| The control of ear emergence by vernalization and photoperiod
in three wheat crosses R.G. FLOOD* and G.M. HALLORAN School of Agriculture and Forestry, University of Melbourne, Parkville, Victoria 3052, Australia Floral development and ear emergence in wheat is largely controlled by the plant's response to vernalization and photoperiod. A third factor, basic development rate, also appears to exert an important influence on wheat development (FLOOD 1983). Optimum flowering time and its consequent effect on yield potential is, therefore, strongly influenced by vernalization, photoperiod and basic development rate. There is conflidence concerning the physiological interaction of vernalization and photoperiod in controlling floral development, although recent evidence suggests that prolonged vernalization does not remove the requirement for long days and short days do not replace the need for vernalization (FLOOD 1983). These responses do, however act alone and together to exert strong influence on leaf number (PUGSLEY 1968) and spikelet number per ear (PUGSLEY 1968 ; HALSE & WEIR 1970). This experiment was designed to study the inheritance of photoperiod response associated with a weak vernalization response in three wheat crosses. The influence of vernalization and photoperiod responses on spikelet number per ear, an important component of grain yield, was also examined. Materials and Methods Three cultivars of different photoperiod responses, Sunset, Kogat and Thatcher were hybridized with the cultivar Condor which has a low level of vernalization response. The developmental characteristics of the parents are listed in Table 1. The three crosses were made by one of us (G.M.H.) and F2 Seed of each cross was used in the present experiment. Seeds of the parents and crosses were vernalized for six weeks by allowing seed to imbibe for 48 hours at room temperature and then sown into a sterile mixture of sand and peat (1 : 1 by volume) with adequate nutrients and placed in a cold room at 3C for vernalization. On emergence, the seedlings were given a 12 hour photoperiod for the duration of the vernalization treatment, provided by two 60 W incandescent lamps 40 cm above them. After vernalization the seedlings were kept at room temperature for three days to prevent possible de-vernalization (CHOUARD 1960). Vernalized seedlings plus an unvernalized set (germinated five days befor the end of the vernalization treatment) were transplanted (4 per 18 cm diameter pot) into of a mixture sand a loam (1 : 1 by volume) with adequate nutrients. Between 20 to 30 plants of the four parents and the three F2's were grown under two photoperiod regimes following two vernalization treatrents, as shown below. 6 weeks vernalization : Short photoperiod-natural photoperiod No vernalization : Long photoperiod-18 h photoperiod The short photoperiod was natural daylength which ranged from 9.6 to 12.3 h during the course of the experiment (11 June to 30 September, 1979). The long photoperiod was obtained by extending natural daylength by the use of incandescent lamps operated through a time clock. Days from transplanting to ear emergence and total spikelet number per ear were recorded for the main stem of each plant. |
| * Present address: Victorian Crops Research Institute, Private Mailbag 260, Horsham, Victoria 3400, Australia. |
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