Trocas Gasosas E Relações Hídricas Em Laranjeira 'Valência' Enxertada Sobre Limoeiro 'Cravo' E Trifoliata E Submetida À Deficiência Hídrica

Abstract

Em citros, diferentes porta-enxertos podem afetar a tolerância da planta à deficiência hídrica. Neste trabalho, avaliaram-se, sob condições controladas, as taxas de assimilação de CO2 (A) e de transpiração (E), a condutância estomática (gs), a eficiência no uso da água (WUE), o potencial da água na folha (Yl) e o conteúdo relativo de água (RWC), em mudas de laranjeira 'Valência' sobre os porta-enxertos limoeiro 'Cravo' e Poncirus trifoliata (Trifoliata) submetidas à deficiência hídrica. As mudas foram cultivadas em vasos e a deficiência hídrica, aplicada pela suspensão da irrigação. Não houve decréscimo em A, E, WUE, Yl e RWC nas plantas quando o potencial da água no substrato (Ysb) esteve acima de -0,04 MPa, mostrando valores semelhantes entre os tratamentos. Para Ysb abaixo de -0,05 MPa, contudo, além de ter ocorrido queda nos valores de A, E, WUE, gs e Yl, as plantas sobre os dois porta-enxertos apresentaram respostas diferentes. As plantas sobre 'Cravo' iniciaram a queda em A, WUE e Yl um dia antes que as plantas sobre Trifoliata e levaram dois dias mais para se recuperarem. Em Ysb de -0,13 MPa, A atingiu 4,1 mmol/m2.s para o tratamento Trifoliata e 1,8 mmol/m2.s para o 'Cravo'. Os valores mínimos de A foram atingidos em Ysb de -0,23 MPa, sendo de 1,0 mmol/m2.s para o 'Cravo' e 2,0 mmol/m2.s para o Trifoliata. A manutenção de maiores valores de A, gs, WUE e Yl, em condições de limitação ao desenvolvimento do sistema radicular, sugeriu maior tolerância à deficiência hídrica de laranjeira 'Valência' enxertada sobre Trifoliata que sobre 'Cravo', em plantas em vasos.<br>Different rootstocks may influence orange tree tolerance to water stress. Under controlled conditions and water deficit, CO2 assimilation rate (A), transpiration rate (E), stomatal conductance (gs), water use efficiency (WUE), leaf water potential (Yl) and relative water content (RWC), were analysed, in potted 2 years old 'Valencia' orange trees grafted on 'Rangpur' lime and Poncirus trifoliata (Trifoliata), rootstocks. There was no decrease in A, E, WUE, Yl and RWC when the substrate water potential (Ysb) was above -0.04 MPa. However, when Ysb was bellow -0,05MPa, plants grafted on both rootstocks showed different responses. In plants 'Rangpur' A, WUE and Yl started lowering one day before plants on Trifoliata and delayed two days to recover. When Ysb =-0.13MPa, A reached 4.1 mmol/m2.s and 1.8 mmol/m2.s to Trifoliata and 'Rangpur' treatments, respectively. The minimum values of A when Ysb = 0.23MPa were 1.0 and 2.0 mmol/m2.s in 'Rangpur' and Trifoliata, respectively. Maintenance of the highest values of A, gs, WUE and Yl suggested that 'Valencia' orange tree grafted on potted Trifoliata showed a higher tolerance to water stress than that grafted on 'Rangpur'

Yield and Quality of ‘Pera’ Sweet Orange Grafted on Different Rootstocks Under Rainfed Conditions

“…The lower Ym in the dry period of the RL rootstock compared to TH confirms the mechanism of increased use of soil water in the position to 1.0 m from the stem by Rangpur lime, which is probably associated to a greater root growth under water deficit, according to findings of Magalhaes Filho et al (2008) and Suassuna et al (2012) and to a greater hydraulic conductivity of roots found by Medina et al (1998). On the other hand, the greater Ym of soil water observed for TH characterizes this rootstock as the conservative genotype associated with lower soil water extraction, which is related to its small size, as reported by Cerqueira et al (2004) and Peixoto et al (2006).…”

“…In this sense, plants grafted on Rangpur lime are considered more tolerant to drought, with mechanisms of greater development of the root system, coupled with the high hydraulic conductivity of roots (MAGALHAES FILHO et al, 2008;SUASSUNA et al, 2012;MEDINA et al, 1998).…”

Rooting of healthy and CVC-affected 'Valência' sweet orange stem cuttings, through the use of plant regulators

“…Gomes et al (2003a) suggested that the bacteria decreased, somehow, the zinc content in the plant, causing less IAA synthesis. However, Medina (2002) worked with the same plants of Gomes et al (2003a) and found no difference in the leaf zinc contents between healthy and CVCaffected plants. CVC-affected 'Valência' sweet orange plants presented a difficult to interpret oscilation in the leaf IAA, GA 1 , ethylen and zeatin contents (Habermann, 2004).…”

“…The biochemical transformation of starch into soluble sugars through auxin action in leaves, stems and roots (Alexander, 1938) is important and it is implicated in the rooting capacity of cuttings. However, further than xylem blockage, CVC-affected plants have low net photosynthesis rates (Machado et al, 1994;Medina, 2002;Gomes et al 2003b;Habermann et al, 2003a;Ribeiro et al, 2003;Habermann, 2004). There is also evidence of decreased rubisco enzyme efficiency (carboxylation efficiency) in CVC-affected plants (Habermann et al, 2003b), that is, the photosynthetic metabolism is affected as well, what indicates a lower starch production, accumulation and translocation from leaves to the base of cuttings.…”

Water relations and photosynthesis as criteria for adequate irrigation management in 'Tahiti' lime trees

“…This response affects both transpiration and photosynthesis of citrus species in different degrees, depending on water stress level (Vu & Yelenosky, 1988;Medina et al, 1998;.…”