Gary C. Peterson

Flavonoid composition of lemon-yellow sorghum genotypes.

Flavonoid composition of lemon-yellow sorghums grown in two locations in Texas, USA was evaluated and compared with that of white and red sorghums using high performance liquid chromatography (HPLC-PDA). Sorghums from Lubbock were brighter in colour and had minimal weathering compared to those from College Station. Sorghums with red/purple secondary plant colour had the highest levels of 3-deoxyanthocyanidins (8-187μg/g) and their levels were highest in grains from College Station (39-187μg/g). Pericarp colour did not have any effect on 3-deoxyanthocyanidin levels (p>0.05). The tan plant lemon-yellow sorghum Tx2953 had the highest levels of flavones (268-362μg/g). Among the genotypes, lemon-yellow sorghums had the highest levels of flavanones (134-1780μg/g), which are located in the pericarp and their levels were increased in the grains with a bright yellow pericarp and minimal weathering. The high flavanone levels in lemon-yellow sorghums makes this sorghum genotype a good source of those compounds.

Molecular analysis of sorghum resistance to the greenbug (Homoptera: Aphididae).

Abstract Chromosomal regions of sorghum, Sorghum bicolor (L.) Moench, conferring resistance to greenbug, Schizaphis graminum (Rondani), biotypes C, E, I, and K from four resistance sources were evaluated by restriction fragment-length polymorphism (RFLP) analysis. At least nine loci, dispersed on eight linkage groups, were implicated in affecting sorghum resistance to greenbug. The nine loci were named according to the genus of the host plant (Sorghum) and greenbug (Schizaphis graminum). Most resistance loci were additive or incompletely dominant. Several digenic interactions were identified, and in each case, these nonadditive interactions accounted for a greater portion of the resistance phenotype than did independently acting loci. One locus in three of the four sorghum crosses appeared responsible for a large portion of resistance to greenbug biotypes C and E. None of the loci identified were effective against all biotypes studied. Correspondingly, the RFLP results indicated resistance from disparate sorghums may be a consequence of allelic variation at particular loci. To prove this, it will be necessary to fine map and clone genes for resistance to greenbug from various sorghum sources.

Ethanol Fermentation Performance of Grain Sorghums (Sorghum bicolor) with Modified Endosperm Matrices

We tested 13 sorghum entries (lines and hybrids) with different endosperm matrices for ethanol production using a laboratory dry grind process. Waxy and heterowaxy samples had the highest efficiencies. Free amino nitrogen (FAN) contents in sorghum samples were positively related to the fermentation rate during fermentation (R2=0.8618). Dried distillers grain with solubles (DDGS) from different sorghums had significantly different crude protein and crude fat contents. Residual starch content in DDGS ranged from 0.60% for the most efficient sample to 2.66% for the least efficient sample. This study showed that the HD lines (TX1, TX3, TX5, TX7, and TX9) with modified endosperm protein matrix have several attributes desirable for ethanol production: easily pasted starch granules, significantly higher FAN content in finished mashes, 30-45% faster ethanol fermentation rate during early stages, and 50-60% higher lysine content in DDGS.

Invasion of sorghum in the Americas by a new sugarcane aphid (Melanaphis sacchari) superclone

In the United States (US), the sugarcane aphid (SCA) Melanaphis sacchari (Zehnter) (Hemiptera: Aphididae) was introduced in the 1970s, however at that time it was only considered a pest of sugarcane. In 2013, a massive outbreak of M. sacchari occured on sorghum, resulting in significant economic damage to sorghum grown in North America including the US, Mexico, and Puerto Rico. The aim of the present study was to determine if the SCA pest emergence in American sorghum resulted from the introduction of new genotypes. To this end we used microsatellite markers and COI sequencing to compare the genetic diversity of SCA populations collected in the Americas after the 2013 SCA outbreak on sorghum (during 2013–2017) to older samples collected before the pest outbreak (during 2007–2009). Our results show that the SCA outbreak in the Americas and the Caribbean observed since 2013 belong to populations exhibiting low genetic diversity and consisting of a dominant clonal lineage, MLL-F, which colonizes Sorghum spp. and sugarcane. The comparison of MLL-F specimens collected post-2013 with specimens collected in Louisiana in 2007 revealed that both populations are genetically distinct, according to COI sequencing and microsatellite data analyses. Our result suggest that MLL-F is a new invasive genotype introduced into the Americas that has spread rapidly across sorghum growing regions in the US, Mexico, Honduras and the Caribbean. The origin of this introduction is either Africa or Asia, with Asia being the most probable source.

Resistance of Selected Sorghum Genotypes to Maize Weevil (Coleoptera: Curculionidae)

Abstract The maize weevil, Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae), is a major insect pest of stored grain. This study evaluated resistance of grain of 26 sorghum genotypes, Sorghum bicolor (L.) Moench, to maize weevil under laboratory conditions. Three female and two male newly emerged maize weevils were reared with 5 g of grain in each of 10 vials for each of the 26 sorghum genotypes in a laboratory experiment. The weevils and grain of each genotype were scored once every 3 wk for a total of five times during 105 d. The numbers of live and newly emerged maize weevils, dead weevils from the initial population, damage score (scale of 1–5), and grain weight loss were used to indicate resistance. The least percentage weight loss of 23.9 and 24.1% was recorded for sorghum genotypes Sureño and (5BRON151*Tegemeo)-HG7, respectively. Genotypes B.HF8 and (A964*P850029)-HW6 had the most weight loss, 70.6 and 67.7%, at 105 d after infestation. Genotypes B.HF8 and (A964*P850029)-HW6 consistently exhibited the highest numbers of maize weevil, 63 and 84, per vial at 105 d after infestation. Sorghum genotypes Sureño, (SV1*Sima/IS23250)-LG15, (5BRON151*Tegemeo)-HG7, and (B35*B9501)-HD9 ranked among the top four genotypes with least damage rating more often than any other genotype across the five sampling dates. On the other hand, genotypes B.HF8, (A964*P850029)-HW6, (Segaolane*WM#322)LG2, and (Tx2880*(Tx2880*(Tx2864*(Tx436*(T x2864*PI550607)))))-PR3-CM1 were more often ranked among the top four genotypes with the highest damage rating. Our results indicate that grain of genotype Sureno is most resistant to the maize weevil among screened genotypes.