Abundance and diversity of arthropod pests infesting stored maize in smallholder farmers and traders systems highlight critical points for pest management in Uganda: Presentation

Knowledge of the diversity of arthropod pests infesting stored maize value chain in Uganda is very scanty to guide the development and implementation of management strategies. From a cross-sectional study conducted in north western, eastern and central regions of Uganda during 2017/2018, the diversity and economic importance of storage arthropod pests of maize in farmer storage, trader/retailer stores in villages and townships, and in milling and processing facilities is presented. A total of 11 insect pests were recorded feeding internally and externally on stored maize. Rhyzopertha dominica, Sitophilus zeamais and Sitophilus oryzae were the primary insect pests followed by Tribolium spp., Cryptolestes spp., Sitotroga cerealella, and Oryzaephilus mercator. The highest insect diversity and damage was recorded when maize was stored with husked cobs in farmers’ houses, a practice farmers use to store seed for next planting. Meanwhile the distribution pattern of the pests in trader/retailer stores in villages and townships, and in milling facilities indicate waves of insect infestation occurring with stocks of grain being brought in storage. The maize grain at the peak of harvesting was in excellent quality but later stocks brought in several months after harvest were infested with diverse insects. Re-drying at farm level and use of chemical dusts at trader/retailer stores in villages and townships were the most common pest management practice. However, the lack of a differentiated market, whereby better quality would fetch premium price, discourages investment to reduce postharvest losses. Subsequently, most farmers sold their grains immediately after harvest and most traders sold their stocks as soon as there was the next bulk buyer. The critical point for pest management is at farm level where pest diversity and damage is greatest, and at the village/ township stores where the grain may be held in anticipation of improvement in price.Knowledge of the diversity of arthropod pests infesting stored maize value chain in Uganda is very scanty to guide the development and implementation of management strategies. From a cross-sectional study conducted in north western, eastern and central regions of Uganda during 2017/2018, the diversity and economic importance of storage arthropod pests of maize in farmer storage, trader/retailer stores in villages and townships, and in milling and processing facilities is presented. A total of 11 insect pests were recorded feeding internally and externally on stored maize. Rhyzopertha dominica, Sitophilus zeamais and Sitophilus oryzae were the primary insect pests followed by Tribolium spp., Cryptolestes spp., Sitotroga cerealella, and Oryzaephilus mercator. The highest insect diversity and damage was recorded when maize was stored with husked cobs in farmers’ houses, a practice farmers use to store seed for next planting. Meanwhile the distribution pattern of the pests in trader/retailer stores in villages and townships, and in milling facilities indicate waves of insect infestation occurring with stocks of grain being brought in storage. The maize grain at the peak of harvesting was in excellent quality but later stocks brought in several months after harvest were infested with diverse insects. Re-drying at farm level and use of chemical dusts at trader/retailer stores in villages and townships were the most common pest management practice. However, the lack of a differentiated market, whereby better quality would fetch premium price, discourages investment to reduce postharvest losses. Subsequently, most farmers sold their grains immediately after harvest and most traders sold their stocks as soon as there was the next bulk buyer. The critical point for pest management is at farm level where pest diversity and damage is greatest, and at the village/ township stores where the grain may be held in anticipation of improvement in price

Genetic basis of maize resistance to multiple insect pests: integrated genome-wide comparative mapping and candidate gene prioritization

Several species of herbivores feed on maize in field and storage setups, making the development of multiple insect resistance a critical breeding target. In this study, an association mapping panel of 341 tropical maize lines was evaluated in three field environments for resistance to fall armyworm (FAW), whilst bulked grains were subjected to a maize weevil (MW) bioassay and genotyped with Diversity Array Technology’s single nucleotide polymorphisms (SNPs) markers. A multi-locus genome-wide association study (GWAS) revealed 62 quantitative trait nucleotides (QTNs) associated with FAW and MW resistance traits on all 10 maize chromosomes, of which, 47 and 31 were discovered at stringent Bonferroni genome-wide significance levels of 0.05 and 0.01, respectively, and located within or close to multiple insect resistance genomic regions (MIRGRs) concerning FAW, SB, and MW. Sixteen QTNs influenced multiple traits, of which, six were associated with resistance to both FAWandMW, suggesting a pleiotropic genetic control. Functional prioritization of candidate genes (CGs) located within 10–30 kb of the QTNs revealed 64 putative GWAS-based CGs (GbCGs) showing evidence of involvement in plant defense mechanisms. Only one GbCG was associated with each of the five of the six combined resistance QTNs, thus reinforcing the pleiotropy hypothesis. In addition, through in silico co-functional network inferences, an additional 107 network-based CGs (NbCGs), biologically connected to the 64 GbCGs, and di erentially expressed under biotic or abiotic stress, were revealed within MIRGRs. The provided multiple insect resistance physical map should contribute to the development of combined insect resistance in maize

Factors influencing genomic prediction accuracies of tropical maize resistance to fall armyworm and weevils

