Breeding maize for resistance to the fall armyworm (Spodoptera Frugiperda J.E. Smith), improved yield and yield-related traits.

Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.Maize production and productivity in sub-Sub-Saharan Africa (SSA), including Zambia, has been severely threatened by the recent arrival of the fall armyworm (FAW) (Spodoptera frugiperda J.E. Smith). Several strategies have been proposed to control FAW. Integrated pest management (IPM), emphasizing host-plant resistance, has been identified as the most sustainable approach. However, validated and locally-adapted FAW-resistant maize cultivars have not yet been developed and deployed in sub-Saharan Africa. The aim of this research was to develop FAW resistant, farmer-preferred and locally adapted maize varieties. The specific objectives of this study were: (1) to identify farmers' maize production constraints and preferred traits, and to assess farmers' perceptions of the impact of FAW on maize production and productivity in Zambia; (2) to screen a diverse population of maize genotypes for FAW resistance, yield, and yield-related traits by phenotyping and genotyping, to select the most promising genotypes for crossing; (3) to optimise the methods for laboratory rearing of FAW, and to conduct artificial screening of promising maize genotypes under controlled conditions and artificial FAW infestation; (4) to determine the level of genetic diversity for agronomic and FAW-related traits among the test population of maize genotypes using SNP markers complemented by phenotypic information to identify suitable parents for developing FAW-resistant breeding populations; and (5) to determine the nature of gene action conditioning FAW resistance, yield, and yield-related traits through combining ability analysis, and to identify the most promising crosses for continued evaluation in FAW resistance breeding. In the first study, participatory rural appraisal (PRA) surveys were conducted in two FAW affected districts in Zambia in 2017 and 2018, using semi-structured questionnaires, preference ranking and focus group discussions. The high cost of fertilizers, the limited availability of agricultural lands, insect pests, and drought stress were reported by 73, 55, 38 and 36.6% of the respondents, respectively, as the main production constraints. There were significant differences (X2 = 12.415; p = 0.002) in the severity of FAW infestation between the two surveyed districts in 2017. Farmer-preferred traits of maize were insect pest resistance, early maturity, drought tolerance and market price of the grain. FAW resistance, drought tolerance and grain yield performance are the key drivers for maize variety development and deployment in Zambia. In the second study, two sets of diverse maize germplasm were assessed for FAW resistance and desirable yield-related traits in a FAW-affected area in Zambia. Set I and Set II, containing 60 and 253 maize genotypes, respectively, were selected, based on their agronomic potential and adaptability. Highly significant differences (P < 0.001) were detected among the test genotypes for FAW leaf damage (FLD), FAW cob damage (FCD) and agronomic traits. The lowest levels of FLD and FCD were 8.87% and 5.36%, recorded for genotypes CML304-B and CML442, respectively. Five principal components (PCs) accounted for ≥80% of the total variation associated with reduced anthesis-silking interval (ASI), plant height, FLD and FCD, desirable ear aspect and grain yield. Genotypes such as Pool 16 and ZM 7114 from Set I, and CZL1310c, CML444-B, CZL15220 and TL1512847 from Set II had low mean FCD and FLD values, suggesting higher levels of FAW resistance. Grain yield was negatively correlated with mean FLD (r = 0.18, p <0.05), and FCD (r = 0.15, p < 0.05). Promising maize genotypes, including CZL1310c, CML444-B, CZL15220, TL1512847 and CML491, were selected for their low mean FLD and FCD, earliness to flowering and high grain yield potential. These genotypes should be useful in developing tropical and sub-tropical maize breeding populations with partial FAW resistance and yield gains. The third study optimised laboratory rearing and artificial inoculation of FAW onto maize plants under controlled conditions. Field-collected FAW egg masses and larvae were used to mass-produce fresh colonies of the larvae and to evaluate 63 maize genotypes for FAW resistance. The study enabled an understanding of the salient features of FAW growth and development under local environments to implement integrated FAW management strategies. Test genotypes had differential reactions to FAW infestation under controlled conditions. Several genotypes, including CML545-B, CZL1310c, VL050120, CZL16095, EBL169550, ZM4236, MM501 and Pool 16, exhibited considerable FAW resistance at the seedling and leaf-whorl growth stages, and were selected for resistance breeding. The study established a standardised laboratory and screen house-based protocol for mass rearing and artificial infestation of FAW to screen maize genotypes for resistance breeding programs in Zambia or other sub-Saharan Africa countries. The fourth study determined the genetic diversity of 59 maize genotypes of diverse genetic backgrounds with variable resistance to FAW, using phenotypic traits and SNP-based DArT markers. The test genotypes were profiled using agro-morphological traits, FAW damage parameters, and Diversity Array Technology Sequencing-derived single nucleotide polymorphism (SNP) markers. Significant (p < 0.001) differences were observed among the genotypes for 13 phenotypic traits, with their phenotypic coefficient of variation ranging from 2.19 to 51.79%. Notable phenotypic variation was observed for ear position, grain yield, and FAW-induced leaf and cob damage. The mean gene diversity and polymorphic information content were 0.29 and 0.23, respectively, reflecting a moderate level of genetic variation among the test genotypes when assessed using SNP markers. Analysis of molecular variance revealed greater genetic variance within a population than between populations. Population structure and cluster analysis grouped the test genotypes into two main clusters. Three genetically divergent, open pollinated varieties were selected for their favourable agronomic performance and FAW resistance for population improvement or hybrid breeding: Pool 16, ZM 4236 and ZM 7114. The genetic diversity detected within and among the tested populations will facilitate the breeding of maize varieties incorporating farmer-preferred agronomic traits and FAW resistance in Zambia and related agro-ecologies. The fifth study investigated the combining ability effects and inheritance of FAW resistance and agronomic traits in maize genotypes selected for breeding. A line × tester mating design was used and 60 experimental hybrids were generated and field-evaluated in three FAW hotspot locations in Zambia. Both the general and specific combining ability effects were significant (p<0.05) for the assessed traits. Non-additive genetic effects were more important for the inheritance of grain yield and FAW-inflicted leaf and cob damage, suggesting that heterosis breeding would be the best strategy for yield gains. The narrow sense heritability (h2) estimates for agronomic and FAW-related traits ranged from 0.14 to 0.47 and 0.37 to 0.49, respectively. The experimental hybrids CML346/EBL16469, ZM4236/CML545-B, CML346/CZL1310c, CML334/EBL173782, CML545-B/EBL169550 were among those selected with favourable specific combining ability estimates for greater grain yield, reduced days-to-50% anthesis, days-to-50% silking, FAW leaf and cob damage resistance, respectively. The selected experimental hybrids are recommended for further evaluation and breeding. Overall, the study developed and optimized the techniques for the artificial rearing and infestation of FAW on maize under controlled conditions. Promising inbred lines and new FAW resistant experimental maize hybrids were developed involving landrace varieties and donor parents sourced from the International Maize and Wheat Improvement Center (CIMMYT). This study contributes to the development of FAW resistant maize varieties in Zambia and SSA

