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ARS Home » Midwest Area » Madison, Wisconsin » Vegetable Crops Research » Research » Publications at this Location » Publication #329854
Title: The effects of time, temperature and plant variety on pollen viability and its implications for gene flow risk

Author
item Brunet, Johanne
item ZIOBRO, ROSS - University Of Wisconsin
item OSVATIC, JAY - University Of Wisconsin
item CLAYTON, MURRAY - University Of Wisconsin

Submitted to: Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2019
Publication Date: 1/17/2019
Citation: Brunet, J., Ziobro, R., Osvatic, J., Clayton, M.K. 2019. The effects of time, temperature and plant variety on pollen viability and its implications for gene flow risk. Plant Biology. 21(4):715-722.
DOI: https://doi.org/10.1111/plb.12959

Interpretive Summary: Bees carry pollen on their bodies and that pollen is available to pollinate a plant. How far a bee travels will affect the distance traveled by pollen. However, pollen viability will influence the probability that a pollen grain that lands on a plant stigma (the female part of the plant) will germinate, grow a tube down the style, fertilize an ovule and produce a mature seed. Even if a pollen grain travels far, if it is not viable it will not produce a mature seed. A mature seed is needed to create a gene flow event. Therefore pollen viability will influence gene flow risk. When bees move pollen from a genetically engineered field of a crop to a conventional field, the relationship between pollen viability and time since pollen is removed from the anthers of a flower will affect the likelihood of transfer of GE genes to the seeds of the conventional crop. Alfalfa is an economically important crop in the United States and two GE traits, Roundup Ready and low-lignin content, are commercially available. The viability of alfalfa pollen declined steadily with increasing time since removal from the anthers of an alfalfa flower. This decrease in pollen viability over time occurred at three temperatures and for different alfalfa varieties. Fewer than 50% of alfalfa pollen grains were viable after 15 minutes and less than 30% after 2 hours following removal from the anthers. Pollen viability was not affected by temperatures ranging between 25° and 37°C and did not vary among plant varieties. Pollen viability did not vary between Roundup Ready (RR) and conventional varieties of alfalfa. This is good news as pollen viability is not providing an advantage to the spread of RR genes over the alfalfa agricultural landscape. Because it reduces the probability that a pollen grain landing on a stigma set a mature seed, low pollen viability can decrease distance isolation requirements and reduce adventitious presence or the unwanted presence of GE traits. Pollen viability must therefore be considered when calculating gene flow risk assessment for GE alfalfa varieties even though conventional and RR alfalfa varieties have similar pollen viabilities. This information benefits regulators interested in estimating gene flow risk of GE crops, seed producers who want to maintain the purity of their varieties, and the alfalfa industry interested in promoting the coexistence of the different alfalfa seed-production markets.

Technical Abstract: Pollen viability affects the probability that a pollen grain deposited on a plant's stigma will produce a viable seed. Because a mature seed is needed before a gene flow event can occur, pollen viability will influence the gene flow risk of genetically-engineered (GE) crops. Alfalfa is an economically important crop in the United States and two GE traits, Roundup Ready and low-lignin content, are commercially available. This study examines the impact of temperature, time since removal from the anthers and plant variety on pollen viability in alfalfa and contrasts pollen viability between conventional and RR varieties. The time elapsed since removal from the anthers most consistently affected pollen viability which declined with increasing time at three temperatures and for different varieties. Fewer than 50% of alfalfa pollen grains were viable after 15 minutes and less than 30% after 2 hours following removal from the anthers. Pollen viability was not affected by temperatures ranging between 25° and 37°C and did not vary among plant varieties. Because it reduces the probability that a pollen grain landing on a stigma set a mature seed, low pollen viability should decrease adventitious presence and must be considered when calculating gene flow risk assessment for GE alfalfa varieties even though conventional and RR alfalfa varieties have similar pollen viabilities.