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Cassava bacterial blight (CBB) caused by Xanthomonas axonopodis pv. manihotis (or XAM) is a serious disease of cassava (Manihot esculenta Crantz). In this study, quantitative trait loci (QTL) associated with CBB infection were identified in the F1 progenies of a cross between the "Huay Bong 60" and "Hanatee" cassava cultivars. The phenotype of disease severity was observed at 7, 10, and 12 days after inoculation (DAI). A total of 12 QTL were identified, of which 5, 6, and 1 were detected in 7, 10, and 12 DAI samples, respectively. Among all identified QTL, CBB14_10dai_1, CBB14_10dai_2, and CBB14_12dai showed the most significant (P < 0.0001) associations with CBB infection, and explained 21.3, 13.8, and 26.5% of phenotypic variation, respectively. Genes underlying the QTL were identified and their expression was investigated in resistant and susceptible cassava plants by real-time quantitative RT-PCR. The results identified candidate genes that showed significant differences in expression between resistant and susceptible lines, including brassinosteroid insensitive 1-associated receptor kinase 1-related (Manes.04G059100), cyclic nucleotide-gated ion channel 2 (Manes.02G051100), and autophagy-related protein 8a-related (Manes.17G026600) at 7 DAI, and regulator of nonsense transcripts 1 homolog (Manes.17G021900) at both 7 and 12 DAI. The expression pattern of all genes showed higher levels in resistant (B82, B32, B20, and B70) as compared to susceptible (HB60, B100, B95, and B47) plants. Overall, this study has identified QTL and markers linked to CBB infection trait, and identified candidate genes involved in CBB resistance. This information will be of use for better understanding defense mechanisms in cassava to bacterial blight disease.

In very high gravity (VHG) ethanol fermentation, the rheological properties of native cassava significantly influence heat and mass transfer, mixing energy, and, thus, the yield of all steps. This study investigated the effect of cassava varieties and their harvest times on starch liquefaction, saccharification, and fermentation. The genotype correlation of the starch properties was revealed for the most suitable cassava varieties. First, the starch content, amylose content, total reducing sugar from liquefaction and saccharification, pasting properties, and ethanol yields of six cassava varieties (Huay Bong 60, Hanatee, Kasetsart 50, Pirun 1, Pirun 2, and Rayong 11) at 6‐, 9‐, 12‐, and 15‐month harvest times were evaluated. The amylose content increased significantly from the 6th to the 12th month but slightly decreased at the 15th month. It was observed that the starch content contributed to a more substantial influence on the change in peak viscosity than on the amylose content. Ethanol fermentation using Saccharomyces cerevisiae TISTR5606 showed that the Rayong 11 variety at the 15‐month harvest time provided the highest ethanol concentration of 104.7 ± 4.1 g L−1 and an ethanol yield of 0.4 ± 0.1 g ethanol g−1 reducing sugar, which corresponded to 74.5% of the theoretical yield.

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Ten newly developed microsatellite loci were isolated from an AG 20 and CAG 20 enriched genomic DNA library of Radix sp. from Iraq. The simple sequence repeats (SSR) comprised 76.0% di-, 20.0% tri-and 4.0% tetra-nucleotide repeats. The number of alleles for all 10 loci ranged from 4 to 18, with a mean of 11.3 alleles per locus. The observed (Ho) and expected heterozygosity (He) values varied from 0.286 to 0.927 (mean 0.640) and from 0.263 to 0.939 (mean 0.753), respectively. The polymorphic information content (PIC) values ranged from 0.336 to 0.923 (mean 0.749). Five loci showed significant deviation from Hardy-Weinberg equilibrium (HWE) and no significant linkage disequilibrium (LD) was observed. Cross transferability was successfully tested on species from the genus Melanopsis. These polymorphic SSRs will be useful for assessment of the genetic diversity and population genetics of a Radix sp. as well as other related species in Iraq.

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