Genetic diversity and geographic distribution of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) genotypes associated with cassava in East Africa Habibu Mugerwa1,4, Marie E. C. Rey4, Titus Alicai1, Elijah Ateka2, Hellen Atuncha2, Joseph Ndunguru3 & Peter Sseruwagi1 1National Crops Resources Research Institute, P.O. Box 7084, Kampala, Uganda 2Department of Horticulture, Jomo Kenyatta University of Technology and Agriculture, P.O. Box 62000-00200, Nairobi, Kenya 3Mikocheni Agricultural Research Institute, Eastern Zone, P.O. Box 6226, Dar Es Salaam, Tanzania 4School of Molecular and Cell Biology, University of the Witwatersrand, P.O. Box 2050, BraamFontein, Johannesburg, South Africa Keywords Cytochrome oxidase I (mtCOI), genetic diversity, geographic distribution, mitochondria, whitefly Correspondence Peter Sseruwagi, National crops Resources Research Institute, P.O. Box 7084, Kampala, Uganda. Tel: +256 782 505 281; Fax: + 256 752 726 554; E-mail: psseruwagi@yahoo.co.uk Funding Information This study was supported by the Bill and Melinda Gates Foundation (Grant no. 51466) as part of the ‘Regional Cassava Virus Diseases Diagnostic Project’ coordinated by Dr. Joseph Ndunguru. Received: 4 April 2012; Revised: 8 August 2012; Accepted: 8 August 2012 Ecology and Evolution 2012; 2(11): 2749–2762 doi: 10.1002/ece3.379 Abstract The genetic variability of whitefly (Bemisia tabaci) species, the vectors of cassava mosaic begomoviruses (CMBs) in cassava growing areas of Kenya, Tanzania, and Uganda, was investigated through comparison of partial sequences of the mitochondria cytochrome oxidase I (mtCOI) DNA in 2010/11. Two distinct species were obtained including sub-Saharan Africa 1 (SSA1), comprising of two sub-clades (I and II), and a South West Indian Ocean Islands (SWIO) spe- cies. Among the SSA1, sub-clade I sequences shared a similarity of 97.8–99.7% with the published Uganda 1 genotypes, and diverged by 0.3–2.2%. A pairwise comparison of SSA1 sub-clade II sequences revealed a similarity of 97.2–99.5% with reference southern Africa genotypes, and diverged by 0.5–2.8%. The SSA1 sub-clade I whiteflies were widely distributed in East Africa (EA). In compari- son, the SSA1 sub-clade II whiteflies were detected for the first time in the EA region, and occurred predominantly in the coast regions of Kenya, southern and coast Tanzania. They occurred in low abundance in the Lake Victoria Basin of Tanzania and were widespread in all four regions in Uganda. The SWIO spe- cies had a sequence similarity of 97.2–97.7% with the published Reunion sequence and diverged by 2.3–2.8%. The SWIO whiteflies occurred in coast Kenya only. The sub-Saharan Africa 2 whitefly species (Ug2) that was associated with the severe CMD pandemic in Uganda was not detected in our study. Introduction Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is widely distributed worldwide and is composed of a com- plex of more than 24 morphologically indistinguishable cryptic species (Dinsdale et al. 2010; De Barro et al. 2011; Shu-sheng et al. 2012). The 3.5% pairwise genetic diver- gence identified by Dinsdale et al. (2010) as being the boundary separating different species is further supported by evidence for either complete or partial mating isolation between a number of the putative B. tabaci “species” (Xu et al., 2010, Wang et al. 2011). The species level groups identified by Dinsdale et al. (2010) conform to the fol- lowing 24 well-defined high-level phylogeographical groups (names of associated biotypes are placed in paren- theses where applicable): Mediterranean (Q, J, L, Sub- Saharan Africa Silverleaf); Middle East-Asia Minor 1 (B, B2); Middle East-Asia Minor 2; Indian Ocean (MS); Asia I (H, M, NA); Australia/Indonesia; Australia (AN); China 1 (ZHJ3); China 2; Asia II 1 (K, P, ZHJ2); Asia II 2 (ZHJ1); Asia II 3; Asia II 4; Asia II 5 (G); Asia II 6; Asia II 7 (Cv); Asia II 8; Italy (T); Sub-Saharan Africa 1; Sub- Saharan Africa 2 (S); Sub-Saharan Africa 3; Sub-Saharan Africa 4; New World (A, C, D, F, Jatropha, N, R, Sida); and Uganda. Bemisia tabaci has gained increased importance as a crop pest and a vector of plant viruses, particularly geminiviruses in the genus Begomovirus (family, Geminiviridae) in tropical and subtropical regions of the world (Poulston and Anderson 1997). In sub- Saharan Africa, B. tabaci is a major vector of cassava ª 2012 The Authors. Ecology and Evolution published by Blackwell Publishing Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. 