Molecular variability of cassava Bemisia tabaci and its effect on the epidemiology of cassava mosaic geminiviruses in Uganda

Bemisia tabaci (Genn.) is the vector of cassava mosaic geminiviruses (CMGs), which are the main production constraint to cassava, both in Uganda and elsewhere in Africa. A severe form of cassava mosaic disease (CMD) was responsible for the devastation of cassava in Uganda beginning in the late 1980s. In subsequent years the severe CMD epidemic spread throughout Uganda, and to neighbouring countries, causing devastating effects to cassava production, and its geographical range continues to expand with the pandemic. To further understand the virus-vector dynamics involved in the spread of CMD in the post epidemic zone in Uganda, we investigated the current distribution of B. tabaci genotypes in selected cassava-growing regions. Additionally, the relationship between the vector genotypes and distribution of CMGs in the post-epidemic zone was examined also. CMD-affected cassava leaves were collected from 3 to 5 month-old cassava plants, and B. tabaci adults and fourth instar nymphs were collected from cassava and twenty-two other plant species occurring adjacent to the sampled cassava fields. The mitochondrial cytochrome oxidase I (mtCOI) sequence was used to establish the genotype of B. tabaci adults and nymphs associated with the sampled plant species. African cassava mosaic virus (ACMV) and East African cassava mosaic virus-Uganda 2 (EACMV-UG2) were confirmed to be present in the post-epidemic zone in Uganda, as reported previously. As expected, EACMV-UG2 predominated. However, unlike previous observations in which EACMV-UG2 was consistently associated with the severe disease phenotype, in this study EACMV-UG2 occurred almost equally in the severely and mildly diseased plants. Phylogenetic analyses of Ugandan B. tabaci genotypes (mtCOI) revealed that their closest relatives were other Old World genotypes, as might be expected. Two previously reported B. tabaci genotype clusters, Uganda 1 (Ug1) and Uganda 2 (Ug2), at ~8% nt divergence, were confirmed to occur on cassava in the post-epidemic zone. However, Ug1 occurred more frequently (83%) than Ug2 (17%), and no definite association was established of a particular vector genotype with cassava plants exhibiting the severe disease phenotype, in contrast to the B. tabaci genotype distribution and association with the CMGs reported there at the height of the spread of the severe CMD epidemic. Based on the presence of B. tabaci fourth instar nymphs, the Ug1 genotypes colonized five additional non-cassava plant species: Manihot glaziovii, Jatropha gossypifolia, Euphorbia heterophylla, Aspilia africana and Abelmoschus esculentus, suggesting that in Uganda the Ug1 genotypes are not restricted to cassava. However, no Ug2 genotypes were detected on the non-cassava plant species sampled. This study revealed also the presence in Uganda of five distinct previously unrecorded B. tabaci genotype clusters, Uganda 3 (Ug3), Uganda 4 (Ug4), Uganda 5 (Ug5), Uganda 6 (Ug6) and Uganda 7 (Ug7), and a sweetpotato colonizing genotype cluster, designated Uganda 8 (Ug8), among the collective Ugandan B. tabaci populations. Ug3 was the only exemplar representing one cluster, which was unlike any previously described genotype in Uganda or elsewhere, and diverged at 8%, 10% and 17% from Ug1, Ug2 and Ug8, respectively. The Ug3 genotypes colonized a single species, Ocimum gratissimum. Ug4, Ug5, Ug6 and Ug7 formed four closely related sub-clusters (93-97% nt identity), and diverged from one another by 1-7%, and by 15-18% from Ug1, Ug2, Ug3 and Ug8, respectively. The Ug4 genotypes had as their closest relatives (at 97-99% nt identity) previously reported B. tabaci from okra in the Ivory Coast, whereas, the Ug5 and Ug6 genotypes shared 95-99% and 99% nt identity, respectively, with their closest relatives from the Mediterranean-North Africa- Middle East (MED-NAFR-ME) region, which also includes the well studied B and Q biotypes. The Ug7 genotypes were closely related (at 98-99% nt identity) to B. tabaci from Reunion Island in the Indian Ocean. The Ug4, Ug5, Ug6 and Ug7 genotypes were identified on 54%, 8%, 8%, and 31% of the sampled plants species, respectively. Ug4 were most polyphagous, followed by Ug7 and Ug6. However, none of the new five genotypes (Ug3-Ug7) was found associated with, or colonizing, xx cassava or sweetpotato plants in this study. Squash plants colonized by the Ug6 and Ug7 genotypes, both members of the B biotype/B-like cluster, developed the silvering phenotype, while those colonized by the Ug4 genotypes (most closely related to a non-B like genotype from okra in the Ivory Coast) did not. In addition to colonizing sweetpotato, the Ug8 genotypes also colonized Lycopersicon esculentum and L nepetifolia

