This study aimed to evaluate the defoliation ability of 56 sugarcane varieties/lines, to identity the germplasm with easy defoliation, and to elucidate the cellular morphological and physiological basis of sugarcane defoliation, so as to provide a theoretical basis for exploring the regulatory mechanism of sugarcane defoliation.

The natural defoliation number, total number of nodes, natural defoliation rate, leaf sheath inclination angle (+8, +9, +10 leaf position) and defoliation force of 56 sugarcane varieties/lines were systematically investigated, and defoliation ability was comprehensively evaluated by entropy weight method and hierarchical cluster analysis. The base of the leaf sheath abscission zone at +2, +5 and +8 leaf positions of the easy-to-defoliate sugarcane variety XTT20 and the hard-to-defoliate sugarcane variety YAU11-818 were analyzed by combining paraffin sections, enzyme activities and endogenous hormone content the cell morphology and physiological basis of sugarcane defoliation.

Entropy weight analysis showed that the comprehensive score of defoliation of 56 sugarcane varieties/lines ranged from 0.001 to 0.978. Systematic cluster analysis divided the 56 sugarcane varieties/lines into 3 groups, including 3 easily-defoliation varieties (XTT20, XTT22, YAU01-106), 7 difficult-to-defoliation lines, and 46 medium defoliation varieties/lines, accounting for 5.36%, 12.50% and 82.14% of the total number of varieties/lines, respectively. Compared with the difficult-to-defoliation line YAU11-818, the easily-defoliation variety XTT20 had a higher natural defoliation rate, larger leaf sheath inclination angle and smaller defoliation force; The cells in the leaf sheath abscission zone of the +8 leaf position of the defoliant varieties were more loosely arranged, the cell density was relatively low, and the cell degradation was larger, the percentage of aerated tissue area was significantly higher than that of the difficult-to-defoliation line (14.54% increase), and the difference between different leaf positions was significant (+8 leaf position increased by 16.97% compared to +5 leaf position). In addition, the polygalacturonase activity, cellulase activity and abscisic acid (ABA) content in +8 leaf sheath of XTT20 were significantly higher than those of YAU11-818. On the contrary, the content of indole-3-acetic acid (IAA) was higher in the difficult-to-defoliation line YAU11-818.

The degree of abscission zone and defoliation ability of +8 leaf sheaths at the maturity stage of sugarcane may be related to the activity of polygalacturonase, cellulase activity, peroxidase activity, ethylene synthesis precursors, abscisic acid, auxin content, etc., which can provide a reference for the identification of defoliation of sugarcane varieties.

Erianthus fulvus, serving as a crucial wild resource for sugarcane, is capable of enhancing the stress tolerance and yield of varieties. In order to utilize E. fulvus for sugarcane breeding, it is important to systematically identify and develop simple sequence repeat (SSR) loci in the E. fulvus genome, screen for polymorphic SSR markers, analyse the genetic diversity characteristics of E. fulvus resources and then develop SSR markers associated with important traits.

Using the SSRminer module in the software TBtools, a comprehensive exploration of SSR loci was conducted on the diploid E. fulvus whole genome sequence. The obtained data were statistically analyzed to reveal their distribution patterns and regularities within the genome. The Batch Target Region Primer Design function was employed for batch designing SSR primers, and the specificity of the primers was evaluated using the Primer check tool. To comparethe SSR polymorphism betweenE. fulvus and sugarcane, amplification experiments were performed on 50 pairs of randomly synthesized SSR primers and 14 pairs of SSR primers sourced from sugarcane across 6 E. fulvus germplasms.

A total of 152 707 SSR loci, which were distributed on E. fulvus genome with an average density of 5.64 kb/locus, were identified. The majority were located in intergenic regions. In terms of SSR type distribution, mononucleotide, dinucleotide, and trinucleotide had the highest density. Dinucleotide SSR types exhibited the greatest variation in motif repeat numbers, while pentanucleotide motif repeat variations were the least. Across the entire genome, 883 distinct SSR motif repeat types were identified, with A/T and AT/TA being the most abundant. A total of 144 692 pairs of SSR primers, of which 85 025 pairs exhibited high specificity, were designed. These specific primers displayed a distribution characteristic of dense ends and sparse middles on the genome. Amplification experiments showed that 42 out of the 50 randomly synthesized SSR primer pairs yielded stable and clear bands in E. fulvus, with 32 exhibiting polymorphisms, yielding a polymorphism rate of 64.0%. In contrast to the 14 sugarcane SSR primers, the E. fulvus SSR primers demonstrated superior amplification efficacy and greater polymorphism. After screening, 16 pairs of SSR primers with good polymorphism and clear amplification bands were determined from the 32 effective SSR primer pairs. These 16 pairs of primers amplified a total of 72 bands, with polymorphism information content (PIC) ranging from 0.63 to 0.83, and an average PIC value of 0.74, indicating their effectiveness and practicality in polymorphism analysis and molecular marker research of E. fulvus germplasm resources.

This study comprehensively identified SSR loci in the E. fulvus genome, revealing the high abundance and diversity of SSR distribution features. Sixteen pairs of highly specific and polymorphic SSR primers were successfully screened.