2749 mosaic begomoviruses (CMBs) and cassava brown streak viruses (CBSVs), the causative agents of cassava mosaic disease (CMD) and cassava brown streak disease (CBSD), respectively. The two diseases cause devastating yield losses in cassava (Maruthi et al. 2005; Legg et al. 2011). An epidemic of severe CMD was first reported to cause devastating effects (100% yield loss) to cassava crops in Uganda in the 1990s (Otim-Nape et al. 1997). Subsequent studies associated the spread of the epidemic with unusually high whitefly populations (Legg 1999; Otim- Nape et al. 2000; Colvin et al. 2004). The high whitefly populations were believed to be a result of several factors including an invasive whitefly (Legg et al. 2002), whiteflies feeding on plants infected with the severe EACMV-UG2 (Colvin et al. 2004, 2006) and the widespread occurrence of whitefly-susceptible cassava varieties (Omongo et al. 2004, 2012) in the severe CMD pandemic affected areas. Using the mitochondria cytochrome oxidase I (mtCOI) marker (Frohlich et al. 1999), Legg et al. (2002) identified two distinct cassava-associated B. tabaci genotype clusters, designated as Uganda 1 (Ug1) and Uganda 2 (Ug2), which currently fall in genetic groups designated as sub- Saharan Africa 1 (SSA1) and sub-Saharan Africa 2 (SSA2), respectively (Dinsdale et al. 2010). The Ug1 occurred in areas “ahead” of the epidemic front, whereas Ug2 was the predominant population at the “front”. It was suggested that the Ug1 was the indigenous or local population, whereas the Ug2 could be an “invader” popu- lation with its closest relatives from Cameroon in West Africa. The occurrence of the two B. tabaci species on cassava in Uganda was further confirmed by Maruthi et al. (2004), although with diminishing proportions of the Ug2 species in 2003 (Sseruwagi 2005). Cassava mosaic disease continues to devastate cassava crops in East and Central Africa threatening the lives of over 200 million people (Legg et al. 2006). As a consequence, a number of programs have been instituted by African gov- ernments through the national agricultural research systems (NARS), and different local and international stakeholders to monitor the spread of the disease and enforce mitigation measures. However, limited research has been conducted to establish the current situation of the B. tabaci species associ- ated with the disease. A clear understanding of whitefly spe- cies associated with the spread of the CMBs in the region would be invaluable to assist the development of durable integrated pest and disease management strategies. This study sought to establish the genetic diversity and geographic distribution of B. tabaci associated with CMD and CBSD on cassava in East Africa (Kenya, Tanzania, and Uganda). We use the term “genotypes” or “haplo- types” to refer to genetically distinct sequences within the species boundary sharing <3.5% nucleotide similarity, whereas “species” refers to a genetic group of closely related sequences exhibiting more than 3.5% divergence with other species as described by Dinsdale et al. (2010). Materials and Methods Study area The study was conducted in three East African countries: Kenya, Tanzania, and Uganda. In each country, major cassava producing areas were demarcated as follows: Wes- tern, Nyanza, and Coast provinces (Kenya); Lake Victoria Basin, Southern zone, and Coast zone (Tanzania); and central, northern, eastern, and western regions (Uganda). Kenya: Western and Nyanza provinces share a similar agro-ecology, which is characterized by: bimodal rainfall ranging from 950 to 1500 mm annually, temperature ranges between 18.4 and 25.4°C, altitude of 900–1800 m, and a savannah grass land. The coast province has rainfall ranging from 500 to 1000 mm annually, temperature ranges between 22.4 and 30.3°C, altitude of 900–1800 m, and a savannah grass land (http://www.infonet-biovision. org/default/ct/690/agrozones). Tanzania: Lake Victoria Basin is characterized by: bimodal rainfall ranging from 1000 to 2000 mm annually, temperature ranges between 17 and 28°C, altitude of 1000 –1800 m, and has savannah vegetation with scattered tall trees. The Southern zone has unimodal rainfall ranging from 600 to 800 mm annually, temperature ranges between 18 and 28°C, altitude of 200–600 m and is com- posed of woodland, bush land thickets, and grassland. Coast zone has a bimodal rainfall ranging from 750 to 1200 mm annually, temperature ranges between 22 and 30°C, altitude of under 300 m, and a savannah grass land (http://www.fas.usda.gov/pecad/highlights/2005/09/tanza- nia_2005/images/TZ_AEZ.htm). Uganda: The cassava growing regions are characterized by: temperatures ranging from 25 to 31°C, and altitude ranging between 900 and 1500 mm. Central region has bimodal rainfall averaging 1000 mm annually and vegeta- tion is savannah grassland with moderate biomass. North- ern region has both unimodal and bimodal rainfall averaging 800 mm annually and covered with short savannah grassland. Eastern region has a bimodal rainfall ranging from 750 to 1200 mm annually with short savan- nah grassland. The western region has bimodal rainfall ranging from 1000 to 1500 mm annually and is a forest savannah area. (http://www.fao.org/ag/AGP/AGPC/doc/ Counprof/uganda/uganda.htm). Whitefly collection Adult whiteflies (Fig. 1) were collected using an aspirator from 3- to 5-month-old cassava plants from different 2750 ª 2012 The Authors. Ecology and