Optimum fertilizer application mitigates the effect of angular leaf spot disease in common beans

Abstract

Common bean production in Uganda is constrained by angular leaf spot (ALS) disease (Pseudocercospora griseola). Without durable resistance to the disease and concerns surrounding pesticide use, management of ALS depends on cultural practices, which unfortunately have not been very effective. Improved fertilization of crops has been used to manage some diseases in crops and thus could be a valuable addition to the integrated management package for ALS disease. The effect of NPK on common bean growth and ALS severity was studied on variety K131 at Makerere University Agricultural Research Institute, Uganda in 2020 and 2021. NPK levels 0, 60, 120, 180 and 240 kg ha-1 were tested in the field, with three replication. Disease progressed fast under low NPK rates, reaching a plateau at high rates. AUDPC ranged from 142.5 to 183 in 240 and 0 kg NPKha-1 plots, respectively. Yield parameters were significant (P<0.001) for, and increased with amount of NPK. Mean pod number ranged from 13.3 to 21.8 in 0 and 240 kg NPKha-1 treatments, respectively. Seed number per pod ranged from 4.75 to 5.3; while 100 seed weight ranged from 22.5 gm to 24.1 gm. Plant dry matter followed the same trend and ranged from 29.7 to 53.2 gm/plant. Marketable grain yield ranged from 1.53 to 3.27 t/ha. Relative yield loss increased as NPK reduced or as ALS AUDPC increased with the highest (53.2%) recorded for zero NPK. Multiple regression resulted into a significant NPK amount effect (R2 = 0.991; P = 0.018) and a non-significant (P = 0.365) AUDPC effect on relative yield loss. NPK application, therefore, does not affect ALS disease but cancels out its effects at optimal fertilizer levels. NPK applications should be deliberately integrated into bean production to minimise the effects of ALS disease.