Optimum breeding schemes for hybrid wheat

Hybrid breeding methods are different than line breeding methods, thus it is of large importance to know what the best breeding methods are for hybrid wheat. We therefore performed model calculation using the selection gain for grain yield as target criterion. Furthermore, our considerations base on the assumption to use a gametozid for seed production. We are convinced, that different strategies should be used for the female and male pool.

For the male pool, selection initially needs to focus mainly on pollination ability and less on GCA. Based on our findings on indirect traits quantifying pollen mass, we recommend a four-step procedure in selecting new male lines. In a first step, a large number of lines is screened at a single location for visual anther extrusion. Only the best ones are then phenotyped for anther extrusion in a second year, if possible at two locations. The final selection criterion for male lines should then be the seed set on well-known female lines in a crossing block. Using elite female testers, these seeds can already serve for a first evaluation of grain yield potential of the best male lines. This will enable to recurrently improve the male pool for pollination ability and GCA.For more details, see the recent publication of Philipp Boeven.

In contrast, for the female pool, GCA for grain yield is the most important target criterion. The main question to be answered is whether to strictly select for GCA or alternatively use line per se performance as indirect measurement of GCA. The latter seems more logical, because currently all breeders have big line breeding programs and no or only small hybrid breeding programs. Thus, a combined strategy might serve both programs. Its efficiency was proven by model calculations. In contrast to strict selection on GCA, breeding schemes combining line per se performance in a first step followed by GCA selection in a second step largely increased the annual selection gain. This is due to the high correlation of line per se performance and GCA in wheat and the fact, that the use of a first line per se performance yield trial shortens the breeding scheme by 1-2 years.

Alternatively to strict phenotypic selection, the use of genomic selection enables to speed up breeding cycles. Owing to the hybrid seed production difficulties in wheat, breeding schemes replacing a first GCA test by a genomic selection step are highly beneficial for short-term selection gain. This holds also true for hybrid breeding in maize, rice and barley.