Water stress signaling and hydraulic traits in three congeneric citrus species under water deficit.

Morpho-physiological strategies to deal with water deficit vary among citrus species and the chemical signaling through ABA and anatomical, hydraulic, and physiological traits were evaluated in saplings of Rangpur lime, Swingle citrumelo and Valencia sweet orange. Trunk and roots of Swingle citrumelo presented lower vessel diameter and higher vessel frequency as compared to the other species. However, relative water content at the turgor loss point (RWCTLP), the osmotic potential at full turgor (Ψ0), the osmotic potential at the turgor loss point (ΨTLP), bulk modulus of elasticity (ε) and the xylem water potential when hydraulic conductivity is reduced by 50% (Ψ50) and 88% (Ψ88) indicated similar hydraulic traits among citrus species, with Rangpur lime showing the highest hydraulic safety margin. Roots of Rangpur lime and Swingle citrumelo were more water conductive than ones of Valencia sweet orange, which was linked to higher stomatal conductance. Chemical signaling through ABA prevented shoot dehydration in Rangpur lime under water deficit, with this species showing a more conservative stomatal behavior, sensing, and responding rapidly to low soil moisture. Taken together, our results suggest that Rangpur lime - the drought tolerant species - has an improved control of leaf water status due to chemical signaling and effective stomatal regulation for reducing water loss as well as decreased root hydraulic conductivity for saving water resources under limiting conditions.

Physiological Plasticity Is Important for Maintaining Sugarcane Growth under Water Deficit.

The water availability at early phenological stages is critical for crop establishment and sugarcane varieties show differential performance under drought. Herein, we evaluated the relative importance of morphological and physiological plasticity of young sugarcane plants grown under water deficit, testing the hypothesis that high phenotypic plasticity is associated with drought tolerance. IACSP95-5000 is a high yielding genotype and IACSP94-2094 has good performance under water limiting environments. Plants were grown in rhizotrons for 35 days under three water availabilities: high (soil water matric potential [Ψm] higher than -20 kPa); intermediate (Ψm reached -65 and -90 kPa at the end of experimental period) and low (Ψm reached values lower than -150 kPa). Our data revealed that morphological and physiological responses of sugarcane to drought are dependent on genotype and intensity of water deficit. In general, IACSP95-5000 showed higher physiological plasticity given by leaf gas exchange and photochemical traits, whereas IACSP94-2094 showed higher morphological plasticity determined by changes in leaf area (LA) and specific LA. As IACSP94-2094 accumulated less biomass than IACSP95-5000 under varying water availability, it is suggested that high morphological plasticity does not always represent an effective advantage to maintain plant growth under water deficit. In addition, our results revealed that sugarcane varieties face water deficit using distinct strategies based on physiological or morphological changes. When the effectiveness of those changes in maintaining plant growth under low water availability is taken into account, our results indicate that the physiological plasticity is more important than the morphological one in young sugarcane plants.

Desenvolvimento e produtividade da tangerina "Fairchild" sobre quatro porta-enxertos / Development and yield of 'Fairchild' mandarin on four rootstocks

Neste trabalho foi avaliado o desenvolvimento vegetativo, a produção e a qualidade de frutos da tangerina "Fairchild" [(tangerina "Clementina" (C. clementina Hort. ex. Tan.) x tangelo "Orlando" (C. paradisi Macf. x C. reticulata Blanco)] sobre os porta-enxertos limão "Cravo" (C. limonia Osbeck), citrumelo "Swingle" (P. trifoliata Raf. x C. paradisi Macf.), tangerina "Cleópatra" (C. reshni Hort. ex Tan.) e tangelo "Orlando" (C. reticulata Blanco x C. paradisi Macf.) em Bebedouro, SP, em experimento instalado em 1997. Plantas enxertadas em citrumelo "Swingle" apresentaram menor porte, maior produção acumulada de frutos nas safras 2005 e 2006, maior eficiência de produção (kgm-3) e menor índice de alternância de produção. A qualidade dos frutos não foi influenciada em função dos porta-enxertos. O citrumelo "Swingle" foi considerado cultivar porta-enxerto adequado para utilização com tangerina "Fairchild".

The vegetative development, fruit yield and quality of 'Fairchild' mandarin [('Clementine' mandarin (C. clementina Hort. ex. Tan.) x 'Orlando' tangelo (C. paradisi Macf. x C. reticulata Blanco)] was evaluated on 'Rangpur' lime (C. limonia Osbeck), 'Swingle' citrumelo (P. trifoliata Raf. x C. paradisi Macf.), 'Cleopatra' mandarin (C. reshni Hort. ex Tan.) and 'Orlando' tangelo (C. reticulata Blanco x C. paradisi Macf.) rootstocks in an experiment installed in Bebedouro, SP, Brazil in 1997. 'Fairchild' trees budded on 'Swingle' citrumelo were smaller, had higher cumulative yield in 2005 and 2006 seasons, higher yield efficiency (kgm-3), showed lower alternate bearing index. Fruit quality was not affected by the rootstock. 'Swingle' citrumelo was considered an adequate rootstock for 'Fairchild' mandarin.