Cassava brown streak disease and the sustainability of a clean seed system

One method of reducing disease in crops is the dissemination of disease-free planting material from a multiplication site to growers. This study assesses the validity and sustainability of this method for cassava brown streak disease, a threat to cassava crops across East Africa. Using mathematical modelling, the effects of different environmental and control conditions on pathogen spread were determined in a single-field multiplication site. High disease pressure, through large vector populations and disease in the surrounding area, combined with poor roguing practice, resulted in unsuccessful disease suppression. However, fields may produce sufficiently clean material for replanting if these factors can be overcome. Assessing the sustainability of a low-pressure system over multiple harvests, well-managed fields were found to maintain low disease levels, although producing sufficient cuttings may prove challenging. Replanting fields from the previous harvest does not lead to degeneration of planting material, only cutting numbers, and the importation of new clean material is not necessarily required. It is recommended that multiplication sites are only established in areas of low disease pressure and vector population density, and the importance of training in field management is emphasized. Cultivars displaying strong foliar symptoms are to be encouraged, as these allow for effective roguing, resulting in negative selection against the disease and reducing its spread. Finally, efforts to increase plant multiplication rates, the number of cuttings that can be obtained from each plant, have a significant impact on the sustainability of sites, as this represents the primary limiting factor to success

Whitefly resistance in African cassava genotypes

Whitefly ( Bemisia tabaci ), a major pest and vector of viruses in cassava, is the greatest current threat to cassava production in sub-Saharan Africa (SSA). Research efforts have focused on management of the two viral diseases: cassava mosaic disease (CMD) and cassava brown streak disease (CBSD), and have ignored the whitefly vector that is driving the spread of the viruses, causing CMD and CBSD in SSA. The objective of this study was to evaluate cassava genotypes for resistance to B. tabaci based on field infestation and damage in Uganda. The study was carried out in four sites with diverse agro-ecologies including: Namulonge, Kasese, Ngetta and Serere during 2015 and 2016.Whitefly nymph abundance and feeding damage were assessed on each test genotype from 3 to 6 months after planting (MAP). In 2015, the highest broad sense heritability estimates were 39% (4 MAP) and 53% (5 MAP) for whitefly nymph abundance and feeding damage, respectively. In 2016, broad sense heritability estimates were 23% (3 MAP) and 41% (4 MAP) for whitefly nymph abundance and feeding damage, respectively.Analysis of variance of whitefly nymph abundance showed a significant (P< 0.05) location 7 genotype 7 season interactions at 3, 4, 5 and 6 MAP. There were also significant (P< 0.05) location 7 genotype 7 season interactions at 3 and 4 MAP for whitefly feeding damage. Ten genotypes showed good levels of resistance to whitefly infestation and feeding damage including: UG120202, UG120174, NASE13, UG120160, UG120286, UG120293, UG130075, CSI-142, CS1-144 and UG130085. These genotypes may serve as parental materials for breeding programmes for whitefly and viral disease control.La mouche blanche ( Bemisia tabaci ), le ravageur et vecteur principal de virus du manioc, constitue actuellement la plus grande menace pour la production de manioc en Afrique Subsaharienne (AS). Les recherches ont port\ue9 sur la gestion des deux maladies virales: la maladie de la mosa\uefque du manioc (MMM) et la maladie de la striure brune du manioc (MSBM) , et ont ignor\ue9 le vecteur de la mouche blanche qui est \ue0 l\u2019origine de la propagation des virus, causant le MMMet le MSBM en Afrique subsaharienne. L\u2019objectif de cette \ue9tude \ue9tait d\u2019\ue9valuer la r\ue9sistance de B. tabaci aux g\ue9notypes du manioc sur la base d\u2019une infestation et de d\ue9g\ue2ts sur le champs en Ouganda. L\u2019\ue9tude a \ue9t\ue9 men\ue9e en 2015 et 2016 sur quatre sites pr\ue9sentant diverses agro-\ue9cologies, notamment Namulonge, Kasese, Ngetta et Serere. L\u2019abondance des nymphes blanches et les dommages alimentaires ont \ue9t\ue9 \ue9valu\ue9s sur chaque g\ue9notype test\ue9 3 \ue0 6 mois apr\ue8s la plantation (MAP). En 2015, les estimations les plus \ue9lev\ue9es de l\u2019h\ue9ritabilit\ue9 au sens large \ue9taient de 39% (4 MAP) et 53% (5 MAP) pour l\u2019abondance des nymphes de la mouche blanche et les dommages caus\ue9s par l\u2019alimentation, respectivement. En 2016, les estimations de l\u2019h\ue9ritabilit\ue9 au sens large \ue9taient respectivement de 23% (3 MAP) et 41% (4 MAP) d\u2019abondance des nymphes de la mouche blanche et des dommages caus\ue9s par l\u2019alimentation. L\u2019analyse de la variance de l\u2019abondance des nymphes de la mouche blanche a r\ue9v\ue9l\ue9 une interaction significative (p <0,05) de lieu 7 g\ue9notype 7 interactions saisonni\ue8res \ue0 3, 4, 5 et 6 MAP. Il y avait aussi des interactions significatives (P <0,05) de lieu 7 g\ue9notype 7 interactions saisonni\ue8res aux niveaux de 3 et 4 MAP pour les dommages caus\ue9s par l\u2019alimentation des mouches blanches. Dix g\ue9notypes ont montr\ue9 de bons niveaux de r\ue9sistance \ue0 l\u2019infestation par mouches blanches et aux dommages caus\ue9s par l\u2019alimentation, notamment: UG120202, UG120174, NASE13, UG120160, UG120286, UG120293, UG130075, CSI-142, CS1-144 et UG130085. Ces g\ue9notypes peuvent servir de mat\ue9riel parental pour les programmes de s\ue9lection visant \ue0 lutter contre mouches blanches et les maladies virales

