Estimation of Yield and Its Components in White Lupin Lines Under Favorable and Dry (Low-Rainfall) Field Conditions

The present study emphasizes the importance of developing breeding lines that combine productivity with stability under variable environmental conditions. Seed yield and its main quantitative components in 15 white lupin lines were analyzed over two years under favorable and dry environmental conditions. In dry conditions and reduced precipitation for vegetation (by 53 and 63%, respectively, compared to the 30-year norm and favorable conditions in the previous year) in Central Northern Bulgaria, seed yield decreased by an average of 35%. The environment had the strongest influence on the traits of plant height, number of pods and seeds, and seed weight per plant (72.2–81.3% of the total variation). The strength of the environmental factor influence was also decisive for seed yield (51.9%), whereas 1000-seed weight was primarily governed by genetic components (52.4%). The broad-sense heritability coefficient (h2) for the evaluated quantitative traits ranged from low values for pods per plant (24.27%) and seed weight per plant (24.99%) to high values for plant height (64.58%). With stable expression and values around the group mean, V21 was distinguished for number of pods, number of seeds, and seed weight per plant, and V28/1 for number of seeds and seed weight per plant, while V6, V27/10, and V28/1 had a relatively constant 1000-seed weight, although below the group mean. V4, V1, and V29 can be characterized as high-stemmed and relatively stable across the two seasons. The conducted multifactor stability analysis and the GGE biplot model identify V425 and V28/1 as the most stable and productive among the tested lines, whose yields (3.025 t/ha and 2.495 t/ha, respectively) were above the average for the group and whose assessments of most of the stability parameters indicated a stable response across the two contrasting seasons.