Ground Cover North : Ground Cover 089 November-December 2010 - North
NOVEMBER -- DECEMBER 2010 GROUND COVER Pastures 13 By Kellie Penfold n BindoonA and RosabrookA subclovers are the outcome of a breeding program started back in 1992 to find varieties with increased seedling resistance to redlegged earth mite (RLEM). Subclover is the most popular pasture legume in the low to medium-rainfall zone with an estimated 22 million hectares sown in Australia. To date the only means of minimising RLEM damage to subclover-dominant pastures is through pesticide applications planned using the TIMERITE program, a system that establishes the best windows for RLEM control in particular areas. By attacking plants at the cotyledon stage, RLEM cause large seedling losses after they germinate in autumn and early winter. They also cause a reduction in seed yield and loss of herbage production in winter and spring. Dr Phillip Nichols, senior research officer (pasture breeding, agronomy and ecology) in the Pasture Science Section of the Department of Agriculture and Food, Western Australia (DAFWA), told a recent Pastures Australia update that resistance among some RLEM populations to two widely used pythethroid chemicals has recently been reported. Pastures Australia is a research collaboration between the GRDC, Meat and Livestock Australia, the Rural Industries Research and Development Corporation, Australian Wool Innovation and Dairy Australia. "The deployment of resistant varieties offers an additional and more cost-effective strategy for reducing RLEM losses," Dr Nichols says. BindoonA and RosabrookA originate from crosses made in 1992 of the cultivar DenmarkA to DG1007 and S3615-H. These are two varieties from Italy with increased seedling resistance that were identified from more than 900 accessions tested from the world's largest subclover collection hosted by DAFWA. Breeding and selection of progeny was conducted in Perth from 1994 to 2003, with selection also being conducted for other criteria such as low oestrogen levels, clover scorch resistance and hard seededness. Field evaluation was carried out from 2004- 07 in target environments across southern Australia as part of the National Annual Pasture Legume Improvement Program (NAPLIP). BindoonA (tested as SM029) was evaluated as one of 12 elite midseason breeding lines in the 450 to 600-millimetre rainfall zone and RosabrookA (tested as SL027) was evaluated as one of 14 elite late-flowering breeding lines in areas with more than 600mm annual rainfall. Herbage production in winter and spring and both seedbank and regeneration densities were measured over a three-year period. Plots were grazed by sheep and no insecticides were used to enable expressions of the benefit of increased RLEM resistance. BindoonA was the outstanding performer in the mid-season group, with 53 per cent greater winter herbage production than YorkA and 22 per cent more than Seaton Park, while the seedling density of BindoonA was 69 per cent greater than YorkA and 72 per cent more than Seaton Park. It also had 33 per cent greater seed production than YorkA and 40 per cent more than Seaton Park, with similar spring herbage production to Seaton Park and 14 per cent more than YorkA. RosabrookA's seedbank was 28 per cent greater than DenmarkA, resulting in a 43 per cent greater seedling regeneration density in the second and subsequent years. This translated into a 23 per cent higher winter herbage production than DenmarkA, while spring herbage production was five per cent higher than DenmarkA. In trials in a paddock heavily infested with RLEM that had RLEM densities manipulated with pesticides, BindoonA and RosabrookA suffered significantly less cotyledon damage in low to moderate RLEM densities than other commercial varieties, but differences in damage levels were similar at high RLEM densities. The excellent early season performance of BindoonA and RosabrookA in field evaluation trials suggests this level of resistance is enough to have a positive effect on pasture productivity in most seasons. BindoonA will be recommended as a replacement for Seaton Park and YorkA and is best suited to areas of southern Australia where the growing season extends to late October with an annual rainfall of around 425 to 625mm. Limited quantities of certified seed were available for sowing this year from PGG Wrightson Seeds with larger quantities expected in 2011. Best suited to areas where the growing season extends to late November and with an annual rainfall of more than 650mm, RosabrookA is a replacement for DenmarkA and is licensed to Seed Force Pty Ltd, with limited quantities of certified seed available in 2011. Dr Nichols says while the use of these cultivars is recommended to reduce RLEM damage, it should be considered an additional strategy and insecticides should still be considered at sowing to guarantee successful pasture establishment and at times of high RLEM densities. □ GRDC Research Code AWR00002 More information: www.grdc.com.au/pasturesaustralia; Dr Phillip Nichols, email@example.com; www.grdc.com.au/AWR00002 NEW VARIETIES LEAVE MITES HUNGRY Subclover is one of the most widely grown pasture species in Australia and one of the most loved food sources of the redlegged earth mite, but two new varieties from a long-term research project may leave them a little hungry Screening pasture legumes for redlegged earth mite resistance as part of the Western Australian research program. 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Ground Cover 090 January-February 2011 - North
Ground Cover 088 September-October 2010 - North