Evolution published by Blackwell Publishing Ltd. Genetic Diversity and Geographic Distribution H. Mugerwa et al. regions in Kenya, Tanzania, and Uganda (Table 1) and stored in 70% ethanol. Geo-coordinates (latitude and longitude) were recorded using a Geographical Position- ing System (GPS) for each sampled location. Extraction of whitefly DNA Three adult female whiteflies were randomly selected from each collection site. Each individual insect was ground in 10 lL of lysis buffer (5 mM Tris-HCl, Ph8.0, 0.5 mM EDTA, 0.5% Nonidet P-40, 1 mg/mL proteinase K) using the tips of 0.2 lL polymerase chain reaction (PCR) tubes. The lysis product was incubated for 15 min at 65°C and further 10 min at 95°C. Subsequently, it was centrifuged (~60 sec) briefly and placed immediately on ice prior to PCR amplification. Lysis was carried out as described by Frohlich et al. (1999). PCR amplification of mtCOI DNA and sequencing A total of 79 (Kenya – 21, Tanzania – 41, and Uganda – 17) whiteflies were used to study the genetic variability and distribution of cassava-associated B. tabaci genotypes in cassava growing areas of Kenya, Tanzania, and Uganda in 2010/11. Amplification of mitochondria cytochrome oxi- dase I (mtCOI) DNA was achieved by the use of a primer pair MT10/C1-J-2195 (5′-TTGATTTTTTGGTCATCCA GAAGT-3′) and MT12/L2-N-3014 (5′-TCCAATGCACTA ATCTGCCATATTA) as per Simon et al., 1994. A DNA template of 5 lL was used in a PCR reaction mixture of 25 lL, containing 19 Taq buffer with Mg2+, 0.2 mM deoxynucleotide triphosphate (dNTPs), 0.32 mM each of primers MT10 and MT12, and 0.625U Taq DNA polymerase. Initial denaturation of template DNA was conducted for 3 min followed by 30 cycles of denaturation at 94°C for 30 sec, primer annealing at 52°C for 30 sec, and extension at 72°C for 1 min. The final extension of 10 min was run at 72°C and the reaction held at 4°C in a Perkin Elmer DNA thermal cycler. Electrophoresis of PCR products was run in 1% agarose gel stained in ethidium bromide in 19 TAE buffer in a submarine gel unit and visualized using ultraviolet light. PCR products of the expected 850 bp size were obtained. Bands were excised from the agarose gel and purified for DNA cloning using a Qiagen gel Purifica- tion kit (QIAGEN, Venlo, the Netherlands) as per the manufacturer’s procedure. Purified PCR products were cloned using the pGEM-T easy vector as per the manu- facturer’s instructions and sent to Bioscience Centre for Eastern and Central Africa, Nairobi for sequencing. Phylogenetic analysis of mtCOI sequence Whitefly mtCOI sequences were edited manually to pro- duce a consensus sequence of 817 bp for each individual whitefly using the Editseq program of DNAStar computer package (DNASTAR, Madison, Wisconsin). The edited sequences were aligned together with reference whitefly sequences obtained in the GenBank using Cluster W (weighted) (Thompson et al. 1994) algorithm option avail- able in the MEGA 5.02 program (Tamura et al. 2011). Aligned sequences were trimmed to about 650 bp and subjected to a heuristic search and subtree-pruning- regrafting branch swapping using maximum parsimony method available in MEGA 5.02. The ML tree was recon- structed using maximum parsimony optimality criterion with among-site rate variation corresponding with gamma distribution and a general-time – reversible substitution model with the rate matrix set to 1. For parsimony analy- sis, bootstrapping (Felsenstein 1985) was performed with PAUP using the heuristic option for 1000 replication at a 70% confident limit (Swofford 1998). The following reference mtCOI sequences and their genbank accession numbers (indicated in brackets) were used for the analysis: Asia1 Thailand [AF164671]; Asia II China [AJ784261]; Asia II China [AJ783706]; Asia II China [AY686083]; Asia II China [AY686088]; Asia II China [AF418666]; Asia II 9 China Hunan [HM137313]; Asia II 10 China Guangdong [HM137356]; Asia II India [AJ748374]; Asia II Pakistan [AJ510065]; Asia III Taiwan [DQ174528]; Australia Bundaberg [GU086328]; Australia Indonesia [AB248263]; China [AY686085]; China [AY686091]; China 3 Yunnan [EU192050]; Italy [AY827596]; Med- AmAF Pakistan [AJ510075]; MedAmAf BioB Reunion [AJ550177]; Med Syria [AB297897]; Ms Reunion [AJ550178]; New World Colombia [AJ550168]; Subsa- hAf1 Ug [AY057185]; SubSahAf1 Ug[AY057181]; Subsa- hAf1 Moz [AF344278]; SubsahAf1 SA [AF344264]; SubsahAf2 Ug [AY057194]; SubsahAF3 Cameroon Figure 1. Adult whitefly (Bemisia tabaci) ª 2012 The Authors. Ecology and Evolution published by Blackwell Publishing Ltd. 2751 H. Mugerwa et al. Genetic Diversity and Geographic Distribution Table 1. Whitefly mitochondria cytochrome oxidase I sequences used in the study. Genotype name Name in database Country Region/province GenBank accession no. Ke-Nyz23a KeNyanza23a Kenya Nyanza JQ286408 Ke-Nyz23b KeNyanza23b Kenya Nyanza JQ286409 Ke-C1 KeCoastC1 Kenya Coast JQ286410 Ke-C2 KeCoastC2 Kenya Coast JQ286411 Ke-C3 KeCoastC3 Kenya Coast JQ286412 