Performance of black gram varieties to mungbean yellow mosaic disease at different sowing dates under spring and summer condition in western terai of Nepal

A field experiment was conducted at Grain Legumes Research Program (GLRP), Khajura, Banke, Nepal during spring and summer season 2019 to elucidate the effect of date of sowing and blackgram varieties on mungbean yellow mosaic disease severity and yield. The experiment was conducted in 2 factorial randomized complete block design with 3 replications. Factor A comprised date of sowing (S1= 5th April 2019, S2= 20th April 2019, S3= 5th May 2019, S4= 20th May 2019, S5= 25th July 2019, S6= 10th August 2019, S7= 25th August 2019 and S8= 10th September 2019) and factor B (Variety): V1= Khajura Mas 1 and V2= Rampur Mas. Disease severity was scored in 1-6 scale. Results revealed that mean values for days to disease appearance, disease score and grain yield in spring season sowing was 26 days, 3.72 and 635 kg/ha, whereas for summer season sowing was 14 days, 5.04 and 185 kg/ha.  Among the date of sowing, April 5th sown crop recorded minimum mean disease score (3.1) with highest yield (719 kg/ha). Whereas, September 10th sown crop recorded maximum mean disease score (5.1) with lowest yield (174 kg/ha). Black gram varieties showed significant response to mean disease score and yield at early sowing condition but when the sowing date was delayed, there was no significant response of varieties to mean disease score and yield. The contribution of regression (R2 =0.791) and (R2 = 0.655) for spring season and summer season indicate that 79% and 65% of the blackgram yield would be affected by disease for the respective season. Therefore, it is better to sow blackgram in early season to escape mungbean yellow mosaic disease and minimize yield loss.