Cassava is a major staple, bio-energy and industrial crop in many parts of the developing world. In Southeast Asia, cassava is grown on >4 million ha by nearly 8 million (small-scale) farming households, under (climatic, biophysical) conditions that often prove unsuitable for many other crops. While SE Asian cassava has been virtually free of phytosanitary constraints for most of its history, a complex of invasive arthropod pests and plant diseases has recently come to affect local crops. We describe results from a region-wide monitoring effort in the 2014 dry season, covering 429 fields across five countries. We present geographic distribution and field-level incidence of the most prominent pest and disease invaders, introduce readily-available management options and research needs. Monitoring work reveals that several exotic mealybug and (red) mite species have effectively colonised SE Asia's main cassava-growing areas, occurring in respectively 70% and 54% of fields, at average field-level incidence of 27 ± 2% and 16 ± 2%. Cassava witches broom (CWB), a systemic phytoplasma disease, was reported from 64% of plots, at incidence levels of 32 ± 2%. Although all main pests and diseases are non-natives, we hypothesise that accelerating intensification of cropping systems, increased climate change and variability, and deficient crop husbandry are aggravating both organism activity and crop susceptibility. Future efforts need to consolidate local capacity to tackle current (and future) pest invaders, boost detection capacity, devise locally-appropriate integrated pest management (IPM) tactics, and transfer key concepts and technologies to SE Asia's cassava growers. Urgent action is needed to mobilise regional as well as international scientific support, to effectively tackle this phytosanitary emergency and thus safeguard the sustainability and profitability of one of Asia's key agricultural commodities. © 2016 Society of Chemical Industry.
The fall armyworm, Spodoptera frugiperda, is an important agricultural pest native to tropical and subtropical regions of the Western Hemisphere, and has invaded Africa and further spread into most countries of Asia within two years. Here, we analyzed the genetic variation of invaded populations by comparing the nucleotide sequences of two genes: the nuclear Z-chromosome linked gene triose phosphate isomerase (Tpi) and the mitochondrial gene cytochrome oxidase subunit I (COI) of 27 specimens collected in Africa (DR Congo, Tanzania, Uganda, and Zimbabwe) and Asia (Bangladesh, Korea, Nepal, and Vietnam). The results revealed that 25 specimens were from a heterogeneous hybrid (Tpi-corn strain and COI-rice strain; Tpi-C/COI-R) of the corn strain male and rice strain female, but two specimens were from a homogenous corn strain (Tpi-corn strain and COI-corn strain; Tpi-C/COI-C). The further analysis of the fourth exon and the fourth intron sequences of the Tpi gene identified at least four subgroups of the corn strain. These four genetic subgroups were identified in Africa and Asia, suggesting no significant genetic change due to the rapid migration within two years. Our study provides essential information for understanding the genetic diversity of fall armyworm in new habitats.
SummaryHere we report that rRNA and mRNA are specifically degraded in oat (Avena sativa L.) cells during apoptotic cell death induced by victorin, a host-selective toxin produced by Cochliobolus victoriae. Northern analysis indicated that rRNA species from the cytosol, mitochondria and chloroplasts were all degraded via specific degradation intermediates during victorin-induced apoptotic cell death but, in contrast, they were randomly digested in necrotic cell death induced by 30 mM CuSO 4 and heat shock. This indicates that specific rRNA cleavage could be controlled by an intrinsic program. We also observed specific cleavage of mRNA of housekeeping genes such as actin and ubiquitin during victorin-induced cell death. Interestingly, no victorininduced mRNA degradation was detected with stress-responding genes such as PR-1, PR-10 and GPx throughout the experimental period. The RNA degradation mostly, but not always, occurred in parallel with DNA laddering, but pharmacological studies indicated that these processes are regulated by different signaling pathways with some overlapping upstream signals.
Members of the Colletotrichum gloeosporioides species complex are causal agents of anthracnose in many commercially important plants. Closely related strains have different levels of pathogenicity on hosts despite their close phylogenetic relationship. To gain insight into the genetics underlying these differences, we generated and annotated whole-genome assemblies of multiple isolates of C. fructicola (Cf) and C. siamense (Cs), as well as three previously unsequenced species, C. aenigma (Ca), C. tropicale and C. viniferum with different pathogenicity on strawberry. Based on comparative genomics, we identified accessory regions with a high degree of conservation in strawberry-pathogenic Cf, Cs and Ca strains. These regions encode homologs of pathogenicity-related genes known as effectors, organized in syntenic gene clusters, with copy number variations in different strains of Cf, Cs and Ca. Analysis of highly contiguous assemblies of Cf, Cs and Ca revealed the association of related accessory effector gene clusters with telomeres and repeat-rich chromosomes and provided evidence of exchange between these two genomic compartments. In addition, expression analysis indicated that orthologues in syntenic gene clusters showed a tendency for correlated gene expression during infection. These data provide insight into mechanisms by which Colletotrichum genomes evolve, acquire and organize effectors.
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