Field performance and quality traits of hot pepper genotypes in Uganda

Hot pepper ( Capsicum annuum ) is increasingly an important economic crop in Uganda that requires attention for increased production. Genotypes with superior growth, quality and yield traits are crucial for use in pepper cultivar improvement efforts and use by farmers. To identify such genotypes, agronomic characteristics including growth, quality and yield traits of 26 exotic and 9 local genotypes were evaluated on-station during the growing seasons of 2009 (2009A and B) in Central Uganda. Significant differences were observed in all plant growth, and most yield and quality (P<0.001) traits. Except for number of seeds per fruit, highly significant genotype X season (P<0.001) interactions were observed in other traits. Pepper genotypes during season 2009B exhibited superior performance than in season 2009A in majority of the traits except for number of seeds per fruit, seed yield, 200 seed weight and percentage non-marketable fruits. Local genotypes performed better in season 2009A than in 2009B. The commercial local check genotype CA -UGCE 09-3 performed better than all the local genotypes and most exotic genotypes in fruit yield and early maturity. The East African Seed Company local genotype CA-EASC-09-1 was the earliest maturing variety among all genotypes. The Asian Vegetable Research and Development Centre (AVRDC) check genotype 12 (PP97-7195-1) performed the best among all the exotic genotypes in all traits except fruit size. Eight of the agronomic traits showed significant correlations between seasons indicating stability for these traits. Fruit length and width were the most stable quantitative traits. These findings reveal that traits of interest in C. annuum that vary with the environment may be improved by using suitable cropping seasons and management practices.Le piment ( Capsicum annuum ) est une culture \ue9conomique de plus en plus importante en Uganda qui m\ue9rite plus d\u2019attention pour accro\ueetre sa production. Les g\ue9notypes \ue0 haute capacit\ue9 de croissance, de qualit\ue9 et traits de rendement sont n\ue9cessaires dans de programmes d\u2019am\ue9lioration des cultivars du piment et l\u2019utilisation par des fermiers. Pour identifier de tels g\ue9notypes, de caract\ue9ristiques agronomiques incluant la croissance, la qualit\ue9 et les traits de rendement de 26 g\ue9notypes exotiques et 9 locaux \ue9taient \ue9valu\ue9s en station au cours des saisons de culture 2009 A et 2009 B au Centre de l\u2019Ouganda. Des diff\ue9rences significatives \ue9taient observ\ue9es dans tous les traits de croissance, surtout le rendement et les traits de qualit\ue9 (P<0.001). Except\ue9 le nombre de grains par fruit, les interactions hautement significatives g\ue9notype X saison (P<0.001) \ue9taient observ\ue9es dans d\u2019autres traits. Les g\ue9notypes de piment ont manifest\ue9 une performance plus sup\ue9rieure qu\u2019en saison 2009 A dans la majorit\ue9 des traits sauf pour le nombre de grains par fruit, le poids de 200 grains et le pourcentage de fruits non commerciables. Les g\ue9notypes locaux ont montr\ue9 de meilleures performances en saison 2009A qu\u2019en 2009B. Le g\ue9notype commercial CA-UGCE 09-3 qui \ue9tait pris pour t\ue9moins local avait \ue9t\ue9 plus performant que tous les g\ue9notypes locaux et laplupart des g\ue9notypes exotiques en terme de rendement en fruits et la pr\ue9cocit\ue9 alors que le g\ue9notype local CA-EASC-09-1 de la soci\ue9t\ue9 de vente de semence \ue9tait la vari\ue9t\ue9 la plus pr\ue9coce parmi tous les g\ue9notypes. Le g\ue9notype t\ue9moins 12(PP97-7195-1) du Centre Asiatique de Recherche et D\ue9veloppement sur les L\ue9gumes (AVRDC) a \ue9t\ue9 le plus performant par rapport \ue0 tous les g\ue9notypes exotiques dans tous les traits sauf la taille de fruits. Huit des traits agronomiques ont montr\ue9 de corr\ue9lations significatives entre saisons indiquant la stabilit\ue9 pour de ces traits. La longueur et la largeur de fruits constituaient des traits quantitatifs les plus stables. Ces r\ue9sultats r\ue9v\ue8lent que les traits d\u2019int\ue9r\ueat dans C. annuum qui varient avwc l\u2019environnement pourraient \ueatre am\ue9lor\ue9s en utilisant des saisons culturales appropri\ue9es et la gestion des pratiques

