Molecular characterization of two Chinese isolates of Beet western yellows virus infecting sugar beet.

Beet western yellows virus (BWYV) has previously been reported as an agent of sugar beet yellowing disease in China. In this article, the complete genomic RNA sequences of two Chinese BWYV isolates infecting beet from Inner Mongolia (BWYV-IM) and Gansu (BWYV-GS) were determined and compared with three beet poleroviruses (BMYV, BChV and BWYV-US) and other non-beet-infecting poleroviruses. The genomes of the two isolates were 5,668 nt in length, and had almost the same genomic organization and characteristics as BWYV-US. The full length of BWYV-IM shared nucleotide sequence identities of 97.4, 86.6, 64.4 and 70.8% with BWYV-GS, BWYV-US, BChV and BMYV, respectively. Further sequence analysis indicated that the Chinese BWYV isolates were more closely related to BWYV-US; however, the identity of any gene product between the Chinese isolates and BWYV-US was <90%. Therefore, on the basis of genome sequence, we propose that these Chinese isolates are a distinct strain of BWYV that infect sugar beet. In addition, recombinant detection analysis revealed that BWYV-IM might be a recombinant virus.

[Production and releasing sites of superoxide anion in phytopathogenic bacteria].

Many phytopathogenic bacteria were founded to release the superoxide anion (O2-) by themselves from different sites and the production of O2- was related to the pathogenicity of strains. The presences of O2- in cytomembrane, cell wall and filtrate were confirmed by chemical method and electron spin resonance (ESR). The results show that filtrate may be the primary site of O2- production due to its higher O2- generating activity either in the presence or the absence of DDC. Additional lines of evidence further suggested a regulatory mechanism of O2- production in phytopathogenic bacteria.

[O2-* burst of tobacco leaves triggered by Erwinia carotovora subsp. carotovora inoculation].

O(-.)(2) production based on chemical method by Ecc-treated intact tobacco leaves was observed. It showed a long-lasting one-phase course beginning 1 h and ending 14 h after Erwinia carotovora subsp. carotovora (Ecc) was inoculated. In Ecc-treated leaves, O(-.)(2) production rate of 3 h is 2 times of 1 h, and of 10 h it remains 1.7 times. It decreases rapidly between 10 h and 14 h, at 14 h it falls to the level before inoculation. This is a completely different course from the widely accepted two-phase course obtained from suspension-cultured cells. Electron spin resonance (ESR) spectrum of O(-.)(2) produced by intact tobacco leaves after Ecc inoculation 2 h and 6 h was also observed, the amplitude of 6 h is larger than of 2 h in Ecc-treated group. In the control group, there is no difference between the amplitude of 2 h and 6 h. This indicated that O(-.)(2) amount of Ecc-treated group is higher than of the control group, which is the same result as obtained through chemical method. The ESR spectrum of O(-.)(2) produced by chloroplasts and mitochondria from tobacco leaves after 2 h and 6 h after Ecc inoculation were observed. In chloroplast experiment, the amplitude of 6 h was larger than of 2 h in Ecc-treated group while it was the same in the control group. ESR spectrum of O(-.)(2) produced by mitochondria was proved to be a same result after a careful comparison, in spite of a greater difference between 2 h and 6 h in control group than chloroplast experiment. The fact that spectra of these two organelles were both synchronous with that of intact leaves implied that these two organelles possibly participated in cellular O(-.)(2) burst. Chloroplasts in the dark showed no ESR spectrum 2 h and 6 h after Ecc inoculation in Ecc-treated group as well as in the control group, indicating that O(-.)(2) in the chloroplast probably originated from the photosynthetic electron transport process.

[Field test and lab experiment on control efficacy of the pathogen of opium poppy mildew].

OBJECTIVE: To screen effectual fungicides for field control because of the seriousness of opium poppy mildew and importance of chemical control on plant diseases. METHOD: Seven fungicides were screened in Lab experiment and field test during 1996-1997. RESULT AND CONCLUSION: All of them and their different dosages were effective to control conidia of Peronospora arborescens. Among them, 72.2% propamocarb of 1203 and 902.5 ppm were the most effective both in Lab experiment and field test with efficacy 79.91% and 79.33% respectively in field test, and the efficacy of other fungicides was over 50%. Seven fungicides tested can be used to control nonsystematic symptom of opium poppy mildew.