The performance of Valencia sweet orange grafted onto 41 hybrid citrus rootstocks was evaluated for 11 years in rainfed cultivation under tropical savannah climate (Aw type) in Brazil, in addition to three selections of the standard drought-tolerant Rangpur lime and two selections of Sunki mandarin. Drought tolerance, assessed by visual score of leaf wilting, was directly related to the mean fruit yield. Indio and Riverside citrandarins, Tropical Sunki mandarin and the hybrid TSKC × CTSW-028 were grouped with the most productive selections of Rangpur lime, all of them inducing large tree size, intermediate fruit production efficiency, and high drought tolerance. The hybrid TSK × TR English-CO was similar except by inducing a higher mean soluble solids concentration in the orange juice. A third group of rootstocks induced high yield and drought tolerance, and a mean 30% reduction in tree size that led to high production efficiency, which comprised the hybrids HTR-053, TSKC × (LCR × TR)-017 and-059, TSKC × CTSW-041, LCR × TR-001 and San Diego citrandarin. The tree mortality on Rangpur lime selections was as least as 46%, while more than 80% of trees grafted onto the aforementioned rootstocks survived without visual symptoms of citrus sudden death disease or graft incompatibility. The selected hybrids and Tropical Sunki mandarin also induced fruit quality, mainly soluble solids, superior to the Rangpur lime and, therefore, are potential rootstocks for rainfed cultivation of Valencia sweet orange.

Resumo -O efeito do estresse salino de intensidade e duração conhecida nos parâmetros de fluorescência da clorofila em plantas de girassol foi estudado objetivando selecionar genótipos tolerantes e sensíveis à salinidade. O delineamento experimental utilizado foi o inteiramente casualizado em um arranjo fatorial entre 10 genótipos e 2 níveis de salinidade, com quatro repetições. As sementes foram semeadas em areia lavada e, após a germinação, foram transplantadas para vasos contendo solução nutritiva ou solução nutritiva com 100 mM de NaCl, em casa de vegetação. Após 27 dias nessas condições, foram avaliadas a fluorescência basal (F 0 ), a eficiência quântica potencial do fotossistema 2 -PS2 (F v /F m ), a razão F v /F 0 e a eficiência quântica efetiva do PS2 (Y). Os coeficientes dos "quenching" fotoquímico (q P ) e não fotoquímico (q N , q CN e NPQ) também foram calculados. O estresse salino aumentou F 0 e diminuiu F v /F m , F v /F 0 e Y, sugerindo injúrias na estrutura dos tilacóides causadas pela salinidade. Esses efeitos foram mais pronunciados no genótipo AG-960 e menos pronunciados no AG-975. O genótipo AG-960 também apresentou os maiores aumentos em q N , q CN e NPQ, em contraste com o observado para o AG-975. Dessa forma, AG-975 e AG-960 foram caracterizados como tolerante e sensível à salinidade, respectivamente. Os demais genótipos apresentaram tolerância intermediária ao estresse salino. Os resultados indicam que a fluorescência da clorofila pode ser utilizada como uma ferramenta para a seleção de genótipos de girassol tolerantes à salinidade. Palavras-chave -Estresse salino. Helianthus anuus.Abstract -The effect of salt stress of known intensity and duration on chlorophyll fluorescence in sunflower plants was studied aiming to identify salt-tolerant and salt-sensitive genotypes. The experimental design was a completely randomized in a factorial arrangement among 10 genotypes and two salt levels, with four replications. Seeds were sown in sand, and after germination were transplanted to plastic pots with nutrient solution or nutrient solution containing 100 mM of NaCl and placed in a greenhouse. After 27 days, ground fluorescence (F 0 ), maximum quantum yield of PS2 F v /F m , the F v /F 0 ratio and effective quantum yield of photosystem 2 -PS2 (Y) were evaluated. The photochemical (qP) and non-photochemical (q N , q CN e NPQ) coefficients were also calculated. Salt stress increased F0 and reduced F v /F m , F v /F 0 , and Y, suggesting salt-induced structural damage in the thylakoid membranes. These effects were more pronounced in genotype AG-960 and lowest in AG-975. The highest increases in qN, qCN and NPQ were also found in genotype AG-960 in contrast with that observed in AG-975. Thus the AG-975 and AG-960 genotypes were characterized as the most salt-tolerant and salt-sensitive, respectively. The other genotypes showed intermediate tolerance to salt stress. Our results suggest that chlorophyll fluorescence could be used as a tool for the screening of sunflower genotypes for salinity tolerance.

