Allium cytogenetics: a critical review on the Indian taxa

The genus Allium Linnaeus, 1753 (tribe Allieae) contains about 800 species worldwide of which almost 38 species are reported in India, including the globally important crops (onion, garlic, leek, shallot) and many wild species. A satisfactory chromosomal catalogue ofAllium species is missing which has been considered in the review for the species occurring in India. The most prominent base number is x=8, with few records of x=7, 10, 11. The genome size has sufficient clues for divergence, ranging from 7.8 pg/1C to 30.0 pg/1C in diploid and 15.16 pg/1C to 41.78 pg/1C in polyploid species. Although the karyotypes are seemingly dominated by metacentrics, substantial variation in nucleolus organizing regions (NORs) is noteworthy. The chromosomal rearrangement between A. cepa Linnaeus, 1753 and its allied species has paved way to appreciate genomic evolution within Allium. The presence of a unique telomere sequence and its conser-vation in Allium sets this genus apart from all other Amaryllids and supports monophyletic origin. Any cytogenetic investigation regarding NOR variability, telomere sequence and genome size in the Indian species becomes the most promising field to decipher chromosome evolution against the background of species diversity and evolution, especially in the Indian subcontinent.

Automated summary

The genus Allium, which includes important crops and wild species, consists of about 800 species worldwide, with 38 species reported in India. A comprehensive chromosomal catalogue of Allium species is still lacking, but this review focuses on the species found in India. The most common base number is x=8, with some records of x=7, 10, 11. Genome size varies from 7.8 pg/1C to 30.0 pg/1C in diploid species and 15.16 pg/1C to 41.78 pg/1C in polyploid species. The variation in nucleolus organizing regions (NORs) is significant, and the chromosomal rearrangement between A. cepa and its allied species provides insights into genomic evolution within Allium. The unique telomere sequence in Allium distinguishes it from other Amaryllidaceae and supports its monophyletic origin. Cytogenetic research on NOR variability, telomere sequence, and genome size in Indian species is crucial for understanding chromosome evolution in the context of species diversity and evolution, particularly in India.