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  • Author or Editor: T. Murashige x
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Abstract

The phenomenon of polyembryony in Citrus was first described in 1719(1). It is now known that many members of the Rutaceae produce several embryos in each seed. The multiple embryos may include a zygotically-derived embryo and several adventive embryos. The adventive embryos result from differentiation of cells within the nucellar tissue, particularly those near the micropylar region of the ovule (1,6). One of the important horticultural characteristics of seedling Citrus, whether derived from zygotic or nucellar embryos, is the fact that they develop free of viruses even though the parent plant is infested with viruses. With polyembryonic Citrus, disease-free clones can be obtained through plants established from nucellar embryos. This has not been possible with monoembryonic species or varieties of Citrus, inasmuch as the seedlings are all of zygotic origin and vary genetically.

Open Access

Abstract

In propagating Asparagus officinalis L. through the method of shoot apex culture, apices of terminal buds of spears produced in vitro were found to be equally satisfactory as explants as those of lateral buds of spears obtained from the field. A maximum number of plants was obtained when the cultures were illuminated 4-20 hr daily with white fluorescent or Gro-Lux lamps at an intensity of 1000 lux. A constant 27°C temp was also optimum for plant formation in vitro. Histological examination revealed that roots arose adventitiously from callus which formed at the base of the explant, whereas spears originated from axillary buds.

Successful transfer of plants from laboratory to soil required a prior reculture in a medium lacking NAA and with the light intensity increased to 3000 or 10,000 lux. Examination of the chromosome numbers of plants propagated through shoot apex culture showed that the original diploid status had been retained in every plant.

Open Access

Abstract

A 30 to 50% frequency of successful grafts was obtained by using 2-week-old dark grown seedlings as rootstocks and 0.14 to 0.18 mm long shoot tips as scions. The shoot tip was inserted into an inverted-T made at the top of the decapitated rootstock epicotyl. Most scion cultivars gave satisfactory grafts on ‘Troyer’ citrange, whereas lemon, lime and citron yielded successful grafts only on ‘Rough’ lemon. The grafted plants were allowed to develop in vitro under 16 hr daily exposure to 1000 lux Grow Lux illumination and were provided with a nutrient solution containing a high concentration (7.5%) of sucrose. The best source of shoot tips was the flush from defoliated branches of field trees or glasshouse plants. It was also possible to use shoot tips from flushes arising in excised lateral buds cultured in vitro. Grafted plants were transplantable to soil 5 to 8 weeks after grafting with over 95% survival. Preliminary data indicated recovery of cultivars freed from tristeza and psorosis viruses, stubborn spiroplasma and exocortis viroid. Pathogen-free plants showed no reversion to the juvenile phase.

Open Access

Abstract

Individual shoot-tip-grafted budlines of ‘Willowleaf mandarin (Citrus reticulata Blanco) and ‘Temple’ tangor [C. reticulata × C. sinensis (L.) Osbeck] were grown to fruiting for evaluation. Fruits of both cultivars were highly uniform among shoot-tip cultures, indicating that this technique for producing disease-free citrus germplasm is reliable and does not increase the production of variant budlines.

Open Access

Genotypes of Lycopersicon peruvianum (L.) Mill. and L. peruvianum var. glandulosum (Rick), selected from accessions that possess resistance to Meloidogyne incognita [(Kofoid and White) Chitwood] at high soil temperature (30C), were used as male parents in crosses with L. esculentum (Mill.) susceptible cultivars UC82, Lukullus, Tropic, and male-sterile line ms-31, respectively. The incongruity barrier between the two plant species was overcome by embryo callus and embryo cloning techniques. Hybridity of the F, progeny obtained from each cross was confirmed by differences in leaf and flower morphology, plant growth habits, and by acid phosphatase isozyme phenotypes using polyacrylamide gel electrophoresis. In greenhouse inoculation experiments, F1 plants were highly resistant to M. incognita in soil at 25 and 30C. These results confirmed the successful transfer and expression of heat-stable resistance to M. incognita from L. peruvianum to hybrids with L. esculentum as a preliminary step to introgressing additional root-knot nematode resistance into tomato.

Free access

Abstract

A nutrient medium which enabled rapid formation of new spears and roots in shoot apices excised from buds as well as lateral branches of Asparagus officinalis L. spears was developed. This medium was composed of the following, in mg/1 : Murashige and Skoog’s inorganic salts; NAA, 0.3; kinetin, 0.1; thiamin·HC1, 1.0; pyridoxin·HCl, 5.0; nicotinic acid, 5.0; myo-inositol, 100; adenine sulfate·dihydrate, 40; sucrose, 25,000; Difco Bacto malt extract, 500; NaH2PO4·H2O, 170; and Difco Bacto agar, 6000. The shoot apices were cultured under 1000 lux Gro Lux or Plant Gro light and at constant 27°C. The explants were 0.15 mm in height and composed of the apical meristem plus a few visible subjacent primordial leaves. Within 6 weeks an avg of 80-90% of the cultures developed into miniature plants with several spears and roots. These plants, however, could not be transferred to soil with much success. The transfer necessitated further culture under another set of conditions, details of which are currently under investigation. The nutrient medium was inapplicable to shoot apex cultures of A. densiflora (Kunth) Jessop cv. Meyers, A. densiflora (Kunth) Jessop cv. Sprengeri, and, A. sarmentosus (Hort.).

Open Access

Abstract

Shoot apices, excised from Citrus cultivars of known virus content, were successfully grafted in vitro onto disease-free rootstock seedlings and some virus-free plants were obtained. The prolonged juvenile phase which characterizes disease-free nucellar lines was bypassed by this procedure.

Open Access