Hot pepper reaction to field diseases

Diseases are major constraints to hot pepper ( Capsicum annum L.) production in sub-Saharan Africa. The search for cultivars resistant to the major diseases of hot pepper has been limited. This study was conducted in Uganda to evaluate exotic and local hot pepper genotypes for disease resistance. Viral diseases and Cercospora leaf spot were the most predominant and severe, followed in descending order by anthracnose, Phytophthora blight and wilt diseases. Highly significant genotypic differences (P<0.001) existed in most scored disease traits. There was no genotype resistant to field diseases of interest in this study; however, a few cultivars exhibited resistance to two or more disease infections. The Asian Vegetable Research and Development Centre (AVRDC) genotype 12 (PP97-7195-1) was exceptionally resistant to fungal and bacterial diseases, but moderately resistant to viral diseases. Highly significant genotype by season (P<0.001) interactions were observed for both disease incidences and severity indices, except for Phytophthora blight severity index. Field disease correlation stability analysis across seasons indicated significant virus and Phytophthora blight severity indices implying some stability in these scores across seasons with virus severity index being the most consistent scored disease trait. Anthracnose incidence and severity contributed more to yield loss.Les maladies constituent des contraintes majeures \ue0 la production du piment ( Capsicum annum L.) , la recherche sur des cultivars r\ue9sistants \ue9tant limitative en Afrique Sub-Saharienne. Cette \ue9tude \ue9tait conduite en Ouganda pour \ue9valuer les g\ue9notypes du piment exotique et local \ue0 la r\ue9sistance aux maladies. Les maladies virales et la t\ue2che foliaire Cercospora \ue9taient les plus pr\ue9dominants et s\ue9v\ue8res, suivis par ordre d\ue9croissant par l\u2019anthracnose, le mildiou et les maladies de fl\ue9trissement. De diff\ue9rences g\ue9notypiques hautement significatives (P<0.001) \ue9taient enregistr\ue9es dans tous les traits de maladies examin\ue9s. Il n\u2019y avait pas de g\ue9notypes r\ue9sistants \ue0 toutes les maladies \ue9tudi\ue9es aux champs; par ailleurs, peu de cultivars ont manifest\ue9 une r\ue9sistance \ue0 deux ou plusieurs infections de maladies. Le g\ue9notype 12 (PP97-7195) du Centre Asiatique de Recherche et D\ue9veloppement sur les l\ue9gumes \ue9tait exceptionnellement resistant au champignon et aux maladies bact\ue9riennes, mais mod\ue9r\ue9ment r\ue9sistant aux maladies virales. Des interactions hautement significatives entre g\ue9notypiques et saison (P<0.001) \ue9taient observ\ue9es pour incidence des maladies et indices de s\ue9v\ue9rit\ue9, except\ue9 pour l\u2019index de s\ue9v\ue9rit\ue9 du mildiou. L\u2019analyse par corr\ue9lation de stabilit\ue9 de maladies en champs \ue0 travers les saisons ont indiqu\ue9 des indices significatifs de s\ue9v\ue9rit\ue9 virale et du mildiou, impliquant un certain degr\ue9 de stabilit\ue9 \ue0 travers les saisons, l\u2019indice de s\ue9v\ue9rit\ue9 virale plus consistant enregistr\ue9. L\u2019indice de l\u2019 anthracnose et sa s\ue9v\ue9rit\ue9 ont le plus contribu\ue9 \ue0 la perte de rendement

Cassava brown streak disease and the sustainability of a clean seed system.

