Rice is a temperature-sensitive crop and its production is severely affected by low temperature in temperate and sub-tropical regions. To understand the genetic basis of cold tolerance in rice, we evaluated the cold tolerance at the seedling stage (CTS) of 295 rice cultivars in the rice diversity panel 1 (RDP1), these cultivars were collected from 82 countries. The evaluations revealed that both temperate and tropical japonica rice cultivars are more tolerant to cold stress than indica and AUS cultivars. Using the cold tolerance phenotypes and 44 K SNP chip dataset of RDP1, we performed genome-wide association mapping of quantitative trait loci (QTLs) for CTS. The analysis identified 67 QTLs for CTS that are located on 11 chromosomes. Fifty-six of these QTLs are located in regions without known cold tolerance-related QTLs. Our study has provided new information on the genetic architecture of rice cold tolerance and has also identified highly cold tolerant cultivars and CTS-associated SNP markers that will be useful rice improvement.

In order to identify the key transport process that determines the Cd concentration in brown rice, this study used 21 hybrid rice varieties as experimental materials and conducted field experiments in Qiyang (cadmium-contaminated site) and Yongding (low-cadmium site). Cd concentrations in 8 organs were measured, and bioconcentration factors and transfer factor were further calculated. The results showed that the Cd concentrations of the organs related to the xylem transport were as follows: root > node > stem > leaf sheath > leaf. In the phloem, the Cd concentrations were as follows: rachis > brown rice > rice husk. And the results of the correlation analysis found that Cd concentration between brown rice and root showed a significant positive correlation in Cd-contaminated site, but no significant correlation in low-cadmium site. Meanwhile, at both experimental sites, the Cd concentration of brown rice showed the most significant correlation with the phloem transfer factor from leaf and leaf sheath to brown rice. Principal Component Analysis (PCA) and stepwise regression analysis likewise found that Cd concentration in leaf and leaf sheath and their phloem transport of Cd to brown rice were significantly and positively correlated with Cd concentration in brown rice. The above results showed that the transport of leaf and leaf sheath to brown rice was a key process, and played a more important role in the accumulation of cadmium in brown rice than in root.

Rice blast caused by pathogenic fungus Magnaporthe oryzae is one of the most serious diseases in rice. The pyramiding of effective resistance genes into rice varieties is a potential approach to reduce the damage of blast disease. In this study, combinations of three resistance genes, Pigm, Pi48 and Pi49, were introduced into a thermo-sensitive genic male sterile (PTGMS) line Chuang5S through marker-assisted selection. The results showed that the blast resistance of improved lines increased significantly compared with Chuang5S, and the three gene pyramiding lines (Pigm + Pi48 + Pi49) had higher rice blast resistance level than monogenic line and digenic lines (Pigm +Pi48, Pigm + Pi49). The genetic backgrounds of the improved lines were highly similar (>90%) to the recurrent parent Chuang5S by using the RICE10K SNP chip. In addition, agronomic traits evaluation also showed pyramiding lines with two or three genes similar to Chuang5S. The yields of the hybrids developed from improved PTGMS lines and Chuang5S are not significantly different. The newly developed PTGMS lines can be practically used for the breeding of parental lines and hybrid varieties with broad spectrum blast resistance.