In my corn breeding days, I used Florida, Hawaii and Puerto Rico as winter research nursery locations along with greenhouses in the Corn Belt. With mega-greenhouses in the Corn Belt today, why do we still need winter nurseries?
Greenhouses are great for incorporating traits in newer elite lines and growing three to four progenies per year. However, winter nurseries allow breeders to use large numbers of inbred lines, increase seed amounts of newer lines and make new crosses of parent lines.
The seed industry is very competitive. Breeders race to make genetic gains as quickly as possible. Along with new DNA technologies that speed up gene editing in the greenhouses, in winter nurseries, breeders try to accomplish four main objectives.
First, we send new crosses of related elite lines, called SO’s, to create S1 populations — the first self-pollinated generation — to start new cycles of selection. Then we send selected S2 second-generation inbred lines for further inbreeding. Third, we send selected S4 lines, which are ears from S3 rows. Last, we send paired rows of lines for making crosses for testing. These may be the crosses we were unsuccessful in making for some reason before, or they may be for making new experimental hybrids.
All-expense paid trip
All this seed gets a free trip and is shipped to winter nurseries in October or November and planted before Thanksgiving. In tropical climates, most lines are ready to start pollen shed in the first to second week of January, 45 to 50 days after planting, because daily temperatures are 80 to 95 degrees F.
We self-pollinate every plant in the S0 rows to create a large amount of seed for starting the new S1 projects at the Corn Belt nurseries. We want from 2,000 to 5,000 seeds of each new population.
Even at the second inbreeding generation, when the plants have only reached 50% genetic uniformity, the progenies are already taking shape and identity. Plant breeders deal with large numbers of plants to select the desirable genotypes.
In the winter nursery, we aren’t selecting plants for their adaptability to the southern climates and soil types. We’re only interested in advancing the process of inbreeding. During inbreeding, certain genetic defects start showing up in some families. We discard these S2 rows. About 80% of the S2 rows will be selected, and two to three ears per selected row will be returned to the Corn Belt research station in March.
In the S4 section of the nursery, we’re less critical in discarding rows, unless these show exceptional genetic defects. We generally save only one good ear per row for further inbreeding and crossing.
In the crossing section of the nursery, we try to produce seed of experimental hybrids so we can create a good supply of seed for testing at several locations.
The winter nursery is harvested during March; each row is harvested and labeled in separate bags, dried on the ears, and shipped back to the Corn Belt nursery. We will do further examination and selection of each ear in the lab, shelling, packaging and later planting for developing better hybrids for the farmers in the Corn Belt. Winter nurseries are essential for staying competitive in making genetic gains.
Nanda is president of Agronomic Crops Consultants LLC. Email [email protected] or call 317-910-9876.