Diversity, distribution, tissue culture and value addition of Strychnos species in Central and North-East Districts of Botswana

Abstract

Strychnos is a widely varied genus from the Loganiaceae family with over 200 species identified worldwide. Most of these species are drought tolerant and used for many things such as food, medicine, tools, and ornaments. In Botswana, 7 Strychnos species have been reported, two of them (S. cocculoides and S. spinosa) have been declared as endangered. In this study, five Strychnos species were identified morphologically and through molecular genetics. Their distribution and abundance were studied in the Central District and North East Districts of Botswana. A fruit pulp-based product was also developed, on which sensory and preference tests were performed. Sterile and non-sterile propagation methods for the Strychnos species were also developed. This study revealed that the morphological and molecular classification using four molecular markers; a nuclear ribosomal marker (ITS 2) and three plastid markers (trnS-trnG IGS, matK, and rbcL) were consistent. They both revealed that S. cocculoides and S. spinosa are more closely related to each other than all the other members. S. madagascariensis was more closely related to S. innocua. S. pungens was more related to the latter group than the former. Therefore, both morphology and molecular markers can be used to distinguish the species. This study also revealed that all the 5 Strychnos species are found in the Central District, while only 3 were recorded in the North-East District. The Strychnos species in both districts are facing similar challenges such as climate change, elephants, urbanization, village expansion and threats from other anthropogenic activities. Five fruit jams were produced using fruit pulp from the species, and panelists did not show significant differences (P>0.05) in preference of the Strychnos jams compared amongst each other. However, S. cocculoides and S. spinosa jams performed better in the sensory evaluations, in attributes such as spreadability and lack of aftertaste. A preference test that included S. cocculoides and S. spinosa jams along with 4 commercially produced fruit jams revealed that the 2 Strychnos jams were amongst the number 1 preferred by the panelists. Therefore, these jams have market potential. In this study additionally, sterile Strychnos seedlings of all the species were propagated using embryo culture. This method had a significantly (P<0.05) faster germination time (7-9 days) than the conventional seed method (58.65 ± 1.67 days). Embryo culture had a germination percentage of 92-100 %, while 76 % of seeds germinated through the conventional method. Therefore, embryo culture may be a more efficient method of propagation for Strychnos species.