Catalases (CAT) play important roles in plant defence mechanisms, stress response, cellular redox balance and aging delay. In order to clone CAT genes in cultivated (Saccharum officinarum L.) and wild (S. spontaneum L.) sugarcane, we designed two pairs of specific primers using a full length cDNA sequence of sorghum CAT gene (XM 002437586.1) as the probe. Two novel full-length sequences of CAT genes (SoCAT-1 in S. officinarum and SsCAT-1 in S. spontaneum) were cloned by nested polymerase chain reaction. Two allelic variants were found at SoCAT-1 (SoCAT-1a and SoCAT-1b, GenBank accession nos. KF864224-25) and SsCAT-1 (SsCAT-1a and SsCAT-1b, GenBank accession nos. KF864226-27) loci. The full lengths of SoCAT-1a, SoCAT-1b, SsCAT-1a and SsCAT-1b were 3816 bp, 3814 bp, 3777 bp and 3812 bp, respectively, and all contained eight exons and seven introns, with a similar gene structure. The length of cDNA for all four genes was 1532 bp, containing 10 bp 5'-untranslated region (UTR) and 43 bp 3'-UTR, and an open reading frame of 1479 bp encoding a polypeptide of 492 amino acids. High homology of DNA (99.0% for SoCAT-1, 98.2% for SsCAT-1) and cDNA (99.3% for SoCAT-1, 99.4% for SsCAT-1) were found. Eleven single nucleotide polymorphisms were found in cDNA SoCAT-1 and nine ones in SsCAT-1, and nine and five amino-acid mutation sites in the predicted proteins, respectively. The predicted proteins encoded by SoCAT-1 and SsCAT-1 showed high homology with CAT in sorghum, rice, corn and other species.

Sugarcane is the major sugar-producing crop worldwide, and hybrid F₁ populations are the primary populations used in breeding. Challenged by the sugarcane genome’s complexity and the sucrose yield’s quantitative nature, phenotypic selection is still the most commonly used approach for high-sucrose yield sugarcane breeding. In this study, a hybrid F₁ population containing 135 hybrids was constructed and evaluated for 11 traits (sucrose yield (SY) and its related traits) in a randomized complete-block design during two consecutive growing seasons. The results revealed that all the traits exhibited distinct variation, with the coefficient of variation (CV) ranging from 0.09 to 0.35, the Shannon-Wiener diversity index (H′) ranging between 2.64 and 2.98, and the broad-sense heritability ranging from 0.75 to 0.84. Correlation analysis revealed complex correlations between the traits, with 30 trait pairs being significantly correlated. Eight traits, including stalk number (SN), stalk diameter (SD), internode length (IL), stalk height (SH), stalk weight (SW), Brix (B), sucrose content (SC), and yield (Y), were significantly positively correlated with sucrose yield (SY). Cluster analysis based on the 11 traits divided the 135 F₁ hybrids into three groups, with 55 hybrids in Group I, 69 hybrids in Group II, and 11 hybrids in Group III. The principal component analysis indicated that the values of the first four major components’ vectors were greater than 1 and the cumulative contribution rate reached 80.93%. Based on the main component values of all samples, 24 F₁ genotypes had greater values than the high-yielding parent ‘ROC22’ and were selected for the next breeding stage. A rapid sucrose yield estimation equation was established using four easily measured sucrose yield-related traits through multivariable linear stepwise regression. The model was subsequently confirmed using 26 sugarcane cultivars and 24 F₁ hybrids. This study concludes that the sugarcane F₁ population holds great genetic diversity in sucrose yield-related traits. The sucrose yield estimation model, $y_{SY}=2.01x_{SN}+8.32x_{SD}+0.79x_B+3.44x_{SH}-47.64$, can aid to breed sugarcane varieties with high sucrose yield.

