Embrapa's lettuces grew at 30°C for 45 days

Embrapa's curly lettuce cultivars, BRS Leila and BRS Mediterrânea, performed best in experiments at higher temperatures. The researchers simulated a scenario of a 5ºC temperature increase, from the average of 25ºC to 30ºC, for 45 days. Unlike the other nine cultivars tested in the same experiment, the two developed well under the new conditions.

The study assessed the effect of temperature on the development of lettuce plants, with the aim of anticipating the effects of climate change. ″For that purpose, we worked with two air temperature values, according to the historical average observed and projected over an extreme scenario of global climate change for Brazil: 25ºC/20ºC and 30ºC/25ºC (day and night, respectively)″, the Embrapa Vegetables researcher Carlos Pacheco.

The experiments were conducted at the research center's Plant Growth Chamber, which can simulate atmospheric parameters like temperature, relative air humidity and carbon dioxide concentration, for instance. The researcher recalls that leafy vegetables are more susceptible to heat; one of which, lettuce, is the most consumed in the country according to the Brazilian Seed and Seedling Trade Association (Abcsem), which makes the study important for the effort of adapting to climate change.

Traits that made the difference

Embrapa's two cultivars have traits that can circumvent the temperature rise, explains the researcher Fábio Suinaga, developer of both materials. "BRS Leila plants have delayed blooming, which makes them withstand, on average, ten days longer in the heat compared to the other lettuces tested," the scientist reports.

Meanwhile BRS Mediterrânea reaches the harvest point faster, seven days earlier than similar cultivars in the market. ″With a shorter production cycle, it is less exposed to heat and avoids early blooming″, Suinaga details. He explains that blooming ahead of time causes deleterious effects such as stem elongation, reduction in the number of leaves, and production of latex, a substance that gives a bitter taste to the leafy green. All of that reduces the commercial value of the lettuce.

In contrast, commercial cultivars under the same temperature changes presented a series of disorders, such as tasseling, edge burning, chlorosis, necrosis, and plant death; in short, they could not be sold. "When it is observed that our cultivars remained steady despite the 30º C, it is a demonstration that we have a genetic material that adapts to certain adverse conditions", the researcher celebrates.

Embrapa's lettuce BRS Mediterrânea reaches its harvest point 7 days earlier than similar cultivars, reducing exposure to the heat.    Photo: Italo Ludke

The Plant Growth Chamber

For researchers evaluating cultivars, the main tool to assess heat tolerance has been an equipment that works as a simulator.

The Plant Growth Chamber is a closed environment that can simulate future climate scenarios. In such small space, it is possible to test the behavior of plants grown in pots by projecting different factors such as temperature, humidity, CO₂, radiation, and others. ″In this simulated environment, the plants are exposed to extreme conditions to identify the most resilient to high temperatures and other factors such as water deficit, for instance″, he adds.

Next step: water stress tests

Pacheco informs that the work is part of a series of strategies to cope with climate conditions. The team intends to continue the studies with other fronts in order to select increasingly more heat-tolerant materials. "At this moment we are working on heat tolerance; at a second stage we will focus on water stress (due to excess or lack of water), involving tolerance to salinization; which will be followed by behavior regarding the use of bioinputs," Pacheco announces.