ReDivia - Repositorio Digital de l'Instit Valencià d'Investigacions Agràries
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Development of Indel Markers from Citrus Clementina (Rutaceae) Bac-End Sequences and Interspecific Transferability in Citrus
No full textPremise of the study: Indel markers were developed from BAC-end sequences of Citrus clementina cv. Nules. Transferability and polymorphism were tested in the Citrus genus to estimate the potential of indel markers mined from a single genotype for use in genetic studies. Methods and Results: Using polyacrylamide gel electrophoresis and DNA silver staining, 89 indel markers were tested for their transferability and polymorphism. Thirty-eight markers were selected. Heterozygosity in C. clementina cv. Nules was confirmed for 33 of these indel pairs. A preliminary diversity study using a capillary electrophoresis fragment analyzer was conducted with 21 indels using 45 accessions representing Citrus genus diversity. Intraspecific and interspecific polymorphisms were observed. Conclusions: These results indicate the utility of indel markers developed from sequence data of a single genotype of interspecific origin. In Citrus, these markers will be useful for genetic mapping, germplasm characterization, and phylogenetic assignment of DNA fragments
Genetic variation and host specificity of Phytophthora citrophthora isolates causing branch cankers in Clementine trees in Spain
No full textConsiderable tree losses have been observed during the past few years in Spain due to Phytophthora branch canker of clementines caused by Phytophthora citrophthora. The emergence of this disease led to the speculation that either the pathogen has evolved increasing its aggressiveness or specificity to clementines. A total of 134 isolates of P. citrophthora collected from 2003 to 2005 in 135 citrus orchards in Spain and 22 reference isolates were analyzed genotypically and phenotypically to determine the structure of the population. Genotypic diversity was evaluated by means of Inter-Simple Sequence Repeat (ISSR) markers. Among the phenotypic characteristics examined, sporangial characters, sexual behavior, growth rates and colony morphology of the isolates at different temperatures were studied. The aggressiveness and host-specificity of selected isolates were evaluated by pathogenicity tests on sweet oranges and clementines under field conditions. Phytophthora branch canker of clementines was associated mainly with one genotype (P-1), which included 88% of the isolates obtained from branches. Strains isolated years before the first disease outbreak clustered also with this major genotype, thus it may be considered as a predominant population. Thirteen other minor genotypes were determined, but most contained only one isolate. Although there was wide variation in the morphological and physiological characters, all Phytophthora isolates obtained from branch cankers were sexually sterile and showed a characteristic petalloid colony pattern. As in previous greenhouse studies, pathogenicity tests under field conditions demonstrated that clementines and their hybrids were more susceptible to P. citrophthora than sweet oranges. However, no evidence was found to support the hypothesis that the emergence of the disease was associated with more aggressive or host-specific forms of P. citrophthora
Water-deficit tolerance in citrus is mediated by the down regulation of PIP gene expression in the roots
No full textWater deficit (WD) is a growing problem in agriculture. In citrus crops, genetically-determined rootstock characteristics are important factors influencing plant responses to WD. Aquaporins are involved in regulating the water supply to the plant by mediating water flow through the cell membranes. Recent studies support a direct role for aquaporins in plant water relations and demonstrate their involvement in WD tolerance. This study investigates the relationship between photosynthetic and water-balance parameters with aquaporin expression levels and hydraulic conductance of roots (Kr) in conditions of moderate WD in citrus rootstocks. The plant materials used were the rootstocks Poncirus trifoliata (L.) Raf. (PT), Cleopatra mandarin (Citrus reshni Hort ex Tan.) (CM) and 030115 (a hybrid of the two former rootstocks), all grafted with the citrus variety 'Valencia Late' (C. sinensis (L.) Osb). Plants were irrigated with two differents irrigation doses (normal irrigation and moderate WD) during 70 days and leaf water potential (psi s), net CO2 assimilation (A(CO2)), transpiration, stomatal conductance (gs) and substomatal CO2 concentration (Ci) were measured periodically under both irrigation conditions. Kr and PIP1 and PIP2 gene expression levels in fine roots of control plants and plants subjected to WD on day 43 of the experiment were determined. Under WD conditions, the hybrid 030115 drastically reduced aquaporin expression and Kr, accompanied by a loss of plant vigour but without reducing the net CO2 assimilation (A(CO2)). PT maintained the same aquaporin expression level and similar Kr under WD as under normal irrigation conditions, but suffered a sharp reduction in A(CO2). CM, which has lower Kr and aquaporin expression than PT under both normal irrigation conditions and WD, responded better to water stress conditions than PT. Low aquaporin levels, or down-regulated aquaporin expression, accompanied by decreased plant vigour led to decreased plasma membrane permeability, thereby facilitating water retention in the cells under water stress conditions. This may induce water stress tolerance in citrus rootstocks
Citrus tristeza virus infection induces the accumulation of viral small RNAs (21-24-nt) mapping preferentially at the 3'-terminal region of the genomic RNA and affects the host small RNA profile
