MATURE SEED-DERIVED REGENERATION AND IN PLANTA TRANSFORMATION OF TROPICAL MAIZE (ZEA MAYS L.)

Abstract

Maize (Zea mays L.) is an important cereal crop, but the application of genetic transformation in tropical germplasm is constrained by genotype-dependent regeneration and the limited availability of suitable explants. The present study evaluated mature seed-derived split internodes as an alternative explant source for plant regeneration and investigated Agrobacterium tumefaciens-mediated transformation in tropical maize genotypes. Six maize genotypes were evaluated for regeneration efficiency based on plantlet production, shoot and root development, and survival after acclimatization. Agrobacterium-mediated transformation was evaluated using sonication-assisted and conventional infection treatments, while transformation was assessed by histochemical GUS staining and PCR amplification of the bar and gus genes. Significant variation in regeneration response was observed among genotypes. HKI-161 showed the highest regeneration efficiency, producing 4.4 ± 0.3 plantlets per explant, whereas Pusa HQPM1 showed the highest survival rate (92%). Sonication-assisted Agrobacterium infection enhanced transient GUS expression compared with conventional infection, with 45 s sonication producing the highest response in most genotypes. HKI-161 showed the highest GUS-positive frequency (26.7%), while PCR analysis detected the expected bar and gus amplification products in selected seedlings, with a maximum putative transformation frequency of 6.7%. Overall, the results demonstrate that mature seed-derived tissues can provide a practical alternative to immature embryos for regeneration of tropical maize and indicate that sonication-assisted Agrobacterium infection can improve gene delivery into germinating seedlings. HKI-161 was identified as the most responsive genotype and may provide useful material for further transformation and genome-editing studies in tropical maize.