Partial Male Sterility Research Articles

Population genetics of partial male-sterility and the evolution of monoecy and dioecy

Selection on reproductive phenotype in plants is studied, using a theoretical model. Fitnesses of mutant phenotypes with altered male and female fertility are derived, assuming an initially hermaphrodite or monoecious population with no self-incompatibility mechanism, with partial self-fertilisation, and with some inbreeding depression. These fitness expressions are used to derive conditions for the spread of such mutations, in terms of the minimum increase in opposite-sex fertility that will give a phenotype with reduced male or female fertility a selective advantage over the original type, taking into account the effect on the selfing rate of altering the sex phenotype. Conditions for polymorphism are also obtained. The conditions are used to study the evolution of dioecy from monoecy, and the evolution of gynomonoecy and monoecy from the hermaphrodite state.

Crossability between a diploidPelargonium × hortorum Bailey cultivar and some of its putative ancestral species

Crosses were made between ‘Mme. Buchner’, a diploid cultivar ofPelargonium × hortorum and four of its putative ancestral speciesP. zonale, P, inquinans, P. scandens andP. stenopetalum. Hybrids derived from these crosses were selfed and records kept of their self-fertility. Crosses between ‘Mme. Buchner’ andP. inquinans andP. zonale were the most successful.Pelargonium scandens andP. stenopetalum were difficult to cross with the cultivar. Lack of cross- and/or self-fertility appears as low seed set, low germination and, in the hybrids particularly, as partial or complete male-sterility. Partial male-sterility often appears in semi-double florets, a characteristic which seems linked to spurlessness.

Graft-transmissio of male sterility in sugar beet (Beta vulgaris L.)

Cytoplasmic male sterility in sugar beet was successfully transmitted across the union where male sterile and equivalent O-type plants were reciprocally grafted. Two experiments are described. In the first, 30 pairs of developing flowering stems were exchange-grafted between male-sterile and O-type plants. Fifteen O-type scions exhibited full or partial male sterility when grafted to male-sterile stocks and sterility was observed in progeny from these in eleven cases. In flowers from side shoots of O-types grafted with male-sterile scions eight cases exhibited some male sterility and progeny from four of these retained the sterility. In the second experiment O-type seedlings were grafted to male-sterile seedlings and out of the 22 success-fully raised to flowering, male sterility was exhibited in 12 of them. Male sterility occurred among progeny of all 22, even where the sterility could not be detected in the scions. In six cases where the scion appeared fully male-sterile no pollen was produced in any of the progeny.

Male Sterility and Partial Male Sterility in Sunflowers1

Two types of genetic male sterility in sunflowers are described. The first, discovered at Bloomington, Indiana, produces no pollen or pollen grains of uneven size which are clumped and do not stain with aceto‐carmine. The second, found at Morden, Manitoba, always produces pollen. The grains are smaller than normal, nonstaining and not clumped. Three crosses of the Bloomington stock indicated the character is controlled by a single recessive gene and two others indicated duplicate genes. More consistent results with the Morden stock showed a single recessive gene governs the male sterility in it, and that this gene is not linked to a recessive gene for branching or to another for dwarf plant. The F1 of reciprocal intercrosses of the two stocks was normal indicating that genetic control of the male sterility in them differs.Partial male sterility, characterized by varying proportions of normal pollen, occurred in breeding material of two lines. It appears possible to select lines with only 10 to 20% normal pollen and that such lines can be maintained easily. These lines cross well when naturally pollinated and it is concluded that they offer a better prospect for producing commercial hybrid seed of sunflowers than the genetic male sterility.

Studies on partial male-sterility in rice plant.

Under the particular cytoplasm (S) which is different from cytoplasm(N) of normal fertile rice plants, partial male-sberility can, in many casesbe monogenic recessive. S-cytoplasm seemed to be variable according to environmental conditions. Consequently it changes the rate of unfertilized spikelets under low temperature. Hypertrophied tapetum induced by low temperature in normal plants and that in partially male-sterile plant are similar and appear in pollen sacs in stages between the first contraction of microspores and pollen extme formation.

FERTILITY AND SIZE INHERITANCE IN A PEROMYSCUS SPECIES CROSS

The North American cricetid genus Peromyscus has long been recognized as a useful group for evolutionary and genetic studies (Sumner, 1932; Dice, 1940; Blair, 1950). The diversity of species and subgeneric taxa (Hall and Kelson, 1959), together with the adaptability of these mice to laboratory conditions, makes this genus especially useful for investigations of experimental hybridization between races or species. Dice (1940) concluded from hybridization studies that within the genus there exists a spectrum of genetic isolation, ranging from complete fertility between most races of the same species, through several grades of partial isolation between species of the same species group, to complete intersterility among species of different species groups or subgenera. In the present study attention was directed toward one of the interesting cases of partial isolation, the cross between Peromyscus maniculatus, the deer mouse, and P. polionotus, the oldfield mouse. This cross appeared to offer promising possibilities for studies of evolving barriers to reproduction, particularly with respect to fertility and disrupted size inheritance. Sumner (1930) and Dice (1933) demonstrated in a limited number of attempts that successful crosses between these species could be achieved and viable hybrids produced. Watson (1942) conducted more extensive investigations of this cross. With 23 matings each of the reciprocal types, using various races of each species, she first showed that the cross in which P. polionotus is maternal succeeds much less frequently than when P. maniculatus is used as the female. These results were subsequently confirmed for other races by Liu (1953a). Liu (1953b) further showed that much of the difference in fertility in the reciprocal crosses was due to pronounced fetal mortality after midgestation in the female P. polionotus x male P. maniculatus cross. This was sometimes accompanied by maternal mortality. Watson (1942), Blair (1944), and other workers demonstrated that F1 hybrids from the interspecific cross were fertile, although Blair and Howard (1944) using the races P. maniculatus blandus and P. polionotus leucocephalus noted partial male hybrid sterility. Watson (1942) reported that F2 and backcross generations were also successfully produced.