Organiser: Department of Crop Production Ecology
Welcome to our next Crop Production Ecology Monthly Seminar. Jonne Rodenburg will give a presentation on an underestimated parasitic weed of rice systems in Africa.
Rhamphicarpa fistulosa (Hochst.) Benth. (common name: rice vampireweed) is a parasitic weed in smallholder rice crops across Africa. The species was first reported as a weed in rice in Madagascar in the 1930's, and in the late 1940's in West Africa.
As the weed became more problematic in the late 1990's, weed scientists and botanists in West Africa (Mali, Burkina, Benin) conducted the first empirical studies on it. In 2006 we started investigating this species, when it was still poorly understood. In this seminar the progress made so far in improving our understanding of R. fistulosa ecology, host dependency, host effects, crop yield and economic losses and agronomic management, will be presented. Where relevant, the ecology, biology and management will be compared to the better-known parasitic witchweed species (e.g., Striga asiatica and S. hermonthica) with a similar host range (e.g., cereals and sugar cane).
Contrary to witchweeds that are mainly found on free-draining soils, rice vampireweed prefers water-logged soils, although it does not survive (long-term) submergence. The parasitism of rice vampireweed is characterized as facultative; whereas witchweeds need a nearby host to germinate and grow, rice vampireweed is less dependent of host presence.
Compared to independently growing plants, rice vampireweed plants do however gain considerably in biomass and reproductive output when they parasitize on a host. The host plant, on the other hand, incurs severe reductions in photosynthetic efficiency and biomass production and host-plant assimilates primarily benefit parasite growth and reproduction.
Crop yield losses caused by rice vampireweed infestations range from 24 to 73% (mean: 50%). Annual crop losses in sub-Saharan Africa are estimated at 204,000 tons of milled rice, with associated annual economic losses of US $82M. The extent of yield losses are highly dependent of host genotype, as variation in both host plant resistance and tolerance has been observed across rice cultivars.
Early sowing has shown to decrease parasite infection levels. Contrary to witchweed, rice vampireweed is not controlled but rather stimulated by application of mineral fertilisers. More agronomic control measures need to be identified in the future to provide affected smallholder rice farmers with options.
This seminar series is a free and online platform for scientific debate about agricultural production and sustainability between academics, stakeholders, and the general public.