Relation between Ion Accumulation of Salt-Sensitive and Isolated Stable Salt-Tolerant Cell Lines of Citrus aurantium.

Four selected NaCl-tolerant cell lines of Sour orange (Citrus aurantium) were compared with the nonselected cell line in their growth and internal ion content of Na(+), K(+), and Cl(-) when exposed to increasing NaCl concentrations. No difference was found among the various NaCl-tolerant cell lines in Na(+) and Cl(-) uptake, and all these cell lines took up similar or even larger amounts of Na(+) and Cl(-) than the NaCl-sensitive cell line. Exposure of cells of NaCl-sensitive and NaCl-tolerant lines to equal external concentrations of NaCl, resulted in a greater loss of K(+) from the NaCl-sensitive cell line. This observation leads to the conclusion that growth and ability to retain high levels of internal K(+) are correlated. Exposure of the NaCl-tolerant cell lines to salts other than NaCl resulted in even greater tolerance to Na(2)SO(4), but rather poor tolerance to K(+) introduced as either K(2)SO(4) or KCl; the latter has a stronger inhibitory effect. The NaCl-sensitive cell line proved to be more sensitive to replacement of Na(+) by K(+). Analyses of internal Na(+), K(+), and Cl(-) concentrations failed to identify any particular internal ion concentration which could serve as a reliable marker for salt tolerance.

Plant regeneration from Citrus protoplasts: Variability in methodological requirements among cultivars and species.

Nucellar callus lines were established from two orange cultivars ('Nucellar Shamouti', 'Shamouti Landau'), three mandarin cultivars ('Murcott', 'Dancy', 'Ponkan') one grapefruit cultivar ('Duncan') and sour orange (Citrus aurantium). These callus lines were initiated from in vitro cultured ovules of young fruits and maintained an embryogenic capacity. The plating efficiencies of protoplasts derived from these calli, as well as those of protoplasts from lemon (cv. 'Villafranca') nucellar callus were differentially affected by the maceration enzymes and by the sugars used as osmotic stabilizers. Plants with normal morphological features were regenerated from cultured protoplasts derived from each of the nucellar callus lines. The establishment of eight new protoplast systems in Citrus paves the way for cell genetics studies and for novel breeding approaches in these economically important orchard trees.

Root peroxidase isoenzymes as an aid in Citrus breeding and taxonomy.

A rapid method for differentiating between Citrus clones as well as between zygotic and nucellar plants has been developed. It is based on determination of peroxidase isoenzyme patterns in small root samples. Ten to 14 bands could be distinguished, in contrast to the small number of bands present in leaves. Tetraploid seedlings gave uniform patterns closely resembling the diploid, while triploids showed segregation in isozyme pattern.

Beginnings of fruit growing in the old world.

The article reviews the available information on the start of fruit tree cultivation in the Old World. On the basis of (i) evaluation of the available archeological remains and (ii) examination of the wild relatives of the cultivated crops, it was concluded that olive, grape, date, and fig were the first important horticultural additions to the Mediterranean grain agriculture. They were most likely domesticated in the Near East in protohistoric time (fourth and third millennia B.C.) and they emerge as important food elements in the early Bronze Age. Domestication of all four fruit trees was based on a shift from sexual reproduction (in the wild) to vegetative propagation of clones (under domestication). Olive, grape, date, and fig can be vegetatively propagated by simple techniques (cuttings, basal knobs, suckers) and were thus preadapted for domestication early in the development of agriculture. The shift to clonal propagation placed serious limitations on selection and on fruit set under cultivation. We have examined the consequences of this shift in terms of the genetic makeup of the cultivars and traced the various countermeasures that evolved to ensure fruit set. Finally, it was pointed out that in each of these classic fruit trees we are confronted with a variable complex of genuinely wild types, secondary weedy derivatives and feral plants, and groups of the domesticated clones, which are all interfertile and interconnected by occasional hybridization. It was concluded that introgression from the diversified wild gene pool facilitated the rapid buildup of variation in the domesticated crops.

Differentiation between nucellar and zygotic citrus seedlings by leaf shape.

Leaf length divided by leaf width, (L/W), was studied as a criterion for differentiating between nucellar and zygotic citrus seedlings. Progeny of crosses of the variety 'King' as a seedparent (known to produce both nucellar and zygotic seedlings) fell into two classes: one with L/W similar to 'King' and the other midway between 'King' and the pollen parent. In several zygotic seedling populations, population means were intermediate between those of the parents. L/W can be an effective criterion for differentiating between nucellar and zygotic citrus seedlings where the parents differ appreciably.

Adventive plants from ovules and nucelli in Citrus.

1- to 8-week-old ovules and nucelli from three Citrus cultivars-Shamouti and Valencia (Citrus sinensis) oranges and Marsh Seedless (C. paradisi) grapefruit-were cultured in vitro. No embryo differentiation was observed in the explants prior to culture. The Shamouti ovules had degenerated and were apparently unfertilized. Embryoids formed on Murashige and Tucker nutrient medium supplemented with 500 mg/l malt extract. Whole plants developed on the same basal medium supplemented with kinetin and indole-3-acetic acid (IAA), coconut milk or gibberellic acid (GA3). A higher kinetin/IAA ratio or the addition of coconut milk favoured stem elongation more than root formation while a lower kinetin/IAA ratio favoured root formation and inhibited stem elongation. The addition of GA3 to the basal medium stimulated rooting and stem elongation. These results can be of aid in mutation research, allowing irradiation at stages prior to embryonic development.