Distributional Range, Population variability and ecology of Striga aspera in Kogi state

Hemiparasitic Striga (Orobanchaceae) commonly called witchweed is native to tropical Africa. Striga aspera parasitizes wild grasses and its distribution range in Nigeria extends from the Sudan savanna to Guinea Savanna to the southern limit of the Derived savanna just before the forest belt is reached. This study aims to identify and delineate the incidence and distribution range and infestation patterns of Striga aspera within the different floristic areas within in Kogi State (Southern Guinea Savanna) and to establish if vegetation type and edaphic have potential influences on Striga presence. To determine the distribution range and potential hosts of Striga aspera, several opportunistic road reconnaissance surveys were conducted traversing six major towns in Kogi State (Kabba, Okene, Lokoja, Idah, Ayingba and Igala-mela) from July to September, 2015. Identified Striga infested sites were georeferenced and subjected to further vegetation analysis obtained from randomly placed 0.5 m x 0.5 m quadrats in triplicates and compared with adjoining uninfected control sites. Data for the following attributes were collected: density, relative frequency, relative density and summed dominance ratio. To isolate and determine potential Striga host, an inventory of common companion plants at infested sites were taken and screened for presence of haustorium. Edaphic soils properties were determined using standard laboratory protocols. Degree of phenotypic variability within and among the different Striga populations were determine using 14 morphological characters obtained from 10 randomly selected witchweed plants at each infested sites and evaluated using Principal Component Analysis and hierarchical cluster analysis. Nine sites: Idaku, Alokoina (1 and 2), Ala, Adogo (1 and 2), Ichekene, Indori and Old-Egume Road) were found to be Striga infested and all were confined to the low open woodland Southern Guinea savanna (SGS) vegetation dominated by Daniellia/Prosopis complex. The common S. aspera host was found to be Digitaria sp. Other companion species common at infested sites were: Sida acuta, Centrosema pubesence, Mariscus flabelliformis, Chloris pilosa, Pennisetum pedicellatum and Synderella nodiflora. Soil chemical profile reveals that S. aspera infestation as commonly occurs in areas acidic soils of pH ranging from 5.3 to 5.7. The Cluster analysis clearly show the similarity among S. aspera identified while the PCA clearly segregated the different locations where S. aspera was found. Findings in this study suggest that not all areas in the Derived savanna in Kogi State despite similar climatic and edaphic conditions support Striga infestation which showed a clustered distribution pattern. This strongly support the hypothesis that vegetation types operating at the microenvironment level may exert influences in witchweed infestation patterns.