ABSTRACT

Report of damage due to stem roton cowpea in some parts of Kaduna and Katsina States calls for urgent attention in finding possible ways of managing the disease.Knowing the status of the disease will help in employing necessary management strategy as it is a prerequisite to any pest management decision. This research was therefore conducted to determine the incidence, severity and causal organism(s) of cowpea stem rot in North - West Nigeria and evaluate some cowpea varieties for their reactions to the causal organism(s). The incidence and severity of cowpea stem rot in farmers‟ fields were assessed in three Local Government Areas each in four cowpea producing states of North - West Nigeria, Kano, Kaduna, Katsina and Zamfara during 2013 and 2014 rainy seasons. The results showed that cowpea fields in Kaduna State had significantly higher incidence (29.09 %) and severity (21.14 %) than those in Kano, Katsina and Zamfara States for the two seasons. Katsina State had the lowest incidence (9.24 %) and severity (7.31 %) of the disease. The fungi isolated from diseased cowpea stem were identifiedas Rhizoctonia solani,Macrophomina phaseolina, Sclerotium sp., Colletotrichum capsici, Fusarium solani and Curvularialunata. Pathogenicity of the isolated fungi on susceptible cowpea variety SAMPEA 10 was conducted and only Rhizoctonia solani reproduced the typical stem rot symptoms observed on farmers‟ fields. Four inoculation methods: soil drench, injury pinprick, spray and millet grain soil inoculations were used to test the progress of the disease with Rhizoctonia solani. Symptoms which were reddish brown lesions on stem which later girdle the stem at base were observed when inoculum was introduced through pinprick, soil drench and millet grain but no symptoms were observed on cowpea sprayed with the inoculum. vii Six improved cowpea varieties (SAMPEA 7, SAMPEA 8, SAMPEA 9, SAMPEA 10, SAMPEA 11 and SAMPEA 12) two accessions (IAR-00-1074 and IAR-07-1050) and four local varieties (Biu local, Maifarin hanci, Kanannado and Dansokoto) were evaluated in the glasshouse and on the field for their reactions to R. solani infection. The R. solani induced symptoms of varying incidence and severity on all the 12 cowpea varieties with SAMPEA 10, IAR-07-1050 and Biu local recording the highest incidence and severity while Dansokoto recorded the least incidence and severity in both glasshouse and field. Correlation analysis showed that stem rot incidence and severity significantly lead to reduced number of pods and grain yield. It is thus concluded that R. solani induced stem rot is wide spread in North - West Nigeria with varying incidence and severity influenced by agro ecological location. The use of cowpea varieties:Dansokoto, Kanannado and SAMPEA 12 should be encouraged by farmers in areas where the disease cause economic yield loss.