Physiological Basis of Successful Breeding Strategies for Maize Grain Yield

Abstract

During the maize (Zea mays L.) hybrid era (1939 to present), commercial grain yields have improved nearly sixfold and the genetic component of the improvement has been estimated as approximately 60%. In this paper, we examine physiological factors and successful breeding strategies that underlie the yield improvement. Grain yield is the product of accumulating dry matter and allocating a portion of the total dry matter to the grain. The processes influencing dry matter accumulation are commonly referred to as the “source” components, while the processes influencing allocation of dry matter to the grain are referred to as the “sink” components. On the source side, changes in leaf canopy size and architecture account for only a minor portion of the improvement. The majority of the improvement in source capacity is due to visual and functional “stay‐green.” On the sink side, the improvement is through changes in the relationship between kernel number per plant and plant growth rate during a period bracketing silking. In a breeding context, these improvements have been made (i) in a “closed” germplasm pool stratified into heterotic groups; (ii) through use of a pedigree method of breeding structured to mimic reciprocal recurrent selection and thereby improving both additive and nonadditive genetic effects; and (iii) by a gradual increase in plant population densities during the hybrid era as the constant source of stress during both inbred line development and hybrid commercialization. Functional stay‐green and the sink establishment dynamics still represent opportunities for yield improvements. It is essential that source and sink are kept in balance, and that improvement in one accompanies a simultaneous improvement in the other. One strategy for exploiting these opportunities is to incorporate high plant population density trials into inbred line development programs.

Direct mapping of density response in a population of B73 × Mo17 recombinant inbred lines of maize (Zea Mays L.)

“…Genetic yield gain as a result of adaptation to continual increases in plant density and drought stress is perhaps the most evident and quantifiable change in maize hybrids over the years (Edmeades et al, 2006;Lee and Tollenaar, 2007;). Cardwell (1982) estimated that increased plant densities accounted for 21% of the gain in maize yield in Minnesota (USA), from the 1930s through the 1970s.…”

Harnessing Genetic Variation in Leaf Angle to Increase Productivity of Sorghum bicolor

“…Leaf angle, or leaf erectness, is a plant canopy parameter that has drawn considerable attention because of the predicted improvement in photosynthetic efficiency and reduction in plant stress afforded by the redistribution of solar radiation from upper to lower levels of canopies (Tollenaar and Wu 1999;Duvick 2005;Murchie et al 2009;Zhu et al 2010;Murchie and Reynolds 2012;Drewry et al 2014;Mansfield and Mumm 2014). Performance improvements predicted by theoretical models are corroborated by positive correlations between small leaf angles and cereal crop yields; post-green revolution rice cultivars have smaller leaf inclination angles and higher yields relative to their pre-green revolution predecessors (Yoshida 1972;Sinclair and Sheehy 1999;Sakamoto et al 2006), and modern maize is also characterized by small inclination angles as a consequence of selection for increased grain yield in breeding programs (Duvick 2005;Lee and Tollenaar 2007;Hammer et al 2009;Tian et al 2011;Mansfield and Mumm 2014).Despite the association of leaf angle with increased productivity, its genetic basis remains to be fully characterized for many of the major grasses. In maize, ligueless1 and ligueless2 have been identified as major regulators of leaf angle that can improve plant productivity (Pendleton et al 1968;Lambert and Johnson 1978;Moreno et al 1997;Walsh et al 1998).…”

Determinantes del peso de grano en cultivares nativos e híbridos de maíz

“…On the contrary, modern hybrids maintained higher levels of GY on limiting environments, in this case under late sowing date and increased competition between plants (LDMS) or reduced availability of nitrogen (LDAS) compared with ancient hybrids and native cultivars; such as has been reported in other studies, modern hybrids have better adaptation to unfavorable conditions that ancient hybrids (Echarte et al, 2006;Lee and Tollenaar, 2007).…”

“…Although in this study did not report data on the growth rate and flowering synchrony in other studies have found that ancient hybrids reported the lowest rates of plant growth Lee and Tollenaar (2007) and for the case of native que los híbridos antiguos reportan las menores tasas de crecimiento por planta Lee y Tollenaar (2007) y para el caso de los cultivares nativos, intervalos antesis-floración femenina más largos (Kibet et al, 2009), siendo estos los atributos que podrían estar limitando la producción final de grano en dichos cultivares.…”

“…It has been consistently shown greater tolerance that modern hybrids present in limiting conditions that often result in higher growth rates per plant in flowering, higher number of grains per plant, higher rates of dry matter accumulation during EPGF, also a lower rate of leaf senescence during the grain filling period (Lee and Tollenaar, 2007). In general, it was observed that modern hybrids presented as strategy to maintain higher GY, an increased NG (Table 3, Figure 2A and 2B), as reported by Echarte et al (2006).…”