ABSTRACT
Seed germination comparison between japonica and indica weedy rice from China

Jiapeng Fang1, 2, Guohui Yuan1, 2, Yuan Gao1, 2, Li'nian Yang3, Jian Sun3, Guohui Shen1, 2*, and Zhihui Tian1, 2*
 
Weedy rice (Oryza sativa L. f. spontanea Roshev.), a pervasive weed in rice cultivation systems, exhibits significant genetic and phenotypic diversity, particularly between its two major subspecies-japonica and indica weedy rice. Seed germination characteristics play a critical role in the establishment, persistence, and competitive ability of weedy rice in agricultural ecosystems. This study aimed to compare the germination behavior of japonica and indica weedy rice under varying environmental conditions, including temperature, pH, NaCl stress, seed buried depth and moisture regimes. The combination of seed morphology comparison and PCR-based methods has enabled accurate identification of two subspecies of weedy rice. Among the ten populations selected for this study, only one was identified as japonica weedy rice. Seeds of both subspecies were subjected to controlled laboratory experiments to evaluate germination rates in response to environmental factors. Results revealed distinct differences between japonica and indica weedy rice, with japonica weedy rice exhibiting lower germination rates, while indica weedy rice demonstrated higher germination rates and adaptability to a broader range of conditions under all treatments. Weedy rice germination responses to environmental factors were population-specific, especially for indica weedy rice. Meanwhile, the germination behavior of indica weedy rice and japonica weedy rice often corresponded to that of indica cultivated rice and japonica cultivated rice, respectively. These findings suggest that weedy rice prioritizes rapid establishment to outcompete coexisting cultivated rice. The study highlights the importance of understanding subspecies-specific germination traits for developing targeted weed management strategies. The research provides valuable insights into the ecological success of weedy rice and offers practical implications for managing its impact on rice production systems.
Keywords: Environmental factors, japonica and indica weedy rice, seed germination behavior, seeds morphology, subspecies identification.
1Eco-Environmental Protection Research Institute, Shanghai Academy of Agricultural Sciences, Shanghai 201403, China.
2Key Laboratory of Low-Carbon Green Agriculture in Southeastern China, Ministry of Agriculture and Rural Affairs, Shanghai 201403, China.
3Shanghai Co-Elite Agricultural Sci-Tech (Group) Co. Ltd., Shanghai Academy of Agricultural Sciences, Shanghai 201403, China.
*Corresponding author (zb5@saas.sh.cn, tianzhihui@saas.sh.cn)