Biserrula pelecinus L.

Description

Biserrula is a monotypic genus and is classified as follows:
Family: Leguminosae
Sub-family: Papilionoideae
Tribe: Galegeae
Sub-tribe: Astragalinae
Genus: Biserrula
Species: pelecinus

The name is derived from the Latin bis "twice" and serrulatus "serrate", a reference to the serrations of the crest on each side of the flattened pod resembling a 2 edged saw; and from the Greek pelecos "axe", a reference to the shape of the pod (Allen and Allen 1981). Biserrula is an annual ± pilose prostrate herb up to 40 cm tall. Leaves are imparipinnate, the stipules are rather papery, ovate-lanceolate up to 4 mm long and 2.5 mm wide. Leaflets are usually opposite in 5-9 pairs, elliptic-oblong, up to 10 mm long and 5 mm wide, cuneate at the base, and notched at the apex. The racemes are axillary, with 1-11 flowers, the calyx is green, the tube 1.5 mm long, the corolla bluish, 5 mm long and 3 mm wide. Stamens are 10 of which only 5 are fertile; the anthers are uniform; the ovary is sessile, and there are many ovules (Gillet 1964). The pod is linear, dorsiventrally compressed, 2-4 cm long, the sutures forming a central line between the sinuate-dentate crests, the valves are indehiscent; the pod is divided inside by a narrow longitudinal septum connecting the sutures, each half containing about 8-10 small yellowish, heart shaped seeds of about 1 mg (Allen and Allen 1981).

Biserrula is native to the Mediterranean areas of Europe and north Africa and the Canary Islands (Allen and Allen 1981). It has also been found in the highlands of east Africa where it was classified as subspecies leiocarpa by Richard (1847) (cited in Gillet 1964) because it lacks the coarse serrations on the crest of each side of the pod. Recently biserrula has been collected in the Greek Islands (Ewing and Howieson 1988, Howieson and Loi 1994, Nutt et al. 1996), Morocco (Beale et al. 1991), Sardinia (Howieson and Loi 1994, Loi et al. 1995), and Syria (Ehrman and Cocks 1990). It is also found in Spain (Malo and Suarez 1995, Espigares and Peco 1995), Portugal, Tunisia and Corsica. Biserrula usually occurs in areas from 0 to 1,000 m above sea level (Pignatti 1982, Howieson and Loi 1994), and in regions receiving from as little as 325 mm annual average rainfall (Greek Islands) (Ewing and Howieson 1988) to more than 700 mm in Sardinia (Loi et al. 1995) and Syria (Ehrman and Cocks 1990). It is common on acid soils, and more than 75% of the accessions collected by Howieson and Loi (1994) were collected from soils of pH 6 or below. Loi et al. (1995) reported that biserrula is often the only legume present on severely acid and coarse sandy sites, demonstrating its high level of drought resistance and ability to survive on poor soils (see also Carr et al. 1999). Biserrula has been introduced into Australia on many occasions. However, it consistently failed in nursery rows, probably because of special requirements for rhizobia. In 1993, biserrula root nodule bacteria were introduced (Howieson and Loi 1994), and the selection of appropriate strains was possible, resulting in the successful establishment of the species in Western Australia (Howieson et al. 1995).

Spring herbage yields of ungrazed and grazed biserrula in Western Australia range from 2.5 to 10 t/ha, which compares favourably with pink serradella, yellow serradella and subterranean clover. Although slow to nodulate in the first growing season, second and subsequent year nodulation of biserrula is excellent. Biserrula has a very good quality forage in terms of dry matter digestibility, metabolisable energy and crude protein. Experience has shown biserrula to be as tolerant as subterranean clover to heavy grazing, and to provide green feed for an extra 2 to 4 weeks compared to subterranean clover in a normal year. This is because of a combination of deeper roots and inherent drought tolerance in association with a semi-determinant nature. It is a prolific seed producer, with seed yields ranging from 300 Kg to 1, 500 Kg/ha, and because of its very small seed size (1/6 of the size of the sub clover) this translates to very high seed numbers. In 1999 at Tincurrin WA, 370 mm rainfall, biserrula subjected to a heavy stocking rate of 35 sheep/ha for 3 weeks, followed by 12 sheep/ha from the middle of October to the middle of January was able to set almost 400 kg of seed per ha, whilst the ungrazed control plots reached over 1 tonne of seed per ha. Biserrula has an acid tolerant microsymbiont (Mesorhizobium spp.) which can persist and give excellent nodulation on soils with pH as low as 4.0 (CaCl₂). The plant has a deep root system (over 2 m), which is very important for plant survival during long periods of drought and to provide a longer period of green feed for grazing animals. Also, young biserrula seedlings appear to survive short periods of drought much better than most other temperate annual pasture legume species.  The prostate growth habit and the small seed size (1 mg) provide very good persistence under both heavy winter and spring grazing. Approximately 40 % of the seed can survive ingestion by sheep. Therefore summer grazing is unlikely to harm the stand density or long term persistence. The hardseededness of biserrula and its pattern of softening suggest that it is ideal for ley farming systems. Our studies indicate that several advantages may be achieved by including biserrula in the rotation.