Fall armyworm infestation and development : screening tropical maize genotypes for resistance in Zambia

DATA AVAILABILITY STATEMENT : All data are provided in the manuscript.SUPPLEMENTARY MATERIAL : TABLE S1: Artificial diet used for laboratory rearing of FAW. TABLE S2: Mean performance and AUPPCs of 63 tropical maize genotypes when evaluated under artificial FAW infestation. TABLE S3: Nature and magnitude of FAW damage revealed by 63 tropical maize genotypes evaluated under artificial FAW infestation. Supplementary FIGURE S1: Diets used for rearing FAW on petri dishes. S1A- Natural diet of maize leaves and stalks. S1BArtificial diet containing wheat, soy and other ingredients. Supplementary FIGURE S2: Rearing cage for adult FAW moths.Knowledge of fall armyworm (FAW) (Spodoptera frugiperda J.E. Smith) rearing, infestation and development and precision screening protocols are preconditions for the successful introgression of resistance genes into farmer-preferred varieties. We aimed to determine FAWdevelopmental stages, screen tropical maize and select resistant lines under controlled conditions in Zambia. Field-collected FAWsamples constituting 30 egg masses and 60 larvae were reared using maize leaf- and stalk-based and soy- and wheat flour-based diets at 27 1 C, 60 5% relative humidity and 12 h day length. The resulting neonates were separated into sets A and B. The life cycles of set A and field-collected larvae were monitored to document the FAW developmental features. Set B neonates were used to infest the seedlings of 63 diverse tropical maize genotypes. Egg, larva, pupa and adult stages had mean durations of 2, 24, 20 and 12 days, respectively. Test maize genotypes revealed significant differences (p < 0.05) based on FAWreaction types, with lines TL13159, TL02562, TL142151, VL050120 and CML548-B exhibiting resistance reactions, while CML545-B, CZL1310c, CZL16095, EBL169550, ZM4236 and Pool 16 displayed moderate resistance. These genotypes are candidate sources of FAW resistance for further breeding. This study will facilitate controlled FAW rearing for host screening in the integration of FAW resistance into market-preferred maize lines.The Alliance for a Green Revolution (AGRA) through the African Centre for Crop Improvement (ACCI) and the International Foundation for Science (IFS).https://www.mdpi.com/journal/insectsam2023Zoology and Entomolog

Prioritizing plant parasitic nematode and mollusca species likely to be introduced and threaten agriculture, forestry, and biodiversity in Zambia: A horizon scanning approach