One method of reducing disease in crops is the dissemination of disease-free planting material from a multiplication site to growers. This study assesses the validity and sustainability of this method for cassava brown streak disease, a threat to cassava crops across East Africa. Using mathematical modelling, the effects of different environmental and control conditions on pathogen spread were determined in a single-field multiplication site. High disease pressure, through large vector populations and disease in the surrounding area, combined with poor roguing practice, resulted in unsuccessful disease suppression. However, fields may produce sufficiently clean material for replanting if these factors can be overcome. Assessing the sustainability of a low-pressure system over multiple harvests, well-managed fields were found to maintain low disease levels, although producing sufficient cuttings may prove challenging. Replanting fields from the previous harvest does not lead to degeneration of planting material, only cutting numbers, and the importation of new clean material is not necessarily required. It is recommended that multiplication sites are only established in areas of low disease pressure and vector population density, and the importance of training in field management is emphasized. Cultivars displaying strong foliar symptoms are to be encouraged, as these allow for effective roguing, resulting in negative selection against the disease and reducing its spread. Finally, efforts to increase plant multiplication rates, the number of cuttings that can be obtained from each plant, have a significant impact on the sustainability of sites, as this represents the primary limiting factor to success

Is high whitefly abundance on cassava in sub-Saharan Africa driven by biological traits of a specific, cryptic Bemisia tabaci species?

In East Africa, the prevalent Bemisia tabaci whiteflies on the food security crop cassava are classified as sub-Saharan Africa (SSA) species. Economically damaging cassava whitefly populations were associated with the SSA2 species in the 1990s, but more recently, it has been to SSA1 species. To investigate whether biological traits (number of first instar nymphs, emerged adults, proportion of females in progeny and development time) of the cassava whitefly species are significant drivers of the observed field abundance, our study determined the development of SSA1 sub-group (SG) 1 (5 populations), SG2 (5 populations), SG3 (1 population) and SSA2 (1 population) on cassava and eggplant under laboratory conditions. SSA1-(SG1-SG2) and SSA2 populations’ development traits were similar. Regardless of the host plant, SSA1-SG2 populations had the highest number of first instar nymphs (60.6 ± 3.4) and emerged adults (50.9 ± 3.6), followed by SSA1-SG1 (55.5 ± 3.2 and 44.6 ± 3.3), SSA2 (45.8 ± 5.7 and 32.6 ± 5.1) and the lowest were SSA1-SG3 (34.2 ± 6.1 and 32.0 ± 7.1) populations. SSA1-SG3 population had the shortest egg–adult emergence development time (26.7 days), followed by SSA1-SG1 (29.1 days), SSA1-SG2 (29.6 days) and SSA2 (32.2 days). Regardless of the whitefly population, development time was significantly shorter on eggplant (25.1 ± 0.9 days) than cassava (34.6 ± 1.0 days). These results support that SSA1-(SG1-SG2) and SSA2 B. tabaci can become highly abundant on cassava, with their species classification alone not correlating with observed abundance and prevalence

