Comparative effects of continuous cultivation of seven crop combinations on soil physicochemical properties in two soils of different land use history in eastern Nigeria

Changes in 29 soil physicochemical properties resulting from crop cultivation in newly cleared virgin forest were compared with those from previously cultivated land. The aim was to assess the effects of the selected common crop combinations on the soil properties so as to obtain the best option for soil fertility enrichment in each location. The crops selected were those commonly grown by the local farmers. They included sole crops of cassava, yam, maize and pigeon pea, as well as a combination of all the four crops. Others were cassava+maize+pigeon pea and cassava+pigeon pea. Both the sole and crop combinations (which were the treatments) were grown in a randomized complete block design in three replicates in the two locations for two years. Changes in soil properties at 0–20 cm and 20–40 cm depths were monitored for the period. The soils were sampled at the beginning of each cropping season from 1998 to 2000.The pedogenic properties obtained from the diagnostic horizons were used to classify both soils as Rhodic Kindiustalfs (Haplic Lixisols). However, the differences in 19 of the properties at 0–40 cm depth were significant (p≤0.05) between the two locations ab initio. Sixteen of these properties were considered to be better in the forestland agronomically. Depth variations did not influence many of the properties significantly, especially between 1999 and 2000. The effects of crop combination were significant (p≤0.05) on physical properties such as the silt content, the total porosity at the forest location; clay content, bulk density, macroporosity, and hydraulic conductivity at the previously cultivated soil (UNN site). The chemical properties significantly (p≤0.05) affected by crop combination were exchangeable calcium (Ca) and total exchangeable bases at the forest; organic matter, exchangeable potassium (K), total exchangeable acidity, and available phosphorus (P) at the UNN site. Among the properties only the clay content, macroporosity and organic matter seemed to show significant differences between the plots allocated to the different crops and mixtures at the UNN site at the beginning in 1998. Within the short period of the study, there appeared to have been substantial improvements in some properties, especially at 0–20 cm depth, relative to their 1998 values. The changes were generally more in the UNN site than at the forest. The changes were adduced to be facilitated by tillage, as the soils were just brought under cultivation from the forest and fallow conditions. This is because the crop effects were less between 1999 and 2000. However, the improvements in some of the properties suggest that some of the crop combinations were capable of reducing soil fertility loss in the area

The relative resistance of cassava cultivars to African Cassava Mosaic Disease (ACMD) as determined by two methods: ranksum and the area under the disease progress curve

Twenty-five newly bred improved cassava cultivars, twenty-three improved from the International Institute of Tropical Agriculture and two local cultivars were evaluated for their relative resistance to African cassava mosaic begomovirus disease (ACMD) at Ibadan, in an area of high disease pressure representative of the forest/savanna transition zone of Nigeria. These cultivars were exposed to natural infection by the viruliferous whiteflies ( Bemisia tabaci Gennadius) and the Disease Incidence (DI) and index of symptom severity (ISS) were assessed for all clones. Results for the Rank-sum (i.e., sum of ranks for DI and ISS for each cultivar) and the area under the disease progress curve (AUDPC) were used to assess the relative resistance of the cassava clones. Those that showed low Rank-sum and AUDPC values were rated 'moderately resistant (MR)', 'resistant (R)', and 'highly resistant (HR)' to ACMD depending on their respective values and deviation from the mean distribution curve. Clones M94/0121 and 94/0239 were rated HR under the two methods. Clone M94/0583 was rated HR under the AUDPC with a deviation from the mean distribution curve of m 2.00 while it was rated R under the Rank-sum method with a deviation from the mean distribution of m 1.99. Also plants of clones ISU and TMS 30572 were rated highly infection (HS) under both methods. Clone TME-1 was intermediate between Moderately Resistant (MR) and Moderately Resistant (MS) under the AUDPC method with a deviation from the mean distribution of 0.00 but observed to be MS under the Rank-sum method with a deviation of + 0.2. The two methods of evaluation gave similar results as revealed by Spearman rank correlation ( r equals; 0.99, P <0.01). However, the AUDPC method is less cumbersome compared to the Rank-sum method. None of the clones was observed to be immune to the disease

Breeding Cassava for Multiple Pest Resistance in Africa

The major constraints to stable production of cassava in Africa are diseases, insects, mites, weeds, soil and agronomic limitations and socio-economic factors. Of the economic diseases, African cassava mosaic, bacterial blight, and anthracnose are the most important. The green spider mite and cassava mealybugs are by far the most economically important arthropod pests. The long growing period and diverse agroecologies in which cassava cultivars are grown expose them to one or more of these problems and the losses can be devastating. Multiple pest resistance helps to ensure stability of crop performance. Research experience, progress and prospects in breeding cassava for resistance to the pests of greatest economic importance in Africa are presented

