Artificial defoliation during anthesis stage in sunflower

Abstract

In order to study the effects of various leaf removal treatments during anthesis stage on sunflower (Helianthus annuus L.) grain yield and other agronomic traits, an experiment was carried out at the Estação Experimental Agronômica da Universidade Federal do Rio Grande do Sul, in Guaíba, RS, Brazil, during the 1981/82 growing season. The leaf removal treatments were: an undefoliated check, leaves of the plant upper third removed, leaves of medium third removed, leaves of lower third removed, leaves of upper third plus lower third removed, leaves of upper plus medium thirds removed, leaves of medium plus lower thirds removed and all leaves removed. These eight leaf removal treatments were applied in two times: at the beginning and at the end of anthesis of ‘Conti-GH 8121’ sunflower cultivar. When compared with the undefoliated check, grain yield decreased from 9 to 80% with the defoliation treatments, except for two: removal of leaves of upper third of the plant and removal of the leaves of lower third of the plant. The yield component grain number in heads was affected only by leaf defoliation levels whereas the other component, grain weight, was affected by date as well as by levels of defoliation. The diameter of sunflower heads and the harvest index were also affected by defoliation date and level. Grain yield was positively associated with all other traits studied.