Variability of grain quality in sorghum: association with polymorphism in Sh2, Bt2, SssI, Ae1, Wx and O2.

To ensure food security in Africa and Asia, developing sorghum varieties with grain quality that matches consumer demand is a major breeding objective that requires a better understanding of the genetic control of grain quality traits. The objective of this targeted association study was to assess whether the polymorphism detected in six genes involved in synthesis pathways of starch (Sh2, Bt2, SssI, Ae1, and Wx) or grain storage proteins (O2) could explain the phenotypic variability of six grain quality traits [amylose content (AM), protein content (PR), lipid content (LI), hardness (HD), endosperm texture (ET), peak gelatinization temperature (PGT)], two yield component traits [thousand grain weight (TGW) and number of grains per panicle (NBG)], and yield itself (YLD). We used a core collection of 195 accessions which had been previously phenotyped and for which polymorphic sites had been identified in sequenced segments of the six genes. The associations between gene polymorphism and phenotypic traits were analyzed with Tassel. The percentages of admixture of each accession, estimated using 60 RFLP probes, were used as cofactors in the analyses, decreasing the proportion of false-positive tests (70%) due to population structure. The significant associations observed matched generally well the role of the enzymes encoded by the genes known to determine starch amount or type. Sh2, Bt2, Ae1, and Wx were associated with TGW. SssI and Ae1 were associated with PGT, a trait influenced by amylopectin amount. Sh2 was associated with AM while Wx was not, possibly because of the absence of waxy accessions in our collection. O2 and Wx were associated with HD and ET. No association was found between O2 and PR. These results were consistent with QTL or association data in sorghum and in orthologous zones of maize. This study represents the first targeted association mapping study for grain quality in sorghum and paves the way for marker-aided selection.

Development of NIRS equations for food grain quality traits through exploitation of a core collection of cultivated sorghum.

A sorghum core collection representing a wide range of genetic diversity and used in the framework of a sorghum breeding and genetics program was evaluated by near-infrared reflectance spectroscopy (NIRS) to predict food grain quality traits: amylose content (AM), protein content (PR), lipid content (LI), endosperm texture (ET), and hardness (HD). A total of 278 sorghum samples were scanned as whole and ground grain to develop calibration equations. Laboratory analyses were performed on NIRS sample subsets that preserved the core collection racial distribution. Principal component analysis performed on NIRS spectra evidenced a level of structure following known sorghum races, which underlined the importance of using a wide range of genetic diversity. Performances of calibration equations were evaluated by the coefficient of determination, bias, standard error of laboratory (SEL), and ratio of performance deviation (RPD). Ground grain spectra gave better calibration equations than whole grain. PR equation (RPD of 5.7) can be used for quality control. ET, LI, and HD equations (RPD of 2.9, 2.6, and 2.6, respectively) can be used for screening steps. Even with a small SEL in whole sample analysis, a RPD of 1.8 for AM confirmed that this variable is not easy to predict with NIRS.

Tannin elimination and improvement of the digestibility of protein sorghum grains.

Three hybrids of sorghum grains [Sorghum bicolor (L) Moench] containing 3.8, 3.0 and 0.2% of tannins were treated. Abrasive dehulling and storage of moist grains were tested separately and in combination to reduce the tannin content and to improve the nutritional quality of grains. The moisture content of the grains was increased from 12 to 30% by humidifying them with water, acetic acid, sodium bicarbonate or sodium hypochlorite solutions. Abrasive dehulling of the grains to a yield between 75 and 80%, humidifying the grains with acetic acid (1% v/v) and storing them during 7 days at 20 degrees C proved to be the most effective procedure. In this way tannin can be totally reduced and the in vitro digestibility of protein can be increased to 87.5%.

[Effect of cooking on protein digestibility of sorghum (Sorghum bicolor (L.) Moench)]. / Efecto de la cocción sobre la digestibilidad proteica del sorgo (Sorghum bicolor (L.) Moench).

