An Investigation on the Initial Source of Inoculum of Cercospora Leaf Spot Pathogens of Groundnut (Arachis hypogaea L.) in Nigerian Southern Guinea Savannah Ecology

Aim: An investigation was conducted in a greenhouse to determine the possible source of initial inoculum of leaf spot of pathogens of groundnut.

Place and Duration of Study: The experiment was conducted at the Teaching and Research Farm of the University of Agriculture Makurdi, Benue State of Nigeria in 2012/2013 cropping seasons:

Methodology: Ex-Daker and Shar-nya were the two groundnut varieties used, while the treatments include: T1- (sterilized soil + sterilized seeds + unsterilized groundnut shells), T2 - (sterilized soil + unsterilized seeds), T3 - (sterilized soil + sterilized seeds + unsterilized debris), T4 - (unsterilized soil + sterilized seeds) and T5 – (sterilized soil + sterilized seeds). The establishment count, disease incidence and severity were the parameters recorded.

Study Design: The 2/5 factorial combination treatments was arranged in Complete Randomized Design (CRD) and replicated 3 times in an area measuring 2.4 / 6.60 m (15.84 m2).

Results: In 2012 and 2013, results show that there was no significant difference (P > 0. 05) among varieties, and the interactive effect between treatments and varieties on percentage of plant establishment. The treatments significantly (P < 0.05) influenced percentage plant establishment in both years. In 2012, higher percentage plant establishment were recorded among T1 (80.56), T2 (94.44), T3 (77.78) and T5 (80.55) compared to T4 (58.33). Similarly in 2013, higher percentage plant establishment were recorded from T5 (97.22) and T2 (94.44) compared to the rest treatments. Results show that the incidence and severity of early leaf spot at 37 and 44 DAS, and combined incidence; severity of both early late leaf spots were not significantly (P > 0.05) influenced by varieties and the interactive effect between treatments and varieties at 51 and 58 DAS in 2012 and 2013. Results revealed that the effect of treatments on incidence and severity of early leaf spot at 37 and 44 DAS; and combined incidence and severity of both early and late leaf spots at 51 and 58 DAS were significantly different (P < 0.05) in 2012 and 2013. Among the treatments, plants grown from T3, T4, and T1 recorded higher and differential levels of early leaf spot incidence and severity at 37 and 44 DAS, and also combined incidence and severity of both early and late leaf spots at 51 and 58 DAS in both years. The results revealed that there was no evidence of disease development on the plants grown to T2 and T5 which affirmatively confirmed that these treatments could not have been the potential sources of the leaf spot pathogens.

Conclusion: The results of this investigation have proved that soil, debris and groundnut shells are the potential initial sources of leaf spot disease inoculums as these pathogens thrives in these sources from one season to another.