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Assessment of the genetic diversity of the Tunisian citrus rootstock germplasm
Get PDFBackground: Citrus represents a substantial income for farmers in the Mediterranean Basin. However, the Mediterranean citrus industry faces increasing biotic and abiotic constraints. Therefore the breeding and selection of new rootstocks are now of the utmost importance. In Tunisia, in addition to sour orange, the most widespread traditional rootstock of the Mediterranean area, other citrus rootstocks and well adapted to local environmental conditions, are traditionally used and should be important genetic resources for breeding. To characterize the diversity of Tunisian citrus rootstocks, two hundred and one local accessions belonging to four facultative apomictic species (C. aurantium, sour orange; C. sinensis, orange; C. limon, lemon; and C. aurantifolia, lime) were collected and genotyped using 20 nuclear SSR markers and four indel mitochondrial markers. Multi-locus genotypes (MLGs) were compared to references from French and Spanish collections. Results: The differentiation of the four varietal groups was well-marked. The groups displayed a relatively high allelic diversity, primarily due to very high heterozygosity. Sixteen distinct MLGs were identified. Ten of these were noted in sour oranges. However, the majority of the analysed sour orange accessions corresponded with only two MLGs, differentiated by a single allele, likely due to a mutation. The most frequent MLG is shared with the reference sour oranges. No polymorphism was found within the sweet orange group. Two MLGs, differentiated by a single locus, were noted in lemon. The predominant MLG was shared with the reference lemons. Limes were represented by three genotypes. Two corresponded to the 'Mexican lime' and 'limonette de Marrakech' references. The MLG of 'Chiiri' lime was unique. Conclusions: The Tunisian citrus rootstock genetic diversity is predominantly due to high heterozygosity and differentiation between the four varietal groups. The phenotypic diversity within the varietal groups has resulted from multiple introductions, somatic mutations and rare sexual recombination events. Finally, this diversity study enabled the identification of a core sample of accessions for further physiological and agronomical evaluations. These core accessions will be integrated into citrus rootstock breeding programs for the Mediterranean Basin
Acta Horticulturae
No full textTranspiration of well watered (C) and regulated deficit irrigated (RDI) trees was determined by means of the compensation heat pulse method during 2009 and 2010 in commercial citrus groves of 'Clementina de Nules' (CN) and 'Navel Lane Late' (NLL). In both species, sap flow (SF) was measured in two trees per treatment instrumented with two gauges per tree. CN trees were equipped with two different types of gauges (type1 shorter than type2) determining heat velocity from crossing time at four different xylem depths according to Green et al. (2003). In NLL oranges, all the gauges were identical and the data were processed according to the compensation heat pulse + calibrated average gradient (CAG) method (Testi and Villalobos, 2009). Plant water status was determined by midday stem water potential measurements (psi(stem)). Results showed that the absolute SF values, and especially those from type2 gauges in CN, clearly underestimated tree water use. Tree to tree variability registered in CN (CV=0.09) was lower than in NLL (CV=0.17) which also showed a 17% of within tree variability. The average nocturnal-to-diurnal sap flow ratio was between 7% and 13%. The evolution of relative SF (e. g. SFRDI/SFC) was in agreement with differences in psi(stem) (r(2)=0.78 in CN and 0.84 in NLL). This SF ratio showed the expected decreasing trend during the water restriction period and the recovery when irrigation was reestablished to normal dose. Overall, the results show that sap flow sensors can detect plant water stress but they also highlight some of the problems for accurately measuring transpiration
Effects of inclusion of sorghum distillers dried grains with solubles (DDGS) in diets for growing and finishing pigs
Get PDFThe effects of sorghum distillers dried grains with solubles (sorghum-DDGS) in growing pig diets on growth performance and carcass quality were investigated. A total of 204 animals of 13.9 +/- 2.60 kg body weight (BW) were allocated into two dietary treatments, a conventional diet (C) and a diet containing sorghum-DDGS (DDGS). DDGS inclusion levels used were 150 g kg(-1) in pigs from 14-40 kg BW, 300 g kg(-1) from 40-80 kg BW and 350 g kg(-1) from 80 kg BW to slaughter. Animals' body weight, feed intake, backfat thickness (BF) and loin depth (LD) were measured throughout the study. Protein, fibre and fat content of sorghum-DDGS were approximately three times-fold those of the whole grain. During the nursery period, feed intake and final BW tended to be lower in the group of pigs fed DDGS compared to the piglets fed C diet (871.4 g d (1) and 30 kg vs 951.1 g d (1) and 31 kg). During the growing period no differences were found on growth performance between treatments. Pigs fed sorghum-DDGS showed higher BF than pigs fed C diet (10.96 mm vs 9.80 mm, p < 0.001). No differences were found on LD and carcass weight and yield between treatments. Thus, although 150 g kg(-1) of sorghum-DDGS in nursery diets tended to reduce growth performance, inclusion rates up to 300-350 g kg(-1) during the finishing phase did not affect it, but led to fatter carcasses
