Seed weight grading improves germination and seedling growth and vigour in Khasi Mandarin (Citrus reticulata Blanco)

Abstract Seed weight is a critical factor influencing germination, seedling establishment, and subsequent crop development. Khasi Mandarin exhibits considerable variation in seed weight, and limited information is available on the effect of seed weight on germination and seedling performance. This study assesses the effects of seed grades on seed germination, seedling growth and vigour in Khasi Mandarin. Based on seed weight (SW), the individual seeds were categorised into three groups: Large Seed Weight (LSW), Medium Seed Weight (MSW), and Small Seed Weight (SSW). Seedling characteristics were assessed at 60, 90, and 120 days after sowing (DAS) through destructive sampling. Results showed that large seed weight reduced the days to germination (36.4 ± 2.29 DAS) compared to SSW and MSW. Similarly, LSW increased germination percentage (88.89 ± 2.11%), and pairwise comparisons showed that LSW had greater odds of germination than MSW (1.78-fold) and SSW (3.11-fold). Seedling characteristics were highest in LSW at 120 DAS, producing substantial increases in root characteristics, including root weight (fresh and dry) and number, and in plant growth (plant height, diameter, and dry weight). Chlorophyll index, leaf-specific weight, and seedling vigour index were also higher in seedlings raised from LSW at 120 DAS. Seed grading with large seed weight (≥ 0.81 g) is a critical determinant of germination, seedling growth, and vigour; therefore, it represents promising seed source for raising vigorous nursery seedlings of Khasi Mandarin.