Fall armyworm in Botswana: impacts, farmer management practices and implications for sustainable pest management.

BACKGROUND: Since first reported in Botswana, fall armyworm (FAW) continues to be a threat to crop production. This study aimed to estimate impacts of FAW on yield and farmers' livelihoods in Botswana, and to obtain data that could be extrapolated to national level. Further, farmer knowledge of the pest, management practices and pesticide use for FAW management were assessed. RESULTS: In fact, 76% of the 220 respondents had seen FAW in their farms in the 2018/2019 cropping season, affecting almost the entire and about half of cultivated area for maize and sorghum, respectively. Thus, 51% of the respondents implemented FAW control measures, with chemical pesticides (27%) being the most common management against FAW. Only 33% of respondents in 2018/2019 were food self-sufficient, as opposed to 80% in an ordinary year, with farmers who reported not to have been affected by FAW more likely to be insufficient with food (88%) compared to 60% of the farmers who reported FAW attack. Drought was ranked the major stress experienced by the famers (35%), and also showed significant yield reducing effects on maize yield with pest and diseases reported second most important. Pesticides (20%) and training on pest management (18%) were the top ranked needs by farmers interviewed. CONCLUSIONS: This study confirms the impact and threat of FAW to crop production in Botswana. Chemicals remain the go-to control option by a majority of the farmers. Other low-risk technologies exist and are proposed for adoption in the management of FAW. Of note is the acknowledgement that a single control strategy will not be effective against FAW and as such integrated pest management (IPM) on an area-wide scale is needed to achieve best results. Mass awareness, training and demonstration will be required to achieve this.

The draft genome sequence of Xanthomonas species strain Nyagatare, isolated from diseased bean in Rwanda.

We announce the genome sequence for Xanthomonas species strain Nyagatare, isolated from beans showing unusual disease symptoms in Rwanda. This strain represents the first sequenced genome belonging to an as-yet undescribed Xanthomonas species known as species-level clade 1. It has at least 100 kb of genomic sequence that shows little or no sequence similarity to other xanthomonads, including a unique lipopolysaccharide synthesis gene cluster. At least one genomic region appears to have been acquired from relatives of Agrobacterium or Rhizobium species. The genome encodes homologues of only three known type-three secretion system effectors: AvrBs2, XopF1 and AvrXv4. Availability of the genome sequence will facilitate development of molecular tools for detection and diagnostics for this newly discovered pathogen of beans and facilitate epidemiological investigations of a potential causal link between this pathogen and the disease outbreak.

Development, characterization and linkage analysis of microsatellite loci for the Ascochyta blight pathogen of faba bean, Didymella fabae.

Eighteen microsatellite markers were developed for Didymella fabae, seventeen of which were highly polymorphic among a sample of D. fabae isolates from Syria. Genetic linkage analysis assigned the markers to eight linkage groups. These markers will facilitate population and evolutionary studies of D. fabae and related species.

Secondary metabolite profile and phytotoxic activity of genetically distinct forms of Colletotrichum gloeosporioides from yam (Dioscorea spp.).

Highly virulent, slow-growing grey (SGG); moderately virulent, fast-growing salmon (FGS); and avirulent/weakly virulent, fast-growing grey (FGG) forms of Colletotrichum gloeosporioides have been described from yam (Dioscorea spp.), but little is known about their chemodiversity or the role of toxins in their pathogenesis. Secondary metabolite profiles in high performance tlc (hptlc) showed that the pathogenic SGG and FGS forms have a chemotype (A or B) that is distinct from the non-pathogenic FGG form (chemotype C). Crude extracts of 35-d-old Czapek-Dox yeast broth cultures of FGS and SGG isolates caused tissue necrosis on treated yam leaves but not those of FGG isolates. Extracts from uninoculated broth cultures showed no phytotoxic activity. Toxicity of the culture filtrate was not host specific and toxic substances were thermostable. Dioscorea genotypes with varying levels of resistance to anthracnose differed in their sensitivity to crude toxin extract of FGS (Cg33) and SGG (Cg25) isolates, indicating that these extracts may be useful in evaluating host resistance to anthracnose in vitro. Analysis of two toxin fractions unique to the pathogenic FGS and SGG forms using hlpc, mass spectrometry and nuclear magnetic resonance suggested the presence of a low molecular weight amide peptide. However, possibly due to low yield and the presence of impurities, the chemical structure of the compound(s) could not be fully elucidated.

