Molecular Epidemiology of Ralstonia solanacearum Species Complex Strains Causing Bacterial Wilt of Potato in Uganda

Abstract

Bacterial wilt (BW) caused by the Ralstonia solanacearum species complex (RSSC) is a serious threat to potato production in Uganda. However, little is known about the extent of the disease and the type of the pathogen strains involved. A nationwide survey was conducted to study BW prevalence and incidence in potato, and potato tuber and stem samples of potential alternative hosts were collected for pathogen isolation. DNA was extracted from pure cultures for genetic diversity studies. The pathogen was phylotyped by multiplex PCR; then, a subset of isolates was typed at sequevar level. Isolates of the same sequevar were then haplotyped using multilocus tandem repeat sequence typing (TRST) schemes. BW prevalence and incidence in potato farms were 81.4 and 1.7%, respectively. Three RSSC phylotypes were identified, with the majority of the strains belonging to Phylotype II (80%) followed by Phylotype I (18.5%) and III (1.5%). Phylotype I strains belonged to Sequevar 31, and Phylotype II strains belonged to Sequevar 1. Potato-associated Phylotype II Sequevar 1 strains were more diverse (27 TRST haplotypes) than nonpotato Phylotype I (5 TRST haplotypes). Mapping of TRST haplotypes revealed that three TRST haplotypes of Phylotype II Sequevar 1 strains play an important epidemiological role in BW of potato in Uganda being disseminated via latently infected seed. [Formula: see text] Copyright © 2019 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Contrasting genetic diversity and structure among Malagasy Ralstonia pseudosolanacearum phylotype I populations inferred from an optimized Multilocus Variable Number of Tandem Repeat Analysis scheme

“…We developed an optimized MLVA scheme capable of characterizing phylotype I isolates with greater reliability and discriminatory power. Consequently, we were able to overcome certain issues, namely the absence of polymorphism, a low typeability rate and the presence of different VNTRs in some loci [20,59]. These problems were highlighted by our in-laboratory preliminary tests with Malagasy isolates.…”

“…IIB-1 populations in Uganda [59]. The study of RSSC populations (phylotypes I, II and III) collected in the central highlands of Madagascar in 2013 was the first project of such magnitude (1224 isolates collected) [19].…”

Understanding seed potato selection practices in Uganda

“…As described by , rogueing within one season may reduce yield, rogueing over successive cycles will reduce seed degeneration by avoiding the spread of the disease and reduce the (total) yield loss. However, own observations showed that bacterial wilt diseased plants and tubers were thrown on neighbouring fields and not destroyed, therefore rampant spread of the disease is assumed; this also confirms findings of Kigundu et al (2019) that bacterial wilt is a major threat in Kabale district.…”

“…Of other major importance are diseases like bacterial wilt caused by Ralstonia solanacearum and late blight induced by Phytophthora infestans; they cause severe yield and quality losses for potato farmers in Sub-Saharan Africa. A study by Kigundu et al (2019) showed that bacterial wilt infection becomes rampant in Kabale district, which causes severe yield losses. Drought and poor agronomic practices, such as inadequate soil fertility management, disease control management and postharvest management also hamper potato yields of smallholder farmers (Scott et al, 2013, Gildemacher et al, 2009b.…”

A Meta-analysis of the known Global Distribution and Host Range of theRalstoniaSpecies Complex

“…We compiled 1625 strains from 35 papers mostly published between 2017 and 2020 [5–39], including the common reference strains for Ralstonia sequevar studies. These strains represent 57 sequevars isolated from 50 countries or territories (Table 1).…”