The effect of host development on the field assessment of disease resistance to Cercospora leaf spots in groundnuts (Arachis hypogaea L.)

Field experiments in Nigeria showed that a general score of resistance to C. arachidicola [Mycosphaerella arachidis] and Cercosporidium personatum [M. berkeleyi] did not always relate to the varietal response to disease control and reasons for this were proposed. The prevention of pod production by removal of flowers did not affect pathogen development, but vegetative growth of the treated plants was increased. It was concluded that host and pathogen development could be confounded during the assessment of disease resistance. In future varietal screening trials, the use of single branch comparisons should prevent this confusion.ADDITIONAL ABSTRACT:In a trial at Samaru, Nigeria with 6 groundnut cv. given weekly sprays of Bavistin [carbendazim], av. pod and haulm yields were 2.06 and 6.77 t/ha compared with 1.64 and 4.98 t resp., in unsprayed plots. Fungicide application increased pod yields most (by 0.93 t) in cv. SP 205 and decreased yields by 0.04 t in cv. 59-127. In a 2nd trial, weekly application of Dithane M45 [mancozeb] increased pod and haulm yields of SP 205 but had no effect on those of cv. S38.