Identification of cytoplasm type and nuclear Ms gene in onion cultivars

Open-pollinated onion cultivars predominate in the southern region of Brazil, due to their higher adaptability to local climatic conditions, unlike commercial hybrids, which have shown a lower adaptability. Cytoplasmic male sterility (CMS) systems are employed to develop hybrid onion cultivars. Two molecular markers, 5’cob and orfA501, were used to differentiate the cytoplasm type, and the AcSKP1 marker to identify the nuclear male fertility-restoring locus (Ms). A total of 1,126 plants from the most common onion cultivars grown in southern Brazil, including Bola Precoce®, Crioula®, Valessul®, Mega®, Joia® and Princesa do Sul®, were analyzed using all the three markers. An extremely rare occurrence of the S cytoplasm was observed among the cultivars, being detected in only 1.8 % of the samples, while the T cytoplasm was the most prevalent, accounting for 56.3 % of the samples. Among the 1,126 plants analyzed, only three exhibited the S cytoplasm and were recessive for the Ms-locus (Smsms). Additionally, 49 plants with the N-cytoplasm (as per the Engelke’s classification) and recessive for the nuclear genotype (Nmsms) were identified, 45 of which were pollen producers. The male-fertility restoration occurred in 22.2 % of the crosses between Tmsms male-sterile plants and male-fertile N cytoplasmic-msms plants (as per the Engelke’s classification).