An improved technique for isolation and characterization of single-spore isolates of Plasmodiophora brassicae

Clubroot, caused by Plasmodiophora brassicae, is a soil-borne disease that occurs in cruciferous crops worldwide. P. brassicae usually exists as a mixture of several pathotypes, which has hampered the research on resistance mechanisms of cruciferous crops against P. brassicae. In this study, clubroot galls were collected from a field in Shenyang, China, as a pathogen source to develop an efficient protocol for a single-spore isolation system of P. brassicae by optimizing the seedling age for inoculation, host inoculation method, and plant culture method. The operational steps of the single-spore isolation method were optimized as follows: the use of two-day-old seedlings for inoculation, substituting a cryobox (100 × 2.0 mL vials) for culture dishes, the addition of nutrient solution culture, and microscopic observations of single spores. The rate of infection success was substantially improved, and single-spore isolates of four pathotypes: 4, 8, 9, and 11, were acquired in this system. Subsequently, the optimized system was used to isolate and characterize the pathotypes of single-spore isolates of P. brassicae collected from five fields in regions in China. Approximately 4 to 9 pathotypes were isolated from each region. Among these, pathotype 4 was the most prevalent. This study provides a source of valuable information that can eventually be used for the genetic analysis of host–P. brassicae interaction.

Characterization of selenium accumulation of different rice genotypes in Chinese natural seleniferous soil

In this study, the difference of Se content in brown rice of different rice genotypes was evaluated on natural seleniferous soil. Firstly, the Se content of brown rice in 80 rice germplasm resources was determined, which ranged from 0.0249–0.1426 mg/kg, showing obvious differences. Next, two cultivars with a significant difference in Se content in brown rice, i.e., cv. Wuyangeng (high) and cv. IR68144 (low), were used to study the distribution pattern of Se in different organs. Moreover, the physiological mechanism of the Se content diversity in brown rice of the two cultivars was explored preliminarily. The results showed that the Se content of cv. Wuyangeng was 2–3 times higher compared to cv. IR68144. However, the Se contents of cv. IR68144 root and leaf were significantly higher than that of cv. Wuyangeng under both natural soil environment and artificial nutrient solution culture. Cv. IR68144 also had a stronger root Se accumulation coefficient and shoot Se transfer coefficient. Consequently, it can be inferred that the stronger Se transfer ability from stem to grain was the key reason for the higher Se content in brown rice cv. Wuyangeng than in cv. IR68144.