Ke-C4 KeCoastC4 Kenya Coast JQ286413 Ke-C5 KeCoastC5 Kenya Coast JQ286414 Ke-C6 KeCoastC6 Kenya Coast JQ286415 Ke-C7 KeCoastC7 Kenya Coast JQ286416 Ke-C8 KeCoastC8 Kenya Coast JQ286417 Ke-N1 KeNyanzaN1 Kenya Nyanza JQ286418 Ke-N2 KeNyanzaN2 Kenya Nyanza JQ286419 Ke-N3 KeNyanzaN3 Kenya Nyanza JQ286420 Ke-N4 KeNyanzaN4 Kenya Nyanza JQ286421 Ke-N5 KeNyanzaN5 Kenya Nyanza JQ286422 Ke-N6 KeNyanzaN6 Kenya Nyanza JQ286423 Ke-N7 KeNyanzaN7 Kenya Nyanza JQ286424 Ke-W1 KeWesternW1 Kenya Western JQ286425 Ke-W2 KeWesternW2 Kenya Western JQ286426 Ke-W3 KeWesternW3 Kenya Western JQ286427 Ke-W5 KeWesternW5 Kenya Western JQ286429 Ug-2a UgArua2a Uganda Northern JQ286430 Ug-2b UgArua2a Uganda Northern JQ286431 Ug-3a UgSoroti3a Uganda Eastern JQ286432 Ug-3b UgSoroti3b Uganda Eastern JQ286433 Ug-24a UgKatakwi24a Uganda Eastern JQ286434 Ug-43a UgMasindi43a Uganda Western JQ286435 Ug-43b UgMasindi43b Uganda Western JQ286436 Ug-43c UgMasindi43c Uganda Western JQ286437 Ug-43d UgMasindi43d Uganda Western JQ286438 Ug-43e UgMasindi43e Uganda Western JQ286439 Ug-43f UgMasindi43f Uganda Western JQ286440 Ug-92a UgAdjumani92a Uganda Northern JQ286441 Ug-101a UgKitgum101a Uganda Northern JQ286442 Ug-101b UgKitgum101b Uganda Northern JQ286443 Ug-113a UgMpigi113a Uganda Central JQ286444 Ug-113b UgMpigi113b Uganda Central JQ286445 Ug-157a UgNakaseke113a Uganda Central JQ286446 Tz-8b TzBunazi8b Tanzania Kagera, Lake zone JQ286447 Tz-10b TzRugera10b Tanzania Kagera, Lake zone JQ286448 Tz-16a TzOukasole16a Tanzania Kagera, Lake zone JQ286449 Tz-16b TzOukasole16b Tanzania Kagera, Lake zone JQ286450 Tz-18a TzChamugisha18a Tanzania Kagera, Lake zone JQ286451 Tz-23a TzNyakanzi23a Tanzania Kagera, Lake zone JQ286452 Tz-23b TzNyakanzi23b Tanzania Kagera, Lake zone JQ286453 Tz-28a TzMpomvu28a Tanzania Mwanza, Lake zone JQ286454 Tz-49a TzKwasunga49a Tanzania Tanga, Coastal zone JQ286455 Tz-53a TzMabukweni53a Tanzania Tanga, Coastal zone JQ286456 Tz-57a TzMkata57a Tanzania Tanga, Coastal zone JQ286457 Tz-57b TzMkata57b Tanzania Tanga, Coastal zone JQ286458 Tz-58a TzMbwewe58a Tanzania Tanga, Coastal zone JQ286459 Tz-58b TzMbwewe58b Tanzania Tanga, Coastal zone JQ286460 Tz-62a TzMbinga62a Tanzania Ruvuma, Southern zone JQ286461 Tz-62b TzMbinga62b Tanzania Ruvuma, Southern zone JQ286462 (Continued) 2752 ª 2012 The Authors. Ecology and Evolution published by Blackwell Publishing Ltd. Genetic Diversity and Geographic Distribution H. Mugerwa et al. [AF344257]; SubsahAf4 Cameroon [AF344247]; Uganda [AF418665]. The species used in the analysis as out group were B. afer [GU220055] and B. subdecipens [GU220056] (Dinsdale et al. 2010). Results Phylogenetic analysis of whitefly mtCOI sequences A PCR fragment of the mtCOI gene (~850 bp) was obtained for each adult whitefly using the primer pair: MT10/C1-J-2195 and MT12/L2-N-3014 (Fig. 2). A con- sensus sequence was obtained for each mtCOI 850 bp nucleotide sequence for the 79 whiteflies. The sequences have been deposited in the GenBank database as accession numbers JQ286408 to JQ286487 (Table 1). Based on the phylogenetic analysis of reference mtCOI sequences, members of B. tabaci generally group into dis- tinct species cluster in the New World or Old World (Dins- dale et al. 2010). The New World B. tabaci from Colombia is genetically distinct from the Old World members from Australia, Mediterranean/North Africa/Middle East, Southeast Asia/Far East/India, and sub-Saharan Africa. Cassava-associated B. tabaci genotypes from Kenya grouped into the New World sub-Saharan Africa 1 (SSA-1) genetic clade with the exception of one genotype, which clustered with the SWIO genetic group (Delatte et al. 2011). Within the SSA-1 genetic group, the Kenyan geno- types clustered further in two sub-clades, hereafter named sub-clade I and sub-clade II. Sub-clade I contained Kenyan genotypes with a sequence similarity of 97.9–99.7% with the published Ug1 genotypes (Fig. 3) that occurred ahead Table 1. Continued. Genotype name Name in database Country Region/province GenBank accession no. Tz-65a TzMkinga65a Tanzania Ruvuma, Southern zone JQ286463 Tz-68a TzMkoha68a Tanzania Ruvuma, Southern zone JQ286464 Tz-70a TzMatomondo70a Tanzania Ruvuma, Southern zone JQ286465 Tz-70b TzMatomondo70b Tanzania Ruvuma, Southern zone JQ286466 Tz-75a TzLikalangilo75a Tanzania Tanga, Coastal zone JQ286467 Tz-77a TzRwengu77a Tanzania Ruvuma, Southern zone JQ286468 Tz-81a TzMajala81a Tanzania Ruvuma, Southern zone JQ286469 Tz-83a TzMasaiyaleo83a Tanzania Mtwara, Southern zone JQ286470 Tz-90a TzMasaiyaleo90a Tanzania Mtwara, Southern zone JQ286471 Tz-90b TzMasaiyaleo90b Tanzania Mtwara, Southern zone JQ286472 Tz-91a TzTikule91a Tanzania Lindi, Southern zone JQ286473 Tz-93a TzWangurukuru93a Tanzania Lindi, Southern zone JQ286474 Tz-93b TzWangurukuru93b Tanzania Lindi, Southern zone JQ286475 Tz-95b TzIkwiriri95b Tanzania Coast, Coastal zone JQ286476 Tz-97a TzNgunja97a Tanzania Coast, Coastal zone JQ286477 Tz-H1 TzMwanzaH1 Tanzania Mwanza, Lake