Combined effect of host plant resistance and insecticide application on the development of cowpea viral diseases

Abstract Cowpea [Vigna unguiculata (L) Wap] is an important food crop which is widely grown in the Soudano-sahelian region of Cameroon. An integrated disease control approach involving insecticide treatment and plant host resistance was used to control virus-induced diseases, which are the most cowpea yield-limiting factor in this part of the country. A field experiment was conducted at Guirin-Maroua location in which three cowpea varieties (CRSP, LORI and VYA) that differ in their resistance to cowpea viral diseases were treated with Cyperdim 220 EC insecticide at different doses (1.75, 1.25 and 0.95 l/ha). In this experiment, severity of cowpea viral diseases including SMVD, YMVD, ABMVD and GMVD, were assessed. Population size of thrips (Megalurothrips sjostedti) and larvae of Maruca testuladis, two main vectors of cowpea viral diseases were evaluated. An evaluation of cowpea grain yield was also made. Visual diagnosis which was confirmed by ELISA test showed that only SMVD, YMVD, ABMVD were present during these investigations. Both viral diseases and the population of vectors reduced with combined treatment consisting of the less susceptible cowpea variety VYA and the highest insecticide dose (1.75 l/ha). This treatment combination also produced the highest cowpea grain yield (29.5 t/ha), a yield that was almost 3 times higher than the control (10.2 t/ha). Our results suggest that cowpea viral diseases that prevail in the Soudano-sahelian region of Cameroon are likely to be under control if less susceptible cowpea varieties such as VYA are treated with some insecticides including Cyperdim 220 EC

Control of leaf spot disease caused by Cercospora sp on groundnut (Arachis hypogaea) using methanolic extracts of yellow oleander (Thevetia peruviana) seeds

Abstract A study was carried out in Yaounde (Cameroon) on two cultivars of groundnuts treated with methanolic extracts of Thevetia peruviana seeds (METPS), to evaluate the epidemiology of Cercospora leaf spots (CLS) and the antifungal potentials of these extracts under natural conditions. METPS were obtained by maceration of seed powder (0,33 kg/l) in methanol. Two concentrations of METPS (1.8 and 3.7 kg/ha), a benomyl and a control treatments were used in four replicates of a randomised block design. Disease severity, incidence, lesion size and yield were assessed. Two foliar applications of antifungal substances were effected at 15 days interval. The epidemic on both groundnut varieties was low in plots sprayed with METPS and benomyl when compared with the control. Disease incidence, lesion size and CLS severity were reduced to 37.25, 33.10 and 32.61 % respectively in plots sprayed with METPS compared to the control. The Bafia var. was more tolerant to CLS than the 55-437 var. Groundnut yield increased by 32.89 and 41.37 % for the Bafia var following applications of METPS and benomyl respectively. These results suggest that integrating host resistance and METPS efficiently protects groundnut against CLS

Prevalence of Six Viruses in Potato Seed Tubers Produced in Informal Seed System in the North West Region of Cameroon

Potato (Solanum tuberosum L.) is an important cash-food crop, which is widely grown in three of the five agro-ecological zones of Cameroon. A study was carried out to determine the prevalence of PVA, PLRV, PVM, PVS, PVX and PVY in 1175 sprouted potato seed tubers of different diameters collected from four seed stores in the North West Region of Cameroon. The study also sorts to ascertain variations in virus incidence in small, medium and large size sprouted tubers prior to planting. The DAS-ELISA method was used to test for the presence of these viruses. Results showed significant differences in the prevalence of the six viruses with PVM being the most prevalent (92%), while PLRV was least prevalent (35%) in all the four seed stores sampled.  Upper-Farm store registered the highest relative prevalence (82%), with PVM detected in all the tubers while samples from Rock-Farm store showed the least relative incidence (55%) with no PLRV detected. Viruses were significantly most prevalent in small size tubers (71%) and least in large size potato tubers (63%). Our results suggest that tuber size can serve as a guide to identify healthy (virus-free) tubers. Farmers could therefore use large size potato tubers for planting