Abstract
Black Sigatoka, caused by Pseudocercospora fijiensis, is a major foliar disease of banana and plantain worldwide. There are few available data regarding the genetic diversity and population structure of the pathogen in East Africa, which are needed to design effective and durable disease management strategies. We genotyped 319 single-spore isolates of P. fijiensis collected from seven regions in Uganda and Tanzania and five isolates from Nigeria using 16 simple sequence repeat markers and mating type-specific primers. Isolates from each country and region within the country were treated as populations and subpopulations, respectively. A total of 296 multilocus genotypes (MLGs) were recovered, representing a clonal fraction of 7%. Subpopulations had a moderate level of genetic diversity (Hexp = 0.12 to 0.31; mean, 0.29). Mating type distribution did not deviate from equilibrium (MAT1-1: MAT1-2, 1:1 ratio) in Uganda; however, in Tanzania the mating types were not in equilibrium (4:1 ratio). The index of association tests (IA and r̄d) showed that all populations were at linkage equilibrium (P > 0.05), thus supporting the hypothesis of random association of alleles. These findings are consistent with a pathogen that reproduces both clonally and sexually. Low and insignificant levels of population differentiation were detected, with 90% of the variation occurring among isolates within subpopulations. The high intrapopulation variation has implications in breeding for resistance to P. fijiensis because isolates differing in aggressiveness and virulence are likely to exist over small spatial scales. Diverse isolates will be required for resistance screening to ensure selection of banana cultivars with durable resistance to Sigatoka in East Africa.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.
Highlights
Banana (Musa spp.) is a major staple and cash crop for many communities in the Great Lakes region of Africa
High genotypic diversity was observed within all subpopulations of P. fijiensis sampled from banana in Tanzania and Uganda, with little evidence for regional differentiation, which is indicative of a common origin or frequent exchange of genetic material (McDonald 1997)
Tests for linkage disequilibrium (LD) showed that the loci in all populations were in equilibrium, which supports the contention of frequent recombination through sexual reproduction (Milgroom 1996) in P. fijiensis in East Africa
Summary
Banana (Musa spp.) is a major staple and cash crop for many communities in the Great Lakes region of Africa. The use of disease-resistant banana varieties is an integral part of sustainable and long-term management strategies for black Sigatoka (Carlier et al 2000; Marin et al 2003). Developing Sigatoka-resistant bananas varieties is challenging because of different ploidy levels, parthenocarpy, and sterility (Tenkouano et al 2011) This is compounded by a limited understanding of the genetic diversity, population structure, and evolutionary potential of P. fijiensis in East Africa. Such information is crucial for identifying suitable sources of resistance and for selecting pathogens with different virulence levels for use in screening for resistance in banana breeding programs. New combinations of alleles increase the potential for the emergence of new genotypes capable of adapting to new environments, overcoming resistance in newly deployed cultivars, and adapting to novel fungicides (McDonald 1997; McDonald and Linde 2002; Milgroom 2015)
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