Resistance of cowpea [Vigna unguiculata (l.) Walp.] to Striga gesnerioides (Willd.) Vatke, a parasitic angiosperm

An in vitro growth system was used to investigate the expression of resistance of cowpea [Vigna unguiculata (L.) Walp.] varieties B301 and 58-57 to the angiosperm parasite Striga gesnerioides (Willd.) Vatke. Variety Blackeye was included in experiments as a susceptible control. Seeds of S. gesnerioides germinated on the roots of all varieties. Two different mechanisms of resistance were expressed in B301 and 58-57 after penetration of host roots by parasite radicles. The first mechanism was expressed in both varieties; host tissue around invading Striga radicles became necrotic in association with the early death of the parasite and lack of tubercle formation. On variety 58-57, the necrosis response was expressed only when the roots were inoculated with Striga from Burkina Faso but Striga from Mali successfully parasitized the roots of variety 58-57. The second mechanism was observed only on variety B301. Striga radicles infected cowpea roots, tubercles were formed but remained at 1-2 mm in diameter with very limited stem growth. No further development of the parasite occurred in vitro or when infected cowpeas were grown in soil or vermiculite. Similarities between the expression of resistance of cowpea to Striga and of plants to plant pathogenic fungi are discussed

Germination capacity and viability of threatened species collections in seed banks

Facing the current biodiversity crisis, the value of ex situ conservation has been increasingly acknowledged in international treaties and legislations. Seed banks are a good way of conserving biodiversity, providing that seeds are of high quality and at maximum viability. However, despite the number of established ex situ facilities, there is little information on seed viability in botanic garden seed banks. This paper analyses the status of the seed collection of the National Botanic Garden of Belgium by determining the germination capacity and viability of seeds that have been stored for 1-26 years. It aims at: (1) ensuring that existing storage conditions provide effective ex situ conservation of threatened species; (2) providing viability data on threatened species; (3) planning future collection and storage efforts for seeds of West European species of conservation value. Results from this study showed that the germination and viability percentages of the 250 tested species reached on average 59 and 79% respectively. Some families typically performed better than others. Within a species, consistent results were not always obtained. Over a quarter of accessions exhibited some degree of dormancy. Considering the current lack of knowledge in seed germination and dormancy of many rare and threatened species, we believe that the quality of a seed collection should be estimated by its viability and not by its germination percentage. This study calls for further research in order to better understand the biology of a range of threatened native species. © Springer Science+Business Media B.V. 2009.SCOPUS: ar.jinfo:eu-repo/semantics/publishe