| Frequency of accessory chromosomes in rye strains from
Korea A. MUNTZING Institute of Genetics, Lund, Sweden Though the typical chromosome number of rye, Secale cereale, is 2n=14, individuals with additional accessory chromosomes of a specific type are known to occur in rye populations from various parts of the world. When such chromosomes are present their number is generally two or more rarely four, plants with uneven numbers (one or three) being quite rare. This preponderance of even numbers of accessory chromosomes is caused by the occurrence of a process of directed non-disjunction, occurring at the first pollen mitosis and at the corresponding stage on the female side. Some commercial varieties of rye seem to be quite devoid of plants with accessory chromosomes, and in other varieties they may be present in low frequencies. In more primitive strains of rye from Turkey, Afghanistan, and Iran accessory chromosomes are, on an average, more frequent, though also in these regions populations may occur which entirely lack such extra chromosomes. In a primitive summer rye strain from Transbaikal the percentage of plants with accessories was found to be as high as 28. However, there are other regions in the Far East, in which such chromosomes are still more frequent. The work of Oinurna (1952) indicated a high frequency of accessories in rye from Korea, and this has now been verified, as may be seen from Table 1. The seven strains examined were raised from seed material most kindly put to my disposal by Dr. Chang Choon Woo of the National Institute of Horticulture, Pusan, Korea. The results of the chromosome counts are, indeed, interesting, the average frequency of accessory chromosomes being much higher than in any other geographical region so far studied. This is especially true of the populations from Yonkii and Booyen, in which the average percentages of plants with accessory chromosomes were as high as 89.5 and 91.5 per cent respectively. The frequencies in question are significantly different in different populations, the lowest value, 19.4 per cent, being found in No. 031 (Seoul No. 2). The accessory chromosomes listed in the table are all of the standard type. In a few plants structurally deviating types were also observed. As usual, even numbers of accessories, 2 and 4, are predominant. So far the surprisingly high concentration of accessory rye chromosomes in Korea is just a puzzling fact, and we do not know if this concentration is correlated with special climatic and edaphic conditions in this part of the world, or if it is only a consequence of historic factors during the distribution of the species Secale cereale. Under such circumstances a thorough study of the rye populations in Korea and adjoining countries is, indeed, urgent. In the meantime investigations of the genetical and cytological effects of the accessory chromosomes in the populations already available may be undertaken. As presence of accessory chromosomes seems to be a primitive trait studies of these chromosomes may be of importance for the problem of the centre or centres of origin of cultivated rye. (Received April 5, 1957) |