Lower temperature thresholds for oviposition and egg hatching of the Red Palm Weevil, Rhynchophorus ferrugineus (Coleoptera: Curculionidae), in a Mediterranean climate
No full textThe red palm weevil, Rhynchophorus ferrugineus Olivier (Coleoptera: Curculionidae), is an economically important pest of palms worldwide. To better understand the phenology of R. ferrugineus populations in the Mediterranean basin, the objective of the present work has been to estimate the effect of temperatures within the range 10-25 degrees C on the reproductive parameters of R. ferrugineus and to determine its lower temperature thresholds for oviposition and egg hatching. Our results confirm that oviposition in R. ferrugineus is strongly affected by temperature. Lower thresholds for oviposition and egg hatching (15.45 degrees and 13.95 degrees C, respectively) are below the mean monthly temperatures registered in winter in most of the northern shore of the Mediterranean basin. Under these circumstances, new palm infestations would be difficult during most of the winter. These results should be taken into account when planning some palm management practices, such as pruning or pesticide treatments, in areas under a Mediterranean climate
Soil Fertility and Nutritional State of Persimmon Rojo Brillante Plantations in the Ribera Alta (Valencia, Spain)
No full textSoil fertility and nutritional state of persimmon (Diospyros kaki, cv. Rojo brillante), together with their relations to productivity, were studied for two growing seasons in 30 orchards within La Ribera Alta, the main persimmon-producing region in Spain. Soil and foliar samples were analyzed and the results were compared after dividing the orchards in two groups (high and low yield) according to their annual production. A general independence of crop yield from soil properties and fertility and nutritional states of trees was found, suggesting other factors such as health conditions or pruning procedures are probably more relevant for final production. Nevertheless, overabundance of available calcium or zinc deficiency seems to be associated with lower than average yields. In addition, the concentration of nutrients in leaves was measured monthly in two selected orchards during both seasons. The observed trends varied according to nutrient, orchard, and season but were in general comparable to those reported by other authors
Influence of organic matter transformations on the bioavailability of heavy metals in a sludge based compost
Get PDFThe agricultural use of anaerobically digested sewage sludge (ADSS) as stable, mature compost implies knowing its total content in heavy metals and their bioavailability. This depends not only on the initial characteristics of the composted substrates but also on the organic matter transformations during composting which may influence the chemical form of the metals and their bioavailability. The objective of this work was to examine the relationships between the changes in the organic matter content and humus fractions, and the bioavailability of heavy metals. A detailed sampling at 0, 14, 84, and 140 days of the composting process was performed to measure C contents in humic acids (HAs), fulvic acids, (FAs) and humin, the total content of Zn, Pb, Cu, Ni, and Cd, and also their distribution into mobile and mobilisable (MB), and low bioavailability (LB) forms. Significant changes of C contents in HA. FA, and Humin, and in the FA/HA, HA/Humin and C-humus/TOC ratios were observed during composting. The MB and LB fractions of each metal also varied significantly during composting. The MB fraction increased for Zn, Cu, Ni, and Cd, and the LB fraction increased for Pb. Stepwise linear regressions and quadratic curve estimation conducted on the MB and LB fractions of each metal as dependent on the measured organic variables suggested that Zn bioavailability was mainly associated to percentage of C in FAs. Bioavailability of Cu, Ni and Cd during composting was associated to humin and HAs. Pb concentration increased in the LB form, and its variations followed a quadratic function with the C-humus/TOC ratio. Our results suggest that the composting process renders the metals in more available forms. The main forms of metal binding in the sludge and their availability in the final compost may be better described when metal fractionation obtained in sequential extraction and humus fractionation during composting are considered together. (C) 2011 Elsevier Ltd. All rights reserved
