Objective An insect-resistant and herbicide-tolerant transgenic inbred line to breed maize hybrid suitable for cultivation in southeast China was generated.

Methods Using the transgenic maize transformation system DBN9936 as donor and the elite inbred line MD823 as recipient, the target cry1Ab and EPSPS were introduced into MD823 through backcrossing combined with marker-assisted selection. After foreground and background selections as well as homozygous identification, the transgenic inbred line was obtained to subsequently develop the desired hybrid.

Results In backcross breeding, protein test strips and glyphosate tolerance were used co-select cry1Ab and EPSPS. After 5 generations of backcrossing followed by self-crossing for one generation, a MD823BC₅F₁ population was obtained. An indoor bioassay confirmed that the transgenic positive lines in the population were significantly resistant to Spodoptera frugiperda. In the control group, the moth larvae developed on the maize plants to an average instar of 5.67, with 55.6% reaching the 6^th instar or beyond with a pupation rate of 22.2%. In contrast, feeding on the transgenic positive line, larvae grew only to an average instar of 3.56–3.71, and none reached 6^th instar nor pupated with 22.2% early mortality. Forty SSR primer pairs were used to background select individual plants with high recovery rates in MD823BC₅F₁. After self-crossing and PCR identification, a homozygous transgenic MD823-Z line was secured and subsequently used as the male parent to breed Minyu 683-Z. The new hybrid was consistent with control on plant and ear morphologically and with Minyu 683 agronomically.

Conclusion The transgenic inbred line MD823-Z and the hybrid Minyu 683-Z were successfully obtained for breeding insect-resistant maize varieties suitable for farming in southeast China.