How plant density affects maize spike differentiation, kernel set and grain yield formation in Northeast China?

A two-year field experiment was conducted to evaluate the effects of plant density on tassel and ear differentiation, anthesis-silking interval (ASI), and grain yield formation of two types of modern maize hybrids (Zhongdan 909 (ZD909) as tolerant hybrid to crowding stress, Jidan 209 (JD209) and Neidan 4 (ND4) as intolerant hybrids to crowding stress) in Northeast China. Plant densities of 4.50x 10(4) (D1), 6.75x10(4) (D2), 9.00x 10(4) (D3), 11.25x 10(4) (D4), and 13.50x10(4) (D5) plants ha(-1) had no significant effects on initial time of tassel and ear differentiation of maize. Instead, higher plant density delayed the tassel and ear development during floret differentiation and sexual organ formation stage, subsequently resulting in ASI increments at the rate of 1.2-2.9 days on average for ZD909 in 2013-2014, 0.7-4.2 days for JD209 in 2013, and 0.5-3.7 days for ND4 in 2014, respectively, under the treatments of D2, D3, D4, and D5 compared to that under the D1 treatment. Total florets, silking florets, and silking rates of ear showed slightly decrease trends with the plant density increasing, whereas the normal kernels seriously decreased at the rate of 11.0-44.9% on average for ZD909 in 2013-2014, 2.0-32.6% for JD209 in 2013, and 9.7-28.3% for ND4 in 2014 with the plant density increased compared to that under the D1 treatment due to increased florets abortive rates. It was also observed that 100-kernel weight of ZD909 showed less decrease trend compared that of JD209 and ND4 along with the plant densities increase. As a consequence, ZD909 gained its highest grain yield by 13.7 t ha(-1) on average at the plant density of 9.00x 10(4) plants ha(-1) , whereas JD209 and ND4 reached their highest grain yields by 11.7 and 10.2 t ha(-1) at the plant density of 6.75x 10(4) plants ha(-1), respectively. Our experiment demonstrated that hybrids with lower ASI, higher kernel number potential per ear, and relative constant 100-kernel weight (e.g., ZD909) could achieve higher yield under dense planting in high latitude area (e.g., Northeast China).