Determining The Effect Of Wheat Photoperiod Sensitivity On Heading Date, Yield, Test Weight And Other Traits

Wheat is considered a long-day or daylength sensitive (also called photoperiod sensitive) plant, meaning that it will not flower until the days reach a certain length. Over time, breeders have selected for early maturity and this has led to the prominence of daylength insensitive varieties today. These daylength insensitive types are not held back by daylength, but rather their rate of development is driven by heat units, AKA growing degree days. The problem is that in Kentucky springs, we frequently experience severe freezes that follow unusually warm periods in the late winter. An example of this was the warm February this year that was followed by a very cold March that included 3 successive nights with lows in the 20’s. Daylength sensitive lines are protected from these spring freezes, while the more common daylength insensitive varieties are susceptible to spring freeze damage. For these reasons, it would be desirable to have daylength sensitive varieties that have all the other traits we need: early maturity, high yield potential, reduced height, scab resistance and good test weight. How can we determine whether a variety is sensitive or insensitive to daylength? The most efficient way is to see which genes they carry for this trait. Wheat is complicated by the fact that has 3 genomes, designated A, B and D. The photoperiod gene in the D genome, Ppd-D1 has the biggest effect, while the other two genes Ppd-A1 and Ppd-B1 have smaller effects. Lines with all 3 Ppd genes will be most sensitive to daylength. The scientific literature reports that these genes can affect yield and yield components like kernel size, but there is no consensus on the direction or the size of the impact. We have several early generation populations that contain various combinations of these photoperiod genes. From these populations we will derive lines that can be tested for the agronomic and grain quality traits of interest. Specifically we propose to: • Plant these populations in October 2023 at Spindletop Farm. Single heads will be threshed and planted as headrows, but we will also plant a bulk of the populations in a space planted fashion using dead barley seed to make sure we get good space between individual plants. • In early March (or late February depending on the weather) we will screen the plantings and identify individual plants or rows that have jointed as well as those that have remained prostrate. • In the rows, we will record heading date, plant height, yield and test weight. We will sickle and thresh individual rows. In the space plantings we will tag the earliest and latest jointing and heading plants and harvest seed from these plants. • After harvest we will germinate seeds from these contrasting types and use DNA marker analysis to tell us what Ppd genes are present. • Lines with different combinations of genes would then be tested in 24-25 to measure the effect of the Ppd genes on the traits of interest. This will give us an indication of the Ppd effect, though it will not be as accurate as a test where we had two lines that had the same genes across the board except for the Ppd genes. This would be great but it takes years to develop those kinds of contrasting lines. Budget • Labor – One full time summer student who also works part time during the school year at $12-$15 per hour: $6500 • Supplies – Tags, sharpies, fieldbooks, genotyping supplies for the lab: $1000 Total requested: $ 7500