Evaluation and Study of Yellow and White Onion Cultivars (Allium cepa L.) in the Climatic Conditions of Southern Kerman Province

Introduction Onion stands as one of the primary and extensively consumed vegetables at global scale, with numerous genotypes, both native and imported, being cultivated in the country annually. The southern provinces of the country have allocated about 50 percent of the cultivated area to onion cultivation. Therefore, selecting superior genotypes compatible with southern regions is essential to achieve maximum yield. Considering the long history of onion cultivation as one of the native plants of our country, there is a lot of genetic diversity in this plant. However, to date, inadequate breeding programs have been conducted to develop new, high-yield varieties in our country, leading most farmers to rely on local cultivars for cultivation. Therefore, it is necessary to design targeted breeding programs to produce new varieties superior in yield potential, flavor, aroma, resistance to pests and diseases, and other characteristics. In this regard, collecting diverse onion germplasm and evaluating genetic diversity in it is one of the basic steps for designing targeted breeding. The main purpose of this project is to evaluate genetic diversity in yellow and white onion cultivars in terms of morphological traits and selecting superior genotypes. The results of this project are a necessary prerequisite for long-term plans for the production of new varieties of onions.   Materials and Methods The research was carried out in the Faryab region, situated in the southern part of Kerman province. We assessed four commercial yellow onion hybrids- Rio Bravo, Soberana, Eiden, and Ascro Goldeneye -and four commercial white onion hybrids-Minerva, Cirrus, Macran, and 4043-using a 4x4 Latin square design during the 2022 growing season. Various observable traits, such as days to bulbing, days to maturity, onion bulb diameter, plant height and leaf length, fresh and dry plant weight, number of edible layers, fusarium infection percentage, and average tuber yield were recorded. To analyze the data, we used descriptive statistics to show the maximum, minimum, and average values of the traits, along with variance analysis, correlation analysis, and mean comparisons.   Results and Discussion The analysis of variance revealed significant variations across the measured traits. Within the yellow onion genotypes, Rio Bravo displayed the shortest maturity cycle, averaging 113 days to maturity, while Aiden exhibited the longest maturity duration with an average of 141 days. The Sobrana cultivar consistently outperformed other varieties across all investigated traits and was introduced as the best yellow onion cultivar. Bulb yield displayed strong and positive correlations with bulb diameter, bulb length, plant height, leaf length, number of edible layers, and both fresh and dry plant weight. However, the correlation between days to maturity and bulb yield was low, suggesting that the duration from planting to maturity did not affect the enhancement of bulb yield in yellow onions. The findings indicated that in contrast to yellow onion cultivars, white onion cultivars exhibited a longer average duration to bulb formation and maturity, alongside a lower bulb yield. Among the white onion genotypes, Minerva displayed the earliest maturity, while Cirrus was observed as the longest maturing genotype. Cirrus cultivar exhibited the highest average bulb diameter, bulb length, plant fresh weight, plant dry weight, leaf length, and bulb yield. Conversely, the Macran genotype displayed the lowest mean values for bulb diameter, bulb length, plant fresh weight, plant dry weight, and bulb yield. Additionally, a significant and strong positive relationship was observed among bulb diameter, bulb length, plant fresh weight, and plant dry weight. Typically, onion quality is often assessed based on bulb diameter, where larger bulb diameters tend to correspond with higher bulb yields. Evidently, both in yellow and white onion cultivars, those with higher yields also demonstrated larger bulb diameters.   Conclusion In the southern regions of Kerman province, the early maturity of onions is very important. Among the yellow onion genotypes, Rio Bravo was the earliest variety. The Soberana cultivar had a higher bulb yield compared to Rio Bravo, but it matured approximately twenty days later than Rio Bravo. Among the white varieties, Minerva was also the earliest maturing variety. However, the Cirrus cultivar had a higher bulb yield compared to Minerva. Yet, in comparison to Minerva, it was both later to mature and more susceptible to fusarium. The selection of onion varieties can significantly depend on the specific conditions of the region and the needs of the farmers. If timing and fusarium sensitivity are crucial factors for farmers, Minerva and Rio Bravo, with lower susceptibility to fusarium, might be suitable options. However, if bulb yield and product quality hold greater importance for farmers, Soberana among yellow onions and Cirrus among white onions are recommended. Additionally, considering breeding goals, these varieties can be utilized in onion breeding programs according to breeding objectives.