Physiological Changes from 58 Years of Genetic Improvement of Short‐Season Soybean Cultivars in Canada

Abstract

In Canada, yield of short‐season soybean [Glycine max (L.) Merr.] cultivars has increased by approximately 0.5% per year since they were first cultivated in the early 1930s. Future yield gains may be dependent on an understanding of the changes made to soybean cultivars by breeding and selection. Our objective was to examine physiological differences associated with seed yield increase within a group of historical cultivars. At Ottawa, Ontario, we grew 14 cultivars representing seven decades of breeding and selection (1934–1992) in a randomized complete block design with four replications, across 4 years. Growth analysis provided data on leaf area and dry weight. Photosynthetic rate per leaf area was measured at several stages of development each year. Yield and harvest index were determined at maturity. The number of days to maturity and the total plant dry weight were not affected by the year of cultivar release. Seed yield, harvest index, and photosynthetic rate were found to have increased by 0.5% per year, while leaf area index decreased by 0.4% per year. The increase in seed yield with year of release was significantly correlated with an increase in harvest index, photosynthesis, and stomatal conductance and a decrease in leaf area index. Today's cultivars are more efficient at producing and allocating carbon resources to seeds than were their predecessors.

Human selection and the relaxation of legume defences against ineffective rhizobia

“…This value is proportional to the cultivar's absolute N from fixation because approximately 90% of N accumulates in the seeds, regardless of soya bean ancestry (Cregan & Yaklich 1986). However, a given percentage of benefit from inoculation will give a larger absolute yield difference with modern cultivars because there is an estimated 0.5% per year yield improvement due to plant breeding and selection ( Voldeng et al 1997;Morrison et al 1999Morrison et al , 2000. We therefore calculated a 'yield difference ratio' for the mixed treatment (mixedcontrol yield)/(effective-control yield).…”

Modelling soybean yield responses to seeding date under projected climate change scenarios

“…Data from the experiment at CEF in 1993 and 1994 were used to calibrate the cultivar coefficients ( Table 1). The calibrated model was evaluated with independent experimental data obtained at CEF in 1995and 1996and at CFIA in 1995, 1999and 2008 comparison include the p-value in paired t-test (P(t)), root-mean squared error (RMSE) and its normalized value (nRMSE) with the measured mean. Mean Error (ME) and relative mean error (rME) were also derived.…”

“…These modifications were conducted on three parameters determining photothermal days from emergence to first flower, first flower to first seed, and first seed to physiological maturity in the CSM-CROPGRO-Soybean model; and two parameters determining degree-days from emergence to the beginning of grain filling, beginning of grain filling to maturity in the STICS model. The harvest index of soybean has increased stably in the last century (Morrison et al 1999). It is reasonable to assume that breeding efforts may continue to improve or, at least maintain, the current harvest index levels by overcoming the potentially negative impacts of a future warmer climate (Cure and Acock 1986;Ruiz-Vera et al 2013;Tacarindua et al 2013).…”

“…Ruiz-Vera et al (2013) concluded that under future climate conditions, the combined effects of elevated CO 2 concentration and higher temperature would likely reduce growth due to overriding environmental factors, but this conclusion was based on current crop cultivars. From (Morrison et al 1999;Rowntree et al 2014), and breeding efforts to keep high harvest index will likely continue. Selecting cultivars from the right MG for the warmer future climate should be an essential adaptation measure for soybean production in regions where it is currently cool.…”

When is short-season soybean most susceptible to water stress?

“…Stegman et al (1990) and Calviño and Sadras (1999). During this phenological period, the cells in the seeds and the developing pods are beginning rapid expansion (Westgate and Peterson 1993), the plant has achieved maximum leaf area (Morrison et al 1999) and is at peak photosynthetic capacity. Water stress reduces photosynthesis and sugar production.…”