Sombreamento na fisiologia, produção e qualidade e efeito da temperatura nos aspectos moleculares da pitaia

Abstract

Pitahaya is a fruit crop native to the Americas, promising for large-scale cultivation. This investigation was aimed to study the shading influence as well as heat stress tolerance on the pitahaya crop. The experiments were performed at the Federal University of Ceará, CE, Brazil and at the Ben Gurion University of the Negev, Israel. Physiology, biochemistry, production, fruit quality, plasticity index and molecular aspects were carried out. Shading triggered major increases on productivity, number of fruits per plant and fresh fruit mass average. On the second year, the maximum yield estimated was 18.84 ton ha-1 under 36.58% of shading, an increase of 71.4% on the production volume compared with full sunlight (10.99 ton ha-1) cultivation. Physico-chemical characteristics and bioactive compounds were little influenced by shading. The highest levels of yellow flavonoids and polyphenols of the skin were observed in the full sunlight condition. There was an increase on the skin betacyanin content by increasing shading percentage. There was no significant effect of shading on the physico-chemical characteristics and antioxidant activity. The interception of about 35 to 50% of the radiation provided better conditions for the plant growth. Shading promoted linear increases on the photosynthetic pigments (Chlor a, Chlor b and Chlor tot). Full sunlight increases the carotenoid percentage and photochemical quenching as well as decreased significantly the optimum quantum yield of PSII, Fv/Fm and Fv/Fm ratio, however, increases on the Fv/Fm and Fv/Fm was observed by around 50% of shading. The high light intensity promoted changes on the cladodes color physiology and Sunburn was observed on full sunlight. Hylocereus sp. showed phenotypic plasticity, which most of the adjustments were biochemical and physiological. Hybridization appears to improve thermotolerance in Hylocereus spp. Based on the gene expression of two heat shock proteins, HSP90 and HSP70, the results suggest the existence of sensitive, intermediate and tolerant hybrids. The use of shading around 35%, increased the productivity, but resulted in little influence on the physico-chemical characteristics and bioactive compounds, while the antioxidant activity was not affected by the shading treatments. Shading was effective on the light efficiency absorbance and on the photoinhibitory damage reduces by full sunlight. The use of shading, around 35% to 50% provided better conditions for the plant growth, promoted linear increases on the photosynthetic pigments, increases on the Fv/Fm and Fv/F0 ratio, decrease in the carotenoid content, decreases on the Clor a/Clor b ratio and on the photochemical quenching. Shading also preserved the cladodes color physiology without sunburn. In addition, Hylocereus sp. showed phenotypic plasticity with adjustments predominantly biochemical and physiological. Gene expression need further investigation aiming at understanding the role of thermotolerance mechanisms in Hylocereus spp.