PSIV-21 - Comparing the nutritional value and the trade-off between sugars and starch of male-sterile with non-sterile sorghum hybrids

Abstract: The objective of this study was to assess the effect male-sterile versus non-sterile sorghum hybrids on nutritional value with emphasis on carbohydrates. The experiment was conducted on a dairy farm in West Texas under center pivot irrigation. Two male-sterile (Non-BMR, F465; and BMR12, F430) and three non-sterile sorghum hybrids (non-BMR F10; BMR12, F382, and F431; Richardson Seeds) were used in a split-plot design to reduce cross-pollination. Because of westerly prevailing winds, male-sterile hybrids were allocated to the west and non-sterile hybrids to the east, plots were blocked by irrigation section, and replicated 3 times. Plots were harvested 148 days after seeding with non-sterile hybrids after the hard dough stage and male-sterile hybrids 7 weeks after boot stage and harvested with a self-propelled forage harvester with a theoretical length of cut of 12 mm and roll gap setting at 2 mm. Duplicate samples of freshly chopped forage were obtained from each plot and immediately placed into a cooler with ice until harvest was completed. Samples were then frozen until shipped to Rock River laboratory where near-infrared spectroscopy analysis was performed. In addition, water soluble carbohydrates (WSC) and NDFD at 30h were analyzed with wet chemistry methods. The statistical analysis was performed using mixed linear regression models (GLIMMIX procedure of SAS). Type (Sterile and non-Sterile), trait (BMR12 and non-BMR) and its interaction were included as predictor variables in all models. Normal distribution of residuals was assessed using Shapiro-Wilk test (P > 0.05) and visual diagnostic of residual plots. A summary of the results is presented in table 1. WSC was 2.5-fold higher for the sterile hybrids when compared to non-sterile, whereas starch was 2.2-fold greater for non-sterile when compared to sterile hybrids (P < 0.0001). Non-fiber carbohydrates were higher for non-sterile over sterile sorghum hybrids (P < 0.0001); however, non-sterile hybrids were past the optimal stage of harvest (soft dough), which would result in poor digestibility of grain starch and protein. In addition, crude protein (CP) was significantly lower for sterile compared with non-sterile (8.29% and 10.2% respectively; P < 0.0001). Compared to non-sterile hybrids, male sterile hybrids DM was lower (28.4% and 40.8%, respectively; P < 0.0001) due to its proportionally higher vegetative plant parts compared to reproductive plant parts. The trade-off between WSC and starch in male-sterile sorghum hybrids is because sugars are not translocated to the grain where starch is developed as in non-sterile hybrids. This research indicates that concerns about low sorghum starch digestibility can be overcome by using male-sterile sorghum hybrids that will, at least partially, compensate for the reduced starch yield by increasing water-soluble carbohydrates storage.