Development of seedless watermelon (Citrullus lanatus (Thunb. Matsum. &Nakai) with improved fruit quality

Abstract

Watermelon (Citrullus lanatus) is a globally important cucurbitaceous crop valued for its sweet taste and nutritional content. Traditional diploid varieties contain numerous hard seeds that reduce consumer appeal, leading to the development of seedless watermelons through triploid breeding. Seedless types are increasingly popular due to their convenience and enhanced nutritional qualities, including higher levels of lycopene, β-carotene, citrulline, and vitamin C. They are widely preferred in domestic and international markets, often commanding a price premium. However, existing triploid seedless watermelon hybrids very often produce fruits with low TSS, false seeds, and hollow heart, which affects the quality. In this context, the present study, entitled “Development of seedless watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) with improved fruit quality,” was undertaken to develop superior quality triploid seedless watermelon hybrids and to assess the potential of diploid male lines in the development of triploid hybrids with improved fruit quality. The research work was carried out in three experiments, viz., introduction and evaluation of watermelon germplasm, development of triploid hybrids, and evaluation of F1 hybrids in the experimental field of the Department of Vegetable Science, College of Agriculture, Kerala Agricultural University, Vellanikkara, Thrissur, over three consecutive years (2022 – 2025), from November to March. In the first experiment, thirty-eight watermelon genotypes collected from different parts of the country were evaluated for various biometric, qualitative, and biochemical traits to identify genotypes with superior quality, yield, and earliness. Analysis of variance revealed that all the characters studied exhibited significant variation among the genotypes. The narrow gap between phenotypic and genotypic coefficient of variation (PCV and GCV) indicated that variability was mainly genetic, making the traits amenable to effective direct selection. High heritability coupled with moderate to high genetic advance as per cent of the mean (GAM) was observed for all traits, except days to first harvest and crop duration, indicating the predominance of additive gene action. Yield per plant showed significant positive correlations with fruit polar diameter (0.690), average fruit weight (0.639), length of main vine (0.473), duration of crop (0.388), fruits per plant (0.380), and fruit equatorial diameter (0.377), while it showed significant negative correlations with days to first male flower anthesis (-0.570), days to first female flower anthesis (-0.465), and node at which first female flower emerged (-0.349). Path analysis revealed that duration of the crop (0.339) had the highest direct positive effect on yield per plant, followed by fruit polar diameter (0.289), average fruit weight (0.195), fruit equatorial diameter (0.189), fruits per plant (0.132), and length of main vine (0.0.067). Twenty superior diploid watermelon genotypes were identified through cumulative scoring for yield and quality traits, including TSS, total sugars, pulp firmness, Vitamin C, citrulline, earliness, and yield per plant. The lines, such as AHW/BR-22 (T21), CL-17 (T12), Arka Shyama (T1), AHW/BR-43 (T27), Crimson Sweet (T10), Arka Manik (T4), CL-19 (T14), CL-9 (T30), CL-12 (T33), Arka Muthu (T8), CL-8 (T29), AHW/BR-40 (T26), CL-14 (T35), CL-10 (T31), AHW/BR-37 (T25), AHW/BR-25 (T23), CL-12 (T32), Asahi Yamato (T6), CL-7 (T28), and CL-6 (T11), showed desirable combinations of quality and productivity and were identified as promising male parents for triploid hybrid development. In the second experiment, the identified diploid parents were crossed with the stable tetraploid female line, KAU-CL-TETRA-1, developed by Kerala Agricultural University in a top cross fashion. The highest fruit set percentage (85 %) and number of seeds per fruit (291.60) were observed in the top cross C9 (KAU-CL-TETRA-1 × CL-17). In the third experiment, twenty newly developed triploid F1 hybrids, along with two standard checks (Shonima and Swarna) and all the parental lines (the tetraploid female line, KAU-CL-TETRA-1, and the diploid male lines of hybrids and checks) used in the breeding programme, were evaluated in a Randomized Block Design (RBD) with three replications. Analysis of variance revealed significant differences among the F1 hybrids and parents for all the biometric and biochemical traits observed. The analysis of general combining ability (GCA) effects for biometric and biochemical traits revealed significant variation among parental genotypes. The diploid lines Arka Shyama, CL-17, AHW/BR-22, AHW/BR-43, Arka Manik, Crimson Sweet, and Arka Muthu were identified as good general combiners for various fruit quality and yield traits. Heterosis values were estimated over mid-parent, better parent, and standard checks, Shonima and Swarna. The triploid seedless hybrids KAU-CL-TETRA-1 × Arka Shyama, KAU-CL-TETRA-1 × CL-17 (orange fleshed), KAU-CL-TETRA-1 × Arka Muthu, KAU-CL-TETRA-1 × AHW/BR-43, KAU-CL-TETRA-1 × Crimson Sweet, KAU-CL-TETRA-1 × AHW/BR-22, KAU-CL-TETRA-1 × Arka Manik, and KAU CL-TETRA-1 × AHW/BR-37 were found to have superior performance over the standard checks across multiple desirable quality traits. These hybrids also expressed low physiological abnormalities. The study also revealed that pollen parent variation significantly influenced the flesh colour expression in triploid hybrids, underscoring the paternal role in carotenoid accumulation and pigmentation. The orange and yellow colour of male parents was found to have a dominant effect on the red flesh of the tetraploid female line. Notably, the development of the first orange-fleshed seedless triploid hybrid (KAU-CL-TETRA 1 × CL–17) from the public sector in India marks a pioneering achievement. The study highlights the potential of triploid seedless watermelon hybrids in combining seedlessness with improved fruit quality and enhanced nutritional attributes. These findings lay a foundation for the commercial exploitation of hybrid vigour and emphasize the need for replicated and multilocational testing. The performance of these hybrids under protected cultivation needs to be evaluated. The potential of diploid pollinizers on these newly developed sterile triploid watermelon hybrids warrants further study.