Watermelon is a crucial horticultural crop worldwide but its genetic base has become extremely narrow owing to long-term cultivation. Induced mutagenesis can create a range of variations with distinctive agricultural characteristics. To broaden the genetic diversity of watermelon, we established a mutagenesis library containing over 4000 M
1 seeds from an inbred line ‘M08’, which was irradiated by 350 Gy of
60Co γ-rays for 3 h. The rates of germination, emergence, and survival of the M
1 seeds were reduced by 5.88%, 18.66%, and 41.96%, respectively. After phenotypic screening, 20 and 10 types of morphological changes were observed in the M
1 and M
2 generations, with approximately 10.57% and 14.17% mutation frequencies, respectively. Six mutants with desirable horticultural alterations were selected for additional presentation, including the leaf color mutant C
1-NO.1, the yellow peel mutant C
1-NO.2, the pericarp thickening mutant C
1-NO.3, the pericarp thinning mutant C
1-NO.4, the seedless mutant C
1-NO.5, and the C
2-No.1 mutant with normal female flowers and malformed male flowers. Moreover, the three mutants M
1-3, M
2-1, and M
1-5 were identified from our EMS-induced M
2 library, exhibiting the fusiform fruit, the dark green peel, and the yellow leaves, respectively. Compared to the wild type (WT), the photosynthetic pigments and parameters were negatively impacted in the yellow-leaf mutant M
1-5. For example, the total chlorophyll was 1.22 and 2.22 mg/g in the young and mature leaves of M
1-5, respectively, which were significantly lower than those in the WT (2.58 and 2.90 mg/g, respectively). Notably, some mutagenesis phenotypes could be stably inherited, including traits such as yellow leaf color, fusiform fruit shape, and thickening and thinning pericarp. Taken together, these results indicate that these two mutant libraries serve as essential resources to discover new phenotypic germplasms, thereby facilitating the genetic breeding and functional gene exploration in watermelon.
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