• Firstly, because of the ability of large seed numbers to survive ingestion, biserrula does not need to be managed as carefully as annual medics during summer grazing.
• Secondly, the hardseeds of biserrula become germinable over the end of summer-autumn, allowing a large proportion of the seed bank to escape false breaks, which are the main cause of poor regeneration of subterranean clover.
• Finally, high seed yield and hardseededness suggest that biserrula will survive in the seed bank for many years. If so biserrula can be used as a tool to control herbicide resistance in weeds (e.g. ryegrass) as seed set is not required in every pasture year.

Biserrula under heavy early winter grazing adopts a prostrate growth habit. This allows biserrula to compete heavily with the more upright weed species which are selectively removed by the grazing animals. Also, the extremely high level of hardseed in biserrula provides longevity to the seed bank from a single season’s production. Therefore, spraytopping, which can seriously limit the persistance of softer seeded species in crop rotations, can be applied to Biserrula pastures without jeopardising long term persistence. Biserrula is well adapted to a wide range of soil types and pH levels, but does not tolerate waterlogging and deep infertile sands, where the serradellas are the only current legume option.            Biserrula can be used as a mixture with either subterranean clover and serradellas in acid soils and medics on neutral to alkaline soils. It is very important to sow biserrula not deeper than 2 cm to obtain an optimal establishment.

Biserrula can be used as a mixture with either subterranean clover and serradellas in acid soils and medics on neutral to alkaline soils. As with other pasture legumes, biserrula should be treated as a seed crop in its first season to ensure a maximum seed set. This practice costs more in time and money but will ensure ongoing success of the pasture and avoid the possibility of a costly resowing. Spray top the paddock in the previous spring or select a paddock coming out of a cereal crop where broad-leaf weeds have been successfully controlled.  Broadleaf herbicides such Broadstrike and Spinnaker can not be used on biserrula. In high rainfall regions delay sowing to achieve good weed control with a knock-down herbicide. Grass weeds can usually be controlled with a selective herbicide.In low rainfall regions, decrease weed burden in the previous season, then sow biserrula as close to the break of season as possible.Seed of biserrula must be inoculated with its unique inoculant Biserrula Special. Follow directions on the packet carefully as biserrula will not nodulate with any other inoculant. For best results biserrula should be lime-pelleted. For each 25 kg of biserrula seed use one packet of inoculant, 1.5 litres of a 2% methocel solution and 5 kg of finely ground calcium carbonate lime.Sow at 2-10 kg/ha, depending on the mixture of pasture legume options available. It is very important to sow biserrula not deeper than 2 cm to obtain an optimal establishment (which can be achieved by dropping seed on the surface and covering with trailing harrows). Sow with 150 kg/ha superphosphate, or super/potash if on deep sand.Control red-legged earth mites until plants have three true leaves. Graze lightly in the first season (particularly spring) to allow maximum seed set. For seed crops, inspect for blue-green and cowpea aphid and control if present in large numbers. Graze heavily over the summer for good regeneration in the second year.

Cultivars

Cv. Casbah (Loi et al. 1997) is the only variety of biserrula currently available in the world. It is a vigorous, mid-season cultivar, flowering about 100-105 days after sowing in south-western Australia. It appears to be adapted to areas with annual rainfall as low as 350 mm. Its flowering time is similar to Dalkeith subterranean clover.

Links

• Murdoch University: research report on "The role of genetic variation in reproductive strategies and host-rhizobia relationships in Biserrula pelecinus L."
• Murdoch University: research report on "The ecology of Biserrula rhizobia and implications for field nodulation of Biserrula pelecinus L."
• Germplasm Resources Information Network USA: short description and list of references

Allen O.N. and Allen E.K. (1981); Beale P.E. et al. (1991); Carr S.J. et al. (1999); Ehrman T. and Cocks P.S. (1990); Espigares, T. and Peco, B. (1995); Ewing M.A. and Howieson J.G. (1988); Gillet, J.B. (1964); Howieson, J.G. and Loi, A. (1994); Howieson J.G. et al. (1995); Loi A. et al. (1995); Loi A. at al. (1997); Malo J.E. and Suarez F. (1995); Nutt B.J. et al. (1996); Pignatti, S. (1982)

Loi A. at al. (1996); Loi A. et al. (1997); Loi A. et al. (1999); Loi A. et al. (1999a);  Loi A. (1999b); Loi A. et al. (2000); Nutt B.J. and Loi A. (1999)