Saccharum arundinaceus is one of the most important species of sugarcane related species, and with strong resistance. Superoxide dismutases (SODs) play an important role in stress tolerance in plants. In this paper, two novel full-length cDNA sequence of the Cu/Zn SOD gene, denoted as SaSOD-1a and SoSOD1a (GenBank Accession number KJ002569 and KT327179), were isolated from S. arundinaceus and sugarcane, respectively. SaSOD-1a cDNA is 689 bp in length, including 33 bp of 5'-untranslated region (UTR) and 35 bp of the 3'-UTR, and a 621-bp open reading frame (ORF) encoding a 206 amino-acid sequence of the protein which has a conserved domain of superoxide dismutase belonging the SOD family. The SoSOD1a sequence is 690 bp, containing a 600 bp ORF, a 36-bp 5’-UTR and 54-bp 3’-UTR. It encoded the 199 amino-acid sequence of the protein which also has a conserved domain of superoxide dismutase belonging the SOD family. Between these two sequences, there was 97.5% similarity, 17 single nucleotide polymorphism (SNP) sites and 4 small insertion/deletion fragments; 95.5% protein similarity and 10 amino-acid mutation sites. In homologous evolutionary analysis, the Cu/Zn SOD genes from different plant species were rather conservative. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that the prokaryotic expression product was a fusion protein. Real-time quantitative polymerase chain reaction analysis demonstrated that the expression profile of SaSOD-1a and SoSOD1a were different under various drought stress duration. It was also suggested that SOD1a has a different drought response mode in sugarcane and the wild species S. arundinaceus.

Selections of drought-tolerant cultivars and drought-stress diagnosis are important for sugarcane production under seasonal drought, which becomes a crucial factor causing sugarcane yield reduction. The main objective of this study was to investigate the differential drought-response strategies of drought-resistant (‘ROC22’) and -susceptible (‘ROC16’) sugarcane cultivars via photosynthetic quantum efficiency (Φ) simulation and analyze photosystem energy distribution. Five experiments were conducted to measure chlorophyll fluorescence parameters under different photothermal and natural drought conditions. The response model of Φ to photosynthetically active radiation (PAR), temperature (T), and the relative water content of the substrate (rSWC) was established for both cultivars. The results showed that the decreasing rate of Φ was higher at lower temperatures than at higher temperatures, with increasing PAR under well-watered conditions. The drought-stress indexes (ε_D) of both cultivars increased after rSWC decreased to the critical values of 40% and 29% for ‘ROC22’ and ‘ROC16’, respectively, indicating that the photosystem of ‘ROC22’ reacted more quickly than that of ‘ROC16’ to water deficit. An earlier response and higher capability of nonphotochemical quenching (NPQ) accompanied the slower and slighter increments of the yield for other energy losses (Φ_NO) for ‘ROC22’ (at day5, with a rSWC of 40%) compared with ‘ROC16’ (at day3, with a rSWC of 56%), indicating that a rapid decrease in water consumption and an increase in energy dissipation involved in delaying the photosystem injury could contribute to drought tolerance for sugarcane. In addition, the rSWC of ‘ROC16’ was lower than that of ‘ROC22’ throughout the drought treatment, suggesting that high water consumption might be adverse to drought tolerance of sugarcane. This model could be applied for drought-tolerance assessment or drought-stress diagnosis for sugarcane cultivars.

The nucleotide-binding site (NBS)–leucine-rich repeat (LRR) gene family is a class of R genes in plants. NBS genes play a very important role in disease defence. To further study the variation and homology of mango NBS–LRR genes, 16 resistance gene analogues (RGAs) (GenBank accession number HM446507-22) were isolated from the polymerase chain reaction fragments and sequenced by using two degenerate primer sets. The total nucleotide diversity index Pi was 0.362, and 236 variation sites were found among 16 RGAs. The degree of homology between the RGAs varied from 44.4% to 98.5%. Sixteen RGAs could be translated into amino sequences. The high level of this homology in the protein sequences of the P-loop and kinase-2 of the NBS domain between the RGAs isolated in this study and previously characterized R genes indicated that these cloned sequences belonged to the NBS–LRR gene family. Moreover, these 16 RGAs could be classified into the non-TIR–NBS–LRR gene family because only tryptophan (W) could be claimed as the final residual of the kinase-2 domain of all RGAs isolated here. From our results, we concluded that our mango NBS–LRR genes possessed a high level of variation from the mango genome, which may allow mango to recognize many different pathogenic virulence factors.