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We investigated tolerance to high salinity in well-irrigated diploid and tetraploid citrus. Comparisons were made between two diploids (2×) of trifoliate orange (Poncirus trifoliata(L.) Raf.) and willow leaf mandarin (Citrus deliciosaTen), their respective doubled diploids (4×) and the allotetraploid (FLHORAG1) obtained from the protoplast fusion of trifoliate orange and Willow leaf mandarin. Salinity stress was applied by progressively increasing the concentration of NaCl from 50mM to 400mM for 8 weeks. Two-year-old plants were watered daily. Maximum quantum yield of PSII, and leaf and root chloride and sodium content were monitored. We previously reported that under moderate saline stress, citrus 4× genotypes were more tolerant that the 2×, but under these experimental conditions, 4× seedlings were certainly more sensitive to salt stress than 2×, as they accumulated more toxic ions and were more affected than 2×. Chloride accumulation in 4× leaves was greater and the maximum quantum yield of PSII was more reduced in 4× than in 2×. The expression of several candidate genes involved in signal transduction, sodium and chloride transport, osmotic adjustment, regulation of the stomata opening and detoxification processes were also investigated by quantitative real-time reverse transcription-PCR. A high correlation was observed between phenotype of sensitivity to stress and gene expression changes. [ABSTRACT FROM AUTHOR]

Abstract  Allopolyploidy is known to induce novel patterns of gene expression and often gives rise to new phenotypes. Here we report on the first attempt to relate phenotypic inheritance in an allotetraploid somatic hybrid with gene expression. Carotenoid compounds in the fruit pulp of the two parental species and the hybrid were evaluated quantitatively by HPLC. Only very low levels of β-carotene and β-cryptoxanthin were observed in Citrus limon, while β-cryptoxanthin was a major component of C. reticulata, which also displayed high levels of phytoene, phytofluene, β-carotene, lutein, zeaxantin and violaxanthin. Total carotenoid content in mandarin juice sacs was 60 times greater than that in lemon. The allotetraploid hybrid produced all the same compounds as mandarin but at very low levels. Transgressive concentration of abscisic acid (ABA) was observed in the somatic hybrid. Real-time RT-PCR of total RNA from juice sacs was used to study expression of seven genes (CitDxs, CitPsy, CitPds, CitZds, CitLcy-b, CitChx-b, and CitZep) of the carotenoid biosynthetic pathway and two genes (CitNced1 and CitNced2) involved in abscisic acid synthesis from carotenoid. Gene expression was significantly higher for mandarin than lemon for seven of the nine genes analyzed. Lemon under expression was partially dominant in the somatic hybrid for three upstream steps of the biosynthetic pathway, particularly for CitDxs. Transgressive over expression was observed for the two CitNced genes. A limitation of the upstream steps of the pathway and a downstream higher consumption of carotenoids may explain the phenotype of the somatic hybrid. [ABSTRACT FROM AUTHOR]

Isozyme variation was studied in 87 plants from 32 cultivated and wild accessions of banana passion fruit (P. tripartita var. mollissima, P. tripartita var. tripartita, P. tarminiana, and P. mixta), rosy passion fruit (P. cumbalensis), tin-tin (P. pinnatistipula), gulián (P. ampullacea), P. antioquensis, P. bracteosa, and P. manicata, from the Andes of Venezuela, Colombia, and Ecuador. Six polymorphic enzyme systems (IDH, PGDH, PGM, DIA, PRX, and ACP) revealed 31 zymotypes characterized by the presence or absence of 31 electromorphs. Cluster analysis separated clearly the accessions of P. tarminiana, P. tripartita, P. mixta, and P. cumbalensis from the less typical species of subgenus Tacsonia, which is consistent with morphological evidence. P. mixta showed the highest intraspecific variation and the closest affinity with P. tripartita. The accessions of these two species formed two clusters, one dominated by Colombian genotypes and the other dominated by Ecuadorian genotypes. One of the P. tripartita var. mollissima accessions clustered close to P. tarminiana accessions. The affinity between these three species is particularly interesting for conservation and use of banana passion fruit genetic resources. All the other species formed monospecific clusters. [ABSTRACT FROM AUTHOR]