Increasing Seed Viability of Maize Haploid Inducing Lines by Genetic and Non-Genetic Approaches

Some haploid inducing lines used in the production of maize doubled haploids (DHs) express germination problems and reduced vigor. In this study, two reciprocal F 1 populations of the haploid inducing lines RWS and RWK-76 were examined for viability by Tetrazolium (TZ) and germination ability by standard germination tests. Evaluation based on TZ tests showed that 59% of the seed of RWK-76/RWS were not viable, compared with only 12% dead seed in RWS/RWK-76. Similarly, the total germination and speed of germination in RWK-76/RWS (25%, 1.53) was lower than for RWS/RWK76 (74%, 4.30). In an effort to develop a quick method for assessing seed viability in these lines, the TZ test was repeated in a different way. Seed from each genotype was placed in beakers containing distilled water. Seed would either float or sink. Subsequent TZ testing confirmed that seed that floated was dead, and seed that sank was alive, although some of them had defective embryos. The dead seed in both genotypes failed to develop an embryo, leaving an empty cavity that would fill with air and cause seed to float on water. This feature can be exploited for a simple and practical method to separate living from dead seed. In addition, we surveyed the ig1 (indeterminate gametophyte) gene as a candidate for germination problems in inducer lines. Sequencing data from the ig1 region showed that RWS and RWK-76 differed in one nucleotide and amino acid in the first exon of ig1. Segregation of ig1 alleles from RWS and RWK-76 was significantly (P <= 0.01) distorted in the respective F 2 population relative to the expected Mendelian segregation ratio (1:2:1). Thus, either ig1 or a linked gene in the ig1 region affected seed viability.