Maize Breeding for High Yield in High-Fertility Soils Selected the Traits Associated with Increased Phosphorus-Uptake-Efficiency of Mycorrhizal Pathway

The breeding process has been improving grain yield and nutrient utilization efficiency in intensive farming since the green revolution. Most current genotypes have been selected for the root traits that enhance P acquisition from the P-rich topsoil. Recent studies demonstrate modern maize genotypes have higher mycorrhizal growth responsiveness (MGR) and mycorrhizal P uptake responsiveness (MPR) than the old genotypes in the high-P soil. The mechanisms are still unclear. Our previous studies showed that the maize breeding selecting from 1950s to 2000s is not always against AM association and the AMF play positive roles in promoting the growth of some maize genotypes in high P soil. We hypothesized that the P acquisition efficiency (PAE) of mycorrhizal pathway (MP) might be higher in modern maize genotype than that of in old maize genotype in high-P soils, that causes the difference in MGR and MPR.

In this study, we selected two maize (Zea mays) genotypes released over the last 60 years (including HMY, landrace released before 1950s and hybrid XY335 released in 2000s) and used ³²P labeling and qPCR to quantify PAE-DP or PAE-MP and the expression of plant PHT genes at low, medium and high soil Olsen P. We find that the PAE-DP was 110-549 times higher than PAE-MP, both reaching the maximum at high Olsen P. The MP contributed on average 25%, 60% and 16% of total shoot P content at low, medium and high Olsen P, respectively. The mycorrhizal responsiveness and PAE-MP were higher in genotype XY335 than HMY at high Olsen P. We conclude that maize breeding for high yield in soils with increased fertility selected the traits associated with increased PAE-MP efficiency.