Plant defence responses against Radopolus similis in East African Highland bananas (EAHB- AAA) inoculated with endophytic non-pathogenic Fusarium oxysporum

In the interactions between fungal endophytes and their hosts, the host may benefit through protection against pathogens and pests, growth promotion and tolerance to abiotic stresses. Non-pathogenic Fusarium oxysporum endophytes of banana have been shown to reduce the damage caused by the Cosmopolitus sordidus and the burrowing nematode Radopholus similis. The mode of protection against the burrowing nematode involves induced resistance, but the molecular basis of this resistance yet to be demonstrated. It has further been reported that protection of the host by multiple endophytes can lead to better control of target pests, probably because of the multiple modes of action involved. This phenomenon, however, has not been fully demonstrated for F. oxysporum endophytes of banana. This study aimed to investigate the molecular and biochemical basis of endophyte protection of East African Highland bananas (EAHB) against C. sordidus and R. similis. Expression of banana defence-related genes following endophyte inoculation and R. similis challenge varied greatly between the nematode-susceptible cv Nabusa and the nematode-tolerant cv Kayinja. In cv Nabusa, only the peroxidase (POX) and lectin genes were responsive to endophyte colonization of roots, or R. similis challenge. POX and lectin activities were significantly down-regulated 2 and 33 days after endophyte inoculation (dai), respectively. In cv Kayinja, endophyte colonization resulted in transient up-regulation of POX and a down-regulation of endochitinase (PR-3), lectin, pectin acetylesterase (PAE), phenylalanine ammonia-lyase (PAL) and PIR7A (peroxidase). Similar to systemic acquired resistance, PR-1 and catalase activities were up-regulated in the cv Kayinja 33 dai. Genes involved in signal transduction, cell wall strengthening, jasmonic acid pathway and defence molecule transport were differentially expressed in endophyte-inoculated plants. The expression profiles of four defence-related genes following endophyte inoculation and R. similis challenge were studied using quantitative real-time PCR. ABC transporter, Β-1,3-glucan synthase, coronatine insensitive 1 (COI1) and lipoxygenase (LOX) were up-regulated following endophyte inoculation. Β-1,3-glucan synthase and COI1 were highly up-regulated following R. similis challenge of endophyte-inoculated plants of the susceptible cv Nabusa, while COI1 and LOX were highly up-regulated following nematode challenge of endophyte-inoculated plants of the tolerant cv Kayinja. However ABC transporter gene activity was not up-regulated following nematode challenge of plants of both cultivars. UP-regulation of phenylpropanoid pathway enzymes PAL, POX and PPO has been observed in roots following colonization by both pathogenic and non-pathogenic fungi. In the current study, endophyte inoculation resulted in down-regulation of PAL activity in both a susceptible (cv Nabusa) and tolerant (cv Yangambi) banana. In cv Nabusa, endophyte inoculation primed PAL activity for up-regulation 30 days post nematode challenge (dpnc). However, in cv Yangambi PAL activity was up-regulated 7 dpnc irrespective of endophyte inoculation. Endophyte inoculation transiently up-regulated POX in cv Nabusa, but activity reduced to the levels in the controls 30 dai. Similar to PAL, R. similis challenge of endophyte-inoculated plants of Nabusa caused significant up-regulation of POX 7 dpnc. Nematode challenge of control plants of cv Yangambi resulted in a non-significant up-regulation of POX compared with non-challenged controls, but a significant up-regulation compared to all endophyte-inoculated plants. PPO activity was transiently up-regulated in cv Nabusa and down-regulated in cv Yangambi 7 dai. For all treatments, PPO activity was significantly reduced between 7 dai and 120 dai (60 dpnc). Fusarium oxysporum endophyte isolates Emb2.4o and V5w2 were successfully marked with benomyl- and chlorate resistance and transformed with fluorescent protein genes, while Eny1.31i, Eny7.11o and V4w5 were marked with benomyl resistance only. Most mutants and fluorescent protein transformants maintained resistance to the selective chemical on PDA and after plant colonization. Benomyl- and chlorate-resistant mutants were successfully used to determine actual plant colonization percentages by inoculated endophytes. Similarly, GFP transformants were successfully used to ascertain the pattern of endophytic root colonization in vivo. In plants dually inoculated with isolates Emb2.4o BR 8 and V5w2 CHR 9, both isolates were recovered from roots and rhizomes 4 weeks after inoculation, but isolate V5w2 CHR 9 proved a better colonizer of the two tissue types. Root colonization by isolate V5w2 CHR 9 was boosted when inoculated dually with Emb2.4o BR 8, while that by Emb2.4o BR 8 was reduced in the presence of V5w2 CHR 9. Where growth advantages were observed for dually inoculated plants, it occurred where plants were challenged with R. similis. In the absence of pests, control plants showed better growth than endophyte-inoculated plants. On the other hand, weevil challenge of control plants resulted in significant reductions in plant height, number of live roots and root fresh weight. Dual endophyte inoculation resulted in a significant reduction in R. similis populations in nematode only challenged plants, compared with plants inoculated with Emb2.4o BR 8 singly and control plants challenged with the nematode. In one replicate banana weevil damage to the outer and inner pseudostem base, and the inner rhizome were significantly reduced for dually-inoculated plants. CopyrightThesis (PhD)--University of Pretoria, 2008.Microbiology and Plant Pathologyunrestricte

