Soybean genetic progress in South Brazil: physiological, phenological and agronomic traits

Yield increase in soybean [Glycine max (L.) Merr.] has occurred due to plant breeding, as well as the improvement in management practices. Genetic gain for important traits in soybean due to plant breeding in South Brazil has not been evaluated. The objective of this study was to measure the genetic progress of several soybean agronomic, phenological and physiological traits, in a historical set of cultivars released for cultivation in South Brazil from 1965 to 2011. Twenty-nine cultivars were evaluated in a three replicate randomized complete block design at two locations in the 2016/17 crop season. Mean genetic gain for yield was 40.06kgha(-1) year(-1) averaged across locations. The modern cultivars had higher biological yield (BY), harvest index (HI), number of pods per plant (NPP), and lower number of branches per plant, plant height, and lodging score compared to older releases. There was a reduction in the vegetative period, and increase in ratio between reproductive and vegetative periods (R/V). Photosynthetic rate (P-N) and transpiration rate (Tr) also increased with year of release. The traits BY, NPP, HI, R/V, number of seeds per pod, P-N, Tr, and chlorophyll content (Chl a and b) was highly associated with seed yield. Breeding strategies that maximize the R/V ratio, and prioritize indirect selection through HI, BY, NPP, P-N, Tr, and Chl a and b, will likely contribute to improving soybean yield in the future.