One-step reverse transcription loop-mediated isothermal amplification for the rapid detection of cucumber green mottle mosaic virus.

Cucumber green mottle mosaic virus (CGMMV) has caused serious damage to Cucurbitaceae crops worldwide. The virus is considered one of the most serious Cucurbitaceae quarantine causes in many countries. In this study, a highly efficient and practical one-step reverse transcription loop-mediated isothermal amplification (RT-LAMP) was developed for the detection of CGMMV. The total RNA or crude RNA extracted from watermelon plants or seeds could be detected easily by this RT-LAMP assay. The RT-LAMP assay was conducted in isothermal (63°C) conditions within 1h. The amplified products of CGMMV could be detected as ladder-like bands using agarose gel electrophoresis or visualized in-tube under UV light with the addition of a fluorescent dye. The RT-LAMP amplification was specific to CGMMV, as no cross-reaction was observed with other viruses. The RT-LAMP assay was 100-fold more sensitive than that of reverse-transcription polymerase chain reaction (RT-PCR). This is the first report of the application of the RT-LAMP assay to detect CGMMV. The sensitive, specific and rapid RT-LAMP assay developed in this study can be applied widely in laboratories, the field and quarantine surveillance of CGMMV.

[Prediction of potential suitable distribution area of Flaveria bidentis in China based on niche models].

Based on the distribution records of Flaveria bidentis in China, and by using five ecological niche models (GARP, Maxent, ENFA, Bioclim, and Domain), 32 eco-geographical variables were chosen to simulate the potential suitable distribution area of F. bidentis in the country, and the simulation precision of the models was assessed by the method of Receiver Operating Characteristic (ROC) curve analysis. Among the models adopted, Maxent model had the best simulation precision. Its prediction showed that the potential suitable distribution area of F. bidenti in this country accounted for 7. 5% of the total, with the central and southern Hebei, Beijing, Tianjin, Henan, Shandong, Anhui, and Jiangsu having high potential invasion risk.

[Potential distribution areas of alien invasive plant Flaveria bidentis (Asteraceae) in China].

Flaveria bidentis (Asteraceae), a potential exotic invasive weed to agro-ecosystem and rangeland ecosystem, has recently invaded Tianjin City and Hebei Province (Hengshui and Langfang) in North China, and is spreading further. Based on its current geographical distribution in the world, the potential distribution areas of this weed in China were predicted by using CLIMEX software, aimed to assess the potential risks of this invasive weed. Following provinces in China could be the potential areas being invaded by F. bidentis, i. e., Guangdong, Guangxi, Yunnan, Hainan, Fujian, Taiwan, Jiangxi, Hunan, Guizhou, Sichuan, Chongqing, Hubei, Anhui, Jiangsu, and Shanghai, among which, Guangdong, Guangxi, Taiwan, Hainan, Fujian, Yunnan, Sichuan, Guizhou, Chongqing, and part of Xizang would be at high risk.

[Cloning, sequencing and fuctional study of gacA gene from Xanthomonas oryzae pv. oryzicola].

A gacA homologue, designated gacA(Xooc), was cloned from Xanthomonas oryzae pv. oryzicola (Xooc), a bacterium that causes leaf streak of rice, with degenerated primers by polymerase amplification reaction (PCR). NCBI blast search indicated that GacA(Xooc) had a similar structure to that of other GacA proteins, and had a CheB (Chemotaxis response regulator containing a CheY-like receiver domain)domain. Sequence comparison showed that the gacA(Xooc) was conserved in the Xanthomonas genus. Homology search revealed that the gacA(Xooc) was 99.7% similarities to gacA (AY870457, this lab) of Xanthomonas oryzae pv. oryzae (Xoo). A gacA(Xooc), disruption mutant was successfully generated by a single cross-over event, and confirmed by PCR and Southern blot. But the mutant still had strong pathogenicity,and its virulence was not obviously different from that of wild type strain. The gacA did not globally regulate metabolism in Xooc, which was different from DC3000 of P. syringae pv. tomato, CHAO of P. fluorescens and IC1270 of Serratia plymuthica. Chemotaxis to 0.1% tryptone of the mutants was reduced compared to wild type strain. The results suggest that gacA(X00c) is involved chemotaxis of Xooc. Nevertheless, how gacA to regulate chemotaxis of Xooc, transcription and expression of genes involved in regulation still need to be further studied.

[Identification of a resistance gene to bacterial blight (Xanthomonas oryzae pv. oryzae) in a somaclonal mutant HX-3 of indica rice].

Using the mature embryo of a susceptible rice variety Minghui 63 as the explant, we have obtained a somaclonal mutant HX-3 through selection in vitro, which has showed resistance to bacterial blight. In 8 successive years, the resistance of R1 to R9 generations of HX-3 was identified by ZJ173, a typical bacterial blight strain in Yangtsu River valley, and the results showed that the resistance of HX-3 was stable and heritable. Genetic analysis also indicated that the resistance of HX-3 to bacterial blight was under a dominant gene controlling. Using 32 bacterial blight strains collected in China, Philippines and Japan, the resistance spectrum of HX-3 and other 13 testers with different major dominant resistance genes were tested. Results of 2 years (1999-2000) experiment showed that HX-3 had a broad resistance spectrum, which seemed to be different with those of the other dominant resistance genes identified. Allelic tests were also conducted by crossing HX-3 with IRBB4, IRBB7, CBB12 and IRBB21, and the F2 populations of each of the 4 crosses demonstrated resistant and susceptible plant segregation, indicating that the resistance gene in HX-3 different from Xa-4, Xa-7, Xa-12 and Xa-21. All these results proved that there was a new resistance gene in HX-3. We have designated the new gene as Xa-25(t).