ABSTRACT C. nutans , a highly advantageous forage grass on the Western Sichuan Plateau, remains poorly studied in terms of its chromosomal structural diversity in this region. The genomic and chromosomal organization of C. nutans was investigated using GISH and ND‐FISH with four oligonucleotide probes. The results showed that repetitive sequence distribution exhibited genome‐specific patterns: the H genome demonstrated high structural stability with low polymorphism, while the St genome showed moderate variation, and the Y genome displayed the highest polymorphism, with chromosomes 1Y, 2Y, and 7Y identified as variation hotspots. Signal density and polymorphism varied with altitude; the materials from middle and low altitudes exhibited relatively higher genetic polymorphism. Notably, (AAG) 10 and (GAA) 7 probes revealed altitudinal trends, with signal abundance peaking at mid‐elevations before declining at higher altitudes. 5S rDNA and pAs1 distributions further highlighted conserved loci alongside altitude‐dependent polymorphisms. Karyotypic analysis based on probe combinations confirmed uneven intragenomic variation, with 3H, 1St/3St, and 1Y/7Y showing the highest diversity. These findings underscore the differential genome plasticity in C. nutans , with the Y genome being the most dynamic, possibly as an adaptive response to environmental gradients. The study provides insights into the evolutionary mechanisms and altitude‐driven genomic diversification in polyploid grasses.
Yang et al. (Tue,) studied this question.