LLAVALLOL, ARGENTINA
Universidad Nacional de la Plata y Cigen (CONICET-UNLP-CIC)

Quality maize hybrids developed in Argentina: chemical evaluation of endosperm

--Corcuera, VR, Bernatené, EA, Naranjo, CA

Although less than 20% of Argentina’s maize production is used in manufacturing, it is convenient to attend to the industrial requirements during the breeding process in improving protein quality and content, as well as starch quality, to obtain new more highly valued commodities. Kernel quality homogeneity of the new hybrids is also a very important concern for maize breeders. Since 1990, inbreds were obtained by Schull’s method from eleven foundational populations of waxy, opaque2 and normal endosperm maizes. Materials were conducted ear-per-row during the first inbreeding generations and later using balanced composites. Several single-crosses amongst developed inbreds were made. Oil content (%), protein content (%), starch content (%), as well as density, were measured at the lab through a non-destructive assay using a NIR device model Isotec 1227. Measurements were carried out on samples of F2 kernels taken from the 106 experimental single crosses and flint maize testers grown in two field trials at Llavallol and Castelar during two consecutive growing seasons (2001/02 and 2002/03). These precommercial hybrids differed from the rest by the nature of their endosperm, and based on this, they can be classified as waxy, high quality protein, and waxy and high quality protein (double recessive). Each sample consisted of 80 grams of whole grain from each location. Data obtained for each hybrid in both locations were averaged. Starches from a flint hybrid (3193), two double recessive hybrids (3165, 3152) and a waxy hybrid (3187) were isolated and purified in treatments with NaHSO₃ 0.005M, successive washes with NaCl, ethanol-water, and washed and dried (Salmoral et al., 2000). Molecular fractioning was performed according to the difference of solubility method in water-buthanol. Quantification and spectrophotometric profiles (λ_max) were done using iodine-potassium iodide reagent in a saturated solution of CaCl₂ using a Shimatzu spectrophotometer. Seventy-two hybrids (26 waxy, 14 high quality protein, 29 double recessive and 3 flint hybrids) showed ≥ 5% oil content, ranging from 3.52 to 6.41%, with an average of 5.24%, if all of the hybrids evaluated are considered. Protein content ranged from 8.2 to 12.6%, average: 10.25%. Twenty-six hybrids had ≥ 10.5% protein content (16 waxy, 3 high quality protein, 5 double recessive and 2 flint hybrids).

Starch content varied from 68.6 to 74.1%, average: 71.6%. Ninety-eight hybrids had ≥ 70% starch content (50 waxy, 40 double recessive, 6 high quality protein and 2 flint hybrids).

Density values fluctuated from 1.169 to 1.313 with an average of 1.264. The lowest value was found in a double recessive hybrid, and the highest in a waxy endosperm hybrid. When the different types of hybrids were considered individually, it was found that waxy hybrids have an average oil content of 5.03 ± 0.43, an average protein content of 10.00 ± 0.97, an average starch content of 71.44 ± 1.10 and an average density of 1.28 ± 0.21. The average oil content for high quality protein hybrids is 5.53 ± 0.43, the average protein content is 10.03 ± 0.56, the average starch content is 71.63 ± 0.70 and the average density is 1.24 ± 0.18. The average oil content observed for double recessive hybrids is 5.39 ± 0.37, the average protein content is 9.83 ± 0.69, the average starch content is 71.91 ± 1.22 and the average density is 1.25 ± 0.29.

Pairwise correlations amongst the endosperm chemical components considered above were calculated. No correlation was observed between oil and protein (r = 0.12), but statistically significant ones were found for oil-starch (r = -0.24, p ≥ 0.05), starch-protein (r = -0.71, p ≥ 0.05), oil-density (r = -0.35, p ≥ 0.01) and starch-density (r = -0.53, p ≥ 0.05) (see Table 1).

Regression equations were also calculated:

Starch, oil and protein content of the endosperm were also measured in the parent inbreds, although they are not published here. In general terms, when the values found for the hybrids are compared to those of the inbreds, it can be stated that oil and starch content do not vary too much amongst them, but protein content in F2 kernels is always markedly lower than that found in the respective inbreds. So, the “dilution effect” observed for protein content in F2’s employed as animal or human feed could be overcome by developing high protein content inbreds to be used as the female parent in the crosses. Otherwise, the results obtained from the preliminary studies on starches showed that the flint hybrid 3193 had a 75% amylopectin and 8.04% amylose content. An 89% amylopectin content and an 11% amylose content was found in the waxy hybrid 3187, and an 80–81% amylopectin content and a 19–20% amylose content were detected in the double recessive hybrids 3165 and 3152. The higher amylopectin content is also confirmed through the high ramification degree (A: λ_max/λ_max spectrum shoulder) that varied from 1.20 to 1.35.

Finally, it can be said that many hybrids tested in the field trials show an exceptional kernel quality based on their oil, protein and starch content, which makes them more than suitable to be used for animal and human feed or as industrial staples.