CLASSIFICATION OF SOME NEW MAIZE HYBRIDS ACCORDING TO EARLINESS AND PHYSIOLOGICAL MATURITY RELATED TRAITS UNDER LOW AND HIGH NITROGEN FERTILIZATION CONDITIONS

Production of new maize hybrids with desirable package of earliness and physiological maturity related traits without compromising grains yield is critical for various agricultural systems worldwide. This investigation were carried out during 2012 season to evaluate the impact of the different genetic makeup of a set of thirteen new hybrids, developed by the authors during 2011 season, on flowering related traits such as anthesis, silking, anthesis-silking intervals (ASI), and the efficiency of light absorption of plant cover as well as physiological maturity related traits such as grains filling period, and grains filling rate. The impact of these traits on ear yield under both N stress and N sufficient conditions was also investigated. The results revealed that the tested hybrids exhibited significant differences in all tested flowering related traits. Based on the phenotype of their earliness traits (days from sowing to 50% flowering) and the general mean value of these traits (60.24 days for flowering), the tested hybrids were relatively categorized into early flowering early flowering (with number of days from ≤ 50 to 55 days, e.g. B73X PHG47, B73X HP301, B73X PH207, B73X PHj40, B73X NC358, B73X Mo17), intermediate flowering (hybrids with number of days from 55 to 65 days, e.g. B73X CML103, B73X Tzi8, B73X B97, B73X Rg5, B73X Inb209, B73X Sids63), and late flowering (with number of days from 65 to ≥ 70 days, e.g. B73X Inb.204, and the check crosses SC3084, SC173, SC168, SC167, SC10) hybrids. The results also revealed significant differences among the tested hybrids in grains filling period, grains filling rate, and physiological maturity under both N stress and N sufficient conditions. The magnitude of grains filling rate ranged from 1.4 g/day to 6.8 g/day. Based on the values of individual and general mean grains filling rates, the tested hybrids were classified into low rate grains fillers (≤ 1.4 to 3.5 g/day, e.g. B73X HP301, B73X PHj40 and B73X PH207), intermediate rate grains fillers (3.5 to 4.5 g/day, e.g. B73X Phg47, B73X B97, B73X Mo17, B73X Inb209, B73X Sids63, B73X Rg5, B73X Inb.204, SC3084, SC168, SC167, SC173, SC10) and rapid rate grains fillers (4.5 to ≥ 6 gram/day, e.g. B73X CML103, B73X TZI8 and B73X NC358) under N stress conditions. The classification of the tested hybrids was slightly changed under N sufficient conditions because of the high N induced changes in grains filling rates. The correlation analysis indicated strong positive correlation between ear yield plant -1 and grains filling rate under low (r = 0.97**) and high (r = 0.98**) N rates. Interestingly, among hybrids, the cross B73X CML103 maintained the highest ear yield with acceptable package of other flowering and physiological traits. It attained the highest values of grains filling rate (6.87 g/day, low N, 6.05 g/day, high N), moderate length of grains filling period (44.33 days), and the shortest ASI (3.67 days). These results indicate that the cross B73X CML103 has strong sink tissues, vigorous and sustainable remobilization of its metabolic resources after pollination and will be less vulnerable for pollination stress. Therefore, the cross B73X CML103 Ibraheem, F. and M. A. Abdel-Moneam 726 exhibits improved physiological adaptation to N stress and better management of its internal N under high N rate, and consequently this study recommend this cross (B73X CML103)for large scale evaluation and commercial production.