zone JQ286478 Tz-H4 TzTangaH4 Tanzania Tanga, Coastal zone JQ286479 Tz-H9 TzKageraH9 Tanzania Kagera, Lake zone JQ286480 Tz-H12 TzKageraH12 Tanzania Kagera, Lake zone JQ286481 Tz-H15 TzKageraH15 Tanzania Kagera, Lake zone JQ286482 Tz-H18 TzMwanzaH18 Tanzania Mwanza, Lake zone JQ286483 Tz-H20 TzMwanzaH20 Tanzania Mwanza, Lake zone JQ286484 Tz-H24 TzTangaH24 Tanzania Tanga, Coastal zone JQ286485 Tz-H27 TzMwanzaH27 Tanzania Mwanza, Lake zone JQ286486 Tz-H30 TzMwanzaH30 Tanzania Mwanza, Lake zone JQ286487 Figure 2. Agarose gel of PCR-amplified products of the expected 850 bp size. Lanes 1, 2, 3, and 4 are individual whitefly (Bemisia tabaci) insects. ª 2012 The Authors. Ecology and Evolution published by Blackwell Publishing Ltd. 2753 H. Mugerwa et al. Genetic Diversity and Geographic Distribution Figure 3. Phylogenetic tree based on the mitochondrial cytochrome oxidase I sequence for Bemisia tabaci collected in Kenya generated using maximum likilihood available in MEGA5 software program. Bemisia subdecipens and B. afer are included as outgroups. Whiteflies used in the study are labeled as follows: Ke-N1, Ke-N2, Ke-N3, Ke-N4, Ke-N5, Ke-N6, Ke-N7, Ke-Nyz23a,KeNyz23b (Nyanza region); Ke-W1, Ke-W2, Ke-W3, Ke-W5 (Western region); Ke-C1, Ke-C2, Ke-C3, Ke-C4, Ke-C5, Ke-C6, Ke-C7, Ke-C8 (Coastal region). 2754 ª 2012 The Authors. Ecology and Evolution published by Blackwell Publishing Ltd. Genetic Diversity and Geographic Distribution H. Mugerwa et al. of the severe CMD epidemic-affected areas in the 1990s (Legg et al. 2002). The sequences were 0.3–2.2% divergent (Table 2). Sub-clade II comprised of genotypes with 97.1– 99.4% sequence similarity to the southern Africa (SA) geno- types from Mozambique and South Africa (Berry et al. 2004; Esterhuizen et al. 2012) (Fig. 3) and 0.6–2.9% sequence divergence (Table 2). Only one sequence clustered with the SWIO genetic group (Fig. 3) with 97.2–97.7% sequence similarity and 2.3–2.8% divergence (Table 2). Phylogenetic analysis of the mtCOI B. tabaci from Tan- zania grouped all the sequences into the SSA-1 genetic group with two sub-clades as was the case for the Kenyan sequences (Fig. 4). A pairwise comparison of mtCOI sequences of the sub-clade I Tanzanian B. tabaci geno- types revealed a sequence similarity of 97.9–99.7% with reference to Ug1 genotypes, and a divergence of 0.3–2.2% among the sequences (Table 2). Sub-clade II genotypes shared 98–99.2% sequence similarity with SA genotypes (Fig. 4). The sequences diverged by 0.6–2% (Table 2). Similar to the Tanzanian grouping, results obtained for Ugandan B. tabaci grouped the genotypes into the SSA-1 genetic group with the sub-clades I and II (Fig. 5). Sub- clades I and II shared sequence similarities of 97.1–99.5% and 98.8–99.5% with Ug1 and SA genotypes, respectively. Within sub-clade I and II, the sequences diverged by 0.5– 2.9% and 0.5–1.2%, respectively (Table 2). A combined phylogenetic analysis of mtCOI sequences of B. tabaci from all three countries (Kenya, Tanzania, and Uganda) grouped all the genotypes into SSA-1 genetic clade with exception of one genotype, which clus- tered with the SWIO genetic group (Fig. 6), confirming the results obtained for the individual countries. Sequences for B. tabaci in the two sub-clades (I and II) within SSA-1 genetic group were 0.3–2.8% divergent (Table 2). As expected, sequences of the Reunion B. tab- aci from Kenyan, which grouped with SWIO genetic group diverged by 2.3–2.8% (Table 2). Analysis of molecular variance (ANOVA) A hierarchical ANOVA (Excoffier et al. 2005) was con- ducted to assess the genetic differentiation of the B. tabaci populations in East Africa (Table 3). The two populations were grouped into the SSA-1 clade, with the two sub- clades (I and II), and SWIO with Reunion whitefly group. Comparative results from this study revealed significant dif- ferences among groups/clades (P < 0.001, FCT = 0.71529), among populations within groups (P < 0.001, FSC = 0.20534), and within populations (P = 0.008, FST = 0.77375). The highest contribution to the total variance was the differences among groups (71.53%). A similar result was obtained with the Tajima and Nei distance method (data not shown). Geographic distribution of B. tabaci genotypes in East Africa Results demonstrated a clear geographic distribution of two B. tabaci species belonging to the SSA-1 (sub-clade I and sub-clade II) and SWIO (Reunion) clades, in each country. The distribution within each region in the three countries was also evaluated. In Kenya, whiteflies were obtained in Western, Nyanza, and Coast provinces. The predominant species in all three provinces was the SSA-1, which comprised of 61.9% (13/21) sub-clade I (Ug1-like) and 33.3% (7/21) sub-clade II (SA-like) genotypes. The SWIO (Reunion) species comprised only 4.8% (1/21) (Table 4). Between regions, the sub-clade I genotypes were predominant in Nyanza (69.2%) and lowest in Western province (30.8%). Sub-clade I genotypes were