Sugarcane (Saccharum spp.) is an important economic crop, supplying up to 80% of the table sugar and ~60% of bio-ethanol worldwide. Due to population growth and dwindling fossil-fuel reserves, the demand for sugar and bio-ethanol requires significant improvement in sugarcane production. Breeding sugarcane cultivars with high-performance agronomic traits is undoubtedly the most efficient way to achieve this goal. Therefore, evaluating agronomic traits and dissecting underlying loci are critically important for this aim steps in providing genetic resources and molecular markers for selection. In this study, we assembled a diversity panel of 236 elite sugarcane germplasms originally collected from 12 countries. We evaluated 28 agronomic traits in the diversity panel with three replicates. The diversity panel was genotyped using amplified fragment length polymorphism markers, and a total of 1,359 markers were generated. Through the genome-wide association study, we identified three markers significantly associated with three traits evaluated at a stringent threshold (P < 0.05 after Bonferroni correction). The genotypes of the three associated markers grouped respective trait values into two distinct groups, supporting the reliability of these markers for breeding selection. Our study provides putative molecular markers linked to agronomic traits for breeding robust sugarcane cultivars. Additionally, this study emphasized the importance of sugarcane germplasm introduced from other countries and suggested that the use of these germplasms in breeding programs depends on local industrial needs.

In China, sugarcane (Saccharum spp.) hybrid cross-breeding began in 1953; approximately 70 years since then, >100 commercial sugarcane varieties have been created. In this study, 88 commercial varieties bred in China between 1953 and 2010 and 12 original foundational varieties were planted to investigate the effect of improving sugarcane varieties in China. Considering 20 years as a time node, the commercial varieties were classified into four improved generations. Retrospective analysis showed significant improvements in sucrose and other technological characteristics of commercial sugarcane varieties. The adoption of improved varieties over generations has continuously increased sugarcane’s sucrose, juice sugar, and gravity purity, and the difference was significant between Gen1 and Gen3, and between Gen2 and Gen4. Gen4 showed 2.06%, 2.35%, and 3.69% higher sugarcane sucrose (p < 0.01), juice sugar (p < 0.01), and purity (p < 0.05), respectively, and 1.13% lower sugarcane fiber (p < 0.01) than Gen1, the original foundational hybrid varieties. The development of new varieties has improved the technological characteristics of Chinese sugarcane. Sugarcane sucrose, juice sugar, and purity showed an increasing trend. Sugarcane fiber content did not significantly change with the development of new varieties but declined in comparison with the original foundational hybrid varieties.

Sugarcane (Saccharum spp.) breeding in China has a history of nearly 70 years. Yunnan province represents the second largest sugarcane planting area in China; therefore, by studying the evolution of sugarcane varieties in this region, it is possible to gain an understanding of the process of improvement since the foundation of sugarcane hybrid breeding. In this study, we compared the main industrial and agronomical characteristics of 107 sugarcane varieties, developed between 1952 and 2020, and discussed the reasons for replacement and exchange. Overall, significant differences were observed (p < 0.01), highlighting notable improvements, especially in terms of yield; however, disease incidence remains a serious issue and the fundamental reason for variety replacement. Meanwhile, analysis of parent traceability revealed that the main varieties cultivated at present have a similar parental relationship based around CP, F, and YC series germplasms. Taken together, these findings suggest that disease-resistant breeding should be strengthened, and susceptible varieties eliminated, while making full use of existing varieties as core parents.

Sugarcane (Saccharum L. spp. hybrids) is a globally important crop. While roots contribute to its net primary production, knowledge of sugarcane root growth is incomplete and limited in scope. The objective of this study was to determine cumulative root density (L A), root distribution, effective rooting depth (ERD), and root growth rate for four sugarcane genotypes across three crop cycles (plant cane [PC], first ratoon [FR], and second ratoon [SR]). The experiment was conducted in a rain shelter on four sugarcane genotypes (ROC22, YZ04-241, YZ05-194, and YZ05-51) using minirhizotron tubes to a soil profile depth of 1.08 m. Most roots in were found at 0-0.36 m-depth, and about 85.0% were within a 0-0.72 m depth in PC. In FR and SR, however, > 81.8% of roots were found at 0-0.54 m-depth regardless of genotype. The L A of ROC22 was often significantly higher than that of the other genotypes at depths < 0.54 m regardless of crop cycle. The genotype ROC22 had greater root length and faster root growth rate than YZ05-194 at 0.18-0.36 m in PC and FR, while SR YZ05-194 had slower root growth than the other genotypes at 0-0.18m. Ratooning ability of sugarcane genotypes may be related to these root growth attributes.

Sugarcane is a complex polyploid aneuploid cash crop, and transgenic varieties are important for molecular genetic and traditional breeding approaches. Herein, the sugarcane variety ROC22 served as the receptor, the Bar gene served as a screening marker, and positive and negative fragments of the ScD27.2 gene, upstream of strigolactones (SLs) biosynthesis genes driven by the 35S promoter, were introduced by Agrobacterium tumefaciens-mediated transformation. Regenerated plants were obtained by co-culture, screening culture, and differentiation induction, and 27 sense and antisense ScD27.2 transgenic seedlings were obtained by herbicide screening. PCR detection and 1% Basta (Glufosinate) application on leaves revealed Bar in all lines, with all testing positive for herbicide application and 23 containing the target gene (positive resistance screening rate = 87.5%). q-PCR and phenotypic analyses showed that ScD27.2 expression, plant height, tiller number, root length, stem diameter, and fresh weight were decreased in transgenic (ScD27.2R-9) compared with non-transgenic (NT and ScD27.2F-2) lines. ScD27.2 expression was downregulated, and growth potential was inhibited. Under 20% PEG treatment, malondialdehyde (MDA) content in ScD27.2R-9 was higher than in NT, while proline content was lower. Under drought stress, ScD27.2 expression, MDA levels, and proline content in ScD27.2F-2 and NT were higher than in non-treated controls, ScD27.2 expression increased with time, and MDA and proline levels also increased. ScD27.2 expression in ScD27.2R-9 decreased under 20% PEG treatment, MDA and proline increased (but not to NT levels), and growth was lower than NT. The 20% PEG treatment also increased the levels of (±)-2′-epi-5-deoxystrigol and (+)-abscisic acid in the rooting culture media of ScD27.2F-2, ScD27.2R-9, and NT lines, but the levels of (+)-abscisic acid content in ScD27.2R-9 was lower than in NT. Thus, interfering with ScD27.2 expression decreased resistance to 20% PEG treatment. ScD27.2 encodes a β-carotene isomerase involved in SLs biosynthesis that might function in sugarcane resistance to drought stress. It explains the role of SLs in sugarcane growth and development and responses to drought stress.