P0 protein of cotton leafroll dwarf virus-atypical isolate is a weak RNA silencing suppressor and the avirulence determinant that breaks the cotton Cbd gene-based resistance

Cotton blue disease (CBD) is the most important disease present in cotton crops in South America and cotton leafroll dwarf virus (CLRDV) is the causal agent. The disease has been controlled by sowing cotton varieties resistant to CLRDV. However, in the 2009/10 growing season, an outbreak due to an atypical CLRDV isolate (CLRDV-at) occurred in northwest Argentina. Although CLRDV and CLRDV-at genomes are very closely related, the symptoms they produce in cotton plants are quite different. P0 is the most divergent protein between the isolates and in CLRDV is a silencing suppressor protein. This work characterized the silencing suppressor activity of the P0 protein encoded by CLRDV-at (P0^CL-at) and evaluated its role in Cbd-resistance break in cotton plants. It was demonstrated that P0^CL-at, despite having a mutation in the consensus of the F-box-like motif, was able to suppress local RNA silencing, but displayed lower activity than P0^CL. P0^CL and P0^CL-at showed no differences in the interaction with Gossypium hirsutum SKP1 orthologue (GSK1) and Nicotiana benthamiana SKP1 and both P0 proteins triggered destabilization of ARGONAUTE1. However, when the ability to enhance PVX symptoms was evaluated, P0^CL-at was shown to be a weaker pathogenicity factor than P0^CL in N. benthamiana. Interestingly, trans-expressed P0^CL-at enabled CLRDV to systemically infect CBD-resistant plants, and a chimeric CLRDV-P0^CL-at infectious clone succeeded in establishing infection in CBD-resistant cotton varieties with symptoms resembling those produced by CLRDV-at. These results strongly suggest that P0^CL-at is the avirulence (Avr) determinant involved in breaking cotton Cbd gene-based resistance.     

Synchytrium endobioticum – risk from biogas plants?

Synchytrium endobioticum is one of the most important pathogens of potato and is known for its persistent propagation structures. Under favourable conditions, infection of highly susceptible potato cultivars leads to clearly visible cauliflower‐like tissue warts, the typical symptom of potato wart disease. However, unfavourable infection conditions or low infection pressure may result in symptoms being overlooked. Thus, the introduction of pathogen structures into stages of the processing industry cannot be ruled out. As the amounts of processed potato products continue to rise, phytosanitary risks from processing discarded potatoes and potato waste in biogas plants have to be considered. Hence, the resilience of resting spores against mesophilic anaerobic digestion was analysed in stirred tank reactors. Laboratory‐scale results show that S. endobioticum not only withstands mesophilic anaerobic digestion but also subsequent storage of the digestate for at least 4 weeks. Large numbers of viable resting spores were detectable by microscopic assessment in all samples. Viability was proved and verified additionally by bioassay. Consequently, potatoes, potato waste and processing water from potato processing industries used in biogas plants pose a phytosanitary risk if the accruing digestates are returned as fertilizer to arable land.     

Comparative performance of the highly invasive Mimosa invisa and its less invasive subspecies under different nutrient and light conditions

Invasive plants may be more plastic than non‐invasive plants and maintain high fitness under various environmental conditions. Previous studies mainly focused on the comparisons between invasive and native plants, and comparisons between highly invasive and less invasive exotic species are still relatively rare, especially for comparisons at the subspecies level. This study examined the effects of nutrient addition and shading on the performance of the highly invasive Mimosa invisa and its less invasive subspecies M. invisa var. inermis under either isolated or competitive conditions. Nutrient addition increased biomass and plant height and decreased root‐to‐shoot ratio (R/S). Shading decreased biomass and R/S and increased plant height. Under isolated conditions, the two invaders did not differ in R/S, plant height and plasticity of these traits in response to nutrient addition or shading, and the two invaders also did not differ in biomass production under each of the nutrient and light treatments. When the two invaders competed with each other, M. invisa outcompeted M. invisa var. inermis under high soil nutrient conditions, and the two invaders did not differ in performance under other growth conditions. Thus, only considering competition may we find out the difference between highly invasive species and their closely related, less invasive subspecies. Management of M. invisa should focus on habitats with high soil nutrient availability, in which M. invisa is more likely to dominate.     

