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Articles by A.G.O. Dixon
Total Records ( 9 ) for A.G.O. Dixon
  C.N. Fokunang , A.G.O. Dixon and T. Ikotun
  A study was conducted at the greenhouse of the International Institute of Tropical Agriculture, Ibadan, Nigeria to investigate the synergistic relationship of Xanthomonas campestris pv. manihotis (causal agent of cassava bacterial blight CBB), and Colletotrichum gloeosporioides f.sp. manihotis (causal agent of cassava anthracnose disease CAD), in cassava multiple infection. There were statistical differences (P 0.05) in disease symptom expression among the cassava genotypes following sequential inoculation of the pathogens and single pathogen inoculation alone. The fastest occurrence and the highest overall mean severity of the disease symptoms (necrotic lesion, shoot die-back, gum exudate release and wilt symptoms) were observed in cassava genotypes sequentially inoculated with bacterial, followed by the fungus one week later (BFW) or in mixed combination prior to inoculation. Defoliation was high in genotypes inoculated with bacterium first followed by the fungus on the same day, with a low disease symptom expression in plants inoculated with the fungus or bacterium alone.
  C.N. Fokunang , A.G.O. Dixon and T. Ikotun
  The aim of this study was to establish the importance of post-harvest survival and over-seasoning of Colletotrichum gloeosporioides f.sp. manihotis on planting materials and in soil. Infected stem cuttings from twelve cassava clones, harvested from two plot sites ES 24 and BSI, then incubated at 25 ± 2 ° for 8 months showed a significant decrease (P=0.05) in fungal survival amongst cassava clones. The lowest fungal recovery of 15% after 8 months incubation was recorded for cassava clones 88/0002336 and 30572. Cassava stakes, stored under shade and high relative humid conditions for 16 months showed a gradual monthly decrease in fungal survival, up to the 10th month. A gradual increase in fungal recovery was recorded from the 11th month up to the 16th month when maximum recovery was attained, due to re-infectivity of newly developed twigs by CAD pathogens from parent plants. Survival of fungus on soil gradually reduced with time and at the 6th month of sampling, there was no recovery recorded for 80% of the field plot sites. Burial of infected materials for 150 days below 30 cm depth significantly reduced the survival of C. gloeosporioides f.sp. manihotis on infected materials. These studies have shown that C. gloeosporioides f.sp. manihotis could survive on infected cuttings for more than 8 months, but less likely to survive in soil for more than 4 months.
  O.O. Aina , A.G.O. Dixon and E.A. Akinrinde
  Genetic variability in shoot and root characteristics among 20 broad-based cassava genotypes was studied in four agroecological zones in Nigeria to determine its effects on root yield. Seventeen agronomic parameters were evaluated on a plot size of 40 m2, at spacing of 1x1 m in a Randomized Complete Block Design (RCBD) in four replicates. Analysis of variance (ANOVA) showed significant differences (p< 0.001) among genotypes within and across locations for most parameters. Significant genotype by environment (GxE) interaction effects was also observed. Estimates of genetic variances for phenotypic and genotypic coefficients of variation were higher for root characters than for shoot characters. PCV ranged from 4.3 to 36.5%; GCV ranged from 3.2 to 22.6%. Broad sense heritability (H2) estimates were high for root characters, ranging from 75 to 88.6%, but low for shoot characters, ranging between 10.6 and 38%. Consequently, considerable scope exists for the improvement of economic traits, such as storage root yield. Shoot traits have little control on storage root yield while root traits with high genetic influence had major control on storage root yield. Number of roots, root size and Harvest Index are major yield determinants to be considered when selecting for root yield in cassava.
  O.O. Aina , A.G.O. Dixon and E.A. Akinrinde
  The associations among different traits and their direct and indirect influence on yield using the path analysis and correlation procedures were examined in 20 broad-based cassava genotypes to understand how inter-character relationships influences root yield. Field evaluation was carried out in 4 agroecological zones of Nigeria for two cropping seasons. Data were collected on morphological and yield parameters such as plant height, stem girth, canopy volume, shoot weight, leaf size, number of roots, root size and root yield. Results showed that root parameters such as medium-sized roots with correlation coefficient (r) of 0.95, number of roots (r = 0.91) and small-sized roots (r = 0.77) were highly significantly (p< 0.001) correlated) with root yield. Path analysis revealed that number of roots had the largest direct effect on root yield with a direct path coefficient effect (P) of 0.61, accounting for 86% of the total direct + indirect effects, followed by number of medium-sized roots (p = 0.23), that accounted for 79.2% of the total direct + indirect effects. Small-sized roots had a negative direct effect on root yield (p = -1.21) but a positive indirect effect (p = 1.91) via number of roots. Number of storage roots and medium-sized roots both contributed the largest influence on storage root yield in cassava. These parameters should, therefore, be considered together while selecting for cassava genotypes with higher storage root yield potentials.
