Modern sugarcanes are polyploid interspecific hybrids, combining high sugar content from Saccharum officinarum with hardiness, disease resistance and ratooning of Saccharum spontaneum. Sequencing of a haploid S. spontaneum, AP85-441, facilitated the assembly of 32 pseudo-chromosomes comprising 8 homologous groups of 4 members each, bearing 35,525 genes with alleles defined. The reduction of basic chromosome number from 10 to 8 in S. spontaneum was caused by fissions of 2 ancestral chromosomes followed by translocations to 4 chromosomes. Surprisingly, 80% of nucleotide binding site-encoding genes associated with disease resistance are located in 4 rearranged chromosomes and 51% of those in rearranged regions. Resequencing of 64 S. spontaneum genomes identified balancing selection in rearranged regions, maintaining their diversity. Introgressed S. spontaneum chromosomes in modern sugarcanes are randomly distributed in AP85-441 genome, indicating random recombination among homologs in different S. spontaneum accessions. The allele-defined Saccharum genome offers new knowledge and resources to accelerate sugarcane improvement.

The black twig borer, Xylosandrus compactus (Eichhoff) (Coleoptera: Curculionidae: Scolytinae), is a pest of coffee and many endemic Hawaiian plants. Traps baited with chemical attractants commonly are used to capture ambrosia beetles for purposes of monitoring, studying population dynamics, predicting outbreaks, and mass trapping to reduce damage. The objectives of this research were to optimize trapping systems for X. compactus and other ambrosia beetles such as Xylosandrus crassiusculus (Motschulsky) and Xyleborinus saxesenii (Ratzeburg) by comparing efficacy of several attractants, repellents, and trap types. The ability of certain chemicals to act as beetle repellents and thus interfere with trap catch was tested for purposes of protecting host plants from attack. Potential attractants and application methods tested were as follows: ethyl alcohol pouch delivery system, ethyl alcohol vial delivery system, α-pinene in Eppendorf tubes, eugenol bubblecaps, ginger oil bubblecaps, manuka oil bubblecaps, phoebe oil bubblecaps, and an unbaited control. Potential repellents tested were limonene and verbenone. Ethyl alcohol vials were as attractive as ethyl alcohol sleeves, and were more effective than traps baited with eugenol and α-pinene. Japanese beetle traps were more effective for black twig borer trapping than Lindgren funnel traps, and were easier to deploy. Verbenone and limonene significantly reduced trap catch of Xylosandrus compactus and X. crassiusculus, suggesting that they may be effective for reducing attraction to host plants. These results show the importance of developing a combination of several monitoring techniques to enhance management procedures for the black twig borer.

BackgroundSugarcane is an emerging dual-purpose biofuel crop for energy and sugar production, owing to its rapid growth rate, high sucrose storage in the stems, and high lignocellulosic yield. It has the highest biomass production reaching 1.9 billion tonnes in 2014 worldwide.ResultsTo improve sugarcane biomass accumulation, we developed an interspecific cross between Saccharum officinarum ‘LA Purple’ and Saccharum robustum ‘MOL5829’. Selected F1 individuals were self-pollinated to generate a transgressive F2 population with a wide range of biomass yield. Leaf and stem internodes of fourteen high biomass and eight low biomass F2 extreme segregants were used for RNA-seq to decipher the molecular mechanism of rapid plant growth and dry weight accumulation. Gene Ontology terms involved in cell wall metabolism and carbohydrate catabolism were enriched among 3274 differentially expressed genes between high and low biomass groups. Up-regulation of cellulose metabolism, pectin degradation and lignin biosynthesis genes were observed in the high biomass group, in conjunction with higher transcript levels of callose metabolic genes and the cell wall loosening enzyme expansin. Furthermore, UDP-glucose biosynthesis and sucrose conversion genes were differentially expressed between the two groups. A positive correlation between stem glucose, but not sucrose, levels and dry weight was detected.ConclusionsWe thus postulated that the high biomass sugarcane plants rapidly convert sucrose to UDP-glucose, which is the building block of cell wall polymers and callose, in order to maintain the rapid plant growth. The gene interaction of cell wall metabolism, hexose allocation and cell division contributes to biomass yield.Electronic supplementary materialThe online version of this article (10.1186/s12864-017-4158-8) contains supplementary material, which is available to authorized users.

Sugarcane is among the most efficient crops in converting solar energy into chemical energy. However, due to its complex genome structure and inheritance, the genetic and molecular basis of biomass yield in sugarcane is still largely unknown. We created an F2 segregating population by crossing S. officinarum and S. spontaneum and evaluated the biomass yield of the F2 individuals. The F2 individuals exhibited clear transgressive segregation in biomass yield. We sequenced transcriptomes of source and sink tissues from 12 selected extreme segregants to explore the molecular basis of high biomass yield for future breeding of high-yielding energy canes. Among the 103,664 assembled unigenes, 10,115 and 728 showed significant differential expression patterns between the two extreme segregating groups in the top visible dewlap leaf and the 9th culm internode, respectively. The most enriched functional categories were photosynthesis and fermentation in the high-biomass and the low-biomass groups, respectively. Our results revealed that high-biomass yield was mainly determined by assimilation of carbon in source tissues. The high-level expression of fermentative genes in the low-biomass group was likely induced by their low-energy status. Group-specific expression alleles which can be applied in the development of new high-yielding energy cane varieties via molecular breeding were identified.

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