Genetic improvement of peanut in Argentina between 1948 and 2004: Seed yield and its components

In Argentina, peanut (Arachis hypogaea L.) breeding has been based on seed yield per se plus defensive and seed quality traits. An important milestone was the shift from cultivars with erect growth habit (CEGH) to cultivars with procumbent (CPGH) growth habit that took place in the 1970s. However, there is no information on the genetic gain obtained for seed yield and related secondary traits (numerical and physiological determinants of seed yield), or on the effect of growth habit shift on these traits. Field experiments were performed to compute this gain and the relationships between traits in potential growing conditions. Eight cultivars released between 1948 and 2004 were evaluated. Introduction of the procumbent habit in 1975 produced a mean increase of 52% in seed yield, which was related to year of cultivar release (YOR) only for CPGH (mean genetic gain of 0.43% y−1). This trend was driven by seed weight, a trait that registered a mean genetic gain of 0.29% y−1 (P = 0.026) only among procumbent cultivars (56% increase with habit change between 1973 and 1975). No genetic gain was computed for seed numbers, and only a 10% difference was registered between growth habits (CPGH > CEGH). Seed number was related to crop growth rate between R3 and R6.5 (r2 = 0.55, P < 0.001). This rate was higher for CPGH than for CEGH. Breeding increased the number of flowers per plant (0.86% y−1), and the number of pods per plant and pod set (CPGH > CEGH). Breeding had a clear effect (P < 0.001) on the determinants of seed weight, and a genetic gain of 0.52% y−1 was estimated for pod growth rate. Introduction of CPGH enhanced pod growth duration (37% increase). No trade-off was detected between seed number and seed weight because there was no source limitation to seed filling. Therefore, peanut seed yield might be further increased by improving the determinants of seed numbers and seed weight simultaneously.