Response of cowpea germplasm to bacterial blight in Uganda

Cowpea (Vigna unguiculata (L.) walp) is a legume crop mainly grown on small scale in low–input farming systems in Uganda. Cowpea bacterial blight (CoBB) disease caused by Xanthomonas axonopodis pv. vignicola (Burkh.) Dye is increasingly becoming a major hindrance to cowpea productivity. Sixty-four cowpea genotypes were evaluated for their response to bacterial blight disease (CoBB). Field experiments were carried out during the first and second rainy seasons using alpha lattice design with three replications. Data on disease incidence and severity, grain yield, days to 50% flowering, number of seeds per pod, pod length, number of peduncles per plant, and number of branches per plant were collected. Disease severity and incidence data was used to determine relative Area Under Disease Progress Curve (rAUDPC). Results showed significant differences (P ≤ 0.001) among the genotypes for rAUDPC in each season. The rAUDPC across the seasons indicated that genotypes NE 32, WC 32A, WC 26 and NE 44 with rAUDPC values ranging from 0.22 to 0.26 were resistant to CoBB whereas genotypes NE 31 and NE 40 with rAUDPC values 0.44 and 0.46 respectively were susceptible. The rAUDPC did not show any significant correlation with days to 50% flowering, yield and its components. This study suggested that the genotypes NE 32, WC 32A, NE 44, and WC 26 be used as prospective parents in breeding initiatives to develop bacterial blight-resistant varieties due to their high yields and resistance to CoBB

Differential gene expression in East African highland bananas (Musa spp.) : interactions between non-pathogenic Fusarium oxysporum V5w2 and Radopholus similis

Endophytic non-pathogenic Fusarium oxysporum isolates are known to control Radopholus similis through induced resistance. Using complementary (c)DNA-amplified fragment length polymorphism (cDNA-AFLP), we identified genes induced in nematode-susceptible and -tolerant bananas following colonization by nonpathogenic endophytic F. oxysporum isolate V5w2. Quantitative real-time polymerase chain reactions (qRTPCR) were then used to analyze expression profiles of selected genes. Accumulated gene transcripts included those involved in signal transduction, cell wall strengthening, Jasmonic acid (JA) pathway and transport of defense molecules. Endophyte colonization primed the expression of β-1,3-glucan synthase and Coronatine insensitive 1 (COI1) in the susceptible cultivar, and that of COI1 and Lipoxygenase (LOX) in the tolerant. We isolate and identify for the first time genes involved in the interaction between endophytic non-pathogenic F. oxysporum and banana. Highlights · We report identification of genes involved in fungal endophyte protection of banana. · We report JA-induced defenses in banana- V5w2- Radopholus similis interaction. · Genes were primed for expression upon nematode challenge of V5w2 inoculated plants.We acknowledge the Bundesministerium für Wirtschaftliche Zusammenarbeit (BMZ) for funding this study.http://www.elsevier.com/locate/pmpphb201

Managing a Transboundary Pest: The Fall Armyworm on Maize in Africa

The fall armyworm (Spodoptera frugiperda J.E Smith) (Lepidoptera: Noctuidae) invaded Africa in 2016, and has since spread to all countries in sub-Saharan Africa, causing devastating effects on mainly maize and sorghum. The rapid spread of this pest is aided by its high reproductive rate, high migration ability, wide host range and adaptability to different environments, among others. Since its introduction, many governments purchased and distributed pesticides for emergency control, with minimal regard to their efficacy. In this chapter, we review efforts towards managing this pest, highlight key challenges, and provide our thoughts on considerations for sustainable management of the pest

Population genetic structure of the bean leaf beetle Ootheca mutabilis (Coleoptera: Chrysomelidae) in Uganda

