The effect of eyespot caused by Oculimacula yallundae and O. acuformis on yield of winter wheat

Abstract

Field experiments (2000-2002) were carried out to determine the effect of eyespot caused by Oculimacula yallundae and O. acuformis (formerly known as W-type and R-type, respectively) on yield or lodging resistance of winter wheat and to identify any differences in the development of the two pathogens throughout the season. A field experiment on artificially inoculated wheat was designed to clarify the effects of the two Oculimacula spp. on plant characteristics associated with lodging resistance and on yield of individual shoots and whole crop. Overall yield of winter wheat in the absence of lodging was reduced by 11% and 6% by eyespot caused by O. acuformis and O. yallundae respectively. Both species reduced the stem safety factor associated with lodging resistance, indicating their ability to cause lodging in winter wheat by reducing stem-bending strength. The ability of O. acuformis to cause significant yield loss was demonstrated in a series of fungicide efficacy experiments in early-drilled winter wheat. Oculimacula acuformis developed more and caused greater yield loss in the first winter wheat in which other stem-base pathogens were absent in the early growth stages of the crop. Fungicide mixtures containing cyprodinil were consistently more effective in controlling eyespot caused by O. acuformis in first, second and third winter wheat crops. Positive relationships were observed between DNA concentrations of O. acuformis, O. yallundae and M. nivale throughout the growing season, indicating that these species co-existed within the crop. While the DNA of M. nivale consistently increased more up to GS 39 in different field experiments, DNA of Oculimacula spp. increased at different times in the growing season and these increases were sometimes associated with the relative quantities of DNA of M. nivale at the early growth stages.