Introduction of invasive alien species (quarantine pests) through intentional or unintentional human-mediated activities has caused enormous economic and environmental impacts necessitating forward planning to identify, prioritise, and prevent their introduction. Using CABI’s Horizon Scanning Tool, 26 mollusca and 199 plant parasitic nematode (PPN) species not reported as present in Zambia were identified. The list was refined to focus on species affecting Zambia’s important value chains resulting in final lists of 130 PPN and 20 mollusca species that were subjected to risk assessment using agreed guidelines. The possible highest and lowest overall risk scores expected were 250 and 2 respectively. The highest overall score was 140 obtained for Arion hortensis, Cornu aspersum, and Deroceras reticulatumi (mollusca) and Pratylenchus penetrans, P. thornei, and Rotylenchulus reniformis (PPN) and the lowest for mollusca was 10, recorded for Arion ater and for PPN, three, recorded by for Peltamigratus luci. Nine (45%; N=20) and 58 (45%; N=130) of the assessed mollusca and PPN species respectively, attained a suggested minimum overall risk score of 54 necessary for instituting phytosanitary measures that limit pest introduction. All assessed mollusca species were likely be introduced through the contaminant and stowaway pathways. The majority (54%; n=70; N=130) of the PPN species were likely to be introduced via contaminant or stowaway pathways, 7 (5%) and 53 (41%) solely as contaminants and stowaways, respectively. Eleven of the PPN are known vectors of pathogenic organisms. Five of the vectored viruses recorded overall risk scores above 54 and included Tomato ringspot virus (105), Tobacco rattle virus (90), Pea early-browning virus (72), Tomato black ring virus (70), and Arabis mosaic virus (60). The assessed PPN were also vectored by insects (order Coleoptera and families, Cerambycidae, Curculionidae, and Dryophthoridae), three of which recorded overall risk scores above the suggested minimum, Monochamus galloprovincialis (60) Orthotomicus erosus (100), and Rhynchophorus palmarum (72). Actions to limit introduction were also suggested for pathogenic organism vectored by PPN and vectors of PPN. The information from this assessment will guide a number of interventions aimed at developing strategies that prevent introduction and spread of assessed mollusca and PPN specie

Rapid risk assessment of plant pathogenic bacteria and protists likely to threaten agriculture, biodiversity and forestry in Zambia

A prioritisation study was conducted to address the lack of adequate information about potential pests likely to be introduced in Zambia and become invasive. The study was conducted by subject matter experts from relevant institutions in and outside Zambia. Although this study focused on major pest categories, this paper only addresses bacteria and Protista. A list of 306 bacterial and 10 Protista species adjudged to affect plants was generated using CABI’s Horizon Scanning Tool. The 316 (total) pest species were refined to focus on pests that affect value chains important to Zambia’s economy. This resulted in a final list of 133 bacteria and eight Protista. Four additional bacteria species considered of phytosanitary interest were added and all 137 bacteria and eight Protista species were subjected to a rapid risk assessment using agreed guidelines. Vectors reported to transmit any of the pathogenic organisms were also subjected to a risk assessment. A proportion of 53% (n = 77 of 145) comprising 73 bacteria and four Protista species were reported as present in Africa. Of these, 42 (57%, n = 73) bacterial species and two (n=4) Protista species were reported in neighbouring countries. Considering a cut-off of 54, the highest scoring pests were 40 bacteria (highest score of 140) and three Protista (highest score of 125). Three actions were suggested for high-scoring pests, a detection surveillance, a pest-initiated pest risk analysis (PRA) or a detection surveillance followed by pest-initiated PRA. A “no action” was suggested where the risk was very low although, for some pathogenic organisms, a “no action” was followed by periodic monitoring. This information will contribute towards proactive prevention and management of biological invasions

Rapid Risk Assessment of plant pathogenic bacteria and protists likely to threaten agriculture, biodiversity and forestry in Zambia

A prioritisation study was conducted to address the lack of adequate information about potential pests likely to be introduced in Zambia and become invasive. The study was conducted by subject matter experts from relevant institutions in and outside Zambia. Although this study focussed on major pest categories, this paper only addresses bacteria and Protista. A list of 306 bacterial and 10 Protista species adjudged to affect plants was generated using CABI’s Horizon Scanning Tool. The 316 (total) pest species were refined to focus on pests that affect value chains important to Zambia’s economy. This resulted in a final list of 133 bacteria and 8 Protista. Four additional bacteria species considered of phytosanitary interest were added and all 137 bacteria and 8 Protista species were subjected to a rapid risk assessment using agreed guidelines. Vectors reported to transmit any of the pathogenic organisms were also subjected to a risk assessment. A proportion of 53% (n=77 of 145) comprising 73 bacteria and 4 Protista species were reported as present in Africa. Of these, 42 (57%, n=73) bacterial species and 2 (n=4) Protista species were reported in neighbouring countries. Considering a cut-off of 54, the highest scoring pests were 40 bacteria (highest score of 140) and three Protista (highest score of 125). Three actions were suggested for high-scoring pests, a detection surveillance, a pest-initiated pest risk analysis (PRA) or a detection surveillance followed by pest-initiated PRA. A “no action” was suggested where the risk was very low although for some pathogenic organisms, a “no action” was followed by periodic monitoring. This information will contribute towards proactive prevention and management of biological invasions