Efeito ambiental e de diferentes regimes de rega e doses de 24-Epibrassinolídeo sobre o crescimento e teor de Clorofila e Nitrogênio foliar em plantas juvenis de cacau

Abstract

Trans-Amazonian and Xingu region has an economy that depends largely on cocoa cultivation (Theobroma cacao). With global climate change, the crop of this species can be highly affected. Therefore, we propose to investigate the effects of the exogenous application of two doses at the concentration in namoles per liter (10 nM and 20 nM and the control) of the phytohormone 24-epibrassinolide, the use and absence of shading and water regimes with different irrigation intervals, on growth characteristics, chlorophyll content, and nitrogen of the leaves of 225 juvenile cocoa plants, in the period of 30 days. For this, we randomized the 225 plants, creating 15 blocks representing the water regimes and in each of them we distributed 15 plants, among which we applied one of the BRs doses (0 nmol, 10 nmol, 20 nmol) to every 5 plants. Collections in the blocks were carried out every five days, recording the morphological growth variables, chlorophyll content, leaf nitrogen and environmental variables. We verified the data distribution with density and frequency graphs of the variables stem length and diameter. We performed a PCA to better understand the data variation correlating all variables to the treatments. Chlorophyll and nitrogen were used as two response variables of two analyses of variance (ANOVA), using the treatments as variables; the Tukey test was performed to confirm the variance within the treatment. Each plant and the application of BRs were used as a random factor and run in a linear mixed effects model (LMM), using restricted maximum similarity (REML). The results demonstrated that the water regime had a great effect on the variation of the growth means in relation to the other treatments, and the environmental factors temperature and humidity had a great correlation with the PCA, which managed to explain 46.32% of the total data variation. Regarding the chlorophyll and leaf nitrogen content, both only suffered a significant effect on their levels of the water regime, specifically the 30-day irrigation interval. There was a difference in the interaction between plants with the 20 nM dosage and the control group, showing a leveling effect, while the 10 nM dosage showed a more intense reaction to environmental changes.