Interacting Effect of Head Bugs, Molds, and Climate on Sorghum Grains in West and Central Africa

摘要

A regional sorghum head bug and grain mold variety trial was conducted in 1996 and 1997 on respectively 15 and 13 research stations from 10 West and Central African countries, in a split-plot design with and without insecticidal protection. It allowedus to update our knowledge on species and generic composition of the entomofauna and the mycoflora of sorghum panicles, and damage caused to a range of cultivars in the region, to identify sorghum genotypes with reasonably high and stable resistance toboth head bugs and grain molds, and to elucidate the relationships between the weather, head bug, and grain mold damage and their various interactions. Two cultivars exhibited consistently high levels of resistance over years and locations, both to headbugs and grain molds, namely IS 14384 and CGM 39/17-2-2. Conversely, S34 was particularly susceptible to both stresses. The trial showed a very clear efficiency of the insecticidal treatment on head bug incidence, as well as, although to a lesser extent,on grain mold incidence, thus confirming the critical role played by head bugs as factors aggravating mold infection. Although sorghum grain microflora varied little from one site to another (with genera Phoma and Fusarium dominating, followed by Curvularia) there were large variations in the specific composition of the head bug entomofauna across sites. This variability in the entomofauna also translated into the virtual absence of any significant correlation between head bug incidence and those weather factors examined. In the case of grain mold, it is high relative humidities during early plant growth (5-40 das) on the one hand, and then between end of flowering and harvest (65-125 das) on the other hand, that are the most strongly correlated withmold incidence (TGMR). The relationships between RHmax and grain mold scores in the scatter diagrams are clearly non-linear, and show a marked increase in grain mold scores when the RH exceeds a threshold of about 95%. Future research directions are proposed.