively impact palms not only in the Caribbean Basin but all over the world (Hemmati et al, 2020). So far, the only known examples are the association of group 16SrII phytoplasmas with R. borinquena in Puerto Rico (Simbaña Carrera, 2019) and of subgroup 16SrII-D phytoplasmas with R. regia in Oman (Hemmati et al, 2021).…”