How is wheat grain weight affected by the pericarp that surrounds it?

The wheat that farmers harvest is a fruit, and grows within the pericarp. This layer around the seed controls the hydration and nutrition of the tissues growing inside. Jamie Herrera and Daniel Calderni have noticed there’s not been a lot of research examining how the pericarp affects the final grain weight. They found that maximum pericarp weight is a determinant of grain weight and size in wheat. This could be an important trait to enhance if targets in increases in wheat yield in further years.

“[Grain weight] is affected by different management and environmental factors, which includes plant density and temperature. For example, the availability of resources per plant positively modulates grain yield, yield components such as grain number per spike and thousand grain weight (Whaley et al., 2000),” write Herrera and Calderni in their article.

“On the contrary, temperature is a major environmental factor that affects both the development and growth of grain crops (Porter and Gawith, 1999), where increased temperatures both at pre-anthesis and post-anthesis temperatures have a negative impact on final GW of wheat and, in turn on grain yield (Calderini et al., 1999; García et al., 2015). Higher night temperatures (Peng et al., 2004) as well as more episodes of heat waves are  expected as a consequence of climate change (McKersie, 2015; Alexander, 2016; FAO, 2016). Therefore, higher night temperatures is a key to evaluate the response of maternal tissue to future climate conditions of wheat cropping systems. However little is currently known about how and to what extent increments in temperature could affect the maternal tissues of wheat grains during grain filling and their relationship with the final grain weight.”

To examine the connection between pericarp and grain weight, Herrera and Calderni compared two spring wheat cultivars with contrasting kernel weights. They used both differing plant densities and night temperatures to see how this affected pericarp development. After anthesis the scientists harvested grains every three or four days. They used a scalpel to remove the pericarp from the grain and weighed it with a precision balance to see how it was developing.

“Interestingly, a positive association was found between final grain weight and both pericarp maximum dry matter and water content, highlighting the importance of maternal tissues on grain weight determination of wheat. Moreover, the maximum dry matter and water content of the pericarp ware reached before key traits considered determinants of final grain weight in wheat such as the maximum grain length and the maximum grain water content,” write Herrera and Calderni.

The study should help plant breeders understand more about seed development beyond the traits that have been studied in the past. The findings may also help in balancing trade-offs between grain weight and grain number.