| Abstrakt: |
Winter wheat (Triticum aestivumL.) cultivars were planted in the field on 11 and 28 Nov. 1977 and on 8 and 24 Jan. 1979 near Weslaco, Texas, at 26° 13' N Lat to document their developmental responses and yield under conditions of temperature and photoperiod that limit vernalization, floral initiation, and grain filling. Such studies help define controlling factors in range of adaptation and necessary inputs for growth models to have wide geographic applicability. For both season's plantings on Hidalgo sandy clay loam (Typic Haplustroll), Feekes‐Large phenological stages were observed and inflorescence development was determined by dissecting sample plants removed from the plots. The number of fully expanded leaves and green leaves per main culm and the number of secondary tillers were also recorded for tagged plants pf the 28 November planting on 33 dates during the growing season. Head length, heads/m2, kernels/head, mg/kernel, and grain weight/m2were determined from five row segments totaling 1 m2in each planting. The 1977 plantings vernalized naturally on 800 cumulative hours of ambient temperature between 0 and 10 C by 4 March, but they remained vegetative during the short days of winter and produced leaves linearly in response to cumulative heat units. Floral differentation (‘double ridge’ stage), stem elongation (first node), and anthesis varied about a week among cultivars. Average yield components across all cultivars were: 1977‐78 season— 442 heads/m2, 11.2 kernels/head, and 8.0 mg/kernel, and 1978‐79 season—436 heads/m2, 14.6 kernels/head, and 22.5 mg/kernel. Grain yield (oven‐dry basis) averaged 48.8 g/m2or about one‐eight commercial levels for the 1977‐78 season, and 141 g/m2for the 1978‐79 season. Duration of grain‐filling (anthesis to mealy ripeness) averaged 17 and 20 days for the respective seasons. Within the temperature range 15 to 27 C, the grain‐filling period (data include three spring wheats also studied) for the 1977‐78 data was shortened by 3.4 days for each 1 C rise in average daily temperature. Evidently insufficient photoperiod for floral initiation is more restrictive on winter wheat production under semitropical conditions than the vernalization requirement. In both seasons nonvernalized wheat headed even when planted as late as 24 January, but regardless of planting date or preplant vernalization it did not floral initiate until March. Consequently, grain filling occurred under a temperature regime that severely shortened its duration, and small kernels were produced. Because of rapid leaf production during mild winter days of the semitropics, wheat could be an excellent winter forage if leaf rust were controlled. |
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