NEMATOLOGICAL ENVIRONMENT AND SELECTION PRESSURE ON SIX SASRI RESEARCH FARMS
Current estimates indicate that the loss in yield of sugarcane from root-feeding nematodes amounts to approximately R250 million per year. Tolerant varieties provide an inexpensive and long-lasting option to reduce crop loss from nematodes. Currently, genotypes are selected on the SASRI research farms without direct attention being given to their tolerance or susceptibility to nematodes. Not much is known about the nematode communities that exist on the research farms and whether these nematode communities exert sufficient selection pressure on the genotypes in the selection programme. The objectives of this work were (i) to characterise the plant breeding selection sites according to their nematode communities, and (ii) to measure the effect that nematodes have on the yield of varieties at plant breeding selection sites and thus identify the selection pressure for nematode tolerance. To achieve this, the 2nd stage single lines at six research farms were surveyed for nematode populations. Results showed that Empangeni, Gingindlovu and Kearsney had similar nematode profiles, whereas other research farms exhibited differences in nematode communities. For example, Bruyns Hill and Glenside had higher numbers of Helicotylenchus, whereas Pongola had higher numbers of Hemicycliophora and Rotylenchulus. The common variety at all sites, NCo376, exhibited a similar nematode community to other sugarcane clones at a particular site, but a substantially different community between sites. Yield data from single line trials showed that nematode communities influenced selection at four of the six sites. Two variety x nematicide trials were planted to assess the loss due to nematodes. At Empangeni, the yield responses (which reflect crop loss) in the plant crop ranged from 10 to 27%. At Gingindlovu, the responses in the plant crop ranged from 44 to 52%.
Les nématodes parasites des racines associés Au riz en Basse-Casamance (Sénégal) et en Gambie
Au cours d’une enquete SUT les Nematodes radicicoles parasites du riz au Senegal et en Gambie, 82 echantillons ont ete etudies, dont 6’7 en Basse-Casamance (Senegal) et 15 en Gambie. Les trois types de rizieres existant en Basse-Casamance ont presente entre eux des differences sensibles tant dans les peuplements que dans les populations de Nematodes parasites du riz. Les rizieres de mangrove ainsi que certaines rizieres moyennes en sont pratiquement exemptes, probablement a cause des phenomenes de sulfatoreduction dont elles sont le siege. Les rizieres moyennes hebergent un petit nombre d’especes a la fois frequentes et abondantes alors qu’elles sont sensiblement plus nombreuses dans les rizieres hautes. En Basse-Casamance, les especes frequentes et abondantes sont : Tylenchorhynchus mashoodi, Hirschmanniella spinicaudata, Criconemoides palustris, Xiphinema bergeri, Heterodera spp. Pratylenchus SP., Paratylenchus sp. et Trichodorus spp. alors qu’en Gambie une seule repond a ces criteres : Hirschmanniella oryzae.
Drivers of Live Cattle Price in the Livestock Trading System of Central Cameroon
Livestock production and trade are critical for the food security and welfare of rural households in sub-Saharan Africa. In Cameroon, animal trade consists mainly of live cattle commercialized through livestock markets. Identifying the factors contributing to cattle price formation is critical for designing effective policies for sustainable production and for increasing food availability. In this study, we evaluated the influence of a range of individual- and market-level factors on the price of cattle that were sold in all transactions (n = 118,017) recorded over a 12-month period from 31 livestock markets in the main cattle production area of the country. An information-theoretic approach using a generalized additive mixed-effect model was implemented to select the best explanatory model as well as evaluate the robustness of the identified drivers and the predictive ability of the model. The age and gender of the cattle traded were consistently found to be important drivers of the price (p < 0.01). Also, strong, but complex, relationships were found between cattle prices and both local human and bovine population densities. Finally, the model highlighted a positive association between the number of incoming trading connections of a livestock market and the price of the traded live cattle (p < 0.01). Although our analysis did not account for factors informing on specific phenotypic traits nor breed characteristics of cattle traded, nearly 50% of the observed variation in live cattle prices was explained by the final model. Ultimately, our model gives a large scale overview of drivers of cattle price formation in Cameroon and to our knowledge is the first study of this scale in Central Africa. Our findings represent an important milestone in designing efficient and sustainable animal health management programme in Cameroon and ensure livelihood sustainability for rural households.