Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 Page 13 Page 14 Page 15 Page 16 Page 17 Page 18 Page 19 Page 20 Page 21 Page 22 Page 23 Page 24 Page 25 Page 26 Page 27 Page 28 Page 29 Page 30 Page 31 Page 32 Page 33 Page 34 Page 35 Page 36 Page 37 Page 38 Page 39 Page 40 Page 41 Page 42 Page 43 Page 44 Page 45 Page 46 Page 47 Page 48 Page 49 Page 50 Page 51 Page 52 Page 53 Page 54 Page 55 Page 56 Page 57 Page 58 Page 59 Page 60 Page 61 Page 62 Page 63 Page 64 Page 65 Page 66 Page 67 Page 68 Page 69 Page 70 Page 71 Page 72 Page 73 Page 74 Page 75 Page 7655 IREC Farmers' Newsletter No. 195 ­ – Rice R&D 2016 traits and QTLs for improved efficiency of the rice breeding program (PRJ-007580). Overall, the project aims to improve breeding efficiencies for the selection of cold tolerance in rice at the booting and flowering stages through the identification of quantitative trait loci (QTLs) — sections of DNA that correlate with cold tolerance and underlying physiological mechanisms. However to ensure that this is achieved, a highly-repeatable, low-temperature screening process was needed. This article describes the design of the screening or phenotyping system developed to enable benchmarking of genetic material (lines of rice) for the identification of improved cold tolerance at the booting and flowering stages of plant development. Background Traditionally based in southern New South Wales, the Australian rice production system can suffer from severe yield reductions due to low temperature damage at any time of the growing season. Other than water availability, year to year variation in rice yield in Australia is largely due to low temperature events. Thus, low temperature is considered a major problem facing the Australian industry. Considerable efforts have been made by various research groups in Australia over the past 20 years to develop cold tolerant rice varieties with high yield potential and acceptable grain quality. During this time, cold tolerant genotypes have been imported and crosses made with Australian-adapted germplasm. However, the inability to routinely test genotypes in a repeatable phenotyping system within the breeding program and across the various research groups has limited the rate of improvement of cold tolerant cultivars in Australia. Previous research in Australia and elsewhere has shown that both cool air and cold water can be used for selection, as they are equally effective in identifying cold tolerance. In Japan and Korea, cold- water facilities have played pivotal roles in cold tolerant variety development. The Australian rice breeding program has used late sowing in the field in an attempt to expose segregating material to low night temperatures. This system is particularly dependent on seasonal temperature fluctuations and the underlying maturity range of the materials being evaluated. In a previous RIRDC project Rice cold tolerance for yield stability and water-use efficiency (RIC05-01), a field-based cold- water irrigation system was constructed at Rice Research Australia Pty Ltd (RRAPL) at Jerilderie, in southern NSW, for large-scale screening for cold tolerance. This RRAPL facility, in conjunction with the staggered sowing strategy, is used to validate the UQ glasshouse phenotyping system. Low temperature stress at the reproductive stage can cause large reductions in yield of rice. The early pollen microspore stage (approximately 10–12 days before heading) is the most sensitive to cold injury. However, identification of the early pollen microspore stage (early booting) is difficult without dissection and is likely to differ among genotypes. Flowering is considered the second-most sensitive development stage for low temperature stress and this can be a problem particularly when crops are planted late in the season in Australia. Spikelet sterility is widely accepted as the best indicator for cold injury at the reproductive stages, and genotypes with low spikelet sterility are considered cold tolerant. Not only does this new phenotyping system enable the identification of cold tolerance at the early booting stage but it also can be simultaneously used to screen for tolerance at the flowering stage. Introducing cold tolerance genes to Australian rice varieties is a major target for the Australian rice industry to overcome low temperature stress at booting, particularly at the early pollen microspore stage. Cold tolerant genotypes from overseas have been used to introduce cold tolerance genes into the genomes of Australian-adapted varieties. The development of a new screening process, or technically, a phenotyping system, is an integral part of the rice breeding program. The system provides a reliable way of benchmarking advanced genotypes and varieties, providing a platform to maximise opportunity for identification of genomic regions contributing to cold tolerance at the booting and flowering stages. Once identified and validated across genetic backgrounds, genetic markers can then be used to reduce the many thousands of early generation genotypes coming through the breeding program. This will ensure that only genotypes possessing the cold tolerance genes, as well as genes for required agronomic and quality traits, are advanced through the breeding program. The system l The phenotyping system in the controlled temperature glasshouse facility at Gatton campus, UQ. The system is based on two sets of pots for each genotype, which are planted 17 days apart. Set 1 was subjected to cold at the flowering stage and Set 2 was subjected to cold at the booting stage. LEFT: 24 August 2015, 24 days after sowing of Set 1 (at the back) and 7 days after sowing of Set 2 (at the front). RIGHT: 14 September 2015, 45 days after sowing of Set 1 (back) and 28 days after sowing of Set 2 (front).