Walter dos Santos Soares Filho

Karyotype diversity and the origin of grapefruit

Grapefruit is a group of citrus of recent origin, probably resulting from a cross between pummelo and sweet-orange. Aiming to investigate this putative origin and the genetic variability among grapefruit cultivars, the karyotype of six grapefruits, two pummelos, and one tangelo cultivar (grapefruit × tangerine) were analyzed using sequential CMA/DAPI double staining and FISH with rDNA probes. The karyotypes of grapefruit ‘Duncan’ and ‘Foster’ differ from those of ‘Flame’, ‘Henderson’, ‘Marsh’ and ‘Rio Red’. The former have two chromosomes with a single CMA+ band in both terminal regions (C type chromosome) and six chromosomes with only one CMA+ terminal band (D type), whereas the latter have three C and five D type chromosomes. All accessions investigated exhibited two chromosomes with 5S rDNA but a variable number of 45S rDNA. The two former grapefruits displayed four 45S rDNA sites, whereas the remaining grapefruit cultivars had five. The two pummelos showed identical karyotypes, homozygous for CMA+ bands and their four rDNA sites. From each pummelo chromosome pair one chromosome seems to be present in grapefruit karyotypes. The different grapefruit karyotypes might result from independent crosses between pummelos of different karyotypic constitution and sweet-oranges. The chromosome markers found in the tangelo ‘Orlando’ and the position of their two 45S rDNA confirm the grapefruit ‘Duncan’ and the tangerine ‘Dancy’ as their parents.

Analysis of the NAC transcription factor gene family in citrus reveals a novel member involved in multiple abiotic stress responses

The NAC (NAM, ATAF1, -2, and CUC2) gene family encodes a large family of plant-specific transcription factors that play diverse roles in plant development and stress regulation. In this study, we performed a survey of citrus NAC transcription factors in the HarvEST: Citrus database, in which 45 NAC domain-containing proteins were identified and phylogenetically classified into 13 different subfamilies. The results suggest the existence of a structurally diversified family of NAC transcription factors in citrus, which has not been previously characterized. One of these NAC genes, CsNAC1 was found to be a member of the stress-NAC subfamily, whose homologs from other plant species function in pathways of environmental stress response and tolerance, and was further characterized. The CsNAC1 deduced protein was shown to contain the five N-terminal A through E NAC subdomains, a C-terminal region containing three transcriptional activation motifs, and a predicted NAC nuclear localization signal, consistent with its putative role as a NAC transcription factor. In silico analysis indicated that CsNAC1 was primarily expressed in leaves and shoot meristems, and was involved in general stress responses. Quantitative real-time reverse transcription PCR analysis revealed that CsNAC1 was strongly induced by drought stress in leaves of Citrus reshni and Citrus limonia, and also by salt stress, cold, and ABA in leaves and roots of C. reshni. Collectively, these results suggest that CsNAC1 encodes a novel stress-responsive NAC transcription factor that is potentially useful for engineering tolerance to multiple abiotic stresses in citrus.

Chromosome number and secondary constriction variation in 51 accessions of a citrus germplasm bank

The mitotic chromosomes of 51 citrus accessions from the Centro Nacional de Pesquisa em Mandioca e Fruticultura Tropical, Cruz das Almas, BA, Brazil, were analyzed. The sample included representatives of 20 Citrus species, one of Poncirus and seven hybrids. All accessions showed 2n = 18 without any evidence of numerical variation. The most clearly variable karyotype feature was the number and position of secondary constrictions (SECs). In 19 accessions the SECs were not identified, mainly due to the degree of chromatin condensation. In the remainder they varied in number from one to three per karyotype. They were found in the proximal region of one of the three largest chromosome pairs, in the terminal/subterminal region of a smaller chromosome or, more seldom, terminally in a larger chromosome. Only in a few cases were such constrictions observed simultaneously in both homologues of the same chromosome pair. The high variability of this karyotype feature may be due to the activation of this region in the previous interphase but may also indicate a high structural variability and heterozygosity of citrus germplasms

Análise de crescimento de diferentes genótipos de citros cultivados sob déficit hídrico

