Comparison of Methods for Amylose Screening Among Amylose‐Extender (ae) Maize Starches from Exotic Backgrounds

Abstract

Cereal Chem. 79(2):317-321Breeding for high-amylose corn requires a rapid analytical method for determining starch amylose so that generating wet chemistry values does not pose a major limitation in the volume of materials that can be screened. Two methods for determining apparent amylose content (AAC) were examined and compared with an iodine-binding method involving the solubilization of isolated starch in a sodium hydroxide solution (method 1). These methods included one based on near-infrared transmittance spectroscopy (NIRT) (method 2) and another iodine-binding method involving the solubilizing of starch from ground whole corn with a DMSO-iodine solution (method 3). These methods were chosen because, aside from initial set up costs, they are relatively rapid and inexpensive to perform. The materials evaluated consisted of various exotic corn populations including plant introductions and experimental materials generated from the Germplasm Enhancement of Maize (GEM) project. Crosses were made between these materials and a Corn Belt dent hybrid (OH43 × H99) converted with the amylose-extender (ae) allele. Grain from F2 ears, presumed to be homozygous for the ae allele based on visual selection of mutant kernels on F1 ears from which they were planted, were then evaluated to identify possible modifiers of ae conditioning high starch AAC. From a total of 1,006 F2 ears, a core set consisting of 155 samples was established and only these were subjected to starch AAC analysis, using all three methods to compare the methods. Method 2 showed poor correlation to method 1 (r = 0.88), however, NIRT did appear to discriminate between samples converted to ae vs. those with a normal or possibly segregating endosperm type. Method 3 showed a slightly better correlation with method 1 (r = 0.92) and appeared to more fully discriminate among samples with AAC values >65% from those at ≈55%. Results from this study suggest that NIRT may be useful when a quick screening method is needed to discriminate mutant from nonmutant genotypes within grain samples of exotic germplasm especially when visual identification is difficult. In addition, method 3 could be used to replace the more timeconsuming method 1 when trying to identify high AAC levels among ae genotypes, even though some inconsistency was observed between the two methods. Finally, this study revealed that exotic germplasm may be an important source of new modifiers to the ae allele because values as high as 70% AAC were identified.

Registration of Maize Germplasm Line GEMS‐0067

“…These included several hundred plant introductions and 70 breeding crosses from GEM. Our results revealed that two plant introductions Zia Pueblo NRC 5357 (PI 218188) and Cochiti Pueblo NRC 5298 (PI 218131) and one GEM breeding cross (GUAT209:S13) contributed high amylose modifiers raising amylose levels to at least 70% in the F 3 kernels as described previously by Campbell et al (2003) Only lines from GUAT209:S13 × (H99 ae x OH43 ae ) were found to survive inbreeding and therefore used in subsequent breeding studies while the others were dropped.…”

Comparison of Methods for Colorimetric Amylose Determination in Cereal Grains

“…Of the DMSO-based solvent systems, the original variant without urea or CaCl 2 provided the most realistic results from defatted starches of the four cereals, but this was at the cost of significant day-to-day variability. Similarly, the coefficient of variation was higher when a DMSO procedure was used on maize starch than when a hot NaOH procedure was used [27].…”

“…The dimethyl sulphoxide may be assisted with calcium chloride [24] or urea [10]. Temperatures for dissolution are usually around the boiling point of water, but in DMSO may be at 857C [25], 707C with sonication [24] or 507C [23] while in perchloric acid [18], NaOH [27], KOH [28] or calcium chloride [24] room temperature may be used. The strong acid or alkali may cause some degradation of the starch [25].…”

Resistant Starch and Starch Thermal Characteristics in Exotic Corn Lines Grown in Temperate and Tropical Environments

“…The Latin American Maize Project (LAMP) evaluated over 12,000 accessions for grain yield and agronomic data (Salhuana and Pollak 2006). Along with the agronomic evaluations, many accessions and related breeding materials have been analyzed for starch traits (White et al 1990;Campbell et al 1995Campbell et al , 1996Campbell et al , 2002Ng et al 1997;Pollak and White 1997). These studies indicated great potential for improving adapted corn for these traits by introgressing exotic materials.…”

“…The U.S. successor to LAMP, Germplasm Enhancement of Maize (GEM) (Pollak 2003;Salhuana and Pollak 2006), enhances useful exotic germplasm to diversify the U.S. hybrid corn germplasm base. This germplasm also provides opportunity to impact starch traits (Singh et al 2001a(Singh et al , 2001b(Singh et al , 2001cCampbell et al 2002;Ji et al 2004;Lenihan et al 2005;Taboada-Gaytan et al 2009, 2010a, 2010bRohlfing et al 2010).…”