Caracterização, quantificação e modelagem de danos provocados pela geada no período reprodutivo da canola

Abstract

The objective of this work was to quantify the damage caused by frosts in the reproductive period of canola and to develop models for their estimation. In 2016 and 2017 two experiments were carried out under controlled conditions and two field experiments. The experiments in a controlled environment were conducted in a completely randomized design and factorial arrangement. Plants with and without cold acclimatization were exposed to the air temperature of -6°C. In the filed, the experiments were conducted in randomized complete block design, with subdivided plot and factorial arrangement. The analyzes were performed considering a factorial sample design within the blocks of the original experiment. Biometric evaluations were performed before and after frosts in controlled and field environment. In the field environment it was evaluated the air temperature (Tar) in the canopy at 5, 40, 100 and 150 cm of the soil and the temperature of reproductive structures (Ter). Models were developed to estimate the minimum air temperature close to the reproductive structures (TnE), minimum temperature of the reproductive structures (Tner) and the ovules mortality in reproductive structures, by linear regression. Ovules death in Flowers (F) and Flower buds (B) begins with Tar of 2.4 and 1.9°C, respectively. Death of all ovules would occur with Tar of -6.7 and -10.2°C in F and B, respectively. Tar of -4.80°C caused the death of 70 to 90% of the ovules in F and siliques with less than 2 cm length (S <2). The equation describing the evolution of ovules numbers in frosty night indicates that ovules death begins with Tar of 0.81°C and total death occurs with Tar of -6.52°C. B, F and S <2 present abortion 27% higher than siliques with more than 2 cm length (S>2). If B, F and S <2 do not abort they present a 79% larger number of grains than S>2. The lowest Tn occurred at the top of the canopy. The mean gradient between the lowest and highest Tn in the canopy is 1.64, 0.91, 1.22 and 0.75°C in severe frosts, moderate frosts, light frosts and cold days, respectively. . It is possible to estimate the Tner during the canola cycle, according to data obtained from the meteorological station, with the model Tner = 1.21 (Tn Aut1) - 2.77 When Tn less than 5°C it is possible to estimate Tner with the model Tner = 1.09 (Tn Aut) - 3.06. Damage caused by frost in the reproductive period of canola can be quantified from Tn measured in automatic weather station and/or Tn measured at reference position within the crop.