A mycological assessment of highly digestible protein sorghum lines.

The improved protein digestibility of the highly digestible protein (HD) sorghum lines is attributed to the invaginated shape of the endosperm protein bodies that provides better proteolytic access to the kafirins containing protein bodies. Recent evidence suggests that by virtue of their modified endosperm matrix the HD sorghum lines are more susceptible to the grain mold disease complex (GMDC). This study tests the hypothesis that the HD sorghum endosperm matrix confers a greater susceptibility to grain molds compared to the wild type endosperm matrix in sorghum (i.e. spherical non-invaginated protein bodies). The parental lines and progeny generated by crosses of two HD lines (P850029 and P851171) with three wild type (WT) sorghum lines (B.Tx635, R.Tx436 and 96GCPOB124) were used in this study. The progeny was advanced through seven generations of self-pollination to develop recombinant inbred lines (RILs). The RILs were grown in five locations in Texas during 2005 (College Station, Weslaco, Beeville, Corpus Christi and Halfway) and two in 2006 (College Station and Weslaco). Finally, grain samples were analyzed using a protease turbidity assay to estimate their level of protein digestibility and classify the RILs into digestible groups (DGs). Several caryopsis characteristics associated with the grain mold disease (seed hardness, endosperm texture, thousand kernel weight, starch content and germination) were also analyzed to estimate the resistance of the HD lines to grain molds. The HD lines susceptibility to grain molds was measured using a threshed grade score and a mycoflora analysis. These studies revealed that the HD sorghum lines have caryopsis characteristics associated with a higher susceptibility to grain molds and significant differences were found between the HD lines and the WT sorghums lines when compared on the basis of fungal incidence providing statistical evidence in support of the tested hypothesis. However, the germination analyses provided evidence that a higher susceptibility to grain mold infection did not render the HD RILs more vulnerable to grain mold damage. The analysis of molds pathogenicity revealed that although several pathogens were isolated from the grain?s internal mycoflora not all of them were found significantly and meaningfully associated with the GMDC.