A Comparative Performance of Early Flowering Subterranean Clover Genotypes

G.A. Sandral¹, B.S. Dear¹, P.G.H. Nichols², C.T. de Koning³, P.M. Evans⁴ and D.L. Lloyd⁵

¹NSW Agriculture, Wagga Wagga Agricultural Institute, Wagga Wagga, NSW 2650²Agriculture Western Australia, South Perth, WA 6151³ South Australian Research and Development Institute, Rosedale, SA 5350⁴Agriculture Victoria, PVI, Hamilton, VIC 3300⁵ Queensland Department of Primary Industries, Toowoomba, QLD, 4350

Abstract

The evaluation of 16 early maturing Trifolium subterraneum genotypes across 6 sites identified two genotypes, SE003 and SE011 to have potential as new cultivars. Both genotypes are early flowering and are within the maturity class of Dalkeith. SE003 had the highest herbage yields of all test lines, while SE011 had a higher seed yield capacity than SE003 and was resistant to RLEM. A positive correlation was obtained between seed yield and seedling regeneration and seedling regeneration and winter herbage yield. Seed yields of 300 to 400 kg/ha provided near maximum seedling regeneration which in turn maximised winter herbage production.

Key words

Pasture legumes, Trifolium subterraneum, early flowering, RLEM.

The first record of subterranean clover in Australia was made by F. Mueller in 1887 (1). However, it was A.W. Howard, a South Australian farmer who recogn-ised the great potential of this plant. He first saw the plant in about 1889 in the Mount Barker district of South Australia and later embarked on a publicity campaign extolling the virtues of the plant. In the mid and late 1930's, certified seed of the subterranean clover cultivars Mount Barker (S.A), Dwalganup (W.A), Tallarook and Bacchus Marsh (Vic.) was commercially available. Of these cultivars, Dwalganup was the only type suitable for sowing in low rainfall environments. In the late 1950's certified seed of another early flowering cultivar, Geraldton was available, however both Dwalganup and Geraldton were found to have high levels of the oestrogenic compound formononetin which is thought to be the most important oestrogen in causing ewe infertility. Sheep grazing these oestrogenic clovers would often be effected by _Clover disease' as it is known, resulting in lambing percentages as low as 10% (3 and 4). In response to this problem a plant breeding program commenced and subsequently released the two cultivars Daliak and Northam in the late 1960's. Both cultivars were low in oestrogenic compounds and early maturing (<150 days to first flower from a mid May sowing). These cultivars have now been replaced by Nungarin, a very early maturing type released in the late 1970's and Dalkeith, released in the early 1980's. Since the release of Nungarin and Dalkeith, there have been no new developments in early maturing subterranean clovers and these cultivars now account for 98% of certified seed sold within the early maturity group.

Despite the success of Nungarin and Dalkeith both have limitations. Neither is suitable for ley farming rotations (1:1 crop:pasture) as their hard seed levels and seed softening patterns do not allow enough seed to persist from the pasture year through the cropping year into the subsequent pasture year. Both cultivars are also susceptible to red legged earth mite (RLEM, Halotydeus destructor). Any new cultivar should also have potential for superior winter and spring herbage production.

Materials and methods

Over the period 1991 to 1993, 8 Stage 1 field experi-ments, with the aim to develop superior early flowering cultivars were conducted using 114 genotypes. Experiments were located in Western Australia (3 sites), South Australia (2 sites), New South Wales (1 site) and Queensland (1 site). From these experiments 13 elite genotypes were selected for testing in stage two field experiments (final stage testing) and an additional 3 genotypes (SE014, 15 and 16) exhibiting RLEM resistance were included to make a total of 16 genotypes. These under went stage two field testing from 1995 to 1997. A total of 16 sites were sown, 5 were located in Western Australia, 3 in South Australia, 1 in Victoria, 5 in New South Wales and 2 in Queensland. All sites were located in low rainfall environments classified as receiving less than 350mm within the growing season. Experiments were sown at 5 to 10 kg/ha, depending on the site. Each had at least 3 replicates and contained the control cultivars Nungarin and Dalkeith. Grazing management systems used ranged from set socking to a loose form of rotational grazing. The Western Australian sites were sprayed out in the second year to simulate a crop.

Measurements were collected in each of the years and included estimates of seedling regeneration, winter and spring herbage yield and seed reserves. In addition, hard seededness, isoflavone content, RLEM resistance and flowering time was determined for each genotype at the University of Western Australia Field Station.

The following paper reports results from 6 stage 2 sites (Telopea Downs, Vic; Point Pass, SA; Wongan Hills, WA; and Morundah, Condobolin and Weethalle; NSW). Genotype performance and the relationships between seed yield and seedling regeneration and seedling regeneration and herbage yield are discussed.

