Comparative Study of Seed Characteristics of Itch Grass Populations in Chitradurga and Chikkaballapura Districts

Itch grass [Rottboellia cochinchinensis (Clayton)] is a highly invasive weed that infests major upland crops in Karnataka. A comparative study was conducted in Chikkaballapura and Chitradurga districts to characterize seed morphology, test weight and germination behaviour of itch grass populations under contrasting agro-ecological conditions. A total of 35 accessions were collected (20 from Chikkaballapura and 15 from Chitradurga) and evaluated using a BioVis image analyser and Leica microscope for seed traits, while germination was assessed through laboratory and greenhouse experiments. Results showed complete uniformity in seed coat colour within districts: golden-yellow in Chikkaballapura and light-yellow in Chitradurga. Seed shape was predominantly oblong, though ovate seeds were more frequent in Chitradurga (33.3%) compared to Chikkaballapura (20%). Seed length varied from 2.89 to 4.89 mm in Chikkaballapura (mean 3.87 mm) and 3.01 to 4.19 mm in Chitradurga (mean 3.52 mm), reflecting a 9.9% reduction in the latter. Similarly, seed width averaged 2.01 mm in Chikkaballapura and 1.74 mm in Chitradurga, showing 15.5% narrower seeds. Test weight ranged from 5.00–5.90 g in Chikkaballapura (mean 5.18 g) and 4.83–5.65 g in Chitradurga (mean 5.21 g), with heavier seeds generally linked to greater vigour. Despite pre-treatments and pot culture trials, no germination was observed, indicating strong innate dormancy. These findings highlight both conserved traits (seed colour, texture) and variable traits (size, shape, weight), underscoring the adaptive strategies of itch grass populations. The results provide baseline information for ecological studies and the design of location-specific management strategies.