Corresponding author: Eltohamy A. A. Yousef, E-mail: tohamyy@yahoo.com, Tel. 01028554522 (Received 06/10/2022, accepted 13/01/2023) DOI: 10.21608/EJOH.2023.167396.1216 ©2023 National Information and Documentation Centre (NIDOC) S UMMER squash seed yield and quality can be improved by the application of boron (B) and fruit set-order, which might affect fertilization and pollination. Two feld experiments were performed during the summer seasons of 2021 and 2022 to investigate the effects of foliar application of boron at levels of 0, 25, and 50 ppm for two times (after 45 and 60 days from the planting date) and different fruit-set orders on seed yield, yield components and quality in summer squash of two genotypes, Shmamy and Cope. The twelve treatments were arranged in a randomized complete block design (RCBD) with a split plot arrangement with three replicates. The results of the current study revealed that foliar application of B at 50 ppm improved seed yield components, such as fruit weight, seed weight per fruit and the number of seeds per fruit, leading to a signifcant increase in total seed yield in the two studied genotypes of summer squash. Also, the B application at 50 ppm increased the seed quality parameters, oil content, crude protein content and total antioxidant activity in both genotypes during the two seasons. In addition, this research revealed that fruit-set order had a signifcant effect on total seed yield, seed yield components and seed quality. Whereas, the fruits in 2 nd and 3 rd order have achieved the highest means of all seed yield components, total seed yield and seed quality parameters in both studied genotypes and during both seasons, compared to the fruits in 1 st and 4 th order. In light of current results, it would be recommended that applying B at 50 ppm as a foliar spray treatment and keep the fruits in second or third order to improve the total seed yield and seed quality of summer squash plants. Keywords: Cucurbita pepo L., Boric acid, Fruit position, Seed weight/fruit, Seed number/fruit, crude protein, Oil content, Antioxidant. Effect of Boron Foliar Application and Different Fruit-set Orders on Summer Squash Seed Yield and Quality Eltohamy A. A. Yousef and Ibrahim N. Nasef Department of Horticulture, Faculty of Agriculture, Suez Canal University, Ismailia, Egypt. Egypt. J. Hort. Vol. 50, No. 1, pp. 85-95 (2023) Egyptian Journal of Horticulture https://ejoh.journals.ekb.eg/ 7 Introduction Squash (Cucurbita pepo L.) is one of the most popular vegetable crops in the world. Normally, the edible part is the fruit. However, consumption of squash seeds has recently received considerable attention in the human diet because of its high nutritional and health-protective value. Squash seeds contain several bioactive functional constituents of lipids, proteins, fbers, thiamin, niacin and micronutrients (Rubatzky and Yamaguchi, 1999, Rezig et al., 2012 and Gomes et al., 2022). It is also an extraordinarily rich source for oil, which is being used as an active ingredient in cosmetics, foods and nutraceuticals (Yadav et al., 2010). Recently, several epidemiological studies have highlighted the health benefts of squash oil against several chronic diseases, including hypertension, diabetes, low density cholesterol and several types of cancer and it also shows antibacterial and anti-infammatory properties (Stevenson et al., 2007, Rabrenovic et al., 2014, Gutierrez, 2016 and Majid et al., 2020). These health benefts of squash oil seeds are attributed to their high content of proteins, polyunsaturated fatty acids, antioxidative phenolic compounds, carotenoids and minerals