Incidence, distribution, and genetic diversity of 'Candidatus Phytoplasma luffae'-related strain (16SrVIII) associated with the cassava witches' broom (CWB) disease in the Philippines.

Cassava (Manihot esculenta Crantz) is widely grown in the Philippines mainly for human consumption, animal feed, and industrial purposes. However, the cassava industry is recently challenged by the cassava witches' broom (CWB) disease which is known to be caused by phytoplasmas. The extent of the disease and the causal phytoplasma strain in the country are not known until this study. Surveys in major cassava areas in the Philippines conducted from 2017 to 2019 revealed that CWB is present in 13 out of 19 provinces assessed in this study, with symptoms ranging from leaf proliferation, little leaf, shortened internodes, stunted growth, discoloration of the vascular system, and small tubers. Molecular detection (through nested PCR) and sequence analysis of phytoplasma 16S ribosomal RNA gene from CWB-infected plants showed high genetic similarity of >98.65% to Candidatus Phytoplasma luffae 16SrVIII. In addition, the 18 phytoplasma isolates from five provinces successfully grouped to Ca. Phytoplasma luffae 16SrVIII clade in the constructed phylogenetic tree. Analysis on the genetic diversity and structure of Ca. Phytoplasma luffae 16SrVIII sequences from cassava and other host plant species revealed low genetic diversity indices and a rudimentary genetic structure with high haplotype diversity. Meanwhile, neutrality tests showed evidence of recent population expansion in Ca. Phytoplasma luffae 16SrVIII. This is the first study to identify ' Ca. Phytoplasma luffae'-related strain (16SrVIII) as the causal pathogen of CWB in the Philippines. The information generated in this study can help in better understanding the etiology of the disease and in formulating proper and effective strategies to detect and manage the disease in the Philippines. • CWB is present in 13 out of 19 provinces surveyed in the Philippines from 2017 to 2019. • CWB symptoms include little leaf proliferation, shortened internodes, vascular system discoloration, and small tubers. • ' Ca. Phytoplasma luffae'-related strain (16SrVIII) was detected from CWB-infected plants through 16S rRNA gene analysis. • Ca. Phytoplasma luffae 16SrVIII displayed low genetic diversity with evidence of recent population expansion. • First study to identify ' Ca. Phytoplasma luffae'-related strain as the causal pathogen of CWB in the Philippines. [ABSTRACT FROM AUTHOR]

Copyright of Crop Protection (02612194) is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)