True yams (Dioscorea): a biological and evolutionary link between eudicots and grasses.

Dioscorea (true yams) is a large genus that contains species important as food (with edible tubers) or as sources of bioactive substances used in a range of applications. Dioscorea is a major staple food in many parts of the world, especially in West Africa and the Pacific islands, and serves as a famine food in many regions. It is a critically important but neglected crop, which is likely to increase in importance as climate change leads to necessary changes in global food systems. It is a herbaceous, climbing, tropical monocot that looks rather like a dicot, and is part of a lineage that is relatively closely related to the phylogenetically derived group containing the grasses. Therefore, it represents an important biological link between the eudicots and grasses--groups that contain all the model flowering plant species--and has the potential to fill gaps in our knowledge of plant biology and evolution. Yams also offer us the possibility to gain new insights into processes such as tuberization and sex determination, which cannot be studied in current model organisms. This combination of rising importance due to its socioeconomic significance and interesting biology and evolutionary position justify its potential as a model organism. This potential remains to be harnessed, and much of the current work on yam is directed toward its role as a food crop. This aspect will remain important, but its potential for answering questions of basic biological interest will be a major motivation for researchers interested in this organism.

Yam (Dioscorea) husbandry: cultivating yams in the field or greenhouse.

This protocol describes how to cultivate yams (Dioscorea) in the field or greenhouse. It refers especially to the tropical food species but it will also work for temperate species. The tropical food species of Dioscorea grow in warm, sunny climates with temperatures between 25 degrees C and 30 degrees C. Short days of 10-11 h result in tuber formation, while days longer than 12 h favor vine growth. Yams require deep, loose, textured loamy soil that is rich in organic matter. They are best planted at the beginning of the rainy season. Mulch around the planted sets protects them from excessive heat and desiccation, especially in areas with hot temperatures and dry weather. It also adds organic matter to the soil, prevents soil erosion, preserves water in the soil, and increases microbial activity in the soil. Yams do not tolerate waterlogged conditions. It is important to stake the plants to allow full exposure of their leaves to light for photosynthetic activity and to reduce disease.

Culturing meristematic tissue and node cuttings from yams (Dioscorea).

This protocol describes how to produce whole yam (Dioscorea) plantlets in vitro through yam meristem culture and from yam node cuttings.

Post-flask management of yam (Dioscorea) plantlets.

This protocol describes how to harden or acclimatize tissue culture-derived yam (Dioscorea) plantlets before transplanting them in the soil. Briefly, the plantlets are first put in pots with a vermiculite and peat moss mixture, and the pots are placed in a humidity chamber, where they are sprayed and watered daily. After 2 wk, the plants are transplanted to pots or plastic bags with ordinary or sterile soil and watered daily. After another 2 wk, they are transplanted into the field.

Producing yam (Dioscorea) seeds through controlled crosses.

This protocol describes how to produce yam (Dioscorea) seeds through controlled pollination of flowers on female plants. Pollination by flower thrips takes place naturally in normal yam-growing environments in the presence of flowering male and female genotypes, although it is not efficient. This protocol leads to the production of hybrid seeds of known parentage for genetic studies and use in breeding programs.

Extraction of DNA from yam (Dioscorea) leaves.

This protocol describes how to extract DNA from the leaves of true yams (Dioscorea) for polymerase chain reaction (PCR) and other analyses.

Delivery of agricultural technology to resource-poor farmers in Africa.

