Semi-sterile Plants Research Articles

Reciprocal translocations induced by X-rays in rice.

1. In order to gain information on artificially induced translocations in rice, dormant seeds, germinating seeds and panicles just before blossoming of two varieties were X-rayed. More than two hundreds strains thus obtained were observed from the second to the fifth generations after the treatment with regard to fcrtility and other characters. 2. In a greater part of strains, fertile and semisterile plants were found in approximately I : I ratio, while in sorne other strains, either fertile or semisterile plants were predominant : in a few strains. the fertility variation seemed to be continuous. In strains segregating into fertile and semi-sterile plants, the fcrmer produced no sterile plant in their offspring, while the latter continued segregation. In strains showing continuous variation, the progeny of semi-sterile plants generally showed a similar continuous variation.

Cytogenetical studies in Oryzeae and Phalarideae

1. The genetical and cytological behaviour of three mutants derived fromX 3 generations of irradiated rice seed are described. 2. The semi-sterile mutant was heterozygous and gave rise to plants like the parent, besides normal fertile plants and dwarfs roughly in the proportions 2:1:1. Semi-sterility was found to be due to the association of four chromosomes during meiosis. The commonest configuration involved a chiasma in the homologous regions proximal to the interchange in a pair of chromosomes. This indicates crossing-over of the interchanged segments resulting in chromatid non-disjunction and 50% gametophytic abortion. 3. One of the semi-sterile plants exhibited the presence of two fragments which had no visible effect on the phenotype. The behaviour of the fragments indicated that they suffer rapid elimination during the formation of gametes. 4. The dwarf plants arose only in the progeny of semi-sterile plants while the normal fertile plants bred true. Cytological examination showed that the dwarfs contained the normal complement of chromosomes and the meiosis was regular, resulting in the formation of fertile pollen, although the plant did not set seed. The origin of this mutant is discussed; it is probably due either to a small deficiency or a gene mutation at or near the point of interchange. 5. The two other mutants, “stumpy” and “beaked sterile”, did not breed true to type, and were found to be (2n + 1) types. In the case of “stumpy” a chain of five chromosomes was of frequent occurrence and indicated that the extra chromosome was composed of segments derived from the two non-homologous chromosomes of the haploid set. The other trisomic was of the primary type, the extra chromosome representing the duplication of one of the chromosomes of the haploid set. 6. The cytological basis of reciprocal translocations and its importance in the evolution of species in plants is discussed.

Inheritance of Semi-Sterility in Maize

(1) Reciprocal crosses between normal and semi sterile maize plants give equal numbers of normal and semi-sterile offspring. Self-pollination of semi-sterile individuals likewise produces the same two classes in the same proportion. (2) In explanation of these results it is suggested that a section of one chromosome carrying genes active in the Gallatin, or an entire chromosome, has become attached to a non-homologous member of the complement. The modified and normal chromosomes assort at random in the reduction divisions. Spores receiving the translocated section in duplicate or lacking it entirely abort. The other two classes are functional. (3) The existence of a new class of normal plants among the offspring of semi-sterile individuals has been definitely established. These plants, called x-normals, are fully fertile and give all semi-sterile when crossed with the original normal type. (4) If semi-sterility arises in a small proportion of the individuals in a population breeding at random the population will return quickly to its original condition. In a self-pollinated species, however, x-normal plants will become established and may eventually constitute 50 per cent. of the population, although attainment of this proportion is extremely slow after the first few generations.