Aiming the identification of citrus varieties better adapted to Coastal Table Lands, considering their potential use as rootstocks, the performance of different genotypes for drought tolerance was evaluated, considering their physiological indices related to the growth analyses. The study was carried out in a greenhouse condition of the Embrapa Cassava & Tropical Fruits. Six genotypes were studied: Rangpur lime, Volkamer lemon, Sour orange, and the hybrids HTR - 051, TSK o CTTR - 002 and TSK o CTTR - 017, all from the Citrus Breeding Program of the Embrapa Cassava & Tropical Fruits. Seedlings were grown in Plantmaxâ growing media, irrigated adequately until they showed two pairs of true leaves. Afterward, they were transplanted to containers with the same growing media, but chemically fertilized. Seedlings were irrigated until sampling began. The experimental design was completely randomized under a 6 o 7 factorial, corresponding to six genotypes and seven evaluation sampling dates. The evaluations were carried out for seedlings under irrigation, water deficit, and re-watering. It was evaluated dry matter accumulation (DM), for their different fractions (root and above ground), and leaf area (LA) as the bases for the determination of the physiological indices: leaf area ratio (LAR), net assimilation rate (NAR) and relative growth ratio (RGR). It could be concluded that the hybrid HTR - 051 presented less sensibility to the water deficit, suggesting that it could be indicated as a promissory citrus rootstock for water deficit conditions.

Características morfológicas, físicas e químicas de frutos de populações de umbu-cajazeira no Estado da Bahia

A umbu-cajazeira (Spondias sp.) e uma frutifera que ocorre de forma esparsa em todos os Estados brasileiros localizados na regiao semi-arida nordestina, normalmente em areas submetidas a movimentos antropicos, sendo seus frutos consumidos tanto ao natural como na forma de sucos e polpa. O potencial produtivo dessa especie ainda e desconhecido, desde quando nao se conhece a variabilidade existente principalmente no que diz respeito as caracteristicas do fruto. O trabalho objetivou estudar essa variabilidade em tres populacoes no Estado da Bahia, sendo possivel verificar, mediante a analise de variaveis morfometricas, fisicas e quimicas do fruto, utilizando analise de agrupamento, a existencia de uma consideravel diversidade genetica entre individuos nas areas amostradas. Dentre eles, destacaram-se o acesso Vavazinho, com potencial para o consumo ao natural, e o acesso Campo Grande-5, adequado ao processamento de polpa.

Produção e partição de matéria seca e abertura estomática do limoeiro 'Cravo' submetido a estresse salino

This research aimed to evaluate the influence of the salinity on some physiological parameters in Rangpur lime (Citrus limonia Osbeck), which is the principal citrus rootstock in Bahia. The importance of this study is based on the possibility of using water of low quality for irrigation, which is a production constraint for citrus crop. Rangpur lime seeds were selected by size and sowed in washed sand. Three days after the germination, the seedlings were transferred to plastic pots containing nutrient solution. After ten days, the saline treatments were applied by addition of NaCl to the growth solution in each pot, reaching the final concentrations of 0, 20, 40 and 80 mM of NaCl. The completely randomized experiment had four treatments (NaCl concentration) and five replications. Forty two days after the beginning of the saline stress the experiment was concluded. The salinity decreased total dry matter production of the stem and roots. In the intermediate levels of NaCl (20 and 40 mM), neither the leaf area nor the leaf dry matter were affected; those characters were only affected in the level of 80 mM. The increase of the salinity levels caused reduction in the root:canopy ratio, in the stomatal conductance, in the transpiration and in the leaf temperature.

Survival strategies of citrus rootstocks subjected to drought.

Two citrus rootstocks, Rangpur lime (RL) and Sunki Maravilha mandarin (SM), were analyzed either ungrafted or grafted with their reciprocal graft combinations or with shoot scions of two commercial citrus varieties: Valencia orange (VO) and Tahiti acid lime (TAL). All graft combinations were subjected to distinct watering regimes: well-watered, severe drought and rehydration. Growth and water relation parameters, gas exchange as well as sugar and hormone profiles were determined. Data indicated that RL adopted a dehydration avoidance strategy and maintained growth, whereas SM adopted a dehydration tolerance strategy focused on plant survival. Compared with RL, the leaves and roots of SM exhibited higher concentrations of abscisic acid and salicylic acid, which induced drought tolerance, and accumulation of carbohydrates such as trehalose and raffinose, which are important reactive oxygen species scavengers. SM rootstocks were able to transfer their survival strategy to the grafted shoot scions (RL, VO, TAL). Because of their contrasting survival strategies, RL reached the permanent wilting point more quickly than SM whereas SM recovered from prolonged droughts more efficiently than RL. This is one of the most complete studies of drought tolerance mechanisms in citrus crops and is the first to use reciprocal grafting to clarify scion/rootstock interactions.