  O.O. Aina , A.G.O. Dixon and E.A. Akinrinde
  The problem of genotype-by-environment (G x E) interactions that often complicates the interpretation of multilocational trial analysis making the prediction of genotype performance difficult can be eased with the adoption of the Additive Main Effects and Multiplicative Interaction (AMMI) model analysis. The AMMI model was used in this study to evaluate 20 broad based cassava genotypes established in eight environments in Nigeria in order to; identify stable and adaptable genotypes, determine the magnitude of G x E interaction and identify factors contributing to the G x E interaction pattern. Analysis of variance showed that the effects of environments, genotypes and G x E were highly significant (p< 0.001) for storage root yield. AMMI estimates ranked genotypes differently from unadjusted means producing sharper and more stratified rankings. Genotypes 4(2)1425 and 91/02324 was found to be stable and adaptable, 96/0326 was found to be unstable but high yielding, while 96/0590 was highly stable but low yielding. Genotypes 96/0529 and 96/0860 were specifically adapted to Zaria (Northern guinea savanna) and 96/0191 was adapted to Ibadan (forest savanna transition zone). High variation in soil moisture availability was identified as a major causal factor of the interaction observed. Ibadan and Mokwa were relatively stable environments but Mallamadori was highly unstable. Mokwa been highly stable could be considered as a good site for selection broad based improved cassava genotypes.
  C.N. Fokunang , A.G.O. Dixon , C.N. Akem and T. Ikotun
  Variability in fungal features in 30 isolates of C. gloeosporioides f. sp. manihotis Henn (Penz). Sacc (causal organism of cassava anthracnose disease CAD), from seven cassava growing regions of Nigeria (Oyo, Ogun, Ondo, Osun, Plateau, Kwara and Cross River State), where the disease is prevalent, were investigated on the basis of culture, morphology and pathogenicity. Culture and morphology showed variations in mycelial pigmentation, growth media colour, radial growth pattern, presence or absence of setae and acervuli production amongst isolates. Spore morphology differed (P<0.05) in conidial length, spore density, germ-tube development. Pathogenicity test showed significant differences (P<0.05) in virulence amongst the isolates. All thirty isolates were pathogenic to two test cassava genotypes, causing necrotic lesions after artificial inoculation by stem puncture. Fungal isolates 05, 10 and 26 were more virulent, causing lesion size exceeding 20 mm in susceptible test cassava genotypes at 21 days after inoculation. The relationship among fungal growth parameters (mycelial growth, conidial length, spore germination and sporulation density) and virulence of the fungal isolates, showed a significant positive correlation between spore germination and sporulation (r=0.72), spore germination and virulence (r=0.76). Sporulation was significantly correlated with virulence (r=0.83), but not correlated with conidial length (r=0.19).
  C.N. Fokunang , A.G.O. Dixon , T. Ikotun , E.A. Tembe , C.N. Akem and R. Asiedu
  Cassava anthracnose disease (CAD) caused by the fungus Colletotrichum gloeosporioides f.sp. manihotis has become one of the major economic diseases of cassava in Africa. The expansion of cassava production farmlands particularly in the humid rainfall zones of West and Central Africa has led to an increase in pathological problems of the crop. The increased epidemic levels of CAD had caused significant crop failure leading to severe food shortages for the poor subsistent farming population depending on the crop for their livelihood. This paper reviews the importance of the crop in terms of food security, CAD disease symptoms, epidemiology, yield losses and the possible control options within the frame work of integrated pest management systems (IPMS).
  O.O. Aina , A.G.O. Dixon and E.A. Akinrinde
  Nine cassava genotypes were evaluated for their growth responses and adaptability to soil moisture stress on the field and in the screenhouse in Nigeria. Genotypes were evaluated in three savanna agroecologies in a randomized complete block design with three replicates. Screenhouse evaluation was conducted using three moisture regimes of 75, 50 and 25% Field Capacity (FC) in a two-factor factorial experiment in CRD with three replicates. Morphological and yield data were collected on the field and in the screenhouse. Results showed significant (p<0.05) difference among genotypes on the field and in the screenhouse. Field moisture stress led to a decline in plant height by 47%, stem girth by 15%, number of tubers by 95% and tuber yield by 87%. Screenhouse moisture condition of 25% FC led to a reduction in plant height by 12.6 and 21.2%, stem girth by 16.3 and 21.7%, number of roots by 94.5 and 88.7% and root weight by 93.3 and 94.9%, respectively at 16 and 30 WAP. Moisture stress therefore resulted into considerable reduction in both vegetative growth and yield of cassava genotypes. Therefore, a concerted effort in breeding cassava for drought tolerance is needed as cassava cultivation is expanding into nontraditional semiarid regions of sub-Saharan Africa. Germplasm introduced from Latin America (especially north-eastern Brazil) is providing a unique source of variability to further broaden the genetic base for drought tolerance in cassava.
  C.N. Fokunang , T. Ikotun , A.G.O. Dixon , C.N Akem , E.A.Tembe and E.N. Nukenine
  This study was conducted to investigate a cheap and readily available alternative control measure for cassava anthracnose disease causal agent (Colletotrichum gloeosporioides f. sp. manihotis), through the use of antimicrobial crude plant extracts such as neem (Azadirachta indica), bitter leaf (Vernonia amygdalina), Ocimum gratissimum and Xylopia aethiopica, on the fungal growth parameters (mycelial growth, sporulation and germtube development). The extracts at concentration levels of 25, 50, 75 and 100% full strength concentration showed an inhibitory effect on mycelial growth, germ tube development and sporulation of fungal isolates 05FCN, 10FCN, 12FCN and 26FCN. Neem seed and leaf extracts at 100% showed a total reduction in sporulation in most of the fungal isolates. The inhibitory properties of the plant crude extracts indicated a promising control option for consideration in cassava treatments of planting stocks, particularly in areas where farming is at a basic subsistent level, and less available money to meet the high cost of pesticides.
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