Phylogeographic evidence of crop neodiversity in sorghum.

Sorghum has shown the adaptability necessary to sustain its improvement during time and geographical extension despite a genetic foundation constricted by domestication bottlenecks. Initially domesticated in the northeastern part of sub-Saharan Africa several millenia ago, sorghum quickly spread throughout Africa, and to Asia. We performed phylogeographic analysis of sequence diversity for six candidate genes for grain quality (Shrunken2, Brittle2, Soluble starch synthaseI, Waxy, Amylose extender1, and Opaque2) in a representative sample of sorghum cultivars. Haplotypes along 1-kb segments appeared little affected by recombination. Sequence similarity enabled clustering of closely related alleles and discrimination of two or three distantly related groups depending on the gene. This scheme indicated that sorghum domestication involved structured founder populations, while confirming a specific status for the guinea margaritiferum subrace. Allele rooted genealogy revealed derivation relationships by mutation or, less frequently, by recombination. Comparison of germplasm compartments revealed contrasts between genes. Sh2, Bt2, and SssI displayed a loss of diversity outside the area of origin of sorghum, whereas O2 and, to some extent, Wx and Ae1 displayed novel variation, derived from postdomestication mutations. These are likely to have been conserved under the effect of human selection, thus releasing valuable neodiversity whose extent will influence germplasm management strategies.

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.