Fig. 1.

Heterosis (hybrid plant vigor) has not yet been systematically explored and extensively utilized for wheat yield improvement. Only 1% of wheat seeds planted worldwide are hybrid. Bread wheat is an autogamous (self-pollinating) species creating a natural barrier to hybrid seed production. Self-pollination occurs quickly primarily within the same floret (spikelet), pollen is short-lived and is shed before or when the flower starts to open, flowers have closed architecture. As a result, cross-pollination is more than an order of magnitude less frequent than self-pollination. Engineering cross-pollination (allogamy) for hybrid seed production requires modification of the reproductive system: engineering male-sterility of the female crossing partner (self-incompatibility) to prevent self-pollination and fertility restoration required for seed-producing crop plants as well as increased shedding of viable pollen and open flower architecture to allow more efficient cross-pollination. Heterotic pools of preferred crossing partners have to be established. Photograph by Jon Raupp, Kansas State University.