This note is a report on an observation that is common to all maize geneticists but has rarely been quantified. A method has been adapted for investigating anthesis that appears useful for examining several features of pollen shedding that include: 1) sequence of anther dehiscence (the order of the onset of anther dehiscence among four spikelet positions of a tassel--see figure), 2) the time period of anthesis of a tassel (number of days when 95% of the spikelets of a tassel have completed anther dehiscence), and 3) the time interval (U:L) (number of days) that separates the upper (U) and lower (L) flowers of the same spikelet.
For anther dehiscence studies, spikelets within each of the four positions were randomly selected. In order to identify the date of the first shedding anther of each position, Dennison marking tags (size 3 x 2 cm2) were tied in each position.
To identify the time interval (U:L) separating pollen shedding between upper (U) and lower (L) flowers, a color code was used to mark spot(s) (Sanford's Sharpie marking pen) on the surface of the inner glume of the examined spikelet. A blue spot marked the first day of pollen shedding of the upper flower of a spikelet; a red spot was used on the second day of the lower flower if the same spikelet did not shed pollen, and the color marks were continually applied until the time the lower flower began to shed pollen. The number of days separating the upper and lower flowers in pollen shedding was obtained by counting the number of color spots on a spikelet. Ten to 20 spikelets from each of the four positions of a tassel were sampled. The time interval (U:L) separating two florets of the same spikelet was estimated by averaging the time interval (U:L) for the examined spikelets at a given position within a tassel. This method provides a convenient way to handle a large number of samples (spikelets) in the field within a relatively short time.
Based on the investigation of a total of 4,941 spikelets among 25 genotypes, the average time interval separating pollen shedding between upper and lower flowers of the same spikelet is 2.06 days (Table 1). There is a longer time interval among tetraploids and Mexican varieties than among inbreds and hybrids. This time interval is longer in position 3 and 4 than in positions 1 and 2 (Table 2)
When genotypes are pooled and observations are averaged, the first pollen-shedding anther is found to be in position 2, followed by 1, then 3 and, finally, 4 (Table 3).
The time period of anthesis of a tassel was similar among inbreds, tetraploids, and hybrids (Table 4); there was a significantly longer time period in Mexican varieties.
Sun-Yuan Hsu and Peter A. Peterson
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