Bean leaf beetle (BLB) (Ootheca mutabilis) has emerged as an important bean pest in Uganda, leading to devastating crop losses. There is limited information on the population genetic structure of BLB despite its importance. In this study, novel microsatellite DNA markers and the partial mitochondrial cytochrome oxidase subunit I (mtCOI) gene sequences were used to analyze the spatial population genetic structure, genetic differentiation and haplotype diversity of 86 O. mutabilis samples from 16 (districts) populations. We identified 19,356 simple sequence repeats (SSRs) (mono, di-, tri-, tetra-, penta-, and hexa-nucleotides) of which 81 di, tri and tetra-nucleotides were selected for primer synthesis. Five highly polymorphic SSR markers (4–21 alleles, heterozygosity 0.59–0.84, polymorphic information content (PIC) 50.13–83.14%) were used for this study. Analyses of the 16 O. mutabilis populations with these five novel SSRs found nearly all the genetic variation occurring within populations and there was no evidence of genetic differentiation detected for both types of markers. Also, there was no evidence of isolation by distance between geographical and genetic distances for SSR data and mtCOI data except in one agro-ecological zone for mtCOI data. Bayesian clustering identified a signature of admixture that suggests genetic contributions from two hypothetical ancestral genetic lineages for both types of markers, and the minimum-spanning haplotype network showed low differentiation in minor haplotypes from the most common haplotype with the most common haplotype occurring in all the 16 districts. A lack of genetic differentiation indicates unrestricted migrations between populations. This information will contribute to the design of BLB control strategie

Host and Seasonal Effects on the Abundance of Bean Leaf Beetles (Ootheca spp.) (Coleoptera: Chrysomelidae) in Northern Uganda

Bean leaf beetles (BLBs) (Ootheca spp.) are serious legume pests in Uganda and sub-Saharan Africa, but their ecology is not well understood. We planted host plants, viz., common bean, cowpea, and soybean, in an experiment in the hotspot areas of Arua and Lira districts in Northern Uganda in order to assess their influence on the density of adults and immature stages of BLBs in different seasons. Overall, the number of adults, larvae, and pupae were higher in cowpea than common bean and soybean plots. The number of adults were highest in cowpea (29.5 adults/15 plants) in Arua during the long rainy season (2018A). The number of adults did not differ significantly during short rains (season B) in 2017 and 2018. Similarly, in Lira district, the highest number of adult BLBs was in cowpea (4.6 beetles) compared to the common bean (2.7 beetles) and soybean plots, with a peak at four weeks after planting (WAP). During 2018A, larvae of BLBs first appeared at five WAP and seven WAP and peaked at 13 WAP and 11 WAP in Arua and Lira, respectively. The pupae were present in the soil after the harvesting of crops during 2018A, but peaked at seven WAP and eight WAP in 2018B season in Arua and Lira, respectively. The occurrence of below-ground adults in 2018B followed the peak abundance of pupae, although this was delayed until six WAP in Arua compared to Lira. We conclude that cowpea is the most preferred by adults and larvae compared to common bean and soybean. Similarly, the first rain season (2018A) attracted higher abundance and damage than the second rain season. Management of the BLBs should thus take into consideration avoidance of host crop rotation and dealing with the below-ground stages

Pathogenic variation of colletotrichum lindemuthianum causing anthracnose of beans (phaseolus vulgaris) in Uganda

Colletotrichum lindemuthianum is a highly variable pathogen of common beans that easily overcomes resistance in cultivars bred with single-gene resistance. To determine pathogenic variability of the pathogen in Uganda, samples of common bean tissues with anthracnose symptoms were collected in eight districts of Uganda, namely Kabarole, Sironko, Mbale, Oyam, Lira, Kapchorwa, Maracha and Kisoro. 51 isolates sporulated successfully on Potato Dextrose Agar and Mathur’s media and were used to inoculate 12 differential cultivars under controlled conditions. Five plants per cultivar were inoculated with each isolate and then evaluated for their reaction using the 1 – 9 severity scale. Races were classified using the binary nomenclature system proposed by Pastor Corrales (1991). Variation due to cultivar and isolate effects was significant (P≤0.001) for severity. The 51 isolates from eight districts grouped into 27 different races. Sironko district had the highest number of races followed by Mbale and Kabarole. Races 2047 and 4095 were the most frequently found, each with 10 isolates grouped under them. Race 4095 was the most virulent since it caused a susceptible (S) reaction on all 12 differential cultivars and the susceptible check. This was followed by races 2479, 2047 and 2045 respectively. Two races, 4094 and 2479, caused a susceptible reaction on the differential cultivar G2333, which nevertheless, showed the most broad spectrum resistance followed by cultivars Cornell 49-242, TU, and AB136 respectively. These cultivars are recommended for use in breeding programs aiming at breeding for broad spectrum resistance to bean anthracnose in Uganda