Agronomic evaluation of Bulgarian elite soybean breeding lines

Abstract

In a three-year field trial conducted from 2023 to 2025 at RIMSA–Troyan, Northern Bulgaria, medium-early-maturing (MGI) stabilized recombinant soybean lines derived from the following varietal crosses—♀Romantica × ♂Oria (line R2), ♀Romantica × ♂Srebrina (line R5), ♀Saikai 20 × ♂Romantika (line S2), ♀Saikai 20 × ♂Galina (lines S3 and S32), ♂Atlanta × ♂Romantika (line A1), and ♂Atlanta × ♂Houta (line A3)—were compared with the Bulgarian standard variety Avigea in terms of productivity, quality, and drought resistance traits. The results demonstrated selection progress in the most important soybean yield components in lines S3 (♀Saikai 20 × ♂Galina) and R5 (♀Romantica × ♂Srebrina). These lines should be included in competitive trials and subsequently registered as new varieties. The superiority of line S3 over the standard in the number of pods and seeds per plant, as well as in harvest index, provides a significant advantage in individual plant productivity, despite its lower absolute seed mass. Line R5 recorded the highest values for absolute seed mass and harvest index. Both lines produce a large number of first-order branches, which contributes to their higher productive potential. They exceeded the standard in crude protein content without statistically significant differences, while showing lower crude fat content. Line S3 was comparable to the standard variety in its ability to regulate transpiration under dry conditions. Line S32 (♀Saikai 20 × ♂Galina) exhibited the highest phenotypic stability for the seed yield components most strongly correlated with individual plant productivity, namely total plant dry mass at harvest, number of pods and seeds per plant, and harvest index.