Abstract
Banana wilt outbreaks that are attributable to Moko disease-causing strains of the pathogen Ralstonia solanacearum (Rs) remain a social and economic burden for both multinational corporations and subsistence farmers. All known Moko strains belong to the phylotype II lineage, which has been previously recognized for its broad genetic basis. Moko strains are paraphyletic and are distributed among seven related but distinct phylogenetic clusters (sequevars) that are potentially major threats to Musaceae, Solanaceae, and ornamental crops in many countries. Although clustered within the Moko IIB-4 sequevar, strains of the epidemiologically variant IIB-4NPB do not cause wilt on Cavendish or plantain bananas; instead, they establish a latent infection in the vascular tissues of plantains and demonstrate an expanded host range and high aggressiveness toward Solanaceae and Cucurbitaceae. Although most molecular diagnostic methods focus on strains that wilt Solanaceae (particularly potato), no relevant protocol has been described that universally detects strains of the Musaceae-infecting Rs phylotype II. Thus, a duplex PCR assay targeting Moko and IIB-4NPB variant strains was developed, and its performance was assessed using an extensive collection of 111 strains representing the known diversity of Rs Moko-related strains and IIB-4NPB variant strains along with certain related strains and families. The proposed diagnostic protocol demonstrated both high accuracy (inclusivity and exclusivity) and high repeatability, detected targets on either pure culture or spiked plant extracts. Although they did not belong to the Moko clusters described at the time of the study, recently discovered banana-infecting strains from Brazil were also detected. According to our comprehensive evaluation, this duplex PCR assay appears suitable for both research and diagnostic laboratories and provides reliable detection of phylotype II Rs strains that infect Musaceae.
Highlights
The Cavendish banana and plantain (Musa spp.) are among the most economically important crops, and they represent staple foods in developing countries
The Recognized as a species complex (Rssc) comprises strains that are capable of causing wilt in Musaceae plants and that cluster into two distant phylogenetic groups: (i) Moko disease-causing strains reported from Latin America, Asia, and the Philippines (Moko is recognized as Bugtok disease [11,12]) and (ii) the blood disease bacterium (BDB) originating in Indonesia and Malaysia
Based on the whole-genome sequences of Moko strains, we developed a robust, simple, and affordable duplex PCR assay that is specific for phylotype II Rssc strains that can be retrieved from banana and plantain tissues (Moko disease-causing strains and IIB-4NPB pathological variants)
Summary
The Cavendish banana and plantain (cooking banana) (Musa spp.) are among the most economically important crops, and they represent staple foods in developing countries. Bacterial wilt caused by Rs on both bananas and plantains continues to be a major constraint on the production of these crops, both for multi-national corporations and for subsistence farmers [5]. Recognized as a species complex (Rssc) [6], Rs is phylogenetically classified into four groups, called phylotypes, that take into account the phylogeography and evolutionary histories of the various strains [6,7]. The Rssc comprises strains that are capable of causing wilt in Musaceae plants and that cluster into two distant phylogenetic groups: (i) Moko disease-causing strains reported from Latin America, Asia, and the Philippines (Moko is recognized as Bugtok disease [11,12]) and (ii) the BDB originating in Indonesia and Malaysia. Bugtok disease only affects the floral bud, leading to hardening of the fruit (stone fruit) [14]
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