Molecular variation and F-1 performance among strains of the sweet corn inbred P39

Some maize (Zea mays L.) inbreds produce morphological variants at unexpect edly high frequencies. In some cases, heterosis has been observed in crosse s between variants and the progenitor inbred. Causes of such variants and r esulting heterosis are unclear. Unique materials for addressing these quest ions me strains of the sweet corn inbred P39, Several morphologically disti nct strains of P39 have been identified. Molecular variation of P39 strains was analyzed by means of three types of molecular markers, including four probes that hybridize to multiple sequences, 78 single copy restriction fra gment length polymorphisms (RFLP), and 671 amplified fragment length polymo rphisms (AFLP). All crosses were made among seven P39 strains. Ear weight a nd plant and ear height of the crosses were measured in 2 yr with one locat ion and eight replications per year. Ten-ear weight ranged from 0.49 to 0.8 4 kg. Significant levels of molecular variation were observed among the str ains. Summing polymorphisms per inbred pair over the multiple sequence prob es resulted in a range among pairwise comparisons of 0 to 18. RFLPs ranged from 6 (7%) to 28 (35%) polymorphisms per inbred pair. AFLPs between inbred pairs ranged from 3 (0.5%) to 145 (22%). Ten-ear weight was correlated wit h the number of polymorphisms between pairs of strains for the multiple cop y probes. RFLP variation was correlated with plant height (r = 0.75**) and ear height (r = 0.91**) but not ear weight. AFLP variation was correlated w ith ear weight (r = 0.82**). While initial isolation of some of the P39 str ains was due to a mutation at a single gene, the amount of molecular variat ion was unexpectedly high. The molecular variation and changes in combining ability indicates the occurrence of alterations throughout the genome.