TEMPORAL AND SPATIAL DYNAMICS OF Bemisia tabaci POPULATIONS AND CASSAVA VIRAL DISEASES ON SELECTED WHITEFLY RESISTANT CASSAVA GENOTYPES IN UGANDA

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a pest that causes widespread damage on cassava ( Manihot esculanta Crantz), a staple food crop for millions of households in sub-Saharan Africa. Bemisia tabaci also acts as a vector responsible for spreading plant viruses that cause two of the most economically damaging diseases in cassava; namely cassava mosaic disease (CMD) and cassava brown streak disease (CBSD). The objective of this study was to determine the population dynamics of B. tabaci on whitefly resistant cassava genotypes in different agro-ecologies in Uganda. Data were collected once a month, for six months on adult whitefly populations, cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) incidence and symptom severity. The results obtained indicated that cropping season (2015 and 2016), agro-ecology, cassava age and genotypes strongly (P 640.001) influenced the population of adult whitefly. Moderate (47.44% \ub1 0.7821) and high (72.04% \ub1 0.6916) overall means incidences of CBSD recorded across agro-ecologies on the whitefly resistant genotypes in 2015 and 2016 trials, respectively, were likely due to use of cutting-infected planting materials that were not detected through visual inspection at trial establishment. The analysis further revealed that the interaction effect of genotype, agro-ecology and crop age (months after planting: MAP) had a highly significant influence (P 64 0.001) on whitefly abundance and high significant effect (P 640.05) on CMD incidence and severity. The CMD and CBSD incidence as well as symptom severity increased with crop age from 3 months after planting across agro-ecologies. The study demonstrates that whitefly population dynamics and viral disease incidence are influenced by cassava genotypes, agro-ecological differences and crop age (MAP). Information generated could be used to guide the development of appropriate area-specific control strategies to mitigate the effect of whitefly and whitefly-transmitted viral diseases in cassava.Bemisia tabaci (Gennadius) (Hemiptera : Aleyrodidae) est un ravageur qui cause des d\ue9g\ue2ts \ue9tendus sur le manioc ( Manihot esculanta Crantz), une culture vivri\ue8re de base dans des millions de m\ue9nages en Afrique subsaharienne. Bemisia tabaci agit \ue9galement en tant que vecteur responsable de la propagation de virus v\ue9g\ue9taux qui causent deux des maladies les plus dommageables sur le plan \ue9conomique du manioc; \ue0 savoir la maladie de la mosa\uefque du manioc (CMD) et la maladie des stries brunes du manioc (CBSD). L\u2019objectif de cette \ue9tude \ue9tait de d\ue9terminer la dynamique des populations de B. tabaci sur les g\ue9notypes de manioc r\ue9sistants aux aleurodes dans diff\ue9rentes agro-\ue9cologies en Ouganda. Des donn\ue9es ont \ue9t\ue9 recueillies une fois par mois pendant six mois sur les populations d\u2019aleurodes adultes, l\u2019incidence de la maladie de la mosa\uefque du manioc (CMD) et de la maladie des stries brunes du manioc (CBSD) et la gravit\ue9 des sympt\uf4mes. Les r\ue9sultats obtenus ont indiqu\ue9 que la saison de culture (2015 et 2016), l\u2019agro-\ue9cologie, l\u2019\ue2ge et les g\ue9notypes du manioc ont fortement influenc\ue9 (P 640,001) la population d\u2019aleurodes adultes. Les incidences moyennes globales mod\ue9r\ue9es (47,44\ua0% \ub1 0,7821) et \ue9lev\ue9es (72,04\ua0% \ub1 0,6916) de CBSD enregistr\ue9es dans les agro-\ue9cologies sur les g\ue9notypes r\ue9sistants aux aleurodes dans les essais de 2015 et 2016, respectivement, \ue9taient probablement dues \ue0 l\u2019utilisation de mat\ue9riel de plantation infect\ue9 par des boutures qui n\u2019ont pas \ue9t\ue9 d\ue9tect\ue9s par inspection visuelle dans l\u2019\ue9tablissement d\u2019essai. L\u2019analyse a en outre r\ue9v\ue9l\ue9 que l\u2019effet d\u2019interaction du g\ue9notype, de l\u2019agro-\ue9cologie et de l\u2019\ue2ge de la culture (mois apr\ue8s la plantation: MAP) avait une influence hautement significative (P 640,001) sur l\u2019abondance des aleurodes et un effet significatif \ue9lev\ue9 (P 640,05) sur l\u2019incidence et gravit\ue9. L\u2019incidence de CMD et de CBSD ainsi que la s\ue9v\ue9rit\ue9 des sympt\uf4mes ont augment\ue9 avec l\u2019\ue2ge de la culture \ue0 partir de 3 mois apr\ue8s la plantation dans toutes les agro-\ue9cologies. L\u2019\ue9tude d\ue9montre que la dynamique des populations d\u2019aleurodes et l\u2019incidence des maladies virales sont influenc\ue9es par les g\ue9notypes de manioc, les diff\ue9rences agro-\ue9cologiques et l\u2019\ue2ge des cultures (MAP). Les informations g\ue9n\ue9r\ue9es pourraient \ueatre utilis\ue9es pour orienter l\u2019\ue9laboration de strat\ue9gies de contr\uf4le appropri\ue9es et sp\ue9cifiques \ue0 la zone pour att\ue9nuer l\u2019effet des aleurodes et des maladies virales transmises par les aleurodes sur le manioc

