Respostas fisiológicas, bioquímicas e transcricionais em porta-enxertos de Prunus persica submetidas ao alagamento do solo

Abstract

The state of Rio Grande do Sul is the largest peach producer in Brazil. Nowadays, the region's producers have been facing problems in their orchards, which affect the productivity and quality of the fruits. This situation is evident when we compare Rio Grande do Sul with other states, because even though it is the largest producer, it has the lowest productivity. The obtaining of rootstocks may be related to the problems faced, since these come from residual peach pits from the canning industry and therefore there is no genetic control, providing great genetic variability, due to the varietal mixture of the scion cultivars. Another problem found in this region is the soil characteristic, which in general presents insufficient drainage, mainly in the Pelotas producing region, associated with periods of frequent and intense precipitation in some periods leading to waterlogging and/or flooding of the soil and causing damage to culture. In these situations, there is a drastic reduction of oxygen in the soil solution and to the roots, impairing the aerobic respiration process and can lead the cells to an energy deficit. Thus, in the present study, two experiments were carried out that aimed to identify and evaluate physiological, biochemical and molecular responses (through the expression of target genes by RT-qPCR) in two rootstocks of P. persica, grafted and non-grafted with scion cultivar ‘Rubimel’, which root systems were imposed to flooding. In the first study, physiological parameters and the expression of twelve genes involved in glycolytic and fermentative metabolism were evaluated, in order to elucidate the initial stress response and identify the initial activation of the fermentative route in Prunus persica rootstocks (cv. Tsukuba 1) submitted to short-term flooding of soil during control (plants under normal irrigation conditions); 1; 2; 4; 8; 16; and 32h of soil flooding. In the first hour of stress imposition, sucrose synthase (SUS) already had a positive expression. The lactate fermentation pathway was activated after two hours of flooding and four hours later, positive expression of the genes of the ethanolic fermentation pathway was verified. Glycolysis was intensified in the face of hypoxia stress during the 8 and 16 hours of experiment. In the second experiment, the objective was to identify the physiological, biochemical and molecular responses adaptive to stress and the influence of two rootstocks of Prunus spp. (‘Capdeboscq’ and ‘Tsukuba 1’) when grafted with the scion cultivar ‘Rubimel’, and their behavior when not grafted and submited to soil flooding. For this, stomatal conductance evaluations were carried out at the following times: control, 8, 24, 28, 48 and 72h; quantification of carbohydrates in leaves and roots in two stages: control and 72 hours; and differential expression of genes involved in the glycolytic and fermentative routes (CINV1; GAPDH; LDH1; PDC and ADH1), sucrose synthesis (G6PI; PGM; UDPase and SPS), sorbitol (S6PDH; SDH and SOT1), in osmotic regulation (P5CS and GTL) and ethylene (ACO1) at times: control, 8 and 72 hours of stress imposition. In general, grafted plants differed from non-grafted plants, presenting a reduction in stomatal conductance when exposed to flooding stress. 'Rubimel' plants grafted on 'Capdeboscq' and 'Tsukuba1' respond differentially to various biochemical, physiological, and molecular parameters under hypoxia stress. The ‘Capdeboscq’/’Rubimel’ combination demonstrated a moreefficient control of its reserves, in the face of stress, due to maintaining stable carbohydrate concentrations. The expression of the SPS and S6PDH genes was very pronounced in the ‘Tsukuba1’/‘Rubimel’ combination indicating the synthesis of sucrose and sorbitol in these plants. The fermentative route was active after 8h and persisted until 72 h in the plants of the ‘Tsukuba1’/‘Rubimel’ combination showing an energy stress. Plants in the ‘Capdeboscq’/‘Rubimel’ combination appear to be more tolerant than those in the ‘Tsukuba1’/‘Rubimel’ combination when under flood stress. Therefore, this study demonstrated the peculiarities of the adaptive responses to stress by flooding the soil (short-medium term) in non-grafted and grafted plants with the ‘Rubimel’ canopy cultivar through physiological, biochemical and molecular analyses, highlighting the importance of the process of grafting. Primarily, this study corroborates with results that go against the selection of rootstocks of Prunus spp. with characteristics that are adaptable to the edaphoclimatic conditions of the state of Rio Grande do Sul and that provide quality production, increased productivity and profitability to producers.