Effect of radiation on the incidence and severity of bacterial blight disease induced by Xanthomonas axonopodis pv. Vignicola on some varieties of cowpea (Vigna unguiculata L. Walp)

Abstract

Cowpea (Vigna unguiculata L.), is a legume that holds great importance in Africa. Around 70% of cowpea production worldwide comes from the arid regions of sub-Saharan Africa, specifically the Savanna and Sahelian areas, where it is primarily cultivated. Nevertheless, this vital crop faces multiple challenges posed by pests and diseases, including a bacterial infection called cowpea bacterial blight (CoBB). It is important to identify resistant sources to develop cowpea varieties that can withstand CoBB, as it has a detrimental effect on cowpea production. The objective of this study was to examine the impact of different radiation treatments on the incidence and severity of the disease. The experiment consisted of eight levels of radiations X-Ray-0Secs (X0), X-Ray-5Secs (X1), X-Ray-10Secs (X2), X-Ray-20Secs (X34), UV-Rays-0Mins (UV0), UV-Rays-15Mins (UV1), UV-Rays-30Mins (UV2) and UV-Rays-60Mins (UV3)), two cowpea varieties (IT97K-819-118 and Dan’ila) and two levels of bacterial blight inoculum (full inoculum (I1) and no inoculum (I0)) combined factorially and laid out in Randomized Complete Block Design with three replications. Disease incidence was determined by assessing the proportion of symptomatic plants as a percentage of the total number of plants per pot, while severity was evaluated using a severity rating scale. The results revealed that disease incidence was highest in the absence of radiation, Danila cultivar, the disease incidence at 0 seconds of X-ray exposure
was 82.63%. Similarly, for IT97K-819-118, the disease incidence was 79.33% whereas longer durations of X-ray and UV-ray exposures, particularly 60 minutes of UV-ray exposure, were associated with lower mean values, Danila had a disease incidence of 18.56% (a decrease of 64.07%). IT97K-819-118 exhibited the lowest disease incidence of 28.03% (a decrease of 50.52%). Additionally, IT97K-819-118 demonstrated generally lower severity mean values compared to Danila, when no X-ray radiation was applied, the disease severity for IT97K-819-118 was recorded as 2, indicating slight infection. The study concluded that both X-ray and UV-ray radiation show potential as suppressive agents against cowpea bacterial blight; however, the effectiveness vary depending on the cultivar and the duration of exposure.