Whole‐genome single nucleotide polymorphism and mating compatibility studies reveal the presence of distinct species in sub‐Saharan Africa Bemisia tabaci whiteflies

In sub‐Saharan Africa cassava growing areas, two members of the Bemisia tabaci species complex termed sub‐Saharan Africa 1 (SSA1) and SSA2 have been reported as the prevalent whiteflies associated with the spread of viruses that cause cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) pandemics. At the peak of CMD pandemic in the late 1990s, SSA2 was the prevalent whitefly, although its numbers have diminished over the last two decades with the resurgence of SSA1 whiteflies. Three SSA1 subgroups (SG1 to SG3) are the predominant whiteflies in East Africa and vary in distribution and biological properties. Mating compatibility between SSA1 subgroups and SSA2 whiteflies was reported as the possible driver for the resurgence of SSA1 whiteflies. In this study, a combination of both phylogenomic methods and reciprocal crossing experiments were applied to determine species status of SSA1 subgroups and SSA2 whitefly populations. Phylogenomic analyses conducted with 26 548 205 bp whole genome single nucleotide polymorphisms (SNPs) and the full mitogenomes clustered SSA1 subgroups together and separate from SSA2 species. Mating incompatibility between SSA1 subgroups and SSA2 further demonstrated their distinctiveness from each other. Phylogenomic analyses conducted with SNPs and mitogenomes also revealed different genetic relationships among SSA1 subgroups. The former clustered SSA1‐SG1 and SSA1‐SG2 together but separate from SSA1‐SG3, while the latter clustered SSA1‐SG2 and SSA1‐SG3 together but separate from SSA1‐SG1. Mating compatibility was observed between SSA1‐SG1 and SSA1‐SG2, while incompatibility occurred between SSA1‐SG1 and SSA1‐SG3, and SSA1‐SG2 and SSA1‐SG3. Mating results among SSA1 subgroups were coherent with phylogenomics results based on SNPs but not the full mitogenomes. Furthermore, this study revealed that the secondary endosymbiont—Wolbachia—did not mediate reproductive success in the crossing assays carried out. Overall, using genome wide SNPs together with reciprocal crossings assays, this study established accurate genetic relationships among cassava‐colonizing populations, illustrating that SSA1 and SSA2 are distinct species while at least two species occur within SSA1 species