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Flowering Time: The Ultimate Study

Saturday, February 1, 2025
filed under: Research and Development


 
        Out of any agricultural production research project inevitably come analyses, summaries and conclusions.  Projects are commonly based on two, three or four years of data gleaned from several replications each year at one or more locations.  Often, the research objective focuses on a single question or trait.
        And then there is this one.  Its database encompasses 46 years, 337 sites, more than 3,300 sunflower varieties and a multitude of traits.
        With a $1.2 million grant from the National Science Foundation, a research team led by scientists at the University of Colorado-Boulder is working to unravel some of sunflower’s genetic mysteries in hopes of making the crop even more resilient and productive in the future.  This project is funded through the summer of 2026, but there’s a good chance it will be extended beyond that timeline as well.
        In its initial phase, the group is working to document answers, to a degree never achieved before, to four questions:
        • When is sunflower’s optimal flowering time — and how commonly do available commercial varieties meet that optimum timing?
        • How much does flowering time impact yield?
        • How does optimal flowering time change with climate?
        • How might optimal flowering time change in the future?
        Going forward, the group also will conduct additional analyses of how hybrids adjust flowering time to different environments.  They’ll even look at the genes involved with determining flowering time and if any are particularly useful for enhancing yield in some/many environments.
        With the three-year NSF award, the researchers are analyzing a half-century of measurements taken from commercial sunflower varieties and USDA germplasm releases grown in dozens of locations and climates across the country.  Their database includes results from commercial variety performance trials published in state sunflower university reports in a variety of states — most notably North Dakota, South Dakota, Kansas, Colorado and Minnesota.  Some of the reports date back to the late 1970s/early 1980s.  All trial data are digitized and quality checked.
        Upon analysis of the data, the scientists are working to pinpoint the genetic underpinning as it relates to sunflower’s adaptation to environment.  In particular, they’re examining how sunflower’s timing (phenology) has changed over time, e.g., when the plant flowers — and whether such shifts have helped or hurt sunflower’s overall productivity.
        The underlying concept is that such knowledge, coupled with future climate modeling predictions, could serve as a roadmap for sunflower breeders — one of them being Brent Hulke, USDA-ARS Fargo-based sunflower research geneticist and a CU-Boulder associate adjunct professor of ecology and evolutionary biology.  Hulke is a co-principal investigator on the NSF grant.
Brent Hulke
Brent Hulke

        “We expect to have a better appreciation for how climate is affecting this important crop in the Great Plains, and [to be able to] tie it back to the plant’s genetics,” Hulke noted at the time the NSF grant was announced.  That, in turn, “will help us adapt breeding strategies to enhance stress tolerance, as well as enhance recommendations for farmers in terms of variety choices in the future.”
Nolan Kane
Nolan Kane

        A primary aim of the project is to help breeders develop sunflower varieties better suited to particular locales, e.g., smaller-acreage states like Colorado. 
        Another top priority is to help improve sunflower breeding in the broad sense in the face of changed climates in the future.

        “I don’t think any one species is going to be the right answer (to adapting to climate change),” stated Nolan Kane, CU-Boulder associate professor of ecology and evolutionary biology and principal investigator on the NSF project.  “It’s important to have a range of species, and I worry that our current agriculture is too dominated by too few species.”  Kane emphasizes that the motive behind improving sunflower’s sustainability is not to replace corn or soybeans; rather, “it’s to provide an additional crop.”
 
developing timing images

        A big challenge faced by all plant breeders is the pace at which the climate is changing, according to Kane — which in turn complicates how to develop plants for an unknown future.  But, he says, that’s all the more reason to dig into the historical data and glean every bit of useful information possible to make the smartest breeding decisions.
        “Right now, we’re not keeping up, we’re not optimizing our crops,” Kane observes.  “Our job is not to predict the future climate; but, if we do assume that some of these climate predictions come true in a particular environment, what should we breed for in the future? 
        “Sunflower is not a huge crop in the U.S.  Yet we can help make it a better, more-efficient, sustainable crop in the future just by taking advantage of the information we already have,” Kane adds.
 
Eliza Clark
Eliza Clark
        Eliza Clark of the CU-Boulder team provided an update on the National Science Foundation project at the 2025 National Sunflower Research Forum.
        Clark noted that the subset of oilseed sunflower trials being gleaned for data on flowering alone comprises 19 sites across 46 years, encompassing 294 site-years and 2,100 varieties.  Several sites in North Dakota include more than four decades of data.
        To date, Clark reported, the actual flowering time of commercial varieties corresponds to the “optimum” flowering time in about 56% of cases.  Taken as a whole, all commercial varieties flowered too late or too early to be considered “optimal” in about 25% of cases, with the remaining percentage not considered clear enough to be categorized.  (“Optimum” here is defined as the flowering time that will give the highest yield in a trial.)
        To what degree does flowering time impact yield?  The NSF team’s analysis indicates that 11% of variation in yield is due to flowering time, i.e., based on flowering time’s association with yield. The data also suggest it’s an even bigger factor the further south from North Dakota that the trials are located.
        When it comes to climate variables, the primary components considered are temperature, precipitation, first frost timing, solar radiation and day length — and drought.  Then also, from an agronomic standpoint, it’s planting date.  Not surprisingly, optimal flowering comes earlier at warmer sites and in warmer years.  But, optimal flowering does not clearly depend on precipitation or — no surprise here — on frost date.
`      Three more points, according to the four decades of data being analyzed by the NSF project team:
        • While there is lots of variation in growing degree days (GDD), the number of GDD units has definitely increased at the Northern trial sites since 2010.
        •. The current drought in the High Plains notwithstanding, precipitation across the four-decade spectrum has, overall, increased in the South and decreased in the North.
        •  First frost date has moved later in the North.
 
optimal flowering time

        What does it all mean?  Assuming the utilized climate predictions prove accurate, faster-flowering and quicker-maturing sunflower varieties will be needed in the future to maintain and improve the crop’s performance.
        “Our work suggest that it would be optimal (i.e., associated with higher yield) to flower earlier when it’s hot — but that can happen by either flowering faster or by planting earlier,” Clark observed.  “So, if we’re thinking about the future, we’ll likely need to do both of those things.” 
        As illustrated in the graph below, the current median for days to flowering is 65 days.  In the future, that median will need to be closer to 55 days, according to the NSF project team.
        “We will want to go with earlier planting of sunflower over time and, on average, based on changes in weather we see in our fields,” Brent Hulke affirms.  “The optimum flowering time of hybrids will adjust, even if we plant earlier.” — Don Lilleboe
flowering days

 
        *Along with Nolan Kane and Brent Hulke (both quoted in this article), other co-principal investigators on this project are: Sarah Elmendorf, a research scientist at the CU-Boulder Institute of Arctic and Alpine Research, and Colin Khoury, senior director of science and conservation at the San Diego Botanical Garden.  Also quoted is Eliza Clark a postdoctoral associate in the CU-Boulder Department of Ecology and Evolutionary Biology.
          Credit for some of the information in this article also goes to the CU-Boulder Communications Department.
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