Utilization of weedy rice for development of japonica hybrid rice (Oryza sativa L.).

Two representative weedy rice lines, three typical japonica varieties and three typical indica varieties were used for 6 pairs of reciprocal crosses. The morphological traits of twelve F(1) hybrid lines, their parents and four elite cultivars were investigated for heterosis over mid-parent (HM), over parent (HP) and competitive heterosis (CH) analysis. Traits detected in weedy rice lines seemed larger than those in cultivars and excellent heterosis was produced in weedy rice crossing with japonica rice. Although weedy rice kept closer relationships with japonica rice compared to indica rice. But the heterosis of reciprocal crosses between weedy rice and japonica was closed to those of crosses between indica rice and japonica rice. In six of one hundred and eighteen weedy rice lines, the fertility restore gene for BT type cytoplasmic male sterility (BT-CMS) were detected. Weedy rice was very valuable germplasm resources with the abundant polymorphism. Meanwhile, the disadvantage, lodging, shattering and incompact plant type, should be modified by hybridization, backcross and multiple cross with japonica rice. Although it is difficult to use weedy rice directly, weedy rice may be available to breed both male sterile line and restorer line through improvement, developing japonica hybrid rice.

Relationship between grain yield and leaf photosynthetic rate in super hybrid rice.

In order to explore the relationship between grain yield and photosynthesis, the yield composition and leaf photosynthetic rate in some super hybrid rices and ordinary hybrid rice 'Shanyou 63' as control were measured in 2000-2005. The results were as follows. (1) The yield levels of the four super hybrid rices, 'Pei'ai 64S/E32', 'P88S/0293', 'Jin23A/611' and 'GD-1S/RB207', were significantly higher, being 108%-120% of 'Shanyou 63'. (2) These super hybrid rices had a better plant type with more erect upper layer leaves and bigger panicles or more spikelets per panicle, being 125%-177% of spikelets Shanyou 63 spikelets. (3) Net photosynthetic rates of these super hybrid rices were significantly higher in the second leaf but not necessarily in the first leaf or flag leaf than those of spikelets Shanyou 63 spikelets. (4) The removal of half flag leaf led to a decline in the seed-setting rate, while the removal of half panicle induced its increase in spikelets GD-1S/RB207 spikelets. Hence, higher yield in these super hybrid rices can be attributed to their bigger panicles, better plant type and higher light use efficiency of their canopies. Raising the photosynthetic capacity of each leaf, especially flag leaf, is the key to overcome the photosynthate-source restriction on grain yield and to make a new breakthrough of yield potential in future breeding of super hybrid rice.