The changes in protein digestibility that occur during cooking have interested many scientists. In this study the effect of cooking sorghum in water on the in vitro protein digestibility (IVPD) was evaluated using sorghum grains not containing tannin (SST), and grains containing detoxified tannin (SPD). The results were compared with rice and maize. The effect of sulfites present in the water used for cooking was also determined. The IVPD of sorghum excent of tannins before cooking was 71.1% smaller (p < 0.05) than that obtained for com (80.8%), polished rice (90.6%) or sorgum with detoxified tannins (80.4%). After cooking in water the IVPD decreased to 23.1%, 66.3%, 3.1% and 3.2% for SST, SPD, polished rice and corn endosperms, respectively. The IVPD of SST and SPD treated with 0.1M sodium bisulfite was 65.2 and 50.1%, which corresponds to a decrease in IVPD of 8.0 and 37.7%, respectively. Similar results were obtained when 0.1M sodium metabisulfite is added to the cooking media. These findings demonstrate that sulfites inhibit the sudden decrease of the IVPD of cooked sorghum grains, and suggest that these compounds may block the formation of disulfide bridges (-S-S-) among the gamma-kafirins molecules located on the surface of the sorghum protein bodies or possibly other factors involved which will be later studied.

Tannin elimination and improvement of the digestibility of protein sorghum grains / Eliminación de taninos y aumento de la digestibilidad proteica del sorgo

Three hybrids of sorghum grains [Sorghumbicor (L) Moench] containing 3.8,3.0 and 0.2 por ciento of tannins were treated. Abrasive dehulling and storage of moist of moist grains were tested separately and in combination to reduce the tannin content and to improve the nutritional quality of grains. The moisture content of the grains was increased from 12 to 30 por ciento by humidifying them with water, acetic acid, sodium bicarbonate or sodium hypochlorite solutions. Abrasive dehulling of the grains to a yield between 75 and 80 por ciento, humidifying the grains with acetic acid (1 por ciento v/v) and storing them during 7 days at 20ºC proved be the most effective procedure. In this way tannin can be totally reduced and the un vitro digestibility of protein can be increased to 87.5 por ciento

Efecto de la cocción sobre la digestibilidad proteica del sorgo (Sorghum bicolor L.) Moench) / Effect of cooking on the protein digestibility of sorghum

Los cambios en la digestibilidad de las proteínas que ocurren durante la cocción han interesado a muchos científicos. Por esta razón en el presente estudio se evaluó el efecto de la cocción en agua sobre la digestibilidad proteca in vitro (DPIV) de granos de sorgo sin taninos (SST) o con taninos previamente detoxificados (SPD) y se comparó con la del arroz y la del maíz. También se estudió la influencia de los sulfitos presentes en el agua de cocción sobre la digestibilidad proteica del sorgo. La DPIV se SST antes de la cocción fue de 71.1 por ciento, menor (p<0.05) que la del SPD, la del maíz y la del arroz pulido, que presentaron respectivamente 80.4 por ciento, 80.8 por ciento y 90.6 por ciento. Todos los granos disminuyeron su digestibilidad después de ser cocidos en agua, la DPIV se redujo en 23.1 por ciento, 66,3 por ciento, 3.1 por ciento y 3.2 por ciento para el SST, el SPD, el arroz pulido y los endospermos de maíz, respectivamente. Los valores de la digestibilidad proteica para el SST y el SPD tratados con bisulfito de sodio (0.1M) fueron de 65.2 y 50.1 por ciento lo cual representa una disminución de la DPIV de 8.0 y 37.7 por ciento, respectivamente. Resultados similares se obtienen con el empleo de metabisulfito de sodio (0.1M) en el medio de cocción. Estos hallazgos demuestran que los sulfitos impiden la disminución brusca de la DPIV de los granos de sorgo sometidos a cocción y sugieren que estos compuestos pueden evitar la formación de los puentes disulfuro entre las moléculas de la gamma-kafirinas (prolaminas) localizadas en la superficie de los cuerpos proteicos del sorgo. Sin embargo, no se descarta la existencia de otros factores que deberán ser estudiados en investigaciones ulteriores. En conclusión, puesto que los sulfitos previenen la formación de puentes disulfuros durante la cocción y hacen al sorgo más digerible por la pepsina, probablemente la formación de los puentes -S-S- es la responsable de la disminución de la digestibilidad proteica del sorgo cocido.