Performance of seedless and sparse-seeded mutants in sweet orange and mandarin genotypes induced through Gamma-irradiation mutagenesis

Abstract

Citrus fruits, a globally significant crop, face consumer and processing challenges due to the presence of seed. Conventional breeding
methods to develop seedless varieties are time-consuming and often unsuccessful due to the complex genetic nature of citrus. This study
explores the potential of gamma-irradiation mutagenesis in producing seedless or sparsely-seeded mutants. Dormant budwoods of sweet
orange cv. Mosambi (Tm-33), Kinnow, and Nagpur mandarin (N-4 and N-74) were irradiated with gamma doses (5–40 Gy) and grafted
onto rough lemon rootstocks. Observations were recorded from mutant generations (MV2) and analyzed over two seasons. Significant
variations in fruit weight, size, rind thickness, juice content, and total soluble solids (TSS) were observed. On average, the physical
parameters of the fruit, such as weight, length, diameter, axis diameter, and rind thickness, were found to be inversely proportional to
increasing doses of gamma-irradiation. Notably, a sweet orange mutant (Tm33-5-B2R2-P01) exhibited reduced seed count (3.67 seeds/
fruit) with satisfactory TSS (9.70°Brix) compared to the parent (12.25 seeds/fruit). Kinnow mandarin mutant KM-40-B2R1-P19 showed
the lowest seed count (1.50 seeds/fruit) and good TSS (9.03°Brix) compared to the parent (14.75 seeds/fruit). Nagpur mandarin mutant
N4-5-B3R1-P05 was identified as seedless (0 seeds/fruit), maintaining favorable TSS (10.07°Brix) compared to parent (12.23 seeds/fruit).
The results demonstrate the potential of gamma-irradiation in citrus breeding to meet consumer demands for quality seedless fruits.