The researchers studied different winter wheat varieties to see which traits affect grain yield. They planted the wheat in a specific way and measured traits like plant height and grain weight. They found that most traits varied among the wheat varieties, except for main spike weight and grain number per plant. The weight of the main spike showed the most diversity, while days to maturity and heading showed the least. They also discovered that four main factors explained most of the variation in traits. By grouping the wheat varieties based on traits, they found two distinct groups: one with seven varieties and the other with five.