III.2. Maintenance and multiplication of male sterile stocks without progeny testing.
C. A. Foster. Welsh Plant Breeding Station, Plas Gogerddan, Aberystwyth, U.K.
Screening of parental lines to identify pairs giving highyielding heterotic F1 hybrids is required in the early stages of a hybrid barley programme. Stocks carrying one of the many male sterile genes available (Hockett et al., 1968) can be used in the smallscale production of experimental F1 hybrids. For this purpose stocks heterozygous for a male sterile gene must be isolated by progeny testing. As the progeny of a heterozygous stock will segregate 3 fertiles to 1 male sterile in their progeny, a large number of fertiles must be removed from the crossing blocks. Automatic roguing systems suitable for use in diploid stocks have been proposed, but are as yet not operational.
A method of maintaining and multiplying a heterozygous male sterile stock that, firstly, obviates the need for repeated progeny testing, and secondly, provides seed stocks that will repeatedly segregate a high proportion of male sterile individuals is as follows:
1. Take a small stock heterozygous for a male sterile gene. In artificial, or spatial, isolation all the fertile segregants to pollinate the male steriles. The fertiles will be of two sorts, homozygous (Ms Ms) and heterozygous (Ms ms) present in the ratio 1 : 2. The pollen produced by these fertiles will be 2 Ms : 1 ms and the seed set on the male steriles will be 2/3 fertile; 1/3 male sterile; all the fertiles being heterozygous.
2. Allow these fertiles to pollinate the male sterile segregants again. The seed set on these male steriles will in this, and in every subsequent interpollination, segregate 1 heterozygous fertile to 1 male sterile. Multiplication or maintenance of the stock, allowing the fertiles to pollinate the steriles, can be carried out as extensively as required and in every generation the seed set on the male steriles will segregate 50% male steriles, and all fertiles will be heterozygous.
By using stocks multiplied in this way repeated progeny testing is not required, while the seed stock itself is more covenient and economical to use, in that it segregates 50% male steriles as opposed to the 25% in the selfed progeny of a heterozygous stock. A range of male sterile stocks is currently being maintained or multiplied in this way.
Reference:
Hockett, E. A., R. F. Eslick, D. A. Reid and G. A. Wiebe. 1968. Crop Sci. 8:754.