Genetic Variation in Sorghum for the Inhibition of Maize Pollen Tube Growth

Aniline blue fluorescence was used to study the growth of maize pollen tubes in the stigmas of 13 diverse sorghum accessions. In 12, only short maize pollen tubes were formed, but in the single exception (Sorghum nervosum Nr481) maize pollen tubes grew at least as far as the base of the style. The S. bicolor genotypes S9B and CMS (a cytoplasmic male sterile line) were hybridized with Nr481, and analysis of maize pollen tube growth in F1 plants, and BC1 plants using Nr481 as the recurrent parent, suggested that differences in inhibition of pollen tube growth were due to variation at a single locus, which we propose to designate lap (Inhibition of alien pollen tubes). Accession Nr481 appears to be homozygous for a recessive allele permitting maize pollen tube growth. Attempts were made to produce sorghum x maize hybrids using Nr481 and CMS derivatives which were known to allow maize pollen tube growth to the base of the style. A putative hybrid endosperm was obtained in one Nr481 × Seneca 60 maize cross, but this was not repeatable and no hybrid plants were produced. A fundamental problem may be the large size of the maize pollen tube, which could have difficulty growing through the sorghum ovary and in entering the micropyle.