conspicuously absent in the Coast province. Interestingly, the sub-clade II genotypes occurred in the Coast province only. The SWIO genotype occurred only in the Coast province (Table 4), whereas sub-clade I was only detected in Western and Nyanza provinces, and sub-clade II pre- dominated in the Coast province. Tanzanian whiteflies were obtained in three zones, including Lake Victoria Basin, Coast, and Southern zones. The SSA-1 sub-clade I and II genotypes comprised 41.5% (17/41) and 58.5% (24/41) of the whiteflies from Tanza- nia, respectively (Table 4). Between region comparisons revealed that the sub-clade I (Ug1-like) genotypes were most abundant in the Lake Victoria Basin (88.2%). The sub-clade II (SA-like) genotypes were predominant in the Southern zone (54.2%). Sub-clade I dominated in the Lake Victoria Basin (83.3%), whereas the sub-clade II genotypes dominated in the Coast and Southern zones (Table 4). In Uganda, whiteflies were obtained in four geographic regions: western, central, eastern, and northern regions. The SSA1 sub-clade II genotypes were the most abundant with 70.6% (12/17) occurrence (Table 4). Between regions, sub-clade I genotypes were most abundant in the western region (80%). Interestingly, no sub-clade I geno- types were detected in the central and eastern regions in this study. The sub-clade II genotypes occurred highest in central (33.3%) region and occurred in equal proportions in eastern and northern regions. Sub-clade I dominated in western region with 66.7% occurrence. On the other hand, sub-clade II was the dominant type in central, east- ern, and northern regions (Table 4). Discussion Using the mtCOI gene (Frohlich et al. 1999) as the molecular marker, our study reports the occurrence of two B. tabaci species belonging to two distinct clades/ ª 2012 The Authors. Ecology and Evolution published by Blackwell Publishing Ltd. 2755 H. Mugerwa et al. Genetic Diversity and Geographic Distribution T a b le 2 . A p ai rw is e co m p ar is o n o f th e m it o ch o n d ri al cy to ch ro m e o xi d as e I (m tC O I) n u cl eo ti d e se q u en ce (r ep re se n ta ti ve s) , ex p re ss ed as p er ce n t n u cl eo ti d e d iv er g en ce b et w ee n ad u lt B em is ia ta b ac i p o p u la ti o n s id en ti fi ed o n ca ss av a in Ea st A fr ic a (K en ya , Ta n za n ia , an d U g an d a) as ca lc u la te d u si n g C lu st al al g o ri th m (T h o m p so n et al . 1 9 9 4 ) A fr ic a (2 0 1 0 /2 0 1 1 ). G e n o ty p e 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0 2 1 2 2 2 3 2 4 2 5 2 6 2 7 1 K e- W 2 - 0 .8 0 .5 3 .3 2 .0 3 .7 1 9 .3 0 .9 0 .6 0 .5 2 .0 1 .7 1 .5 0 .6 1 .1 2 .0 1 .9 2 .5 2 .5 2 .2 0 .8 1 .5 2 .0 2 0 .3 2 0 .9 9 .5 2 4 .6 2 K e- N 2 - 0 .3 3 .1 1 .9 3 .9 1 9 .1 0 .8 0 .5 0 .3 1 .9 1 .5 1 .4 0 .5 0 .9 1 .9 1 .7 2 .3 2 .3 2 .0 0 .6 1 .4 1 .8 2 0 .1 2 0 .7 9 .3 2 4 .2 3 K e- N 3 - 2 .8 1 .5 3 .6 1 8 .7 0 .5 0 .2 0 .0 1 .5 1 .2 1 .1 0 .2 0 .6 1 .5 1 .4 2 .0 2 .0 1 .7 0 .3 1 .1 1 .5 1 9 .7 2 0 .3 9 .0 2 4 .0 4 K e- C 5 - 1 .8 4 .1 2 0 .0 3 .3 3 .0 2 .8 1 .8 2 .5 3 .3 2 .9 3 .4 3 .7 1 .7 2 .3 2 .3 4 .4 3 .1 2 .0 1 .8 2 1 .1 2 1 .7 1 0 .2 2 5 .9 5 K e- C 1 - 2 .8 1 8 .5 2 .0 1 .7 1 .5 0 .6 1 .2 2 .0 1 .7 2 .2 2 .5 0 .5 1 .1 1 .1 3 .1 1 .9 0 .8 0 .6 1 9 .5 2 0 .1 9 .0 2 4 .7 6 K e- C 3 - 2 0 .3 4 .1 3 .7 3 .6 2 .8 3 .4 4 .2 3 .8 4 .2 4 .6 2 .6 2 .9 3 .3 5 .2 3 .9 2 .9 2 .8 2 1 .3 2 1 .9 1 1 .1 2 6 .4 7 K e- C 7 - 1 9 .3 1 8 .9 1 8 .7 1 8 .1 1 8 .6 1 9 .1 1 8 .9 1 9 .3 1 9 .3 1 8 .3 1 7 .7 1 8 .4 2 0 .5 1 8 .7 1 8 .5 1 8 .4 2 .3 2 .8 1 8 .3 2 5 .2 8 Tz -1 0 b - 0 .6 0 .5 2 .0 1 .7 1 .5 0 .6 1 .1 2 .0 1 .9 2 .5 2 .5 2 .2 0 .8 1 .5 2 .0 2 0 .3 2 0 .9 9 .5 2 4 .4 9 Tz -H 9 - 0 .2 1 .7 1 .4 1 .2 0 .3 0 .8 1 .7 1 .5 2 .2 2 .2 1 .8 0 .5 1 .2 1 .7 1 9 .9 2 0 .5 9 .2 2 4 .2 1 0 Tz -H 4 - 1 .5 1 .2 1 .1 0 .2 0 .6 1 .5 1 .4 2 .0 2 .0 1 .7 0 .3 1 .1 1 .5 1 9 .7 2 0 .3 9 .0 2 4 .0 1 1 Tz -5 8 b - 1 .2 1 .7 1 .7 2 .2 2 .5 0 .5 1 .1 1 .1 3 .1 1 .9 0 .8 0 .6 1 9 .1 1 9 .7 9 .0 2 3 .8 1 2 Tz -7 0 b - 1 .7 1 .4 1 .8 2 .5 1 .1 1 .7 1 .7 2 .8 1 .5 1 .1 1 .2 1 9 .7 2 0 .3 8 .8 2 4 .9 1 3 Tz -6 5 a - 1 .2 1 .7 2 .6 1 .9 2 .5 2 .5 2 .6 1 .4 1 .5 2 .0 2 0 .1 2 0 .7 9 .7 2 4 .0 1 4 Tz -4 3 a - 0 .5 1 .7 1 .5 2 .2 2 .2 1 .8 0 .5 1 .2 1 .7 1 9 .9 2 0 .5 9 .2 2 4 .2 1 5 U g -4 3 d - 2 .2 2 .0 2 .6 2 .3 2 .3 0 .9 1 .7 2 .2 2 0 .3 2 1 .0 9 .5 2 4 .5 1 6 U g -4 3 e - 2 .3 3 .0 2 .6 3 .0 1 .9 2 .3 2 .5 2 0 .3 2 0 .9 9 .9 2 4 .9 1 7 U g -1 1 3 b - 0 .9 0 .9 3 .0 1 .7 0 .6 0 .5 1 9 .3 1 9 .9 8 .8 2 4 .5 1 8 U g -9 2 a - 1 .2 3 .6 2 .3 1 .2 1 .1 1 8 .9 1 9 .5 9 .2 2 4 .5 1 9 U g -4 3 b - 3 .4 2 .3 1 .2 1 .1 1 9 .4 2 0 .1 9 .1 2 4 .6 2 0 Su b Sa h ar an A fr ic a 1 U g - 1 .7 2 .6 3 .1 2 1 .5 2 2 .2 1 0 .2 2 6 .0 2 1 Su b Sa h ar an A fr ic a 1 U g - 1 .4 1 .9 1 9 .7 2 0 .3 8 .6 2 4 .5 2 2 Su b Sa h ar an A fr ic a 1 SA - 0 .8 1 9 .5 2 0 .1 9 .0 2 4 .7 2 3 Su b Sa h ar an A fr ic a 1 M o z - 1 9 .4 2 0 .1 9 .0 2 4 .6 2 4 M s R eu n io n - 0 .8 1 9 .1 2 4 .0 2 5 M s R eu n io n - 1 9 .7 