Developing New Varieties Larry Darrah Research Geneticist and Adjunct Professor USDA-ARS Plant Genetics Research Unit and Department of Agronomy, UMC

Self- vs. cross-pollinated crops Self-pollinated: Uses pollen and egg from the same plant to produce seed. Examples—Wheat and soybeans. Cross-pollinated: Uses pollen from one plant to fertilize an egg from another plant. Examples—Corn and squash.

Self- vs. cross-pollinated crops Soybean—Selfs easily and crosses with great difficulty; 3-4 seeds per pollination, if you are good! Only about 10% of the crosses set any seed. Wheat—Selfs easily and crosses with difficulty; seeds per pollination. 95% of the crosses will set seed. Corn—crosses and selfs easily; kernels per pollination. Anyone can pollinate corn! Determines what type of product is available to the farmer (hybrid vs. variety).

Corn anatomy ♂ Tassel - ♂ Sheds pollen at maturity ♀ Ear - ♀ Each silk is attached to one ovule. Pollen tube grows down silk and fertilizes ovule.

Shoot bagging

Cutting back the ear

Tassel bagging

Pollination

Terminology Inbred: A plant that is produced through self-pollination over many generations. Hybrid: A plant that is produced by cross-pollinating two inbreds.

Does plant breeding work? You betcha it does! Lets look at corn yields over time.

Corn yields (10 tons/ha = 159 bu/a)

How’ed they do that?

Population improvement/ basis of gain from selection

Stalk lodging damage

Rind penetrometer use

Rind penetrometer in action

Divergent selection results

Response to selection in MoSCSSS Cycle 0 and B73 x Mo17 Cycle 6 low and high

Rind penetrometer resistance

Recurrent selection Generate families. Test family performance. Recombine selected families to complete a cycle of selection. Extract inbred lines by selfing in selected families and testcrossing at S 2 or S 3.

Family structure Selfed plants (S 1 or S 2 ). Crossed plants (Half-sib families with various testers. Selfed and crossed plants (S 1 or S 2 testcrosses to various testers. Reciprocally crossed plants (two half-sib testcrossing schemes.

Family evaluation (Yield) Test families. 2-row plots spaced 30” apart and about 7” between plants for a total of 60 plants; 26,000-30,000 plants/a. 4-9 replications at 2-6 locations in one season (3 reps. at 3 locns., 2 reps. at 4 locns., or even 1 rep. at 6 locations might be used. Locations are representative of the region of adaptation. Combine harvest to obtain grain weight, test weight, and moisture.

Recombination of selected families Bulked pollen, 1 male for 2 females. Diallel: 1 x 2, 1 x 3,..., 9 x 10; in paired rows or by chain crossing where most rows are used as both a male and female where the species allows (as in corn).

Partial Diallel x 61 x 71 x 81 x 91 x x 62 x 72 x 82 x 92 x x 63 x 73 x 83 x 93 x x 64 x 74 x 84 x 94 x x 65 x 75 x 85 x 95 x 10 ♂ ♀

Germplasm sources for population improvement Existing varieties (landraces and improved populations). Crosses within heterotic groups of existing elite lines for corn. Synthetic populations (contain varieties, lines, other synthetics, etc.). For example, germplasm with resistance to the European corn borer.

Look at many—save a few!

Wheat variety ‘Ernie’ Came from pedigree selection in a cross of ‘Pike’ and Exp. Mo9965. Pike is an old variety with a very mixed pedigree.

Triticale: A “new” crop Triticale is a cross of wheat (female) and rye (male). Confers traits of high yield and baking quality. Confers traits of tolerance to acid soils and salinity, drought tolerance, winter hardiness, rust and mildew resistance, and higher lysine. Grown on 7.5 million acres (acid and marginal soils) in the world—primarily Australia, Brazil, France, Germany Poland, and South Africa.

New birdsfoot trefoil with rhizomes U.S. trefoil has persistence problems because of root and crown rot. U.S. varieties lack rhizomes. Paul Beuselinck, USDA-ARS, Columbia, collected a rhizomatous birdsfoot trefoil in Morocco and has bred it into U.S. germplasm resulting in release of ARS Grazing studies show increased persistence in pastures.

No rhizomes Rhizomes

Pedigree selection in self-pollinated crops

Where do most new varieties come from? Selfing out of existing varieties and testing. Crosses among existing lines and varieties followed by selfing and testing. Yes, this approach seems to be self-limiting (funnel), but it has worked well thus far in many crops. See the following data from the Kenya Maize Breeding Project:

Genetic variance estimated from ear-to-row selection in Kitale Composite A (E7) from 1965 to 1974 Cycle Cycle Cycle Cycle Cycle Cycle Cycle Cycle Cycle Cycle 9 263