Results

Positive relationships between seed yield and seedling regeneration occurred at Condobolin site (P<0.01), Morundah, Wongan Hills and Weethalle (P<0.05, Fig. 1). There was no significant difference between the intercepts for each quadratic equation fitted, however the linear and quadratic coefficients for Condobolin and Wongan Hills were significantly different while the same coefficients were not significantly different when the Morundah and Weethalle sites were compared (table 1). Within the data range shown in Fig 1, 21 to 33% of the seed bank emerged at Morundah in the autumn, 30 to 43% at Condobolin, 12 to 27% at Weethalle and 7 to 15% at Wongan Hills. This resulted in large differences in seedling regeneration between sites. For example at Condobolin 1500 seedlings/m² emerged from a seed set of 300 kg/ha while the same seed yield at Weethalle resulted in 450 seedlings/m². Despite the differences in seedling regeneration some genotypes performed consistently across sites with the better performing genotypes which had high seedling regeneration comprising SE003, SE014, SE011, Nungarin and Dalkeith. SE003 and SE014 often had lower seed yields than SE011, Dalkeith and Nungarin. SE010, SE002 and SE013 were consistently poorer performers across all 4 sites.

The correlation between seedling regeneration in autumn 1996 and winter herbage production for the Telopea Downs, Condobolin, Weethalle and Point Pass sites was highly significant (P<0.01, Fig. 2). Differences in the intercept and the linear and quadratic coefficients are shown in Table 1. Peak herbage yields ranged from 350 kg/ha to 1300 kg/ha (Fig. 2) and at the Condobolin and Weethalle sites these were achieved from seed yields of 300 to 400 kg/ha (Fig. 1). Genotype performance showed some consistency across sites with SE003 and SE011 having higher herbage yields, while SE010 and SE013 were generally amongst the lower yielding (Fig. 2). The herbage yields of SE014, identified as a better regenerating line in Fig. 1, were lower than those of SE003 and SE011(Fig. 2). Dalkeith and Nungarin were also amongst the top performers although Dalkeith's performance at Point Pass in South Australia was poorer relative to its performance at other sites.
Flowering times in Table 2 indicate that 7 genotypes flower around the same time as Nungarin. These genotypes all have hard seed levels higher than Nungarin (27 to 38% higher). There are no genotypes in this, the Nungarin maturity group that are considered to be resistant to RLEM. The remaining genotypes flower between 92 and 102 d.t.f. and have hard seed levels ranging from 53 to 84%. In this maturity group (Dalkeith types) 4 genotypes (SE011, SE014, SE015 and SE016) are considered to have adequate RLEM resistance.

Discussion

Positive correlations between seed yield and seedling regeneration, and seedling regeneration and herbage yield were evident at all sites. These correlations justify the emphasis placed on selecting genotypes for seed yield and seedling regeneration in Autumn with the aim to maximise winter production (2). At the Condobolin and Weethalle sites (Fig. 1) seed yields in the 300 to 400 kg/ha range achieved near maximum seedling regeneration. To achieve maximum seedling regeneration at the Wongan Hills site a seed set of 350 kg/ha was required, while 400 - 500 kg/ha was required at the Morundah site. Maximum herbage yield was achieved at Telopea Downs and Point Pass with approximately 800 to 1000 plants/m². At Weethalle maximum herbage was achiev-ed with 450 to 500 plants/m² while at Condobolin 1400 to 1600 plants /m² were required. The different seedling populations at Condobolin and Weethalle were achieved with a similar seed yield of 300 to 400 kg/ha.

SE003 and SE011 both flowered in the maturity class of Dalkeith. These lines were superior in regeneration at 3 of the 4 sites (Fig. 1). At Wongan Hills the seedling regeneration of SE003 was lower relative to its perform-ance at other sites. This was probably due to the substantially lower seed yield it set at that site. Despite this, SE003 produced the highest herbage yields at all sites (Fig. 2). Within the Nungarin maturity class none of the test lines performed as well as Nungarin.

Conclusion

The results show that both Dalkeith and Nungarin subterranean clover are particularly well adapted to low rainfall environments of the wheat belt. The experimental lines SE003 and SE011 are also well adapted and show promise as potential cultivars within the Dalkeith maturity class. SE011 has the added advantage of possessing RLEM resistance.

Acknowledgments

Financial support for the development of the early flowering subterranean clover genotypes has been provided by the Grains Research and Development Corporation and the International Wool Secretariat. The technical assistance of all personnel involved in this research program is greatly appreciated.

Reference

1. Audas, J.W. 1921. J. Depart. Agric. Vic.. 19, 650-60.

2. Rossiter, R. C. 1977. In "Exotic species in Australia- their establishment and success." Edited by D. Anderson. Proc. Ecol. Soc. Aust.. 10, 76-88.

3. Schinckel, P.G. 1948. Aust. Vet. Jour.. 24, 289-94.

4. Underwood, E.J. and Shier, F.L. 1951. Aust. Vet. J.. 27, 63-7.