Ear Development in Maize - Growth Chamber Observations to Field Trials.

Ear development in maize (Zea mays  L.) is a reiterative process of meristem initiation and organ differentiation beginning with the inflorescence meristem and ending with the development of spikelets.  Historically sink potential in maize has been viewed as being equal to the number of spikelets that develop on the ear.   And the discrepancy that exists between spikelet number and final kernel number has been attributed to pollination failure or kernel abortion during the grain-filling period.   Ear initial growth was being characterized as part of a heterosis study involving growth chamber grown plants.  During this experiment observations were made that the spikelets in the distal portion of the “mature” ear initial displayed atypical morphology that phenocopies spikelets from studies involving plant growth regulators.  We have and are currently examining several hypotheses related to spikelet development.  Using both growth chamber and field grown plants we tested the hypothesis that spikelets with atypical morphology do not contribute to final kernel number.  The initial findings suggested that not all spikelets are “functional”.  This led to testing our second hypothesis that a treatment known to affect kernel number (plant density) should alter the proportion of spikelets exhibiting atypical morphology.  We confirmed the previous findings that spikelets with atypical morphology are not contributing to final yield, and demonstrated that increasing plant density increases the proportion of atypical spikelets.  We are currently examining year effects on spikelet development in an effort to determine the extent of year-to-year variation in atypical spikelet development.  As spikelet development may be one of the processes which give rise to GxE effects.  Interestingly we are also examining genetic improvement in spikelet development across an ERA series of hybrids.  Initial findings suggest that there has been no genetic improvement for spikelet number, and the effect of plant density and year effects on the proportion of atypical spikelets.  Given our findings, we suggest that sink potential is directly proportional to the number of normally developed spikelets and that this is a yet unexploited avenue for genetic improvement in maize grain yield.