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Seedling vigor at suboptimal temperatures is an important characteristic in maize (Zea mays L.) growth in cool regions. Selection for improved vegetative growth and seasonal dry matter accumulation at suboptimal temperatures would be more efficient if seedling traits related to field performance could be identified under controlled conditions. This study evaluated if root traits of seedlings grown at cool or warm temperature regimes are predictive of early growth and silage yield in the field. Twenty early- to medium-late maturing European hybrids (FAO maturity ratings 200-280) were grown in a solid substrate until the third leaf stage under two controlled temperature regimes (25/22.5 ° C and 15112.5 ° C, day/night) and until silage maturity in three field environments on a Orthic Luvisol soil in Central Germany. The closest relationships with early field growth were found for the total length of the main roots (r = 0.65, P < 0.01) and total length (r = 0.60, P < 0.01) and number (r = 0.68, P < 0.01) of first-order laterals of the seminal roots at 25/22.5 ° C. Silage yield was best correlated with the branching density of the seminal roots (r = 0.66, P < 0.01) at 15/12.5 ° C and the total root surface area (r = 0.58, P < 0.01) at 25/22.5 ° C. These root traits could potentially be used only in combination with other secondary characters for the indirect selection for shoot performance because individual root traits explained less than 50% of the variation in shoot weight in the field. Negative correlations between the chilling stability of most seedling traits, as expressed by the relative difference of trait means at 15/12.5 ° C and 25/22.5 ° C, and silage yield indicated that chilling-tolerant genotypes may be less capable of benefiting from the warmer temperatures during later growth stages., Low temperature is a major factor in the growth reduction of maize in temperate climates, especially at the seedling stage (Miedema, 1982). Cold tolerance, therefore, is considered to be an [...]

Maize (Zea mays L.) grain yield depends on the number of kernels per plant that reach maturity. In this work, associations between floral development within the ear and final grain number of maize hybrids differing in prolificacy were studied under nonstress conditions in Argentina. In one experiment at Rojas (34 ° 08'S), four hybrids were sown on four dates, at 8 plants [m.sup.-2] during 2 yr. Ears were observed at silking to determine the variation in the number of spikelets per ear. In the second experiment at Salto (34 ° 33'S), a nonprolific (DK638) and a prolific (DK 3S41) hybrid were sown at 7 plants [m.sup.-2] on three dates. Ears were examined between the three-leaf stage and silking + 12 d to determine floral differentiation. No sowing date effect was evident for the number of spikelets per ear, the number of rows per ear, or the number of spikelets per row, but hybrids differed for these characters (P [is less than] 0.05). During active spikelet initiation, spikelet number in apical ears increased at a rate of 0.13 (DK 638) or 0.17 (DK 3S41) spikelets per row per ° Cd. At silking, almost all spikelets along a row in the apical ear had completed floral development in both hybrids, but the prolific type showed less spikelet abortion in the apical ear and a more synchronous development between ears. Kernel number per ear was independent of floral development stage at silking, but was related to the rate of ear growth (in length) around silking. These results suggest that assimilate partitioning to the ear during this period is critical for kernel set., Grain yield of maize is mainly dependent on the number of kernels per plant that reach maturity (Cirilo and Andrade, 1994a; Otegui et al., 1995b); this yield component is very [...]

Adaptation of maize (Zea mays L.) to early planting dates requires the improvement of cold tolerance, which implies high percentage emergence and vigorous seedling growth under cold temperatures. The objectives of this work were to evaluate the combining ability of elite European maize inbreds for cold tolerance and to study the inheritance of cold tolerance. Five maize inbreds, differing in sensitivity to cold temperatures, were crossed by means of a diallel design. Hybrid seed was obtained at two production environments. Hybrids were planted on trays filled with sterilized peat in a cold chamber at four minimum temperatures, and these hybrids were also grown in field trials at two locations in northwestern Spain. The most cold-tolerant inbreds, according to previous unpublished inbred evaluations in the cold chamber, F7 and EA2087, produced the most cold-tolerant hybrids, inbred F7 performed slightly better in hybrid combinations than EA2087 for emergence-related traits in the cold chamber, and EA2087 was superior in hybrid combinations to F7 for seedling growth. The inbred 177 may contribute cold tolerance at emergence, whereas EA2087 contributed cold tolerance for both emergence and seedling growth. In the field, inbreds F7 and H104W were the best parent for cold-tolerant hybrids. Percentage emergence was not related to the other traits. Generally, the genetic regulation of cold-tolerance traits conformed to an additive-dominance model, and it should be possible to combine both high percent emergence and vigorous seedling growth. A promising source of new cold-tolerant inbreds is the cross between EA2087 and F7., MAIZE IS PRESENTLY GROWN at 55 ° latitude in both the northern and southern hemispheres, even though it is widely considered a warm weather crop (Shaw, 1988). As generally accepted, [...]