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Early maturity improves grain yield and water use efficiency of wheat in low rainfall regions of Western Australia

K.L. Regan, K.H.M. Siddique, D. Tennant and D.G. Abrecht

Department of Agriculture, Baron-Hay Court. South Perth. WA 6151

Summary. Wheat cultivars appropriate for late sowings in low rainfall short season environments are currently unavailable to farmers in the eastern and north-eastern wheatbelt of Western Australia. In 1991 and 1992. field experiments were conducted in low rainfall regions of the Western Australian wheatbelt to study phenology, water use and grain yield components of some early maturing genotypes. Early maturing genotypes had faster developmental rates and reached anthesis up to 12 days quicker than some of the standard cultivars without any reduction in biological yield, harvest index and grain yield. The pattern of water use also changed for these genotypes with more water used in the post-anthesis period. which resulted in greater water use efficiency.

Introduction

Analysis of historical rainfall records shows that the break of the season occurs after I June in about 25% of years in the low rainfall (< 325 mm) eastern and north-eastern wheatbelt of Western Australia ( I). Wheat seeding may be even later because earliest planting opportunities in each year are often used to plant grain legumes. Yields in these seasons are likely to be low as the high yielding package of early sowing, longer season cultivar and greater fertiliser input, that has been successful where the season breaks early (2), does not apply.

At present. cultivars flowering earlier than those currently grown commercially are not available to farmers in the low rainfall parts of the Western Australian wheatbelt. Demonstration that very early maturing genotypes can out-perform current cultivars would open new opportunities for breeding programs to select high stable yielding cultivars for these environments. The experiments reported here are part of a project to investigate whether improved water use efficiency and greater and more stable wheat yields can be achieved with wheat genotypes that reach anthesis earlier than currently available cultivars in low rainfall, short season environments.

Materials and methods

Field experiments were conducted at Merredin in 1991. and Merredin, Morawa and Mullewa in 1992 in the eastern and north-eastern wheatbelt of Western Australia. Sowing dates and growing season rainfall for each experiment are presented in Table I. At Merredin in 1991 two standard cultivars and five early maturing genotypes were sown in a randomised block design with three replicates. In 1992. the experiments at Mcrredin, Morawa and Mullewa included five standard cultivars and six early maturing genotypes sown in a randomised block design with five replicates. Plot size was 2.16 m (12 rows), wide by 40 m except Morawa. which was 1.42 m (8 rows) wide by 20 m.

The early maturing genotypes used in this study included F, derived lines grown in the F5 generation in 1991 and F6 in 1992 from the WADA wheat breeding program (W87-022-511, W87-072-523. W87-1 14549 and W87-410-509). TFQ-I 13 is an introduced line from eastern Australia which is very early and the other lines (113-2 and BD9-I B) were obtained from Dr R. Richards, CSIRO, Canberra. Kulin. Gamenya, Halberd, Spear and Wilgoyne were selected as standard cultivars.

Table I. Site. year, sowing date and growing season rainfall for field experiments at Merredin. Morawa and Mullewa

Anthesis dates for each genotype were determined in days after sowing (DAS) and thermal time or degree days (3). Grain yields were determined from I m2 quadrat samples harvested at ground level at maturity. Soil water measurements at Merredin in 1991 were monitored at fortnightly intervals from sowing until maturity using a neutron moisture meter.

Results and discussion

In this study. the time from sowing to anthesis varied from 71 to 123 DAS across sites and years and some genotypes (TFQ-1I3 and W87-022-51 I) reached anthesis up to 11 and 12 days earlier than Kulin (Table 2). One of the potential problems with rapid development is that it may reduce the amount of biomass produced at anthesis, and hence, potential yield (4). Although we observed lower anthesis biomass in some of the earlier genotypes by maturity, biological yields were comparable to standard cultivars (results not presented here).

Table 2. Time to anthesis in days after sowing and mean thermal time (C.day) for wheat genotypes at Merredin (ME), Morawa (MO) and Mullewa (MU) in 1991 and 1992

The mean grain yield was greatest at Merredin in 1992 (Table 3). There was a trend, although this was generally not significant (P=0.05), for the earlier maturing genotypes to yield more and have a higher harvest index than the standard cultivars at all sites in 1991 and 1992. Poorer yield trends were evident at the Mullewa site due to herbicide damage. Herbicide applied when early maturing genotypes had extended flag leaves resulted in leaf bleaching and, consequently, may have reduced photosynthesis. Harvest index was fairly consistent for each genotype across sites, except Merredin in 1992. Despite having the highest yield at this site, the mean harvest index was only 0.28 compared to 0.37 (Merredin 1991), 0.36 (Morawa) and 0.38 (Mullewa). This was probably due to the large amount of biomass produced in the pre-anthesis period as a result of higher than average rainfall.

At Merredin in 1991. total water use was greater for Gamenya than the other genotypes (Table 4). Water use was greater with later maturing genotypes due to greater water e \ traction. except for Kulin (5). The ratio of pre- to post-anthesis water use was generally lower for genotypes reaching anthesis quicker. Grain yields and water use efficiency for grain production were highest in the range of genotypes flowering between 91 and 99 DAS. lowest for Gamenya and intermediate for TFQ 113 (88 DAS). Despite some of the genotypes reaching anthesis from five to twelve days before Kulin there were no yield penalties and water use efficiencies remained high.

Table 3. Grain yield (g/m2) and harvest index for genotypes grown at Merredin (ME). Morawa (MO) and Mullewa (MU) in 1991 and 1992

Table 4. Pre-anthcsis water use (Eta), post-anthesis water use (Eta), total water use (E1). ratio of pre to post-anthcsis water use (Eta/Etpa) and water use efficiency for grain yield (WUE2r) for genotypes at Merredin in 1991

Greater yields in early maturing genotypes are likely to be expressed more in years where rainfall diminishes rapidly in the post-anthesis period. Although in 1992 the rainfall received in October was low, all sites received more than double the average during August and September. This increased the amount of stored water available and the amount of assimilate reserves as a consequence of greater biomass production and may have reduced the penalty in yield expected for the later maturing genotypes. In 1991, Merredin received 12% less rainfall than the seasonal average with low rainfall in August and a dry finish. The amount and distribution of rainfall in this season is more consistent with the type expected to illustrate yield advantages of early maturing genotypes with late sowing.

The results from these initial experiments illustrate a potential for wheat with early maturity in low rainfall, short season environments. However, they are from a limited number of sites and years and the genotypes used were selected on maturity alone. Further research is currently underway to identify appropriate agronomic practices for these and other genotypes to establish their value for commercial crop production.

Acknowledgements

This project is funded by the Grains Research and Development Corporation (WA).

References

1. Kerr. N. and Abrecht. D.G. 1992. J. of Agric. Dept. of Agric. Western Australia. 33, 32-35.

2. Anderson. W.K. and Smith. W. 1990. Aust. J. Exp. Agric. 30. 607-614.

3. Weir. A.H.. Bragg. P.L.. Porter. J.R. and Rayner, J.H. 1984. J. Agric. Sci. 102. 271-382.

4. Fischer. R.A. 1979. J. Aust. Inst. Agric. Sci. 45, 83-89.

5. Siddique. K.H.M.. Tennant. D.. Perry. M.W. and Belford. R.K. 1990. Aust. J. Agric. Res. 41. 431-447.

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