The complex polyploid genome architecture of sugarcane.

Sugarcane, the world's most harvested crop by tonnage, has shaped global history, trade and geopolitics, and is currently responsible for 80% of sugar production worldwide1. While traditional sugarcane breeding methods have effectively generated cultivars adapted to new environments and pathogens, sugar yield improvements have recently plateaued2. The cessation of yield gains may be due to limited genetic diversity within breeding populations, long breeding cycles and the complexity of its genome, the latter preventing breeders from taking advantage of the recent explosion of whole-genome sequencing that has benefited many other crops. Thus, modern sugarcane hybrids are the last remaining major crop without a reference-quality genome. Here we take a major step towards advancing sugarcane biotechnology by generating a polyploid reference genome for R570, a typical modern cultivar derived from interspecific hybridization between the domesticated species (Saccharum officinarum) and the wild species (Saccharum spontaneum). In contrast to the existing single haplotype ('monoploid') representation of R570, our 8.7 billion base assembly contains a complete representation of unique DNA sequences across the approximately 12 chromosome copies in this polyploid genome. Using this highly contiguous genome assembly, we filled a previously unsized gap within an R570 physical genetic map to describe the likely causal genes underlying the single-copy Bru1 brown rust resistance locus. This polyploid genome assembly with fine-grain descriptions of genome architecture and molecular targets for biotechnology will help accelerate molecular and transgenic breeding and adaptation of sugarcane to future environmental conditions.

Proceedings of the workshop on quantitative evaluation of periodontal diseases by physical measurement techniques.

Most of the participants agreed that the destruction of connective tissue is the single most significant criterion for assessing the severity of periodontal disease. Members were equally divided between favoring a measure of bone height or density and a measure of soft tissue destruction, such as attachment level or pocket depth. A measure of the rate of destruction of bone at the time of examination was considered to be especially useful. Opinion was equally divided as to the second most important parameter related to periodontal disease, either measures of gingival inflammation or measures of dental plaque. Measurements of gingival fluid and measures of tooth mobility were less favored by the group as a whole, but each measurement area was favored by strong proponents.