What are aerobic rice varieties?
Varieties adapted to aerobic management systems require the ability to maintain rapid growth in soils with moisture content at or below field capacity. They share this ability with traditional upland rice varieties, which usually have deep root systems and tolerate water stress at both the vegetative and reproductive stages. However, varieties for aerobic production systems also need to be able to produce yields of 4-6 t ha-1 under favorable conditions. Traditional upland varieties, which are usually low-tillering, tall, and have a low harvest index, rarely achieve yields higher than 3 t ha-1 even under the most favorable conditions. Achieving high yields under aerobic soil conditions requires new varieties of “aerobic rice” that combine the drought-resistant characteristics of upland varieties with the high-yielding characteristics of lowland varieties.
Aerobic rice varieties combining high yield potential with tolerance to aerobic soil conditions have usually been derived from breeding programs in which varieties are developed and evaluated under aerobic soil conditions and with fertilizer applications sufficient for a 4-6 t ha-1 yield target. The first generation of varieties that performed well in a wide range of aerobic rice environments (e.g. IR55423-01 (“Apo”) and UPLRI-5 from the Philippines, B6144-MR-6-0-0 from Indonesia, and CT6510-24-1-2 from Colombia) were developed in upland rice breeding programs. They were often derived from crosses between indica and tropical japonica parents, whereas traditional upland varieties are usually derived from the aus or tropical japonica germplasm groups. Some aerobic rice breeding programs, (notably that of the China Agricultural University in Beijing), also have developed successful varieties by crossing high-yielding lowland rice varieties with traditional upland types. In northern China, new elite aerobic varieties were released in the late 1990s such as Han Dao 277, Han Dao 297 and Han Dao 502, with yield potentials of up to 6.5 t ha-1.