Evaluating diverse systems of tobacco genetic resistance to Phytophthora nicotianae in Yunnan,China

Black shank, caused by the soilborne pathogen Phytophthora nicotianae, is one of the most devastating diseases affecting tobacco production in China. The most effective strategy for reducing economic loss from this pathogen is development and use of resistant tobacco varieties. Multiple sources and systems of resistance have been developed in the Western Hemisphere; however, populations of P. nicotianae are variable around the world, including the predominance of different races. Different P. nicotianae isolates may react differently on tobacco plants with different systems of resistance, a possibility that could complicate the breeding of cultivars with resistance that is effective in different tobacco production regions worldwide. The objective of this research was to evaluate an array of tobacco germplasm possessing different systems of genetic resistance to black shank disease in tobacco-growing regions of Yunnan, China. Resistance types included simply inherited resistance mechanisms introgressed from wild Nicotiana relatives and polygenic partial resistance systems of N. tabacum origin. The loci of Wz exhibited high level resistance to black shank in the five diverse disease environments in Yunnan, China. K326 Php/−Wz/− genotype and Beinhart 1000 exhibited the greatest levels of resistance in both 2015 and 2016. Field observed results for 13 tobacco genotypes were highly correlated with those tested in growth chamber evaluation. These findings suggest that both Wz− and Beinhart 1000-mediated resistance have important commercial value in flue-cured tobacco breeding programmes in China. Cultivars developed for black shank resistance in China may also have utility in other tobacco-growing areas.     

Phytophagous insect fauna of Onopordum spp. thistles in the south of Syria

Thistles from the genus Onopordum (Asteraceae) are of Mediterranean and Eurasian origin. They are very common in the south of Syria, in particular in Damascus and Al Suwayda, and are found in fallow fields, pastures, roadsides and neglected areas. In 2015–2017, several sites with large populations of Onopordum spp. were identified. Weekly surveys of some of the sites, mainly in the regions of Damascus and Al Suwayda, revealed a significant diversity of phytophagous insect species, some of which had a very high population density. A total of 29 insect species were detected, belonging to four orders and 21 families. The most abundant species were from the order Coleoptera. These were observed to be feeding on different plant parts of Onopordum spp. Purely endophagous species comprised 38% of the species observed on Onopordum spp., ectophagous species comprised 45% with 17% of species mixed ectophagous and endophagous. Species that only fed on Onopordum spp. represented 34% of all the species observed.     

雾滴图像粘连特征改进判断及分离计数方法优化

雾滴在靶标上常出现粘连的情况,为准确测量雾滴尺寸、掌握雾滴分布规律,需要判断雾滴是否粘连,并用图像处理技术将粘连雾滴分开。首先提出判断雾滴是否粘连的改进方法,该方法结合雾滴的形状因子和面积阈值对粘连雾滴进行判断和特征提取,并用极限腐蚀法和迭代开运算法对粘连雾滴进行计数处理,其次调用迭代开运算标记的分水岭算法分割,最后对分割后雾滴的连通域进行标记及形状圆整。试验结果表明：该方法可实现粘连雾滴的自动判断和特征提取,弱粘连准确率100%,强粘连可达97.2%以上。该算法获得的雾滴粒径参数与激光粒度仪试验测量结果接近,其尺寸测量准确度较Deposit Scan软件计算平均提高了7.67%。基于相同的样本,与人工计数标定结果对比表明,该方法获得的雾滴个数快速且精准度达97.06%以上。     

Phosphate-solubilizing microorganisms associated with the rhizosphere of mangroves in a semiarid coastal lagoon

