Breeding rice for the sloping uplands of Yunnan

Farmers have been growing upland rice for more than 4,000 years in Yunnan Province of China using traditional varieties under shifting cultivation systems that are based on slash-and-burn practices. Even now, upland rice production is still primarily a subsistence-oriented activity in southern Yunnan,with farmers using a large share of their resourcesto meet food needs. Our efforts over the years have been to develop japonica cultivars with strong seedling vigor,drought tolerance,blast resistance,a daptation to the intermediate elevation of southem Yunnan, and weed competitiveness.In the meantime,germplasm introduction from outside Yunnan has been kept through active domestic and international cooperation since 1989.These endeavors have led to the release of varieties IRAT104,B6144F-MR-6, Yunlu 29, and Yunlu 52 in Yunnan.The goal of hybridization breeding in Yunnan is to combine the good adaptation of Yunnan traditional upland rice cultivars with good plant type, blast resistance, and the drought tolerance of foreign upland rice accessions. The keys in our inbred and hybrid breeding programs are the identification of donors for intermediate stature and blast resistance,of recombinants of aerobicadaptation and high yield, and of promising crosses. A traditional upland cultivar, Mengwanggu, usually yields about 2 t ha-1 with optimized fertilizer management on terraces and favorable lower slopes, whereas improved cultivars Yunlu 29, Yunlu 52, and B6144F-MR-6 yield 4 t ha-l. The yield advantage of the improved cultivars results mainly from the significant increase in tiller and panicle size.I n 2002, breeding researchs hifted from breeding rice for sloping uplands to developing aerobic rice with high yield, blast resistance, and fine grain quality under favorable environments and good management indica type, because of its input response, became our major target type. Ones trategy fo r improving the yield potential of aerobic rice cultivars is to transfer their aerobic adaptation to lowland high-yielding varieties (HYVs), which partition up to 50% of total dry matter to grain, but do not perform well under upland conditions.