Invasive holoparasitic plants of the genus Cuscuta (dodder) threaten Africa's ecosystems, due to their rapid spread and attack on various host plant species. Most Cuscuta species cannot photosynthesize, hence rely on host plants for nourishment. After attachment through a peg-like organ called a haustorium, the parasites deprive hosts of water and nutrients leading to their death. Despite their rapid spread in Africa, dodders have attracted limited research attention, although data on their taxonomy, host range and epidemiology are critical for their management. Here, we combine taxonomy and phylogenetics to reveal presence of field dodder (Cuscuta campestris) and C. kilimanjari (both either naturalized or endemic to East Africa), and for the first time in continental Africa, presence of the giant dodder (C. reflexa) a south Asian species. These parasites have a wide host range, parasitizing species across 13 angiosperm orders. Evaluating the possibility of C. reflexa to expand this host range to tea, coffee, and mango, crops of economic importance to Africa, revealed successful parasitism, following haustorial formation and vascular bundle connections in all three crops. However, only mango mounted a successful post-attachment resistance response. Furthermore, species distribution models predicted high habitat suitability for all three Cuscuta species across major tea- and coffee-growing regions of Eastern Africa, suggesting an imminent risk to these crops. Our findings provide relevant insights into a little-understood threat to biodiversity and economic wellbeing in Eastern Africa, and providing critical information to guide development of management strategies to avert their spread.

Invasive holoparasitic plants of the genus Cuscuta (dodder) threaten African ecosystems due to their rapid spread and attack on various host plant species. Most Cuscuta species cannot photosynthesize and hence rely on host plants for nourishment. After attachment through a peg-like organ called a haustorium, the parasites deprive hosts of water and nutrients, which negatively affects host growth and development. Despite their rapid spread in Africa, dodders have attracted limited research attention, although data on their taxonomy, host range, and epidemiology are critical for their management. Here, we combine taxonomy and phylogenetics to reveal the presence of field dodder (Cuscuta campestris) and Cuscuta kilimanjari (both either naturalized or endemic to East Africa), in addition to the introduction of the giant dodder (Cuscuta reflexa), a south Asian species, in continental Africa. These parasites have a wide host range, parasitizing species across 13 angiosperm orders. We evaluated the possibility of C. reflexa to expand this host range to tea (Camelia sinensis), coffee (Coffea arabica), and mango (Mangifera indica), crops of economic importance to Africa, for which haustorial formation and vascular-bundle connections in all three crops revealed successful parasitism. However, only mango mounted a successful post-attachment resistance response. Furthermore, species distribution models predicted high habitat suitability for Cuscuta spp. across major tea- and coffee-growing regions of Eastern Africa, suggesting an imminent risk to these crops. Our findings provide relevant insights into a poorly understood threat to biodiversity and economic wellbeing in Eastern Africa, and provide critical information to guide development of management strategies to avert Cuscuta spp. spread.

The parasitic plant purple witchweed [Striga hermonthica (Del.) Benth.] poses a serious threat to cereal production in sub-Saharan Africa. Under natural infestation, the wild pearl millet [Pennisetum glaucum (L.) R. Br.] line 29Aw demonstrates resistance against the parasite, but the mechanism of its resistance is unknown. Striga resistance can be due to: (i) low induction of Striga germination (pre-attachment resistance) or (ii) inhibition of parasite attachment and development (post-attachment resistance). Germination bioassays and root chamber (rhizotron) resistance screening assays were used to determine the extent of pre- and post-attachment Striga resistance in 29Aw compared with the Striga-susceptible SOSAT-C88-P10 variety. Regarding pre-attachment resistance, 29Aw stimulated 10-fold less Striga seed germination at a maximum germination distance of 7.96 ± 2.75 mm from the host root compared with 35.94 ± 2.88 mm in SOSAT-C88-P10. Post-attachment resistance revealed 10 to 19-fold fewer, 2.5-fold shorter, and 28-fold less Striga seedling biomass growing on 29Aw compared to SOSAT-C88-P10. Microscopic analysis showed that Striga penetration in 29Aw was blocked at endodermis and cortex levels. Post-attachment resistance in 29Aw was further supported by fewer (22%) Striga-host vascular connections in 29Aw compared to 79% in SOSAT-C88-P10. Together, these findings demonstrate that 29Aw harbors both pre- and post-attachment resistance mechanisms against S. hermonthica.

Societal Impact Statement Eastern Africa is currently infested with dodders—highly invasive vines that threaten agriculture and biodiversity. We describe historical and ecological factors that have potentially shaped dodder invasion in this region. Our results reveal high levels of genetic diversity within dodder populations, which could enhance their ability to colonize new niches. Further, we identify two main population clusters in eastern and western Kenya, a pattern that is mirrored in an established invader (Cuscuta campestris) and a recent introduction (C. reflexa). Immediate control strategies are needed to limit deliberate or inadvertent seed/vine dispersal, eradicate existing populations, and monitor influx of propagules. Summary Invasion by dodder (Cuscuta spp.), holo‐parasitic plants of the Convolvulaceae family, has recently surged in Eastern Africa. Particularly, colonization by two species, Cuscuta campestris and Cuscuta reflexa that have a broad host range and rapid invasiveness, has escalated. We examined the first assessment of genetic diversity of these invasive species in Kenya to inform subsequent management practices. A comparative phylogeographic analysis, based on chloroplast and nuclear ribosomal DNA, was performed to determine genetic diversities, population structure, and isolation of C. campestris and C. reflexa in Kenya. Results reveal high genetic variation in both species within populations across localities. C. campestris had more haplotypes and higher gene diversity (P = .0001) and heterozygosity (P = .004) than C. reflexa. Both species were geographically separated, evidenced by two distinct lineages that mostly corresponded to localities east and west of Kenya. Correlation between genetic and geographic distances revealed evidence of isolation by distance (IBD). We attribute these genetic variation patterns to establishment via similar invasion routes for the studied Cuscuta spp. and suggest that Cuscuta invasion in Kenya is in the early stages of establishment. Rapid eradication is urgently needed to prevent shifts to economically important hosts, which would have devastating impacts. We recommend (i) development of targeted efforts to curb new introductions to limit the potential for genetic variability and adaptation, (ii) prevention of seed and vine dispersal from current incursions, and (iii) complete eradication of existing populations where this is feasible.

Declining food production in African agroecosystems is attributable to changes in weather patterns, soil infertility and limited farming inputs. The exploitation of plant growth-promoting soil microbes could remedy these problems. Such microbes include Azotobacter ; free-living, nitrogen-fixing bacteria, which confer stress tolerance, avail phytohormones and aid in soil bioremediation. Here, we aimed to isolate, characterize and determine the biodiversity of native Azotobacter isolates from soils in semi-arid Eastern Kenya. Isolation was conducted on nitrogen-free Ashby's agar and the morphological, biochemical and molecular attributes evaluated. The isolates were sequenced using DNA amplicons of 27F and 1492R primers of the 16S rRNA gene loci. The Basic Local Alignment Search Tool (BLASTn) analysis of their sequences revealed the presence of three main Azotobacter species viz., Azotobacter vinelandii, Azotobacter salinestris and Azotobacter tropicalis . Kitui County recorded the highest number of recovered Azotobacter isolates (45.4%) and lowest diversity index (0.8761). Tharaka Nithi County showed the lowest occurrence (26.36%) with a diversity index of (1.057). The diversity was influenced by the soil pH, texture and total organic content. This study reports for the first time a wide diversity of Azotobacter species from a semi-arid agroecosystem in Kenya with potential for utilization as low-cost, free-living nitrogen-fixing bioinoculant.