No full textTo get an insight into the host RNA silencing defense induced by Citrus tristeza virus (CTV) and into the counter defensive reaction mediated by its three silencing suppressors (p25, p20 and p23), we have examined by deep sequencing (Solexa-Illumina) the small RNAs (sRNAs) in three virus-host combinations. Our data show that CTV sRNAs: (i) represent more than 50% of the total sRNAs in Mexican lime and sweet orange (where CTV reaches relatively high titers), but only 3.5% in sour orange (where the CTV titer is significantly lower), (ii) are predominantly of 21-22-nt, with a biased distribution of their 5' nucleotide and with those of (+) polarity accumulating in a moderate excess, and (iii) derive from essentially all the CTV genome (ca. 20 kb), as revealed by its complete reconstruction from viral sRNA contigs, but adopt an asymmetric distribution with a prominent hotspot covering approximately the 3'-terminal 2,500 nt. These results suggest that the citrus homologues of Dicer-like (DCL) 4 and 2 most likely mediate the genesis of the 21 and 22 nt CTV sRNAs, respectively, and show that both ribonucleases act not only on the genomic RNA but also on the 3' co-terminal subgenomic RNAs and, particularly, on their double-stranded forms. The plant sRNA profile, very similar and dominated by the 24-nt sRNAs in the three mock-inoculated controls, was minimally affected by CTV infection in sour orange, but exhibited a significant reduction of the 24-nt sRNAs in Mexican lime and sweet orange. We have also identified novel citrus miRNAs and determined how CTV influences their accumulation
Chemical control of 'Pezothrips kellyanus' in citrus and its side-effects on some important natural enemies
No full textAssessing lodging resistance in rice: A comparison of two indirect testing methods
Get PDFRice lodging is still a problem in many countries, as all rice-growing countries have some varieties that get lodged. Direct evaluation of lodging resistance requires visual estimates in plots, but is not feasible in early generations of breeding programs, where genetic variability is too high. The aim of this study was to compare two methods for indirect evaluation of lodging resistance, especially in field conditions: the recovery ability after bending (measured as the tiller angle difference before and after bending); and, to test the sturdiness of the lower part of the plant, we have measured its resistance to pulling. Sixteen rice varieties and two F(5) breeding lines were grown in plots and rows; 20 additional F(5) breeding lines were only tested in rows. Visual estimates of plot lodging were significantly correlated with their tiller angle difference (r = 0.56*), but not with plant height or pulling resistance, although the latter was also correlated with visual lodging when only susceptible accessions were considered (r = -0.72*). Tiller angle difference was not significantly correlated with pulling strength, but it correlates with plant height (r = 0.56*). The scoring of tiller angle difference is simpler and less dependent on the evaluator than pulling resistance. It is concluded that it can be a valuable trait to select for resistance to lodging in early segregating generations of a pedigree breeding program
Narrowing down the apricot Plum pox virus resistance locus and comparative analysis with the peach genome syntenic region
Get PDFSharka disease, caused by the Plum pox virus (PPV), is one of the main limiting factors for stone fruit crops worldwide. Only a few resistance sources have been found in apricot (Prunus armeniaca L.), and most studies have located a major PPV resistance locus (PPVres) on linkage group 1 (LG1). However, the mapping accuracy was not sufficiently reliable and PPVres was predicted within a low confidence interval. In this study, we have constructed two high-density simple sequence repeat (SSR) improved maps with 0.70 and 0.68 markers/cm, corresponding to LG1 of ‘Lito’ and ‘Goldrich’ PPV-resistant cultivars, respectively. Using these maps, and excluding genotype–phenotype incongruent individuals, a new binary trait locus (BTL) analysis for PPV resistance was performed, narrowing down the PPVres support intervals to 7.3 and 5.9 cm in ‘Lito’ and ‘Goldrich’, respectively. Subsequently, 71 overlapping oligonucleotides (overgo) probes were hybridized against an apricot bacterial artificial chromosome (BAC) library, identifying 870 single BACs from which 340 were anchored onto a map region of approximately 30–40cm encompassing PPVres. Partial BAC contigs assigned to the two allelic haplotypes (resistant/susceptible) of the PPVres locus were built by high-information content fingerprinting (HICF). In addition, a total of 300 BAC-derived sequences were obtained, and 257 showed significant homology with the peach genome scaffold_1 corresponding to LG1. According to the peach syntenic genome sequence, PPVres was predicted within a region of 2.16 Mb in which a few candidate resistance genes were identified
Acta Horticulturae
No full textIn citrus trees, regulated deficit irrigation (RDI) can be a useful irrigation strategy to reduce water supply without affecting yield. Previous studies conducted in this sense have determined irrigation water savings achieved by RDI but less is known about the actual transpiration values of the RDI trees. This information is crucial to properly carry out a water balance of an RDI orchard. In an experiment performed during 2009 on mature ‘Clementina de Nules’ citrus, we determined sap flow (SF) of well irrigated and RDI trees by means of the compensation heat pulse method. SF was measured in two trees per treatment instrumented with one unit of two different gauge types per tree, determining heat velocity at four different xylem depths. SF values obtained at 30-min intervals during the entire experimental period were compared with whole canopy gas exchange measurements carried out during two representative days with custom designed Mylar plastic chambers. Plant water status was determined by midday stem water potential measurements (Ψstem). Results showed that absolute SF values clearly underestimated tree water use. After calibrating SF against canopy gas exchange determinations, corrected SF values appeared more reasonable but it also increased tree-to-tree variability (CV from 0.08 to 0.17). The transpiration ratio (SFRDI/SFcontrol) had a somewhat decreasing trend during the water restriction period according to Ψstem, but recovering before the irrigation was resumed to normal dose. Overall, the results highlight some of the problems and uncertainties when using a limited number of sap flow sensors for detecting plant water stress and for accurately measuring transpiration