The effect of forced shedding on pollen traits, seedsetting, and transmission at various Maize (Zea mays L.) endosperm mutant loci

Under field conditions, attached maize tassels shed pollen daily between 800-1200 h with all or most of the pollen grains in the tassel released in 7-10 days. Detached tassels with their cut ends submerged in water and exposed to low light intensity, high humidity, and 25-30 °C, shed pollen continuously with all or most of the pollen grains in the tassel released in three days. After cutting at I600h on day 0, pollen grains from 15 detached tassels from three heterozygous (Wx wx, Su su, Sh2 sh2) populations at the waxy, sugary-1, and shrunken-2 loci, were collected at the end of eight collection periods (A = 1600 h, day 0-1000 h, day 1; B = 1000 h, day 1-1600 h, day 1; C = 1600 h, day 1-2200 h, day 1; D = 2200 h, day 1-1000 h, day 2; E = 1000 h, day 2-1600 h, day 2; F = 1600 h, day 2-2200 h, day 2; G = 2200 h, day 2-1000 h, day 3; H = 1000 h, day 3-1600 h, day 3). The volume of pollen released and pollen grain diameter was measured at each collection period. On the resulting selfed ears, seed number ear-1 and deviations from the genetic ratio at collection period A at each locus were used as an index of seedset and pollen transmission, respectively. The volume of pollen grains released, pollen grain diameter, relative starch content of the pollen grains, and seedset decreased at the later collection periods, but the amount and the collection period where the decrease occurred depended on the locus. Significant increases in the transmission frequency of the recessive allele were found in collection periods B. C, D, E, and F at the waxy locus and collection period B at the shrunken locus. Apparently, less mature pollen grains are released at the later collection periods and this immaturity alters seedset and pollen transmission. This forced shedding procedure may be useful in amplifying pollen transmission differences and, in so doing, improve the selectivity and efficiency of pollen genotype selection programs.