Recently there has been much interest in producing high-oil corn from hybrids using the TopCross® system. The TopCross system has the potential of producing greater yields than previously developed high-oil corn hybrids.

A TopCross Blend™ is a mechanical mixture of two types of corn seed. One type, representing 90 to 92 percent of the seed in a bag, is a hybrid that is designated as the "Grain Parent." The normal male fertile version is called the "Grain Parent Check." The second type, representing all remaining seed, is a special "Pollinator." The Grain Parent is a male sterile version of an elite hybrid that may already be in commercial production. The Pollinator is a special line, available from DuPont and licensed to the seed company, that sheds pollen within a TopCross Blend production field. The pollen shed from these Pollinator plants contain special genes that cause a kernel to produce a much larger than average germ or embryo (commonly called xenia effect). Since most of the oil and protein is in the germ, the oil, and thus the energy level, and protein quality of the grain produced by fertilization with these pollinators is enhanced.

Pollinator plants contribute little to overall grain yield, but use resources such as soil nutrients, water and sunlight. Their function is to provide pollen to the male sterile Grain Parent. TopCross fields must be somewhat isolated from other "wild" corn pollen sources because wild pollen will not transfer the high-oil trait. Standard seed production procedures, require that corn fields must be isolated by 660 feet from the nearest corn field which would be the source of wild pollen. Most pollen from a plant usually falls within 50 to 100 feet of the plant.

Because of the isolation requirements needed to express the high oil trait, it is difficult to test these hybrids and evaluate performance. Testing more than one replication, or set of hybrids, at a location is difficult if not nearly impossible. During 1995, in cooperation with a seed company, farmers and county agents, a set of high-oil TopCross Grain Parents and their normal Grain Parent Checks were evaluated at Bangor, Chippewa Falls, Dane, and Janesville, WI. Regular dent Grain Parent Checks were planted on the outside of a block where TopCross Blend Grain Parents were grown. A buffer area of 40 rows was established between the Grain Parent Checks and the Grain Parents. One Pollinator was used in the TopCross Blend area of the field. Grain yield was measured in the middle of rows which were 200 to 300 feet long. Plant populations ranged between 27,500 and 32,500 plants per acre depending upon location. Plot management was similar for all plots. Comparisons were made between the Grain Parent and the Grain Parent Check.

In 3 of 19 comparisons, grain yield of high-oil Grain Parent was 1 to 7 percent greater than its regular dent Grain Parent Check. In 16 of 19 comparisons, grain yield of the high-oil Grain Parent was 5 to 22 percent lower than its Grain Parent Check. A statistical analysis was made on three hybrids pairs grown at four locations (Table 1). Small differences in test weight and grain moisture at harvest were observed. Grain yield of the high-oil TopCross Grain Parents averaged 10 percent lower than its regular dent Grain Parent check.

Table 1. Comparison of "TopCross® high-oil corn with its regular dent corn counterpart.
Hybrid	Trait	Grain yield	Grain moisture	Test weight
		bushels/acre	percent	pounds/bushel
Hybrid A	high-oil	136	26.0	53
	regular dent	154	25.2	53
Hybrid B	high-oil	146	27.6	54
	regular dent	158	25.2	54
Hybrid C	high-oil	147	28.7	53
	regular dent	165	26.9	52

	high-oil	143	27.4	53
	regular dent	159	25.7	53

Mean		151	26.6	53
LSD_0.10		8	1.0	NS

Agronomically, the TopCross hybrids had similar maturity, standability and disease resistance as the Grain Parent Checks. There were no obvious pollination problems in the trials. Plant populations were similar between hybrid pairs. Although yield decreases were observed, the TopCross hybrids were very close to the performance of the Grain Parent Checks. This has not been the case with other methods of producing high-oil corn, i.e. usually yield decreases are more significant and there are other agronomic problems including lodging and disease problems. Oil content results were not yet available for these plots, so yield trade-offs would have to be balanced against any oil content increases. Typically oil content of regular dent corn is 3 to 4 percent while TopCross hybrids have been reported to produce oil contents of 6 to 7 percent.