A tetraploid annual male sterile form of Beta vulgaris L. (2n = 4x = 36) was crossed with the wild beet species Beta intermediu BUNGE (2n = 36). The resulting F1-plants were male sterile annuals being two or three times back-crossed to diploid and tetraploid sugar and fodder beets in the next years. Apart from tetraploid material (36 chromosomes) hexaploid (54 chromosomes) and a number of aneuploid plants developed.The results obtained justify the conclusion that, at a tetraploid level the material mostly propagates apomictically after the Fr generation. The presence of penta-, hexa-, septa-and even octaploid plants might be explained by assuming that no meiosis has taken place in the crossing partners. Triploid plants are sometimes found in the progeny of hexaploid material and may presumably be considered haploids. Moreover some pentaploid plants were found in the progeny of the open pollinated Fr which after two generations of bagging are still pentaploids although they produce no pollen. This is another clear indication of apomictic reproduction.The tetraploid generation from the cross between the hexaploid material and diploid sugar beets probably contains the best prospects for breeding.
A population of 2x ms sugar beets was crossed with 4x Beta lomatogona F. et M. The 3x F~-plants were male sterile and were backcrossed with 2x and 4x sugar beets and multiplied without pollination as well. After the 1 st backcross mainly 3x apomict types arose again and, among others, a small number of successful 4x backcrosses. After pollination by 4x sugar beets this 4x F~B1 produced. besides predominantly apomictically multiplied 4x plants, also about 7 ~ haploid 2x hybrids. The latter probably possess 1 genome from B. vulgaris and 1 genome from B. lomatogona. In the meiosis of the PMC's a certain amount of homeology between a number of chromosomes of both species could be established. The amphihaploid hybrids can be used as breeding parents for the creation of types in which introgession can occur. During hybridization in addition to 2x and 4x B. vulgaris types a number of2x-, 3x , 5x and 6x hybrids arose. This is presumably caused by the presence of gametes with the somatic number of chromosomes and the occurrence sometimes of haploid apomictic multiplication.The presence of large numbers of bolters in the F~ and F~B1 suggests that the bolting tendency of both species is based on different genes.
Attempts have been made to find a method to control the male sterility-male fertility balance in beets. It proved not possible to induce male sterility in O-types by means of grafting. Nor was transmission by infection with aphids or by rubbing with juice successful.In some cases exposure of germinated seed of plasmatic male sterile annual beet material to temperatures of up to 55°C resulted in the occurrence of male fertile plants. The accompanying change could not be uniformly explained from the propagation obtained. It is possible that S-plasm has changed into N-plasm. Further investigations are in progress. | NTRODUCTIONIn 1945 OWEN gave a genetical explanation for the occurrence of a certain tbrm of male sterility in beets. He could explain his observations by means of two plasmic forms, S standing for male sterility (ms), N for normal flowering, and by two chromosome genes X and Z. The genetic structure Sxxzz causes full ms and can be maintained by pollinating with the form Nxxzz (= O-type), which normally flowers.OwEN observed abnormalities in his material for which he could not account even with the aid of this simple scheme. Only occasionally did an ms plant produce a fertile branch while external circumstances often influenced the expression of ms. ROHR-BACH (1965, III) is of the opinion that this influence is governed by genes. It was also in Epilobium that JONES and GAaELMAN (1965) discovered a normal fertile subclone produced by a cytoplasmic-sterile clone.Carrying out investigations, BLISS and GABEL (1965) found that the X-gene is the determining factor regarding ms florescence and the Z-gene (hypostatically to X) is responsible for the characteristic semi ms. ROHRBACH also concluded (1965, II) that the X-gene and the Z-gene differ in action and that the forms of S-plasm may differ as well.Ms plants and matching O-types have been found in various beet varieties and the practical breeder has been able to manage with OWEN'S scheme. Using ms material numerous hybrid varieties have been introduced into commerce over the years. It is true, that it is possible to recognize ms plants by the inflorescence but O-types (nonrestorers) have to be traced by means of test crossing. This time-consuming procedure has to be repeated to check genetic purity. It would facilitate the maintenance of the ms material if one could control the balance sterile-fertile so as to be able to dispense with the O-types or to develop them from ms-material by means of some prompt interference. A 2.3-dichlorosisobutyrate induction of male sterility (Wla-, 1960) also en-23
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