Resposta de porta-enxertos de citros ao déficit hídrico

This work was carried out under green house condition at the Embrapa Cassava and Tropical Fruit Crops, Cruz das Almas - Bahia- Brazil, aiming to identify citrus rootstocks better adapted to Coastal Table Land ecosystem as for their drought tolerance. It was studied the Rangpur lime, Volkamer lemon, Sour orange and the trifoliated hybrids HTR - 051, TSK x CTTR - 002, and TSK x CTTR - 017, the last three from the breeding program of the Embrapa Cassava and Tropical Fruits Crops. The experimental design was completely randomized under a 6 x 9 factorial, with six genotypes and nine period of evaluations. The evaluations followed the sequence: irrigation, water deficit, and irrigation when the plants had two to three leaves pairs. It was analyzed the variables root dry matter, dry matter of above ground parts, plant water potential, and leaf transpiration. For the above ground dry matter the genotypes Volkamer lemon and Sour orange showed decrease during the water deficit condition. The other genotypes showed no significant differences for this variable. Without irrigation, all genotypes decreased in their water potentials. The hybrids kept it unchanged maintaining increased transpiration rates. The hybrids HTR - 051, and TSK x CTTR - 017 presented the best performances for all variables studied being more promising as rootstocks for water deficit conditions.

Adequação de nutrientes do meio MT para o cultivo de embriões imaturos de tangerineira 'Cleópatra'

The objective of the present work was to adjust the macronutrient, micronutrient and vitamin concentrations of the Murashige & Tucker (MT) culture medium in order to promote the germination of ´Cleopatra´ Tangerine immature embryos, smaller than 3 mm. Seeds from fruits, 4 to 5 months after anthesis, in which the embryos do not germinate in recently indicated culture media for citrus, were used. Initially, the embryos were cultivated in basic culture medium containing sucrose and agar, followed by a sequence of steps, carrying out the adjustments of the normal concentration of macronutrients (1/1, ½ and ¼), micronutrients (1/1, ½, ¼ and 1/1, 3/2, 2/1) and vitamins (2/1, 1/1 e ½) of the MT medium. The experimental design was completely randomized in factorial scheme 3 (concentrations of MT) x 4 (embryo size), with 10 repetitions. The following variables were evaluated thirty days after embryo inoculation in culture medium: percentage of germination, percentage of normal plantlets and plantlet length. The best results were obtained using half the normal concentration of macronutrients, whereas the concentrations of micronutrients and vitamins remained unaltered.

Rootstock-induced physiological and biochemical mechanisms of drought tolerance in sweet orange

The poorly understood physiological and biochemical drought responses induced in sweet orange by citrus rootstocks of contrasting drought tolerance were investigated during a drought/rewatering cycle under controlled conditions. Long-term exposure of the grafted trees to a gradually increasing water deficit and subsequent recovery revealed distinct strategies of drought acclimation that were induced by the different rootstocks. Trees grafted onto the drought-tolerant rootstock ‘Cravo’ rangpur lime were less water conservative, exhibiting an increased cell-wall elasticity that contributes to turgor maintenance and its related processes of growth and photosynthesis over a wider range of soil–water potentials. On the other hand, the drought-tolerant ‘Sunki Tropical’ mandarin and drought-sensitive ‘Flying Dragon’ trifoliate orange rootstocks induced a water conservation strategy by increasing tissue rigidity under drought. ‘Sunki Tropical’ was also able to induce osmotic adjustment, conferring thereby a more efficient water conservation strategy than ‘Flying Dragon’ by allowing for turgor maintenance at lower soil–water potentials while attenuating cell dehydration and shrinkage. In contrast to ‘Cravo’ and ‘Sunki Tropical’, trees grafted onto ‘Flying Dragon’ exhibited a significant photoinhibition of the photosystem II reaction centers, as well as an increased H2O2 production and lipid peroxidation under drought treatment. A significantly higher activity of the antioxidant enzyme GPX was also observed in drought stressed trees grafted onto ‘Flying Dragon’. Collectively, these results support the involvement of elastic and osmotic adjustments, as well as the control of oxidative stress, as functional leaf traits associated with the rootstock-induced drought tolerance in sweet orange.