Genetic Male Sterility (Ms44) Increases Maize Grain Yield

Abstract

During reproductive development in maize (Zea mays L.), the tassel and the ear compete for available nutrients, at the expense of ear development. The objective of this study was to determine if male sterility (MS) genes could be used to reduce the competition between developing reproductive organs and to improve ear and kernel development. Nitrogen (N) budget experiments conducted in the greenhouse revealed that, under N limiting conditions, the tassel continued to accumulate N prior to anthesis while the ear stopped accumulating N. This finding confirmed prioritization of N partitioning to the tassel at the expense of the developing ear during the critical period of kernel set. Genetic male sterile (GMS) genes were used to terminate pollen production. At anthesis, ear biomass of male sterile plants carrying the ms1 allele increased 92% compared with male fertile plants in a greenhouse experiment. In subsequent field testing, GMS (Ms44 allele) male sterile plants increased grain yield across six N rates between 0 and 170 kg ha−1 (784–2301 kg ha−1), three plant densities between 79,070 and 158,140 plants ha−1 (489–3706 kg ha−1), and in flowering drought stress environments (2768 kg ha−1), compared with male fertile plants. Yield was improved due to increased silk number per ear, kernel number per ear, and reduced barren plants. The dominant GMS allele, Ms44, can be used to produce completely sterile or 50:50 segregating male fertile:male sterile hybrid seed through the use of a transgenic maintainer line. Growing a blend of male sterile and male fertile plants can improve grain yield under a range of growing conditions, including those where drought and N limit crop yield.

Nitrate Assimilation Limits Nitrogen Use Efficiency (NUE) in Maize (Zea mays L.)

“…According to the PSNT, soil nitrate concentrations greater than 25 mg N L −1 (1.78 mM) require no supplemental N fertility, suggesting this level of soil nitrate is sufficient for optimum economic maize yield. R1 ear-weight response to nitrate concentrations from 1 to 4 mM KNO 3 is consistent with the PSNT with 1 mM KNO 3 being insufficient to support R1 ear-weight whereas 2 mM KNO 3 is sufficient and 3 mM KNO 3 , and above, being luxurious levels of fertilizer N [41]. In the results shown in Figure 4, R1 ear-weight was established by V12 and increasing or decreasing KNO 3 levels from V12, on, had little effect on R1 ear-weight.…”

“…A Conviron PGR15 growth chamber set at 30 • C, 60% RH, 16 h light/25 • C, 50% RH, 8 h dark was used to grow the maize model system plant, Gaspe Flint-3 (GF3) (manufacturer, city, state, country) [41] under controlled environmental conditions. A semi-hydroponics irrigation system [41], similar to that described [42], was used in growth chamber and field hydroponics to attain a high level of control of N input. When ammonia was used as an N source 1 mM NH 4 Cl was substituted for KNO 3 but KCl was maintained at 4 mM.…”

“…Ciampitti et al [54] observed a similar relationship between biomass and grain yield, though no direct correlation with N fertility was made. Loussaert et al [41] showed the developing ear competes for N with the developing tassel, with the tassel having priority; increased R1 ear-weight in male sterile plants was independent of R1-biomass but associated with reduced tassel biomass. Ear length and ear-weight at R1, but not ear-width, were responsive to N and were highly correlated to grain yield in both high and low N ranges.…”

Silk Development and Kernel Set in Maize as Related to Nitrogen Stress

“…A method investigated by DuPont Pioneer has been the integration of the Ms44 sterility allele into hybrids. Sterile plants produced a greater number of silks under both limited and adequate N, supported by increased ear biomass at R1, and led to an increase in the number of KPE across N rates relative to fertile plants (Loussaert et al, 2017). Further testing of this trait in a range of environments including low N and drought stress confirmed yield enhancement, most likely through increased KPE (Fox et al, 2017).…”

Selfish genes and sexual selection: the impact of genomic parasites on host reproduction

“…For example, in dioecious plants there is evidence that mitochondria can induce cytoplasmic sterility and abort pollen production altogether, instead diverting these resources to enhance the female function which will favour mitochondrial transmission (e.g. Loussaert et al , 2017). This generates selection on the nuclear genome to suppress the action of such selfish mitochondria and restore sex ratio to unity (Fujii, Bond & Small, 2011).…”