Evaluation of the biocontrol potential of Aspergillus welwitschiae against the root-knot nematode Meloidogyne graminicola in rice(Oryza sativa L.)

The root-knot nematode Meloidogyne graminicola is considered one of the most devastating pests in rice-producing areas,and nematicides are neither ecofriendly nor cost effective.More acceptable biological agents are required for controlling this destructive pathogen.In this study,the biocontrol potential of Aspergillus welwitschiae AW2017 was investigated in laboratory and greenhouse experiments.The in vitro ovicidal and larvicidal activities of A.welwitschiae metabolites were tested on M.graminicola in laboratory experiments.The effect of A.welwitschiae on the attraction of M.graminicola to rice and the infection of rice by M.graminicola was evaluated in a greenhouse.The bioagent AW2017 displayed good nematicidal potential via its ovicidal and larvicidal action.The best larvicidal activity was observed at a concentration of 5×AW2017,which caused an 86.2%mortality rate at 48 h post inoculation.The highest ovicidal activity was recorded at a concentration of 5×AW2017,which resulted in an approximately 47.3%reduction in egg hatching after 8 d compared to the control.Under greenhouse conditions,the application of A.welwitschiae significantly reduced the root galls and nematodes in rice roots compared to the control.At a concentration of 5×AW2017,juveniles and root galls in rice roots at 14 d post inoculation(dpi)were reduced by 24.5 and 40.5%,respectively.In addition,the attraction of M.graminicola to rice roots was significantly decreased in the AW2017 treatment,and the development of nematodes in the AW2017-treated plants was slightly delayed compared with that in the PDB-treated control plants.The results indicate that A.welwitschiae is a potential biological control agent against M.graminicola in rice.

Potential impacts of climate change on Welwitschia mirabilis populations in the Namib Desert,southern Africa

Climate change is threatening natural ecosystems in the Earth, and arid regions of southern Africa are particularly exposed to further drying. Welwitschia mirabilis Hook. （Welwitschiaceae） is an unusual gymnosperm tree that is recognized as an icon of the Namib Desert, southern Africa. Many aspects of its biology were investigated in the past, with a special emphasis for its physiology and adaptations, but nothing is known about its potential sensitivity to current climate changes. In this study, we adopted an approach based on distribution data for W. mirabilis and ecological niche models for clarifying the species-climate interactions and for predicting the potential impacts of climate change on W. mirabilis populations in three well-separated sub-ranges （northern, southern and central） in northwestern Namibia, southern Africa. We evidenced that the populations occurring in the northern sub-range have peculiar climatic exigencies compared with those in the central and southern sub-ranges and are particularly exposed to the impact of climate change, which will consist of a substantial increase in temperature across the region. These impacts could be represented by demographic changes that should be detected and monitored detailedly to plan efficient measures for managing populations of this important species on the long-term scale.

Complete loss of RNA editing from the plastid genome and most highly expressed mitochondrial genes of Welwitschia mirabilis

Comparative genomics among gymnosperms suggested extensive loss of mitochondrial RNA editing sites from Welwitschia mirabilis based on predictive analysis. However, empirical or transcriptome data to confirm this massive loss event are lacking,and the potential mechanisms of RNA site loss are unclear. By comparing genomic sequences with transcriptomic and reversetranscription PCR sequencing data, we performed a comprehensive analysis of the pattern of RNA editing in the mitochondrial and plastid genomes(mitogenome and plastome, respectively) of W. mirabilis and a second gymnosperm, Ginkgo biloba. For W.mirabilis, we found only 99 editing sites located in 13 protein-coding genes in the mitogenome and a complete loss of RNA editing from the plastome. The few genes having high editing frequency in the Welwitschia mitogenome showed a strong negative correlation with gene expression level. Comparative analyses with G. biloba, containing 1,405 mitochondrial and 345 plastid editing sites, revealed that the editing loss from W. mirabilis is mainly due to the substitution of editable cytidines to thymidines at the genomic level, which could be caused by retroprocessing. Our result is the first study to uncover massive editing loss from both the mitogenome and plastome in a single genus. Furthermore, our results suggest that gene expression level and retroprocessing both contributed to the evolution of RNA editing in plant organellar genomes.

剑麻茎腐病的研究进展

剑麻(Agave sisalana Perr.ex Engelm.)是一种重要的硬质纤维作物。茎腐病(Bole rot)是剑麻的主要病害之一,严重制约了剑麻产业的持续向好发展。本文从剑麻茎腐病的病害症状、病原菌及其生物学特性、发生规律、病害防治等方面进行综述,以期为该病害的深入研究提供参考。

百岁兰愈伤的诱导与悬浮细胞培养

为探究稳定高效的百岁兰叶片愈伤组织诱导体系及其悬浮细胞培养方法,利用百岁兰叶片作为材料,采用正交法使用两种激素(NAA与6-BA)配置植物培养基,运用避光与昼夜节律两种处理诱导愈伤组织产生,并利用愈伤组织与其对应配比的液体培养基培养悬浮细胞。结果表明,百岁兰叶片在0.5 mg/L 6-BA+1.0 mg/L NAA浓度下的诱导愈伤具有最好的稳定性与成功率,在昼夜节律条件下诱导与生长的效率很高,以此为基础培养的悬浮细胞取得了一定进展。研究可为百岁兰的保护与稳定遗传提供技术参考。