Corn (Zea mays) rusts (Puccinia sorghi, P. polysora, Physopella zeae). IV. Estimation of losses caused by the common corn rust (P. sorghi)

Abstract

A field plot experiment (split plot) is described. Treatments were: four inbred corn lines, two of them with active susceptibility and the other two with passive susceptibility, half of all individual plants inoculated by hypodermic injection with a mixture of thirteen P. sorghi races, the other hall non-inoculated. Analysis shows a 35 to 36% loss in susceptible inoculated susceptible lines but no significant loss neither in non inoculated susceptible lines nor in resistant inoculated or non-inoculated lines. Record of production field rust observations in the Brazilian Center-South in 1963/1964 does not evident any significant loss in fields visited by the author. But P. polysora in the coastal low and hot region near Rio de Janeiro is indicated as atacking quite violently in corn fields sown late in the season. Inbred lime field and basic seed production field observations, made in the Instituto de Pesquisas Agropecuarias do Centro-Sul (IPEACS), suggest considerable losses due to both pathogens.