A chromosomal male-sterility system of producing hybrid wheat¹⁾

C. J. DRISCOLL

School of Botany, University of New South Wales, Kensington, N.S.W., Australia 2033

It appears reasonable at this point in time to examine in considerable detail the various ways in which hybrid wheat may be produced. Three general methods of obtaining large homogeneous blocks of male-sterile plants are being subjected to examination by various investigators. These three methods involve cytoplasmic male sterility, male gametocides, and chromosomal male sterility, respectively. This paper is concerned with the possible use of chromosomal male sterility in production of hybrid seed.

Proposed system

The system that is being examined involves a recessive male-sterility gene, ms, on a wheat chromosome and the corresponding male-fertility gene, Ms, on a homoeologous alien chromosome (DRISCOLL, 1972). The three lines involved in the system, which are referred to as the X, Y, and Z lines, are all homozygous ms and contain 2, 1, and Odoses of the alien chromosome, respectively. The Ms gene operates on sporophytic tissue such that Y lines produce 21-chromosome gametes and 22-chromosome gametes; however, the former function preferentially because of certation of hyperploid pollen. The X line produces 22-chromosome pollen only and is relatively pure-breeding.

The system in which a pure stand of Z plants is produced involves (i) the production of an original, small amount of Z seed, and (ii) increase of this to required quantities.

Small, initial amount of Z seed

This is obtained from the selfed progeny of a limited number of Y plants, which segregate approximately 25% Y and 75% Z plants, the latter being male-sterile. These Z plants are pollinated by the 21-chromosome, ms pollen of the Y plants. The Y plants are removed after pollen has shed, and seed is harvested from the Z plants. This is homogeneous Z seed.

Increase of Z seed

This is achieved by the two steps shown in Table 1. Part of the initial Z seed is used in Step 1. The remainder is used in Step 2 with the Y seed obtained from Step 1. The Z seed obtained from Step 2 can be further increased by recycling through Steps 1 and 2.

The Z seed can then be used as the female block in hybrid seed production. The male block consists of a normal variety, and the hybrid plants are then heterozygous Ms ms on the pertinent wheat chromosome. No alien chromosome is present in the hybrid seed; thus its effect on production characteristics is not a consideration.