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The feasibility of thermography as a technique for plant screening aiming at drought-tolerance has been proven by its relationship with gas exchange, biomass, and yield. In this study, unlike most of the previous, thermography was applied for phenotyping contrasting maize genotypes whose classification for drought tolerance had already been established in the field. Our objective was to determine whether thermography-based classification would discriminate the maize genotypes in a similar way as the field selection in which just grain yield was taken into account as a criterion. We evaluated gas exchange, daily water consumption, leaf relative water content, aboveground biomass, and grain yield. Indeed, the screening of maize genotypes based on canopy temperature showed similar results to traditional methods. Nevertheless, canopy temperature only partially reflected gas exchange rates and daily water consumption in plants under drought. Part of the explanation may lie in the changes that drought had caused in plant leaves and canopy structure, altering absorption and dissipation of energy, photosynthesis, transpiration, and partitioning rates. Accordingly, although there was a negative relationship between grain yield and plant canopy temperature, it does not necessarily mean that plants whose canopies were maintained cooler under drought achieved the highest yield.

ResumoO objetivo do estudo foi verificar o efeito do sombreamento na produção de óleo essencial, biomassa e quantidade de tricomas glandulares em cidrão (Lippia citriodora Lam.) no Norte de Minas Gerais. O delineamento experimental foi inteiramente casualizado, com quatro tratamentos e cinco repetições. Os tratamentos consistiram em quatro níveis de radiação fotossinteticamente ativa (RFA) utilizando telas tipo sombrite que permitem a passagem de 25, 50, 70% de luz e a pleno sol (controle). Foram determinadas as variáveis: matéria seca da raiz, matéria seca da parte aérea, número de flores, matéria seca total, relação raiz/parte aérea, produção de óleo, teor de óleo essencial e quantidade de tricomas glandulares. Foram observadas diferenças estatisticamente significativas para massa seca da raiz, massa seca da parte aérea, número de flores, matéria seca total, razão raiz/ parte aérea, produção de óleo e quantidade de tricomas, todavia o mesmo não ocorreu para o teor de óleo. Os resultados evidenciaram que a pleno sol houve uma maior produção de biomassa que nos demais tratamentos e no sombreamento de 70% o número de tricomas foi maior. O teor de óleo não sofreu nenhuma alteração em relação aos tratamentos. AbstractInfluence of shade on the biomass and essential oil production of Lippia citriodora (Lam.), Brazil. This study aimed to evaluate the effect of shading on the production of essential oil and biomass in Lippia citriodora (Lam.) -known as cidrão -in the north of Minas Gerais, Brazil. The experimental design was Biotemas, 22 (4): 9-14, dezembro de 2009

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