Molecular Breeding for Rainfed Lowland Rice in the Mekong Region

In the past 20 years, the rice-breeding program in Thailand had little success in developing new cultivars to replace Kao Dawk Mali 105 (KDML105) and Kao Khor 6 (RD6) for the tainted lowland rice environments. The main reason for the poor adoption of new cultivars by farmers is the susceptibility to diseases and unacceptable grain qualities. The conventional breeding program also takes at least 15 years from initial crossing to the release of new cultivars. A new breeding strategy can be established to shorten the period for cultivar improvement by using marker-assisted selection (MAS), rapid generations advance (RGA), and early generation testing in multi-locations for grain yield and qualities. Four generation of MAS backcross breeding were conducted to transfer genes and QTL for bacterial blight resistance (BLB), submergence tolerance (SUB), brown plant hopper resistance (BPH) and blast resistance (BL) into KDML105. Selected backcross lines, introgressed with target gene/QTL, were tolerant to SUB and resistant to BLB, BPH and BL. The agronomic performance and grain quality of these lines were as good as or better than KDML105.

Minimising cold damage during reproductive development among temperate rice genotypes. I. Avoiding low temperature with the use of appropriate sowing time and photoperiod-sensitive varieties

Multiple-sown field trials in 4 consecutive years in the Riverina region of south-eastern Australia provided 24 different combinations of temperature and day length, which enabled the development of crop phenology models. A crop model was developed for 7 cultivars from diverse origins to identify if photoperiod sensitivity is involved in determining phenological development, and if that is advantageous in avoiding low-temperature damage. Cultivars that were mildly photoperiod-sensitive were identified from sowing to flowering and from panicle initiation to flowering. The crop models were run for 47 years of temperature data to quantify the risk of encountering low temperature during the critical young microspore stage for 5 different sowing dates. Cultivars that were mildly photoperiod-sensitive, such as Amaroo, had a reduced likelihood of encountering low temperature for a wider range of sowing dates compared with photoperiod-insensitive cultivars. The benefits of increased photoperiod sensitivity include greater sowing flexibility and reduced water use as growth duration is shortened when sowing is delayed. Determining the optimal sowing date also requires other considerations, e. g. the risk of cold damage at other sensitive stages such as flowering and the response of yield to a delay in flowering under non-limiting conditions. It was concluded that appropriate sowing time and the use of photoperiod-sensitive cultivars can be advantageous in the Riverina region in avoiding low temperature damage during reproductive development.

Summer dormancy in Dactylis glomerata L.: the influence of season of sowing and a simulated mid-summer storm on two contrasting cultivars

A series of trials to increase understanding of the summer dormancy trait in Dactylis glomerata was conducted. Autumn-sown reproductive and younger, spring-sown plants of 2 drought-resistant cultivars, contrasting for summer dormancy, were established and then tested in summer 2002 under long drought, drought + midsummer storm, or full irrigation. The autumn-sown reproductive plants of cv. Kasbah were summer dormant under all moisture regimes and exhibited the characteristic traits including growth cessation, rapid herbage senescence, and dehydration of surviving organs (-6.7MPa). Cultivar Kasbah used 8% less soil water over the summer and also began to rehydrate its leaf bases from conserved soil water before the drought broke. The non-dormant cv. Medly grew for 10 days longer under drought and whenever moisture was applied; Medly also responded to the storm with a decline in dehydrin expression in leaf bases, whereas no decline occurred in Kasbah, presumably because it remained dormant and therefore much drier. The irrigated, younger, spring-sown swards of cv. Kasbah had restrained growth and produced only about 25% of the herbage of cv. Medly. Drought reduced activity and growth of young plants of both cultivars, but whereas Medly regrew in response to the storm, cv. Kasbah did not, indicating that dormancy, although only partially expressed after spring sowing, was reinforced by summer drought. A longer drought in 2003 caused a 22% loss of the basal cover in cv. Medly, whereas Kasbah fully maintained its sward and therefore produced a higher post-drought autumn yield. This work confirms summer dormancy as a powerful trait for improving persistence over long, dry summers.

Molecular breeding for rainfed lowland rice in the Mekong Region

In the past 20 years, the rice-breeding program in Thailand had little success in developing new cultivars to replace Kao Dawk Mali 105 (KDML105) and Kao Khor 6 (RD6). Main reason is a poor adoption of new cultivars by farmers due to poor adaptation of new cultivars to the rainfed environments, susceptibility to diseases and insect pests and unacceptable grain qualities. The conventional breeding program also takes at least 15 years for releasing new cultivars. New breeding strategy can be established to shorten period for cultivar improvement by using marker-assisted selection (MAS), rapid generations advance (RGA), early generation testing in multi-locations for grain yield and qualities. Four generation of MAS backcross breeding were conducted to transfer gene and QTL for bacterial blight resistance (BLB), submergence tolerance (SUB), brown planthopper resistance (BPH) and blast resistance (BL) into KDML105. Selected backcross lines, introgressed with target gene/QTL, were tolerant to SUB and resistant to BLB, BPH and BL. The agronomic performance and grain quality of these lines were as good as or better than KDML105.