2 4 .2 2 6 Su b Sa h ar an A fr ic a 2 U g - 2 4 .9 2 7 B em is ia af er - 2756 ª 2012 The Authors. Ecology and Evolution published by Blackwell Publishing Ltd. Genetic Diversity and Geographic Distribution H. Mugerwa et al. Figure 4. Phylogenetic tree based on the mitochondrial cytochrome oxidase I sequence for Bemisia tabaci collected in Tanzania generated using maximum likelihood available in MEGA5 software program. Bemisia subdecipens and B. afer are included as outgroups. Whiteflies used in the study are labeled as follows: Tz8b, Tz10a, Tz16a, Tz16b, Tz18a, Tz23a, Tz23b, Tz28b, TzH9, TzH12, TzH15, TzH18, TzH20, TzH27, TzH30 (Lake Victoria Basin), Tz49a, Tz53b, Tz57a,Tz57b, Tz58a, Tz58b, Tz75b, Tz95a, Tz95b, Tz97a, TzH4, TzH24 (Coastal region) and Tz62a, Tz62b, Tz65a, Tz68a, Tz70a, Tz70b, Tz75b, Tz77a, Tz81a, Tz83a, Tz90a, Tz91a, Tz93a, Tz93b (Southern zone). ª 2012 The Authors. Ecology and Evolution published by Blackwell Publishing Ltd. 2757 H. Mugerwa et al. Genetic Diversity and Geographic Distribution Figure 5. Phylogenetic tree based on the mitochondrial cytochrome oxidase I sequence for Bemisia tabaci collected in Uganda generated using maximum likelihood available in MEGA5 software program. Bemisia subdecipens and B. afer are included as outgroup. Samples are labeled as follows: Ug3a, Ug3b, Ug24a (East); Ug43a, Ug43b, Ug43c, Ug43d, Ug43e, Ug43f (West); Ug2a, Ug2b, Ug92a, Ug101a, Ug101b (North); Ug113a, Ug113b, Ug157a (Central) Uganda. 2758 ª 2012 The Authors. Ecology and Evolution published by Blackwell Publishing Ltd. Genetic Diversity and Geographic Distribution H. Mugerwa et al. groups of whiteflies, namely sub-Saharan Africa 1 (SSA-1) and South West Indian Ocean Islands (SWIO), on cassava crops in Kenya, Tanzania, and Uganda. Phylogenetic trees were predicted using both maximum parsimony and the maximum likelihood methods with similar results, but only the maximum likelihood results are discussed. Genetic differentiation of the cassava-associated East Afri- can B. tabaci populations using ANOVA had the highest contribution to the total variance as differences among groups, which corroborates the results obtained with mtCOI sequence phylogenetic analysis. The SSA-1 species had two closely related sub-clades (I and II), which were earlier reported on cassava as Uganda 1 (Ug1) and south- ern Africa (SA) genotypes in Uganda (Legg et al. 2002) and southern Africa (Berry et al. 2004; Esterhuizen et al. 2012), respectively. We reported here for the first time the occurrence of a Reunion whitefly species that clustered among the SWIO genetic group on cassava in Kenya. It is not clear whether this whitefly can reproduce on cassava as only the adults were used for the mtCOI analysis in this study. A Reunion (Ms) whitefly was also reported to colonize a number of non-cassava plants species, including Commelina benghalensis, Gossypium hirsutum, and Phaseo- lus vulgaris in Uganda (Sseruwagi et al. 2005). It is possible that the Reunion whitefly was just “visiting” or “feeding” at the time of sampling cassava. More definitive studies should be carried out to ascertain the colonization status of cassava by these whiteflies. There was a clear geographic distribution of the cassava B. tabaci species in the East African region (Kenya, Tanzania, and Uganda). Previous studies reported the sub-clade I genotypes to occur widely in areas ahead of the severe CMD pandemic “front” indigenous popula- tions, and were associated with very low numbers (Legg et al. 2002; Maruthi et al. 2004). However, in this study, the SSA-1 sub-clade I genotypes were not only widespread in Western and Nyanza provinces (Kenya), the Lake Vic- toria Basin and Southern zone (Tanzania), and western and northern regions (Uganda), but they also occurred in high population abundance (data not presented). Previously, the super abundant whitefly populations were a characteristic of the severe CMD pandemic (Legg 1999; Otim-Nape et al. 2000; Colvin et al. 2004), which was attributed in part due to entry into Uganda of an invasive whitefly species of the sub-Saharan Africa 2 (SSA-2) genetic group with closest relatives in Cameroon, commonly referred to as the “invader/Ug2” (Legg et al. 2002). Interestingly, we did not detect the SSA-2 whitefly species on cassava in any of the three countries in this study. The diminishing occurrence of the SSA-2 whiteflies in the severe CMD-affected areas in Uganda was reported (Sseruwagi 2005). A likely explanation for their complete Figure 6. Phylogenetic tree based on the mitochondrial cytochrome oxidase I sequence for Bemisia tabaci collected in East Africa(Kenya, Tanzania, and Uganda) generated using maximum likelihood available in MEGA5 software program. Bemisia subdecipens and B. afer are included as outgroups ª 2012 The Authors. Ecology and Evolution published by Blackwell Publishing Ltd. 2759 H. Mugerwa et al. Genetic Diversity and Geographic Distribution absence in this study and the