In this study, we isolated and characterized the bacterial strain Pseudomonas sp. BYT-1, which is capable of degrading pymetrozine and using it as the sole carbon source for growth. Strain BYT-1 could degrade 2.30 mM pymetrozine within 20 h under the optimal conditions of 30 °C and pH 7.0. Investigation of the degradation pathway showed that pymetrozine was oxidatively hydrolyzed to 4-amino-6-methyl-4,5-dihydro-2H-[1,2,4]triazin-3-one (AMDT) and nicotinic acid (NA). The former accumulates as the end product in the culture, whereas the latter was hydroxylated to 6-hydroxynicotinic acid (6HNA) and subjected to further degradation. The transformation of pymetrozine to AMDT and NA by the cell-free extracts of strain BYT-1 also supported that the oxidative hydrolysis of the CN double bond in pymetrozine was the initial degradation step. This is the first report on a pure bacterial culture with the ability to degrade pymetrozine. These findings enhance our understanding of the microbial degradation mechanism of pymetrozine.

Cold hardiness evaluation is important for screening woody species in cold areas. We compared cold hardiness by estimating the 50% lethal temperature (LT50) using electrolyte leakage test (ELLT50) and triphenyltetrazolium chloride test (TTCLT50) for 26 woody species in the Bashang region of China. One-year-old shoots were collected in January and exposed to five subfreezing temperatures in a programmable temperature and humidity chamber. LT50 was estimated by fitting relative electrolyte leakage and percentage of dead tissue against test temperature. For all tested species, triphenyltetrazolium chloride (TTC) staining of the pith was weak and the cambium TTCLT50 was lower than the extreme minimum temperature (−37 °C) recorded in the region. The cambium TTCLT50 and the sd were lower than that for the phloem and xylem. The phloem TTCLT50 was lower than the xylem TTCLT50, and the two sds were similar. The ELLT50 showed no significant correlation with any TTCLT50. For most species, the ELLT50 was higher than the cambium and phloem TTCLT50 and was not significant different with the xylem TTCLT50. The ELLT50 showed higher sd than any tissue TTCLT50. Based on results obtained in this study, when choosing cold hardiness of single stem tissue as an indicator for screening woody species, the xylem should be considered first, followed by the phloem; the cambium and pith were unsuitable. The cold hardiness estimated by ELLT50 was more suitable as indicator for screening woody species than that of stem tissue in winter estimated by TTCLT50.

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