As in several fruit crops, citrus trees with decreased size allow for a higher planting density, which may lead to higher productivity and facilitate operations such as harvesting and spraying. The use of dwarfing rootstocks is one of the most feasible methods for tree size control, but few commercial varieties are available to date. In this work, the long-term performance of Valencia sweet orange grafted onto 51 hybrid citrus rootstocks was evaluated in rainfed cultivation at 6.0 m × 2.5 m tree spacing in Northern São Paulo State, Brazil. About a third of the evaluated hybrids were classified as dwarfing and semi-dwarfing rootstocks, that is, respectively inducing a relative canopy volume of <40% and 40–60% compared withthe standard rootstock, the Rangpur limeSanta Cruz selection. The production efficiency and soluble solids concentration were conversely related to the canopy volume. Three citrandarins of Sunki mandarin (TSKC) × Flying Dragon trifoliate orange (TRFD) were grouped within the most productive dwarfing rootstocks. Other hybrids that expressively decreased tree size were mainly sensitive to drought; therefore, the mean fruit yield was low, indicating the need for irrigation, albeit fruit quality was high. Estimated productivity on the selected TSKC × TRFD rootstocks would double to an average of 40 t·ha−1·year−1 if tree spacing wasadjusted to the smaller tree size. Although the HTR-208 citrandarin and the LCR × CTSW-009 citrumelimonia were as vigorous as the Santa Cruz Rangpur lime, they induced an outstanding fruit yield due to their highertolerance to drought and, hence, can be considered for rainfed cultivation at wider tree spacing.

The objective of this work was to evaluate five nonparametric selection indices for the selection of hybrid citrus rootstocks grafted with 'Valência' sweet orange, using horticultural traits relevant for the juice processing industry. Forty-six rootstocks were evaluated in a randomized complete block design, with three replicates and five trees in the plot, in the period from 2009-2015, in a rainfed cultivation. The means of the variables plant height, accumulated fruit yield, fruit yield efficiency, total soluble solids concentration, juice yield, and drought-tolerance were used to calculate the following indices: multiplicative index (IEi), sum of classification (IMMi), genotype-ideotype distance (DiI), and ranking indices (IRKi, based on simple means; and IRKii, based on linear normalization). The indices were efficient to classify the hybrids in relation to general performance. Spearman’s correlation showed a high similarity between most nonparametric indices, notably between IRKi and IRKii. The ranking indices, mainly IRKii, provide a more coherent classification of the hybrids, which allows of the selection of more productive and drought-tolerant rootstocks to produce high-quality fruit for processing.

The search for alternative rootstocks to the 'Rangpur' lime tree is a challenge to the sustainability of citrus in the Tabuleiros Costeiros (Coastal Tablelands) of Northeastern Brazil. New varieties should meet high drought tolerance with water deficit, cohesive soils, resistance to citrus diseases and inducing high production of fruit. In this work, the performance of 'Pera' sweet orange was evaluated on 'Tropical Sunki' mandarin and 27 hybrid citrus rootstocks in Umbaúba, Sergipe. A local selection of the 'Rangpur' lime was the control. Planting was in 2013 at tree spacing of 6.0 × 3.0 m, without irrigation. Tree size, fruit yield and quality, tree survival rate and graft-compatibility were assessed until 2019. Experimental design was completely randomized blocks with 29 treatments, three replicates and four plants in the plot.Two selection indices were applied to the data to assist in decision making. The 'Tropical Sunki' mandarin induced similar cumulative fruit yield in relation to the 'Rangpur' lime, suggesting a good drought tolerance of the former rootstock. The TSKC × (LCR × TR) -073 induced slightly lower productivity, compensated by higher productive efficiency and higher concentration of soluble solids, whereas LCR × TR -001 and HTR -166 were highly efficient dwarfing rootstocks. The multiplicative and the rank sum indices showed high correlation, both classifying 'Tropical Sunki' mandarin, 'Santa Cruz Rangpur' lime, LVK × LCR -010 and -038, HTR -127, in addition to the three aforementioned hybrids, as superior to the local selection of 'Rangpur' lime.

The North region of São Paulo has a high incidence of citrus sudden death (CSD), making Rangpur lime an inappropriate rootstock for use in this region. Identified CSD-tolerant rootstocks require supplementary irrigation. An ideal rootstock must be CSD-tolerant, provide high yields of fruits with high quality juice, be tolerant to drought, and induce some level of dwarfism in order to allow closer spacing. These characteristics were evaluated for Valencia orange trees on rootstocks of Dancy mandarin, Santa Cruz Rangpur lime (LCRSC) and 25 diverse hybrid rootstocks. The main parents of the hybrids were Citrus sunki, C. reshni, C. volkameriana, C. limonia, C. sinensis and Poncirus trifoliata. The experiment was performed in Colômbia, SP, Brazil, from 2009 to 2015 in rain-fed cultivation. At seven years of age, 54% of the rootstocks presented tree size similar to or higher than LCRSC, whereas in the others there was a reduction between 75 and 8% compared to LCRSC. Sacaton citrumelo rootstock resulted in substantial dwarfism and the hybrids of C. volkameriana x C. limonia were semi-dwarfing. All rootstocks presented juice with soluble solids varying from 9.89 to 11.06 °Brix and ratio from 13.52 to 18.31. A Selection Index (SI) was developed to compare rootstocks. Twelve rootstocks exhibited SI superior to LCRSC. Citrange 25 and C. reshni x P. trifoliata Swingle 224, 287 and 71158 produced smaller tree size with greater production efficiency, soluble solids and processing index superior to LCRSC. The latter citrandarin rootstock presented incompatibility with Valencia sweet orange at age eight.

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