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[en] The response of habituated embryogenic ovular callus of the 'Shamouti' orange, Citrus sinensis, to gamma irradiation was studied. Stimulation of embryogenesis was observed when only callus, but not when the medium was irradiated. Age of callus prior to subculture modified the response to irradiation as regards optimal dose for embryogenesis and radiosensitivity. Radiation intensities also modified callus response to radiation dose. Addition of unirradiated IAA to irradiated callus cultures increased embryo formation and furthered development of embryos into plantlets, with some combinations of radiation dose and IAA concentration. Addition of IAA also decreased radiosensitivity at high doses (32 kR). (author)

[en] Constraints of conventional cross breeding in fruit trees, wide market acceptance of definite cultivars, especially in apple, pear, citrus and wine grape, and the increased impact of natural mutants provide incentives for mutation breeding. Only few induced mutants in fruit trees have been commercialized and are being planted on a large scale. The main method followed in mutation breeding of tree fruit has been acute irradiation of meristematic multicellular buds but, Chimera formation and reversion present a serious problem. 87 refs, 4 tabs

[en] The constraints of conventional cross-breeding in fruit trees, wide market acceptance of definite cultivars, and the increased impact of natural mutants provide incentives for mutation breeding. Only few induced mutants in fruit trees have been commercialized and are being planted on a large scale, contrary to the situation in ornamentals. Thermal neutrons, X-rays or gamma rays have yielded commercial mutants, with only isolated cases of success with chemical mutagens or chronic irradiation. The latter method often results in severe cumulative injury to plants. The main method followed in the mutation breeding of tree fruits has been acute irradiation of the meristematic multicellular buds. Chimera formation and reversion present serious problems. Selection is usually performed in the second vegetatively propagated progeny, mV₂, in an attempt to overcome chimerism. Some induced mutants have already been used as parents in conventional cross-breeding programmes. Future targets for mutation breeding will probably not deviate essentially from those formulated in the past, although more emphasis will have to be placed on easily selectable simple traits and the problem of reversion. 83 refs, 2 tabs

[en] Though fruit gathering from the wild began long before domestication, fruit tree domestication started only after the establishment of grain agriculture. Banana, fig, date, grape and olive were among the first fruit trees domesticated. Most fruit trees are outbreeders, highly heterozygous and vegetatively propagated. Knowledge of genetics and economic traits controlled by major genes is limited. Ease of vegetative propagation has played a prominent part in domestication; advances in propagation technology will play a role in domestication of new crops. Changes toward domestication affected by major genes include self-fertility in peach, apricot and sour cherry, while the emergence of self-fertile almond populations is more recent and due probably to introgression from Amygdalus webbii. Self-compatibility in the sweet cherry has been attained only by pollen irradiation. A single gene controls sex in Vitis. Wild grapes are dioecious, with most domesticated cultivars hermaphrodite, and only a few females. In the papaya changes from dioecism to hermaphroditism have also occurred. Self-compatible systems have also been selected during domestication in Rubus. Changes towards parthenocarpy and seedlessness during domestication occurred in the banana, citrus, grape, fig and pineapple. In the banana, parthenocarpy is due to three complementary dominant genes; stenospermocarpy in the grape depends on two complementary recessive genes; parthenocarpy and sterility in citrus seems more complicated; however, it can be induced in genetic material of suitable background with ease by irradiation. Presence of persistent syconia in the fig is controlled by a mutant allele P dominant to wild +. Thornlessness in blackberry is recessive, while in the pineapple spineless forms are dominant. Changes affecting fruit composition owing to major genes include the disappearance of amygdalin present in bitter almonds (bitter kernel recessive to sweet), shell hardness in almond, and a recessive controlling low acid fruit in apple. (author). 55 refs

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[en] Conditions for embryoid differentiation in Shamouti orange ovular callus were studied. Lines differing in embryogenic capacity were established. Ageing of callus prior to subculture enhanced embryoid development. A pronounced habituation effect has been found in most cultures. Protoplasts have been obtained from callus after treatment with cellolytic enzymes. Irradiation of any embryogenic line of callus with 12-20 kR seemed to promote embryoid formation, after a time lag in their appearance. Transferrence of embryoids into agar+sucrose and GA₃ and a further transfer into agar+sucrose, GA₃ and adenine sulphate gave best results as to rooting of embryoids and plant survival. The technique of using decapitated nucellar seedlings for mutagenic treatment was developed further with Shamouti orange and Marsh grapefruit. Irradiation 48-72 hours after decapitation with 2 kR resulted in shoot neoformation and survival not much below that of control, while 6 kR impeded de novo shoot formation in Marsh grapefruit. A tendency towards mutants with earlier fruit maturity was found in mV₂ plants from material originating from irradiation with the 8-kR dose. (author)

[en] Full text: Parthenocarpic tendency is an important prerequisite for successful induction of seedlessness in breeding and especially in mutation breeding. A gene for asynapsis and accompanying seedless fruit has been found by us in inbred progeny of cv. 'Wilking'. Using budwood irradiation by gamma rays, seedless mutants of 'Eureka' and 'Villafranca' lemon (original clone of the latter has 25 seeds) and 'Minneola' tangelo have been obtained. Ovule sterility of the three mutants is nearly complete, with some pollen fertility still remaining. A semi-compact mutant of Shamouti orange has been obtained by irradiation. A programme for inducing seedlessness in easy peeling citrus varieties and selections has been initiated. (author)

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No abstract available