Yield and Quality Analysis of Japonica Varieties from Cold Region Cultivated as Double Cropping Early Season Rice in the Lower Reaches of the Yangtze River

The aim of the study was to evaluate the differences between rice yield and its components, as well as quality of double cropping early japonica rice which was selected from various accumulated temperature zones in cold region to plant in the lower reaches of the Yangtze River, so as to provide a theoretical basis to select the proper japonica varieties as the double cropping early season rice in this area.

Field experiments were carried out at Taizhou (121°13′ E, 28°78′ N) and Hangzhou (119°94′ E, 30°08′ N) of Zhejiang province in 2018, 2021 and 2022. Six (2018), thirteen (2021) and forty-one (2022) japonica varieties were selected from different accumulated temperature zones in Heilongjiang province, respectively, and the early indica rice Zhongzao 39 was picked out as a control in 2018 and 2022. The differences of productive panicle number, spikelets number per panicle, percentage of filled grain, thousand grains weight, number of spikelets unit area, yield, and harvest index were analyzed among double-cropping early japonica and indica rice; the quality indexes were compared among this two types rice too, such as head rice rate, diaphaneity, gel consistency, amylose content, chalkiness degree, and chalky grain rate.

The harvest dates of early japonica rice with beforehand sowing were about 0-15 days earlier than that of local double-season early indica rice. The total mean yield of early japonica rice was 6 637.77 kg·hm^-2 in 2018; and the yield of Kongyu 131 were the highest with 7 724.70 kg·hm^-2. Moreover, the field production verification in 2022 suggested that the yield of Kongyu 131 could reach 7 194.77 kg·hm^-2. The averages of chalkiness degree, diaphaneity, gel consistency and amylose content in all varieties met the quality of second-class edible rice variety criterion, but the head rice rate was low. The total mean yield early japonica rice was 6 630.45 kg·hm^-2 in 2022, in order as follows: Longken 257 (8 324.99 kg·hm^-2), Longken 263 (8 170.94 kg·hm^-2), and Liandao 1 (8 108.34 kg·hm^-2). Compared with Zhongzao 39, the productive panicle number in early japonica rice were higher, however, the spikelets number per panicle, percentage of filled grain, thousand grains weight were lower than the control, which induced the yield decrease of 54.75%-93.28%. The average yield of the third accumulated zone was higher than that of other accumulated zones due to the relative superior percentage of filled grain. The correlation analysis within yield and its components of different japonica cultivars showed that, the yield had significantly positive correlation with productive panicle number (P<0.05) and number of spikelets unit area (P<0.01).

It was practicable to plant double cropping early japonica rice varieties in the Yangtze River area selected from different accumulated temperature zones in Heilongjiang province, confirmed by appropriate performances on growth duration, yield and quality. It was suggested that Kongyu 131, Longken 257, Longken 263, and Liandao 1 could be selected as double cropping early japonica rice for the next large-scale demonstration planting.