Removing secondary branch to produce commodity watermelons is labor-costing and time-consuming work in traditional watermelon cultivation. Moreover, because elderly farmers work for a long time with their backs bent, musculoskeletal disorders reduce the quality of life of farmers. To improve this working condition, we developed the watermelon 'Soonless' variety that does not need to be pruned because there is no secondary branch. For diploid oval watermelons, the stripe width of the fruit is wide, the color of it's skin is green, and the flesh is pinkish-red. It contains 480 seeds of ‘Soonless’, and the fruit weight is 8.6 kg, which is heavier compared to ‘Sambokggul’. The thickness of the pericarp is 1.3 cm, and the total soluble solids content is 12.0 °Bx, which is similar to ‘Sambokggul’. The characteristics which distinguish it from the control variety include the leaf blade length and width, the ovary size, the width of the fruit stripes, and the thickness of the pericarp. The yield was 6,450 kg/10a, an increase of 5.3% compared to ‘Sambokggul’. As a result of this research, ‘Soonless’ has been registered as a variety with the Korea Seed and Varieties Service in 2022 as it was filed for breed protection in 2019 (Registration No. 8808).

Watermelons are grafted to prevent soil-borne diseases such as Fusarium wilt (FW) and increase their resistance to abiotic stress. Root-knot nematodes (RKN) are a contributing factor to economic loss in several cucurbits, including watermelon. Growing resistance varieties is an effective way to reduce the damage caused by soil-borne diseases. Resistance evaluation was performed on 50 watermelon lines to select rootstocks resistant to FW and RKN. Fusarium oxysporum f. sp. niveum race 2 was inoculated into 10-day-old seedlings using a root dipping method, and resistance was evaluated for four weeks. The 37-day-old watermelon seedlings were inoculated with Meloidogyne incognita and evaluated 60 days later. Three lines (IT199860, PI296341-6, and PI532811) were resistant to FW race 2, while one line (PI494527) was moderately resistant. Three lines (PI296341-5, PI457916-2, and PI457916-5) were RKN resistant. The PI296341-6 line was selected for its resistance to FW and moderate resistance to RKN. These findings imply that the identified resistant lines can be used in rootstock breeding programs against FW and/or RKN.

Fusarium wilt is a serious disease that causes damping-off, serious wilt symptoms, or death in melon. The aim of this study was to evaluate the resistance of melon germplasm to Fusarium wilt and select promising disease-resistant accessions for further applications. Resistance to Fusarium wilt was examined in 216 melon germplasms by the root-dipping inoculation method with Fusarium oxysporum f. sp. melonis fungal isolate KACC43206 (race 2). Inoculated seedlings were incubated for four weeks and assessed for disease symptoms using indices ranging from index 1 (no symptoms) to 5 (plant wither). A total of 34 accessions showed a disease index < 2.0. Disease indices of 10 accessions were 1.0 four weeks after inoculation. The resistant accessions of melon are expected to help in breeding commercial varieties with Fusarium wilt resistance.

In this study, watermelon accessions introduced from the USDA were characterized for 12 morphological characteristics of leaf, flower, fruit, and seed, according to the National Agrobiodiversity Center descriptor list. In addition, to confirm the genetic composition of each watermelon accession, genetic profiling was performed using 20 simple sequence repeat (SSR) markers. A total of 154 watermelon accessions from the USDA were collected from 31 different countries, among which, 12.3% (19 accessions) were from Turkey. Morphological characterization revealed that the accessions displayed a large diversity. Genetic profiling using 20 SSR markers showed that six accessions (K192117, K192028, K193400, K192376, K192499, and K192800) were expected to be inbred lines among the 154 watermelon accessions. The 12 characters scored were analyzed using discriminant analysis of principal components (DAPC). The result revealed 68.1% of the total variability and indicated variations among accessions, mainly based on fruit stripes and fruit shape along the longitudinal section. The accessions were divided into eight groups according to DAPC, although the geographical origin was not a great source for the grouping. Our results will be helpful for the efficient management of germplasms and in understanding and selecting watermelon accessions for the breeding process.