Extensive citrus triploid hybrid production by 2x x 4x sexual hybridizations and parent-effect on the length of the juvenile phase
No full textThe citrus fresh market demands the production of seedless citrus fruits, as seedy fruits are not accepted by consumers. The recovery of triploid plants has proven to be the most promising approach to achieve this goal, since triploids have very low fertility, are generally seedless and do not induce seeds in other cultivars by cross pollination. Triploid plants can be recovered by 2x x 4x sexual hybridization. In this work, we present an effective methodology to recover triploid plants from 2x x 4x hybridizations based on in vitro embryo rescue, ploidy level analysis by flow cytometry and genetic origin of triploid plants. The pollen viability of diploid and tetraploid citrus genotypes was analyzed by comparing the pollen germination rate in vitro. The pollen viability of tetraploid (doubled-diploid) genotypes is generally reduced but sufficient for successful pollination. Triploid embryos were identified in normal and undeveloped seeds that did not germinate under greenhouse conditions. The influence of parents and environmental conditions on obtaining triploid plants was analyzed and a strong interaction was noted between the parents and environmental conditions. The parental effect on the length of the juvenile phase was also demonstrated through observations of a large number of progeny over the last 15 years. The juvenile phase length of the triploid hybrids obtained with 'Fortune' mandarin as female parent and tetraploid 'Orlando' tangelo as male parent was shorter than the juvenile phase obtained with a clementine as female parent and tetraploids of 'Nova', 'W. Leaf' and 'Pineapple' male parents. Key message Effective methodology to recover citrus triploid plants from 2x x 4x sexual hybridizations and the parental effect on the length of the juvenile phase
Chilling-Dependent Release of Seed and Bud Dormancy in Peach Associates to Common Changes in Gene Expression
Get PDFReproductive meristems and embryos display dormancy mechanisms in specialized structures named respectively buds and seeds that arrest the growth of perennial plants until environmental conditions are optimal for survival. Dormancy shows common physiological features in buds and seeds. A genotype-specific period of chilling is usually required to release dormancy by molecular mechanisms that are still poorly understood. In order to find common transcriptional pathways associated to dormancy release, we analyzed the chilling-dependent expression in embryos of certain genes that were previously found related to dormancy in flower buds of peach. We propose the presence of short and long-term dormancy events affecting respectively the germination rate and seedling development by independent mechanisms. Short periods of chilling seem to improve germination in an abscisic acid-dependent manner, whereas the positive effect of longer cold treatments on physiological dwarfing coincides with the accumulation of phenylpropanoids in the seed
Nitrogen-use efficiency of young citrus trees as influenced by the timing of fertilizer application
No full textThe aim of this study was to improve the fertilizer-nitrogen-use efficiency (NUE) for a sustainable citrus production where yield, fruit quality, and environment are reconciled. A soil pot experiment was conducted using 5-year-old orange trees (Citrus sinensis cv. Navel Lane Late) to determine the response of NUE to timing of N-fertilizer supply. An equal N rate (50 g tree1) following two seasonal supply distributions was tested: (1) ENS (early supply from March to June of 75% of the N rate, with the remaining 25% administered between July and October) and (2) LNS (late supply of the bulk of the N rate with 25% between March and June and 75% between July and October). Labeled fertilizer (5 atom% 15N excess) was applied in order to accurately quantify N uptake, its partitioning among plantsoil compartments and NUE at the end of fruit drop and at fruit maturity. LNS resulted in a significant increase in NUE in both stages (up to 19% at the end of fruit drop and 9% at fruit maturity), while also increasing summer/autumn flush development. ENS showed lower fruit abscission, an enhanced final fruit load (up to 45%), and a more profuse development of spring flush. It is worth mentioning that LNS led to higher 15N content in the majority of the tree storage organs available for next spring growth resumption. The amount of 15N remaining in the soil of ENS trees at the end of the trial, which represented 16% of the supplied 15N, was 1.5-fold higher than that of LNS trees as a result of the lower NUE of the former. Irrespective of the seasonal distribution of the fertilizer, mean 15N recovery in the soilplant system at the end of the trial was about 71%. The results clearly confirm that the N seasonal distribution curve affects NUE in young citrus trees and NUE increases when the bulk of supply of the N rate is delayed to the summer months