S. Jampatong², L. L. Darrah, B. D. Barry, G. F. Krause, D. A. Sleper, and A. L. Mckendry

1. Ph.D. dissertation. University of Missouri. Columbia, Missouri. 65211. U.S.A.

2. National Corn and Sorghum Research Centre. Pakchong, Nakhonratchasima. Thailand.

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Success in yield improvement of maize (Zea mays L.) to the present day has been through utilization of single-eared germplasm, increase plant density, and high nitrogen rates. Maize yield now is increasing at a slowing rate, which might be a sign for maize breeder to look for a new plant type. Prolificacy, one of the characteristics of maize ideotype (5), is the most attractive characteristic for yield improvement. Several researchers reported that prolificacy was associated with higher grain yield (2, 3). Furthermore, some researchers suggested that prolific maize gave more stable yield for a series of environments (1, 6) while others reported that prolificacy was advantageous only at low plant densities or in favourable environments (4, 7). One serious drawback often discussed is that prolificacy appears to be closely related to poor stalk quality and plant standability (6).

An approach to study the effects of prolificacy is to compare prolific vs. non-prolific genotypes. To avoid genetic background differences, three populations were developed by crossing of one-eared and multiple-eared populations. After random mating, selection for one- and two-eared types was done. The objective of this research was to compare stalk strength and other agronomic characteristics of one- and two-eared selections in three maize populations evaluated at different nitrogen levels and plant densities.

The six entries included three one- and two-eared populations. The populations were:

[MoSQA(S7-H)C8 x Georgia Cow Corn](H-1Ear)C8

[MoSQA(S7-H)C8 x Georgia Cow Corn](H-2Ear)C8

The six entries were grown in nine combinations of three level of nitrogen application (90, 180, and 270 kg N ha^-1) and three level of plant density (35,800; 47,800; and 59,800 plant ha^-1). A randomized complete block design with treatments in a split-split plot arrangement with three replication was used with nitrogen levels assigned to the main plots, plant density to the sub plots, and entries to the sub-sub-plots. The experiment was conducted in 1995 and 1996 in a total of five environments in Missouri. Each split-split plot consisted of three rows 6.8 m long and spaced 0.9 m apart.

Selection of one- and two-eared sub populations resulted in yield superiority of two-eared sub-populations compared to one-eared sub-populations at all combinations of different nitrogen levels and plant densities. However, root and stalk lodging were significantly higher in two-eared selection than one-eared selections, except for the SI171 population for root lodging. Two-eared selection also resulted in greater ear height than for one-eared selections. In general, two-eared selections resulted in poorer root and stalk strength.

1. Collins, W. K., W. A. Russell, and S. A. Eberhart. 1965. Performance of two-ear type of corn belt maize. Crop Sci. 5:113-116.
2. Lonnquist, J. H. 1967. Mass selection for prolificacy. Der Zuchter 37:185-188.
3. Maita, R., and J. G.Coors.1996. Twenty cycles of biparental mass selection for prolificacy in the open-pollinated maize population Golden Glow. Crop Sci. 36:1527-1532.
4. Mareck, J. H., and C. O. Gardner. 1979. Responses to mass selection and stability of resulting populations. Crop Sci. 19:779-783.
5. Mock, J. J., and R. B. Pearce. 1975. An ideotype of maize. Euphytica 24:613-623.
6. Motto, M., and R. H. Moll. 1983. Prolificacy in maize: A review. Maydica 28:53-76.
7. Prior, C. L., and W. A. Russell. 1975. Yield performance of non–prolific and prolific maize hybrids at six plant densities. Crop Sci. 15:482-486.

Sansern