Evaluation of flowering characteristics, bulb yield and quality in commercial cultivars of short-day onion (Allium sepa L.)

Background and objectives: Genetic diversity and knowledge of the yield potential, quality characteristics and onion flowering and relationship between traits will help the researcher to consider important traits in breeding programs and advancing generations to achieve the maximum bulb and seed yield. In order to produce a quality product and have a uniform farm in accordance with the technical principles of cultivation, it is necessary to know the characteristics of onion flowering and the relationships between traits. In fact, obtaining acceptable amounts of seeds is only possible based on having sufficient information about the flowering of this plant. The genotypes investigated in this research are a part of the onion breeding project which is still ongoing in order to obtain open-pollinated cultivars of short-day onion. Therefore, identifying the flowering characteristics of genotypes is very important. This research was carried out in order to investigate and compare the bulb yield potential, quality and flowering characteristics of nine short-day onion genotypes and to study the relationships between flowering traits.

Materials and Methods: In this research, nine short day onion genotypes (including eight hybrids: Sahar, Paliz, Saba, Savanah Sweet, Golden Eye, Duster, Imperatriz, Primavera and the open-pollinated cultivar Texas Early Grano) was performed for bulb yield and flowering traits during three growing years 2018-2021. In the two first year, the genotypes bulb characters was evaluated in Isfahan and Khuzestan locations and in the third year, the flowering characteristics of genotypes (Number of flower stalks/plant in three stages intervals of 10 days from each other, Number of open flower stalks/plant in three stages intervals of 10 days from each other, Number of open flower stalks/plant,Seed harvest day, 1000 seed weight, Seed yield/inflorescence, Seed yield/plant) were compared with each other in a randomized complete block design experiment with three replications. Variance analysis and average comparison was performed using Duncan's method at a probability level of 5%. Correlation analysis between traits and cluster analysis were performed on the average of repetitions. All statistical calculations were done with SAS 9.2 software.

Results: The comparison results of the bulb yields showed that in both locations, with significant difference, the commercial hybrids Saba, Savannah Sweet and the open-pollinated variety Texas Early Grano were the highest, and Sahar and Paliz cultivars were the lowest for bulb yield. The highest and lowest seed yield belonged to Saba and Paliz cultivars, respectively. Correlation between flowering traits showed that 1000 seed weight had a significant positive relationship at the 5% level with seed yield and a significant negative relationship with number of flower stalks/plant. Seed harvest day did not show any correlation with none of the traits. The results of this study showed that Saba with the highest bulb yield, the highest number of flower stalks/plant and the highest 1000 seed weight, has the highest seed yield in inflorescences and in plant and Paliz with low bulb yield and the lowest 1000 seed weight, has the lowest seed yield in inflorescences and in plant. For seed harvesting day, Paliz and Primavera were the earliest and Imperatriz and Texas were the latest.

Conclusion: According to the results of bulb traits evaluation in two years and in two locations, the traits were not affected by year effect, which was mainly due to relatively stable weather conditions in the experiment two years. Bulb yield in both years in Khuzestan was significantly higher than in Isfahan, which is due to the long growth period in Khuzestan location.