Recent developments in agricultural science and technology have the potential to transform the agricultural sector in the developing world. These technological advances constitute key drivers of economic growth and hold great promise for poverty reduction in sub-Saharan Africa (SSA). Agricultural research and development in Africa is undergoing a major paradigm shift. Until recently, public-sector institutions in Africa worked in isolation to create and disseminate agricultural technologies to smallholder farmers. However, they need access to improved proprietary technologies developed for the most part by the private sector in developed countries. These technologies are currently concentrated in the hands of a few large corporations and are protected by intellectual property rights. The African Agricultural Technology Foundation (AATF) is a new initiative addressing the challenges associated with the access, development, and deployment of agricultural technologies to smallholder farmers in SSA. This article describes the AATF model of facilitating the creation of partnership alliances dedicated to promote and support collaboration among a wide variety of public- and private-sector organizations around shared agricultural research and development goals for the public good. It explains AATF's public-private partnership framework for technology delivery in the light of market failures, institutional constraints, and systemic weaknesses, which impede public-sector organizations from accessing and delivering pro-poor knowledge and technology to farmers. The article provides policy makers, research managers, and business decision makers with an understanding of how access to, and delivery of, proprietary technologies could contribute to food security and the improvement of farmers' livelihoods in Africa.

Genetic diversity of Rhynchosporium secalis in Tunisia as revealed by pathotype, AFLP, and microsatellite analyses.

Genetic variability among 122 Rhynchosporium secalis isolates collected from barley in three regions of Tunisia was investigated using host differentials, amplified fragment length polymorphism (AFLP), and microsatellite markers. The isolates were collected from a widely grown scald-susceptible barley cultivar Rihane and a range of local landrace cultivars in geographically distinct regions with different agroclimatic conditions. Pathotypic diversity (the proportion of unique pathotypes) was high in R. secalis populations from the high (100% diversity), moderate (95%), and low (100%) rainfall areas of Tunisia, and from both Rihane (which is the sole variety grown in the high rainfall region) and local landraces (which predominate in the low rainfall area). This may reflect a general adaptability for aggressiveness and suggests that the widely grown cultivar Rihane has exerted little or no selection pressure on the pathogen population since its release in 1983. Genotypic diversity (GD), defined as the probability that two individuals taken at random had different genotypes, was high for populations from Rihane, local landraces, and different agro-ecological zones (GD = 0.96-0.99). There was low genetic differentiation among pathogen populations from different host populations (G(ST) < or = 0.08, theta < or = 0.12) and agro-ecological zones (G(ST) < or = 0.05, theta < or = 0.04), which may be partly explained by gene flow due to the movement of infected stubble around the country. There was no correlation (r = 0.06, P = 0.39) between virulence phenotype and AFLP haplotype. A phenetic tree revealed groups with low bootstrap values that did not reflect the grouping of isolates based on host, pathotype, or agro-ecological region. The implications of these findings for R. secalis evolutionary potential and scald-resistance breeding in Tunisia are discussed.

Differential Selection on Rhynchosporium secalis During Parasitic and Saprophytic Phases in the Barley Scald Disease Cycle.

ABSTRACT Competition among eight Rhynchosporium secalis isolates was assessed during parasitic and saprophytic phases of the disease cycle in field experiments conducted at two locations and over two growing seasons. The eight isolates were inoculated onto six barley populations exhibiting varying degrees of resistance. Microsatellite analysis of 2,866 isolates recovered from the field experiments showed significant, and sometimes opposite, changes in the frequencies of R. secalis genotypes during the growing season (parasitic phase) and between growing seasons (saprophytic phase). Isolates that showed the most complex virulence in greenhouse seedling assays had the lowest fitness in the field experiment. Significant differences in isolate fitness were found on different host populations and in different environments. Selection coefficients were large, indicating that evolution can occur rapidly in field populations. Although inoculated isolates had the lowest overall fitness on the moderately resistant landrace cv. Arabi Aswad, some isolates were more virulent and consistently increased in frequency on this landrace, suggesting a risk of directional selection and possible erosion of the resistance following its widespread deployment in monoculture. These results provide the first direct evidence that R. secalis pathogen genotypes differ in their saprophytic ability and parasitic fitness under field conditions.