Comparative Evaluation of Onion Germplasm (Allium Cepa L.) Of Bangladesh for Physical And Antioxidant Properties

Determination of antioxidant activity is one of the key elements for understanding the biological properties of a widely used spice onion (A. cepa). In contrast, physical properties help understand the textural quality of onion necessary for postharvest operations of sorting and grading in particular. Considering the physicochemical importance of onion, the present study focused on the determination of physical attributes and antioxidant content of the onion germplasm in Bangladesh using visual methods and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, respectively. The five-onion germplasms (BARI Piaz-2, BARI Piaz-3, BARI Piaz-4, BARI Piaz-5, Faridpuri Vati) collected from selected onion growers of the Department of Agricultural Extension (DAE) of the southwestern part of Bangladesh were used as treatments for physicochemical analysis at the Horticulture laboratory of the Agrotechnology Discipline, Khulna University, Khulna, Bangladesh during the period from February to August 2019. The laboratory study was laid out in Completely Randomized Design (CRD) with three replications. Most of the physical characteristics of onion were highest in germplasm-1 than those of the other germplasm tested. The results showed that the DPPH free radicals were scavenged by all onion germplasm extracts in a concentration-dependent pattern. The highest IC50 value (238.10 ppm) was noticed in germplasm-3 and the lowest in germplasm-5 (161.29 ppm) with no statistical difference from germplasm-4 (172.41 ppm). The lower IC50 value indicating that onion germplasms-5 and -4 extracts were more potent in scavenging free radicals than the other onion germplasms. Thus, the low IC50 value facilitated the germplasm-5 and -4 to be enriched with antioxidant compounds significantly in higher amounts than the others. SAARC J. Agric., 19(1): 113-123 (2021)

Genetic diversity of tropical-adapted onion germplasm assessed by RAPD markers

Onion is a crop of significant socioeconomic importance to Brazil. Onion germplasm with adaptation to tropical and sub-tropical conditions has played an important role in the development of this crop in the country. In this context, we studied the genetic diversity in a germplasm collection potentially useful for the development of cultivars for tropical and subtropical regions. The genetic variability of 21 accessions/cultivars that have been used as germplasm and/or were developed by onion breeding programs in Brazil was evaluated via RAPD markers. The following accessions were included in the study :'Red Creole', 'Roxa IPA-3', 'Valenciana 14', 'Beta Cristal', 'Diamante', 'Composto IPA-6', 'Aurora', 'Bojuda Rio Grande', 'Alfa Tropical', 'Pêra IPA-4', 'Primavera', 'Belém IPA-9', 'Crioula Alto Vale', 'Conquista', 'Pira-Ouro', 'Vale-Ouro IPA-11', 'Franciscana IPA-10', 'Serrana', 'CNPH 6400', 'Petroline', and 'Baia Periforme'. From the 520 primers used in the initial screening only 38 displayed stable polymorphisms. They produced 624 amplicons, of which 522 (83.7%) were monomorphic and 102 (16.3%) were polymorphic. An average similarity coefficient of 0.72 was calculated among accessions based upon this subgroup of polymorphic amplicons. This allowed the discrimination of this germplasm collection into six groups with only one of them comprising more than one accession. The main group was formed by 16 accessions ('Diamante', 'Composto IPA-6', 'Aurora', 'Bojuda Rio Grande', 'Conquista', 'Pira-Ouro', 'Serrana', 'Vale-Ouro IPA-11', 'Baia Periforme', 'Primavera', 'Franciscana IPA-10', 'Belém IPA-9', 'Crioula Alto Vale', 'Petroline', 'Pêra IPA-4' and 'Alfa Tropical'), for which the genetic origin (with few exceptions) can be traced back to the variety 'Baia Periforme'. The populations 'Red Creole', 'Roxa IPA-3', 'Beta Cristal', 'CNPH 6400', and 'Valenciana 14' comprised a set of five isolated groups, showing genetic divergence among them and in relation to main 'Baia Periforme' group. This germplasm displayed a relatively low genetic diversity, with the predominance of materials originated from the base population 'Baia Periforme'. There are, however, some accessions, which can add genetic diversity to this germplasm and they can be exploited by onion breeding programs aiming to develop cultivars for tropical regions of the world.

040 Pedigree of Publicly Released Onion Germplasm in the United States, 1931-1997

Since the 1930s, more than 130 inbred lines and 60 hybrid cultivars of onion have been released in the public sector in the United States. Other than breeder's reports from the period 1946-1965 and anecdotal information kept by onion workers, no systematic treatment of the pedigree of public onion germplasm releases has been developed. The objective of this research was to collect, characterize, and display the genetic relationships among more than 200 public onion germplasm sources used in the United States since 1931. Pedigree information revealed that most modern onion cultivars in the United States descend from a few open-pollinated populations brought to this country by immigrants. For example, selection in the open-pollinated populations Common Yellow and Silverskin by onion farmers in the eastern U.S. resulted in the formation of Yellow Globe Danvers, which was a precursor to virtually all Eastern storage onion germplasm in the U.S. Open-pollinated populations such Yellow Globe Danvers, Valencia, Sweet Spanish, Bermuda, and Grano formed the foundation germplasm for the first public U.S. onion breeding programs. Findings from this study suggest a relatively narrow germplasm base of public onion germplasm in the United States; however, this narrow pool coexists alongside significant gains through scientific breeding efforts, particularly during the past 75 years.

SCREENING WORLD ONION GERMPLASM COLLECTION AND COMMERCIAL CULTIVARS FOR RESISTANCE TO SMUT

Two hundred and fifty-five accessions to the USDA world onion germplasm collection and 66 commercial cultivars of Allium cepa were screened for resistance to Urocystis magica, the causal agent of onion smut. The trial was conducted in Cloverdale, British Columbia on a muck soil heavily infested with U. magica. Percent smut infection in bulbs at harvest was measured and significant differences (P = 0.01) among the accessions and cultivars occurred. Three plant introduction lines and one commercial cultivar were completely resistant to U. magica in the trial and significant levels of resistance were found in six other plant introduction lines and one commercial cultivar.

SCREENING WORLD ONION GERMPLASM COLLECTION FOR RESISTANCE TO WHITE ROT

Two hundred and ninety-four accessions to the USDA world germplasm collection of Allium cepa were screened for resistance to Sclerotium cepivorum, the causal agent of white rot. The trial was conducted on organic muck soil in Burnaby, British Columbia, with uniformly high levels of added inoculum. Percent white rot infection in bulbs at harvest was measured and significant differences (P = 0.05) among the accessions occurred. High levels of resistance were found in at least three of the accessions, but none was immune.