Studies On Panicle Structure And Its Relationship With Stability Of Seed Setting Rate In Large Panicle Indica Rice Varieties

The large panicle is one of the main target traits in rice breeding in China.whereas, trapped in how to keep the stability of seed setting rate, for it’s easily affected by the contents of Nitrogen, climate, insufficient sunlight and droughts, and kindred environmental factors.In the present study, firstly, according to the characteristics of panicle structure, we categorized32large panicle rice materials, and chose some representatives breeds from each category. Then we observed and analyzed the relationship between the characteristics of panicle structure and the stability of seed setting rate under the high/low nitrogen or low-light conditions. The results as followed:1. In large panicle India or rice indica-Indica (and japonica) combinations, seed setting rate was dominantly determined by the rate of second branches on main panicles.By cluster analysis the ratio of the first/second branches’numbers (BI) and the breed rate of all the experimental breeds. we got3types:Type I,BI=0.18-0.40,more than85%of breed rate, was considered as the category having a high breed rate on second branches; Type Ⅲ,only BL006,BI=1.15,92%of breed rate,a high breed rate on first branches;Type Ⅱ,BI=0.18-0.36, less than83%of breed rate, a low breed rate on second branches.2. We found that the characteristics of first branches and breed rate keep on a stable and high level even under different nitrogen conditions in both large and small panicle rice materials.There were stronger Vascular tissues and faster filling rates on the first branches than those second branches.The characteristics of BL-006(Type I)in different nitrogen circumstances:stronger first branches and less numbers of second branches on the panicle bottom; a stable breed rate;fast filling rate and less affected by environment; stronger and more Vascular tissues on the first and second internodes from the panicle bottom,and therefore accumulated amount of dry matter and owned better running abilities to use.In Y-liangyou1(Typelll),there was a decrease in breed rate under a low nitrogen condition, while a longer filling time under a high nitrogen condition. The breed rate on second branches played a dominant role in determining the whole plant’s breed rate.In JinYou63(Type Ⅱ),there were a poor stability in breed rate and a slower filling rate induced by its high carbohydrate/spikelet ratio. We also found the rate on second branches of the whole plant changed significantly with the changes of condition. HeHui66and small panicle rice breeds showed stable breed rates and fast filling rates. With small number of grains on the bottom of panicle, its breed rate even changed under different nitrogen conditions slightly affected the whole plant.3. After being treated with low-light during the period from Meiosis stage to flowering stage, We found that the number of all the experimental materials’first branches on all plant positions and their breed rates varied negligibly, but significantly reduced on second branches at the low and middle positions. The decreases were also evaluated in area of a single large vascular bundle;the NSC contents of stem sheath and dry weight in the heading stage;even the substances’output is negative.There appeared to be a higher pollen inactivation rate and an obvious re-accumulation phenomenon.Respectively, in BL-006,there is a markable decrease in the area of vascular bundles of the first branches, but a stable breeding rate; the filling rate of grains on second branches slowed in the early grain filling stage, but later quickly compensated. Y-liangyou1showed a low breed rate on second branches, but its vascular bundles were little influenced by low light; the time of reaching the maximum grain weight put off, while the grains weight statistics represented light values during the whole filling stage. In Jin You63,On the low and middle position of the panicle, breed rate decreased; the area of vascular bundles on second branches downsized dramatically; the maximum weight per1000grains on first branches is lower than its contrast’s; likely, in contrast to the plant under normal conditions,the filling process of second branches is relatively slow; the NSC content of stem sheath and dry weight in the heading stage, carbohydrate/spikelet ratio and pollen vitality were in low level, which probably the main reason for low breed rates. In HeHui66, a relatively high carbohydrate/spikelet ratio, a light decrease in pollen activation, a stable breed rate, and slightly affected by low light. As stated as above, cultivate large panicle rice breeds with high resistance to low light, they have to be equipped with stronger first branches, obvious secondary upper branches, higher saccharification and magnificently ability to transfer substances between the sources and the libraries.4.In this study, according to the ratio of panicle branch and seed rate, the southern China indica large panicle germplasm resources (including existing super hybrid rice restorer line) and typical super hybrid rice varieties were divided into three categories:primary branches high SSR, secondary branches high SSR and secondary branches low SSR type. BL-006(Primary branches high SSR type) has following characteristics:(1) Primary branche dominated the grains of whole panicle.(2)The secondary branch grain upper advantage was obvious. Peduncle vascular bundle and Branch vascular bundle were highly developed.(3) Sink was activity.(4)The functiong of material transporting and accumulating was highly developed etc. The SSR was maintained stability both in high or low nitrogen and low light conditions. In the future, the variety, which has the structure of panicle like the BL-006, should be selected, In this way, the problem of the SSR is instability of super hybrid rice, with large panicle and more grain.will be solved.