Increasing Kernel Density for Two Inbred Lines of Maize

Improving grain quality of maize (Zea mays L.), including endospermhardness and density, is often a breeding objective.Dense seed is preferred by dry millers and for alkaline processing, and can command a price premium at market. This study attempted to increase kernel density in a backcrossing program for two inbreds of maize using two selection techniques, specific gravity of kernels and the percentage of sinking kernels in a salt solution (or sinkers). Two inbreds, B73G and A632, were crossed with synthetics exhibiting apparent high kernel density, and several generations of backcrossing and self-pollination followed. Examples of mean comparisons of backcross-derived inbreds with the recurrent parents, B73G and A632 are as follows: B73G–Specific gravity, 1.251 and 1.206; Sinkers, 62.3 and 14.9%; and A632–Specific gravity, 1.266 and 1.250; Sinkers 45.4 and 29.1%. Both the specific gravity and sinkers techniques were successful for increasing kernel density during backcrossing. THE TERM SEED QUALITY is a broad concept with many connotations, depending on the end-use of the seed (Okoruwa andKling, 1996; Rooney et al., 2004). Eckhoff and Paulsen (1996) have discussed many of the factors, including endosperm hardness and density, relating to grain quality for different end-uses. Hard, dense seed is often equated to seed quality and has significance for harvesting, handling, and other considerations (Watson, 1987). It is preferred by dry millers (Wu and Bergquist, 1991) and often commands a 10%market premium (Hill et al., 1991; Hahn et al., 2000; U.S. Grains Council, 2001). In dry milling, profits largely depend on the amount of large “flaking” grits that are produced since flaking grits are the highest value endosperm product; larger grits result from denser kernels. Dense-kernelled maize is the preferred type for alkaline-cooking processes formaking masa, tortilla chips, and snack foods as well. There is even limited evidence that dense kernels result in higher yields of ethanol (Murthy et al., 2004a, 2004b). Dense seed is usually hard, with vitreous endosperm (Mestres et al., 1991), and the degree is often determined or inferred by visual examination. In contrast to visual examination, this research was designed to select for kernel density by two quantitative determinations, namely, specific gravity and sinkers (i.e., the percentage of sinking kernels in a salt solution). Initial success with these two techniques was reported by Bergquist and Thompson (1992). In that paper the term “floaters” referred to the percentage of floating kernels, which is the complement of “sinkers” used in this research. The objective of this research was to evaluate these two techniques, specific gravity and sinkers, for their effectiveness in increasing the kernel density of inbred lines B73G and A632 by backcrossing. MATERIALS AND METHODS