 The phosphate-solubilizing potential of the rhizosphere microbial community in mangroves was demonstrated when culture media supplemented with insoluble, tribasic calcium phosphate, and incubated with roots of black (Avicennia germinans L.) and white [Laguncularia racemosa (L.) Gaertn.] mangrove became transparent after a few days of incubation. Thirteen phosphate-solubilizing bacterial strains were isolated from the rhizosphere of both species of mangroves: Bacillus amyloliquefaciens, Bacillus licheniformis, Bacillus atrophaeus, Paenibacillus macerans, Vibrio proteolyticus, Xanthobacter agilis, Enterobacter aerogenes, Enterobacter taylorae, Enterobacter asburiae, Kluyvera cryocrescens, Pseudomonas stutzeri, and Chryseomonas luteola. One bacterial isolate could not be identified. The rhizosphere of black mangroves also yielded the fungus Aspergillus niger. The phosphate-solubilizing activity of the isolates was first qualitatively evaluated by the formation of halos (clear zones) around the colonies growing on solid medium containing tribasic calcium phosphate as a sole phosphorus source. Spectrophotometric quantification of phosphate solubilization showed that all bacterial species and A. niger solubilized insoluble phosphate well in a liquid medium, and that V. proteolyticus was the most active solubilizing species among the bacteria. Gas chromatographic analyses of cell-free spent culture medium from the various bacteria demonstrated the presence of 11 identified, and several unidentified, volatile and nonvolatile organic acids. Those most commonly produced by different species were lactic, succinic, isovaleric, isobutyric, and acetic acids. Most of the bacterial species produced more than one organic acid whereas A. niger produced only succinic acid. We propose the production of organic acids by these mangrove rhizosphere microorganisms as a possible mechanism involved in the solubilization of insoluble calcium phosphate. Received: 21 April 1999     

Methyl jasmonate reduces chilling injury and maintains postharvest quality of mango fruit

Exposure of mango (Mangifera indica cv. Tommy Atkins) fruit to methyl jasmonate (MJ) vapors (10(-)(4) M) for 24 h at 25 degrees C reduced chilling injury during subsequent storage for 21 days at 7 degrees C and after 5 days of shelf life at 20 degrees C. The chilling tolerance induced by MJ was positively correlated with the reduction in the percent ion leakage of mango tissue. The overall quality of MJ-treated fruit was also better than that of control fruit. MJ treatment increased the total soluble solids but did not affect titratable acidity or pH. MJ also did not change the normal climacteric rise in respiration, water loss, and softening rates. The efficacy of MJ to reduce chilling injury and decay of mango could be related to the tolerance induced at low temperature. It was concluded that MJ treatment may prevent chilling injury symptoms of mango without altering the ripening process.     

Influence of dietary fat and vitamin E supplementation on free radical production and on lipid and protein oxidation in turkey muscle extracts

The objectives of this study were to investigate the effects of dietary fat (6% soy oil or rapeseed oil or tallow) and alpha-tocopheryl acetate supplementation at two levels (30 or 200 ppm) on radical production, measured by ESR spectroscopy, and on lipid and protein oxidation in turkey muscle extracts oxidized by an enzymic system (NADPH, ADP, FeSO(4)/cytochrome P450 reductase). Two muscles were tested: pectoralis major (glycolytic) and sartorius (oxidative) muscles. Radical production measured by ESR was higher in pectoralis major muscle than in sartorius muscle, whereas lipid and protein oxidation was more important in sartorius muscle, showing the importance of the pro-/antioxidant ratio in oxidative processes in muscular cells and of the measurement methodology to appreciate the free radical production. Dietary fat had no effect on the level of ESR signals, whereas feeding of animals with soy oil induced higher oxidation of lipids. Protein oxidation was less sensitive to the nature of the dietary fat than lipid oxidation. Vitamin E supplementation significantly decreased radical production, as measured by ESR spectroscopy. Vitamin E also decreased lipid and protein oxidation, but the effect of vitamin E on protein oxidation was less pronounced than on lipid oxidation.