|Effect of waxy (low amylose) on fungal infection of sorghum grain|
D. L. FUNNELL-HARRIS (1), S. E. Sattler (2), P. M. O'Neill (2), K. M. Eskridge (3). (1) USDA ARS, Lincoln, NE, U.S.A.; (2) USDA-ARS; Grain, Forage and Bioenergy Research Unit, Lincoln, NE, U.S.A.; (3) Department of Statistics; University of Nebraska, Lincoln, NE, U.S.A.
Loss of function mutations in the <i>Waxy </i>(<i>Wx</i>) gene, encoding Granule Bound Starch Synthase (GBSS) that synthesizes amylose, results in starch granules containing mostly amylopectin. Grain with this trait has increased usability for feed, food and grain-based ethanol, due to altered starch properties. In sorghum, two classes of <i>waxy </i>(<i>wx</i>) alleles had been previously characterized for absence or presence of GBSS: <i>wx<sup>a</i></sup> (GBSS<sup>-</sup>) and <i>wx<sup>b</sup> </i>(GBSS<sup>+</sup>, with reduced activity). Field-grown grain of wild-type; <i>waxy</i>, GBSS<sup>-</sup>; and <i>waxy</i>, GBSS<sup>+</sup> Plant Introduction accessions, were screened for fungal infection. Overall, results showed that <i>waxy</i> grains were not more susceptible than wild-type. GBSS<sup>-</sup> and wild-type grain had similar infection levels. However, height was a factor with <i>waxy</i>, GBSS<sup>+</sup> lines: <i>wx<sup>b</sup> </i>accessions, which were short, were more susceptible than tall <i>waxy </i>accessions, with an undescribed allele. In greenhouse experiments, grain from accessions and near-isogenic <i>wx<sup>a</i></sup>, <i>wx<sup>b</i></sup> and wild-type lines, were inoculated with <i>Alternaria </i>sp., <i>Fusarium thapsinum </i>and<i> Curvularia sorghina</i>, to analyze germination and seedling fitness. As a group, <i>waxy </i>lines were not more susceptible to grain pathogens than wild-type, supporting field evaluations. Amongst most <i>waxy </i>and wild-type lines, reduced emergence, survival and seedling weights were observed after <i>C. sorghina </i>and <i>F. thapsinum </i>inoculations. These results are valuable for developing <i>waxy</i> hybrids with resistance to grain-infecting fungi.