Genomic selection (GS) can accelerate variety improvement when training set (TS) size and its relationship with the breeding set (BS) are optimized for prediction accuracies (PAs) of genomic prediction (GP) models. Sixteen GP algorithms were run on phenotypic best linear unbiased predictors (BLUPs) and estimators (BLUEs) of resistance to both fall armyworm (FAW) and maize weevil (MW) in a tropical maize panel. For MW resistance, 37% of the panel was the TS, and the BS was the remainder, whilst for FAW, random-based training sets (RBTS) and pedigree-based training sets (PBTSs) were designed. PAs achieved with BLUPs varied from 0.66 to 0.82 for MW-resistance traits, and for FAW resistance, 0.694 to 0.714 for RBTS of 37%, and 0.843 to 0.844 for RBTS of 85%, and these were at least two-fold those from BLUEs. For PBTS, FAW resistance PAs were generally higher than those for RBTS, except for one dataset. GP models generally showed similar PAs across individual traits whilst the TS designation was determinant, since a positive correlation (R = 0.92***) between TS size and PAs was observed for RBTS, and for the PBTS, it was negative (R = 0.44**). This study pioneered the use of GS for maize resistance to insect pests in sub-Saharan Africa

Plant-Parasitic Nematodes and Food Security in Sub-Saharan Africa

Article purchasedSub-Saharan Africa (SSA) is a region beset with challenges, not least its ability to feed itself. Low agricultural productivity, exploding populations, and escalating urbanization have led to declining per capita food availability. In order to reverse this trend, crop production systems must intensify, which brings with it an elevated threat from pests and diseases, including plant-parasitic nematodes. A holistic systems approach to pest management recognizes disciplinary integration. However, a critical under-representation of nematology expertise is a pivotal shortcoming, especially given the magnitude of the threat nematodes pose under more intensified systems. With more volatile climates, efficient use of water by healthy root systems is especially crucial. Within SSA, smallholder farming systems dominate the agricultural landscape, where a limited understanding of nematode problems prevails. This review provides a synopsis of current nematode challenges facing SSA and presents the opportunities to overcome current shortcomings, including a means to increase nematology capacity

Sweetpotato weevil (Cylas spp.) resistance in African sweetpotato germplasm

Host-plant resistance could be a useful tool for managing the weevils Cylas puncticollis and C. brunneus, which are major insect pests of sweetpotato in Africa. There is currently little information on existing resistance mechanisms against Cylas spp. in African cultivars, except where lower levels of weevil damage were attributed to escape due to deep rooting and reduced soil cracking, limiting the exposure of roots to weevils. Here, we evaluate weevil resistance in 134 sweetpotato cultivars and landraces over two seasons in two agroecologically diverse locations. Several sweetpotato cultivars, including New Kawogo, expressed resistance to Cylas spp. The resistance characteristics have been demonstrated in previous laboratory experiments to be quantifiable and thus potentially useful in targeted plant-breeding against Cylas spp. We showed external root and stem base damage to be an accurate quantitative indicator of internal root damage, offering rapid and accurate evaluation of resistance in field trials for screening. Moreover, weevil resistance can be assessed earlier in plant development, so saving time in the selection of the progeny from breeding programmes

The relationship between stem base and root damage by Cylas spp. on sweetpotato

The Sweetpotato weevils Cylas puncticollis Boheman and C. brunneus Fabricius are the most prevalent pests of sweetpotato in Africa. There was need to develop techniques for quick germplasm categorization for resistance to the weevil. This study aimed at identification of the relationship between levels of weevil damage on stem bases and root damage by the Cylas weevil. A total of 130 varieties were planted at the National Semi-arid resources Research Institute in Uganda in 2 seasons in a RBD. Plots were composed of 15 plants 30cm apart in 3 replicates. Artificial weevil infestation of plots to augment field weevil population was done at 90, 120 and 240 days after planting (DAP). Plants were harvested at 7 MAP. The mean external and internal damage of the stems damage and % root damage of the plants were investigated. Data was analysis using MSTATIC Statistical package. There was a high positive correlation between internal and external stem base damage values and levels of sweetpotato root damage by C. brunneus and C. puncticollis weevils. Using the stem base damage indicator technique to categorise resistance in sweetpotato could enable quicker selection of sweetpotato varieties with relative resistance to weevils

Recombination fraction and genetic linkage among key disease resistance genes (Co-42 /Phg-2 and Co-5/"P.ult") in common bean.

Anthracnose (Colletotrichum lindemuthianum), Angular leaf spot (Pseudocercospora griseola) and Pythium root rot are important pathogens affecting common bean production in the tropics. A promising strategy to manage these diseases consists of combining several resistance (R) genes into one cultivar. The aim of the study was to determine genetic linkage between gene pairs, Co-42 /Phg-2, on bean-chromosome Pv08 and Co-5/"P.ult" on-chromosome Pv07, to increase the efficiency of dual selection of resistance genes for major bean diseases, with molecular markers. The level of recombination was determined by tracking molecular markers for both BC3F6 and F2 generations. Recombination fraction r, among gene pairs, the likelihood of linkage, L(r), and logarithm of odds (LOD) scores were computed using the statistical relationship of likelihood which assumes a binomial distribution. The SCAR marker pair SAB3/PYAA19 for the gene pair Co-5/"P.ult" exhibited moderate linkage (r = 32 cM with a high LOD score of 9.2) for BC3F6 population, but relatively stronger linkage for the F2 population (r = 21 cM with a high LOD score of 18.7). However, the linkage among SCAR marker pair SH18/SN02, for the gene pair Co-42 /Phg-2 was incomplete for BC3F6 population (r = 47 cM with a low LOD score of 0.16) as well as F2 population (r = 44 cM with a low LOD score of 0.7). Generally, the weak or incomplete genetic linkage between marker pairs studied showed that all the four genes mentioned earlier have to be tagged with a corresponding linked marker during selection. The approaches used in this study will contribute to two loci linkage mapping techniques in segregating plant populations