Respostas de trigo à geada

Abstract

The incidence of frost has caused significant grain yield losses in wheat. The environmental conditions that plants are exposed prior to frost interfere in the extent of damage. The objective of this work was to characterize wheat cultivar response to frost incidence. The experiments were carried out at Embrapa Trigo, during the years 2004 and 2005, under screen houses and growth chamber conditions. Experiments were planned to determine the effect of regimes of acclimatization, frost intensity and water stress on symptoms of leaf scorching and grain yield of two commercial wheat cultivars BR 18 and BRS 194. Frost was simulated at growth stages of tillering, stem elongation and heading. In another experiment the effect of frost, based on leaf symptoms and grain yield, at growth stages of stem elongation and heading was evaluated in 29 genotypes of wheat and frost and 7 near-isogenic lines (vrn). Frost intensity at -4° C and -7° C, at stem elongation stage, reduced grain dry matter by 27.4% and 35.2%, respectively, if compared to the control temperature of 2 ° C. A frost intensity of -7 °C, at heading, caused spikelets sterility. A dry spell of 9 days, at heading and stem elongation reduced leaf scorching symptoms increased total grain dry weight compared to shorter periods of water stress. The cultivar BR18 showed the highest levels of leaf scorching while BRS Umbu, BRS Guabiju and PF 990606, showed almost no symptoms. The cultivars IAC-5 Maringá and BR18-Terena had the highest total shoot dry weight. The Pitic wheat showed the highest shoot weight at stem elongation and heading stage, while the genotype Yecora Rojo winter had lowest grain dry matter content when frost was simulated at stem elongation. In contrast, only the cultivars Phoenix and Yecora Rojo spring set some grains when frost was simulated at the heading stage. The cultivar Phoenix had 96% more grains when compared to the others. Among the genotypes and the near-isogenic lines of wheat evaluated exists materials tolerant of frost, especially, at the stem elongation and when subjected to acclimatization and / or water deficit prior the frost incidence