Yeast Extract Peptone Based Co-cultivation Media Promotes Transient GUS Expression in Tropical Maize Genotypes

Background and Objective: Tropical maize is the most cultivated crop in sub-Saharan Africa and is a staple food to over 220 million people. This study, evaluated the competence of four tropical maize (Zea mays L.) inbred lines to callus induction and regeneration through somatic embryogenesis when co-cultivated on yeast extract peptone medium (YEP). Materials and Methods: Transient GUS assay was used to evaluate the competence of the genotypes to Agrobacterium-mediated transformation using YEP as co-cultivation media or when YEP was supplemented with 2,4-D (YEP+2,4-D), cysteine (YEP+CYS), proline (YEP+PRO) or in combination (YEP+ALL). Data on all parameters were analyzed using multivariate ANOVA and SAS. Results: Co-cultivation media based on YEP alone did not impact callus induction and immature embryos exhibited preconscious germination. When YEP was supplemented with 2,4-D at concentrations 1.5 and 3 mg LG1 2,4-D, the formation of embryogenic calli was induced and regeneration initiated. Immature embryos had high transient GUS expression when co-cultivated with Agrobacterium on YEP, YEP+PRO and YEP+ALL media than when co-cultivated on MS media, suggesting that YEP promotes Agrobacterium-mediated integration of transgenes in tropical maize. Agrobacterium tumefaciens at a concentration of 0.07 (OD660) gave the highest transient GUS expression (20.90%) while concentrations of 0.8 and 0.2 resulted in low transient GUS expression (9.17 and 12.22%, respectively). Conclusion: The integration of YEP media in the Agrobacterium-mediated transformation protocols is likely to contribute in the development of a more efficient Agrobacterium-mediated transformation system for tropical maize genotypes.