resurgence of the SSA-1 (sub-clade 1) whitefly species in high populations in EA could be the result of backcrosses between the indigenous whitefly population (SSA-1 sub-clade I) and the SSA-2 invasive population, that resulted in a hybrid population with SSA-1 (sub-clade I) mtCOI and the invasive traits of the SSA-2 species (J. K. Brown, pers. comm.). Further studies are required to affirm the hybrid hypothesis. On the other hand, the complete absence of the SSA-1 (sub-clade I) genotypes in Coast Kenya and Tanzania, and central and eastern Uganda could possibly be due to displacement by the SSA-1 (sub-clade II) genotypes, which comprised a majority of the whiteflies in these areas. Elsewhere, population increase in B. tabaci, particularly in areas where whiteflies were previously unimportant, was attributed to the appearance of new “biotypes”/species complexes (Bedford et al. 1994; Brown 2001). For example, in southwestern United States of America, the B-biotype/Middle East-Asia Minor species (De Barro et al. 2011) was introduced in the region through ornamental plants (Brown et al. 1995; Frohlich et al. 1999), where it increased steadily in distribution and abundance, ultimately displacing the “local” A-bio- type/New World species (Costa et al. 1993; De Barro et al. 2011). On the other hand, the Middle East-Asia Minor species (B-biotype), which invaded southern Spain failed to displace the Q-biotype/Mediterranean indigenous species (Moya et al. 2001; De Barro et al. 2011). Displace- ment of indigenous B. tabaci species by the invasive Middle East-Asia Minor (B-biotype) and Mediterranean (Q-biotype) species has also been reported recently in China (Xu 2009; Chu et al. 2010; Crowder et al. 2010; Wang et al. 2011), and the Q-biotype has recently been reported in South Africa (SA) (Esterhuizen et al. 2012). We report for the first time the occurrence of SSA-1 (sub-clade II) whitefly in East Africa. These whiteflies predominated in Coast Kenya, Southern and Coast Tanzania, and were low in the Lake Victoria Basin of Tanzania, and widespread in all four regions in Uganda. The SSA-1 (sub-clade II) may be the indigenous whitefly species in Coast Kenya, Southern and Coast Tanzania. It is generally believed to be the indigenous whitefly in southern Africa, including SA, Malawi, and Mozambique (Berry et al. 2004; Esterhuizen et al. 2012), countries that share common boundaries and climate with Tanza- nia. However, the occurrence of the SSA-1 (sub-clade II) whiteflies in the Lake Victoria Basin of Tanzania and in Uganda was unexpected and requires further investigation. In conclusion, our results indicate that the two SSA-1 sub-clades (I and II), which group together as a single species in the SSA-1 B. tabaci genetic group due to their less than 3.5% divergence in the mtCOI (Dinsdale et al. 2010), could differ in important aspects of their biology, such as fecundity, virus transmission, and mating ability. This requires further investigation. Table 4. Geographic distribution of Bemisia tabaci species in Kenya, Tanzania, and Uganda, 2010/2011. Country Region Species occurrence (%) No. of samples (n) Sub-Saharan Africa 1 South West Indian OceanSub-clade I Sub-clade II Kenya Western 30.8(100) 0(0) 0(0) 4 Nyanza 69.2(100) 0(0) 0(0) 9 Coast 0(0) 100(87.5) 100(12.5) 8 13 7 1 21 Tanzania Lake zone 88.2(83.3) 12.5(16.7) 0(0) 18 Coastal zone 0(0) 33.3(100) 0(0) 8 Southern zone 11.8(13.3) 54.2(86.7) 0(0) 15 17 24 0 41 Uganda Western 801(66.7)2 16.7(33.3) 0(0) 6 Central 0(0) 33.3(100) 0(0) 3 Eastern 0(0) 25.5(100) 0(0) 3 Northern 20(25) 25.5(75) 0(20) 5 5 12 0 17 1Comparison across regions within each country. 2Comparison between species/genotypes obtained within a region. Table 3. Hierarchical analysis of molecular variance and F-statistics of genetic differentiation for East African Bemisia tabaci populations grouped according to species (groups), among populations within groups and within populations. The population structure was obtained using a pairwise difference distance method in ARLEQUIN version 3.1 (Excoffier et al. 2005), where Va is the variation due to differences among groups (Sub-clade I, Sub-clade II, and Reunion), Vb is the variation due to population differences within groups and Vc is the variation due to population differences. Source of variation df Sum of squares Variance components % of variation F-statistics P-value* Among groups 1 98.812 40.95471 Va 71.53 0.71529 <0.0001 Among populations within group 1 141.357 4.34738 Vb 5.85 0.20534 <0.0001 Within populations 76 984.528 12.95432 Vc 22.63 0.77375 <0.0001 Total 78 1224.696 57.25641 *P < 0.05. 2760 ª 2012 The Authors. Ecology and Evolution published by Blackwell Publishing Ltd. Genetic Diversity and Geographic Distribution H. Mugerwa et al. Acknowledgment We thank the country team leaders and scientists who provided the whitefly material used in this study from Kenya, Tanzania, and Uganda. 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