Heat-resistant broccoli testing with a multistate squad

It’s no secret that summers are getting hotter – as are autumns, winters and springs. That can make growing cold-season crops, such as broccoli, difficult.

Luckily, a team of university researchers have assembled like the Avengers to help mitigate this dilemma. Conducting a multistate evaluation of heat-resistant broccoli cultivars for spring production in the eastern U.S. are Emmanuel Torres Quezada and Tomas Quezada Baez of North Carolina State University; Andre Luiz Biscaia Ribeiro da Silva of Auburn University; Benjamin Phillips of Michigan State; Jianyu Li of UMass; Mark Reiter of Virginia Tech; Ted McAvoy of the University of Georgia; and Wenjing Guan of Purdue.

Emmanuel Torres Quezada shared the first year of results at this summer’s American Society for Horticultural Science conference.

As spring broccoli production in the Southeast and the Mid-Atlantic has become increasingly vulnerable to high temperatures and variable rainfall, a multistate trial was devised to evaluate the performance of eight broccoli cultivars across seven states (North Carolina, Virginia, Georgia, Alabama, Massachusetts, Michigan and Indiana). The super team wanted to assess plant growth and yield performance under heat stress and determine thresholds that could predict marketable yield.

“There is little funding available for cultivar evaluation,” Torres Quezada shared, and very few growers want single-season data. To expand their funding for this important work, he initially teamed up with UMass’s Li to try some seeds – and they reached out to other faculty to see if they’d be interested in joining.

Broccoli cultivar testing is important to display which varieties can adapt to heat and humidity; to account for regional differences (in soil, elevation and planting windows); to help boost yield and quality; and to manage pests and diseases, especially with resistance to local pressures. The results can provide data-backed recommendations to growers and enhance the market supply with consistency and quality.

“The key issue in hosting these trials is labor costs,” Torres Quezada said. “We fly drones for data collection – only one person is needed for that.”

In the trial, which took place in early 2025, there were 30 plants per plot in double rows on black plastic mulch. Fertility and irrigation were site-specific and monitored through soil testing and evapotranspiration estimates. Soil samples, weather data and pest control measures were also recorded at each location.

Drone-based RGB (red-green-blue) and multispectral imagery was collected biweekly (four to 12 weeks after transplanting) at midday under clear-sky conditions. This imaging showed each cultivar exhibited a distinct NDVI profile that correlated with crown greenness and shape.

The drones used NDVI (normalized difference vegetation index) and NDRE (normalized difference red edge) imaging, which Torres Quezada explained helps identify stresses earlier, helps with yield predictions, allows for standardized crop monitoring and improves fertility and irrigation decisions. The results from four states (Georgia, Indiana, Michigan and North Carolina) were available at the time of the conference.

The cultivars analyzed were ‘Asteroid,’ ‘Castle Dome,’ ‘Eastern Crown,’ ‘Eastern Magic,’ ‘Emerald Crown,’ ‘Green Magic,’ ‘Imperial’ and ‘Millennium.’ All cultivars were planted later than optimal at each location, due to excessively wet springs.

The researchers measured average crown weight per site, the yield classification (commercial vs. non-commercial), the final count of commercial heads/acre, the percentage of plants with axillary meristems (aka “suckers”) and harvest timing distribution.

Torres Quezada reported the biggest difference in yield between two locations was found in North Carolina and Indiana: In the Tar Heel State, crown weights averaged 464 grams. In Indiana, crown weights averaged just 294 grams. (Michigan had similar results.) In Georgia, crown weights averaged 313 grams (and every cultivar except ‘Eastern Magic’ had an average season).

With all factors considered, ‘Castle Dome’ and ‘Eastern Crown’ had the best performance overall, featuring few suckers as well as very low disease incidence. All eight cultivars performed fairly well in North Carolina.

Also of note was that ‘Millennium’ tended to have the largest heads in Indiana. ‘Eastern Crown’ did best in Michigan. Ultimately, cultivar performance was largely consistent across regions with similar growing conditions.

The broccoli research buddies determined that cultivars such as ‘Eastern Magic’ and ‘Green Magic’ maintained acceptable head quality and yield despite elevated temperatures, suggesting suitability for late spring planting.

They also reported that the use of NDVI imaging proved to be a promising tool for identifying plant vigor and for optimizing management decisions during periods of heat stress.

The trial will be repeated for better results. And, Torres Quezada concluded, the cross-university team is also looking to team up for tomato and pepper cultivar testing too.

by Courtney Llewellyn