Agronomic Performance Of Newly Developed Ultrashort-duration Lines For Direct-seeded And Double-season Rice

Double-season rice（DSR）,an important rice planting pattern in China,plays an essential role in increasing the domestic rice production and thus guarantees the food security.However,the cumbersome process,high labor intensity and low economic benefit of traditional DSR pattern have alleviated farmers’planting willingness,further leading to the sharp induction of planting area of DSR in recent years.In this context,the direct-seeded DSR,a more labor-saving rice establishment method,need to be developed to retain the planting area of DSR.Nevertheless,the development of direct-seeded DSR in central China which is a traditional DSR region is limited by the temperature and light resources,based on which only the ultrashort-duration rice varieties with a growth duration around 95days can meet the safety production of direct-seeded DSR.Since 2014,our research group has carried out the breeding work of ultrashort-duration rice varieties.So far,two ultrashort-duration lines,CPPC05-207-26-B-B-19（CPPC-15）and CPPC05-235-B-1-6-9（CPPC-18）have been cultivated,yet their yield formation mechanisms and pivotal agronomic characteristics under direct-seeded DSR need to be further studied.In addition,the differences of ultrashort-duration lines in experimental and on-farm demonstration performance under direct-seeded DSR were not clear.Therefore,the two ultrashort-duration lines,and four controls varieties（Xiangzaoxian 6（early-late sason）,Zaoxian 615（early-late sason）,Zhongzao 39（early-season）,and Liangyou 152（late-season））were used as materials for the experiment and on-farm demonstration in 2021.The plot experiment were carried out in Jiupu Village,Chidong Town,Qichun County,Huanggang City,Hubei Province.The on-farm demonstration was carried out in Xishui County Family farm,Huanggang City,Hubei Province.The objectives of this study were as follows:1)To determine whether the tested varieties can meet the requirements of direct-seeded DSR in central China regarding growth duration,yield and lodging resistance;2)To explore the key agronomic traits for yield formation of ultrashort-duration lines under direct-seeded DSR;3)To evaluate the economic benefits of ultrashort-duration lines of direct-seeded DSR.We described the main conclusions of this study as follows:（1）The growth duration of newly developed ultrashort-duration lines across different places and seasons was 85-95 days,and their annual growth duration（178-183 days）was16-24 days shorter than Zhongzao 39（early season）and Liangyou 152（late season）,4-10days shorter than Zaoxian 615,but 4-7 days longer than Xiangzaoxian 6.From the perspective of growth duration,the two ultrashort-duration lines could meet the requirements of direct-seeded DSR safety production in central China.（2）In plot experiment,the average yield of early season of the two two ultrashort-duration lines was 7.46 t ha^-1,9.1%lower than Zhongzao 39,similar to Zaoxian 615,and13.5%higher than Xiangzaoxian 6.The yield of CPPC-18 was significantly higher than other varieties in late season,followed by Xiangzaoxain 6,Zaoxian 615 and CPPC-15,and Liangyou 152 had the lowest yield.The annual yield of different varieties was 13.0-14.9 t ha^-1,and CPPC-18 was 14.0%,7.9%and 6.8%higher than Xiangzaoxian 6,Zaoxian 615and Zhongzao39 with Liangyou 152,respectively.The annual yield of CPPC-15 was higher than Xiangzaoxian 6,but lower than Zhongzao39 with Liangyou 152.In the production demonstration,the yield level in early and late seasons was significantly lower than plot experiment,and the difference among different varieties was small.Across all varieties,the annual yield was 10.6-11.5 t ha^-1,and CPPC-18 showed no yield advantage.Unreasonable fertilizer management and low soil fertility in production demonstration were the main reasons for the failure of newly developed lines to show yield advantages.（3）The rapid growth of tiller and leaf area in seedling stage in early rice increased the light interception rate,further promoted the dry matter accumulation before heading,which was the key to obtain higher yield in the short growth duration of ultrashort-duration lines.The high yield of CPPC-18 in late season was attributed to the higher panicles per m² and grain filling percentage,and the slower leaf senescence in flag leaf at grain-filling stage promoted dry matter accumulation after heading.Compared with plot experiment,the lower yield in early and late season of production demonstration experiment was mainly attributed to the decrease of spikelet number per panicle,grain filling percentage,biomass and harvest index at maturity.（4）No obvious lodging occurred in the early season under plot experiment and production demonstration.Whereas in the late season of plot experiment,the lodging area of Zaoxian 615 and Liangyou 152 was more than 50%,and the apparent lodging index was4.55 and 5.40,respectively;while the apparent lodging index was 0.00-0.20,and no obvious lodging occurred in the two ultrashort-duration lines and Xiangzaoxian 6,which was mainly due to the low plant height,center of gravity height and bending moment,and higher internode dry weight per unit volume.CPPC-15 had a slightly higher lodging risk than CPPC-18.（5）The annual production cost of two ultrashort-duration lines under direct-seeded DSR was 23815.8（?）ha^-1,and the cost of land transfer,fertilizer and mechanical operation accounted for 28.3%,25.5%and 17.6%of the total production cost,respectively,while the labor cost accounted for only 7.1%.Ultimately,annual output value and net income of two ultrashort-duration lines were 29948.0-29831.2 and 6015.4-6132.2（?）ha^-1,respectively.Although the annual net income of the ultrashort-duration lines and Xiangzaoxian 6 was lower than Zaoxian 615(7000.0（?）ha^-1)and Zhongzao39 with Liangyou 152(7444.2（?）ha^-1),their shorter growth duration increased the flexibility of crop rotation and reduced the production risk of double cropping.In conclusion,the growth duration and yield of the newly developed CPPC-15 and CPPC-18 could basically meet the requirements of direct-seeded and double-season rice in central China,and CPPC-18 had higher single and annual yield and stronger lodging resistance than CPPC-15,for which reason it had a broader application prospect.Nevertheless,these advantages were not fully expressed in the production demonstration.In the future,the optimization of cultivation management of ultrashort-duration lines should be further studied to ensure the high and stable yield of direct-seeded DSR under large area production.