PREDICTION OF EAR EMERGENCE IN WINTER WHEATS GROWN AT TEMORA, NEW-SOUTH-WALES

This study examined factors that determine ear emergence in winter whe ats grown at Temora, New South Wales. Three development factors were c onsidered: degree of winter habit, response to photoperiod, and intrin sic earliness. The effect of winter habit was first examined by using 3 pairs of related wheats that differed for spring-winter habit. Wheat s were sown under irrigation from mid February to June, for up to 4 co nsecutive years. Ear emergence was recorded in days of the year for ea se of field interpretation, and in photo-thermal time to measure delay in development. Winter habit was found to delay ear emergence through out this sowing range. Ear emergence was then studied in 23 winter whe ats that as a group encompassed a broad range for each of the 3 develo pment factors, and these winter wheats were grouped on the basis of co mbinations of development factors. Differences in ear emergence betwee n these groups guided the construction and testing of regression equat ions that described ear emergence as a function of sowing date and of the 3 development factors. Many combinations of factors were associate d with the time of ear emergence (i.e. 1 October) at Temora that best optimises the balance between frost risk and yield potential. Combinat ions oi development factors also influenced the flexibility of sowing time for winter wheats grown at Temora. These findings may assist the breeding of new winter wheats that can be sown over a longer period th an current winter cultivars.