In maize, hybrid vigour is exploited by:
(a) bombarding the seeds with DNA
(b) crossing of two inbred parental lines
(c) harvesting seeds from the most productive plants
(d) inducing mutations
(b) Hybrid varieties were first developed in maize, which is a cross-pollinated crop. In such crops, the parents of hybrid varieties are ordinarily, inbred lines. An inbred line is a nearly homozygous line produced by continuous inbreeding in a cross-pollinated crop and is maintained by strict inbreeding. In maize, hybrid vigour or heterosis is exploited by the crossing of two inbred parental lines.