The influence of host genotype X environment Interactions on the response of Cassava Anthracnose disease in diverse agro-ecologies in Nigeria

Nine cassava ( Manihot esculenta ) genotypes were grown for three years (1992-1993, 1993-1994 and 1994-1995) in three agro-ecological zones in Nigeria to study their reaction to cassava anthracnose disease (CAD), caused by Colletotrichum gloeosporioides , investigate genotype x environment (G x E) interaction patterns for their reaction to anthracnose, and to identify genotypes with stability of resistance to the disease. Mean squares for environments, genotypes and G x E interactions were highly significant (P<0.0001) for anthracnose infection. Significant G x E interactions, accounting for 19% of the treatment sums of squares, indicated that genotypes responded differentially to anthracnose infection across environments. The additive main effects and multiplicative interaction (AMMI) statistical model selected AMMI3 as the best predictor for anthracnose because it had the smallest root mean square prediction difference (0.41), and explained 99% of the G x E interaction for cassava anthracnose disease. Anthracnose severity was low in all three years. Highest disease severity was recorded in 1992-93 (2.1) and the least in 1994-95 (1.69). Clone U/41044 was the most resistant and TME1 the most susceptible to CAD. Clone 30555 showed the most stable reaction and TME1 the least stability to CAD. The most disease was recorded in Ibadan and Owerri, making them good sites for screening cassava for anthracnose resistance.Neuf génotypes de manioc ( Manihot esculenta ) étaient cultivés pour trois années (1992–1993, 1993–1994 et 1994–19995) dans trois zones agro écologiques au Nigeria en vue d&apos;étudier leur réaction à la maladie d&apos;anthracnose du manioc (CAD), causée par les Colletotrichum gloeosporioides , examiner les modèles d&apos;interaction génotype x environnement (G x E) pour leur réaction à l&apos;anthracnose, et identifier les génotypes ayant une stabilité de résistance à la maladie. Les carrées des moyennes pour les interactions environnements, génotypes et G x E étaient significativement élevées (P<0,0001) pour l&apos;infection à l&apos;anthracnose. Les interactions significatives G x E, comptant pour 19% des sommes des traitements des carrées, ont indiqué que les génotypes ont répondu différentiellement à l&apos;infection d&apos;anthracnose à travers les environnements. Les principaux effets additifs et multiplicatifs d&apos;interaction (AMMI) du modèle statistique sélectionné AMMI3 comme le meilleur prédicteur d&apos;anthracnose parce que ayant la plus faible moyenne des racines carrées de différence de prédiction (0,41), et a expliqué 99% d&apos;interaction G x E de maladie d&apos;anthracnose de manioc. La sévérité d&apos;anthracnose était faible pendant toutes les trois années. La plus forte sévérité de la maladie était enregistrée en 1992–93 (2,1) et la plus faible en 1994–95 (1.69) le clone U/41044 était le plus résistant et le TME1 le plus susceptible à la CAD. Le clone 30555 a montre la plus stable réaction et le TME1 la plus faible à la CAD. La plupart des maladies était enregistrée en Ibadan et Owerri, faisant d&apos;eux les bons sites d&apos;étude de résistance de manioc à l&apos;anthracnose

Combining Ability Analysis of Resistance to Mosaic Virus Disease in Cassava

A North Carolina design II experiment, with three improved cassava ( Manihot esculenta Crantz) accessions as the female parents, 15 cassava landraces and three improved cassava accessions as the male parents (3 x 18), was evaluated in three environments in Nigeria to determine the mode of gene action and the combining ability, and also to estimate heterosis for resistance to cassava mosaic disease (CMD), in various sources of resistance. General combining ability (GCA) effect due to females and males was significant in each environment; while the GCA effect due to males and the specific combining ability (SCA) effect were significant across environments. The relative magnitude of the total GCA components to the total GCA plus SCA component, however, suggested that GCA was more important that SCA in controlling CMD resistance among the crosses. The test for heterosis was significant in the individual environments; one across, involving the best general combiner, exhibited significant heterosis for resistance in all three environments. The implication of the findings in breeding for resistance to CMD is discussed

Evaluation Of Cassava Cultivars For Canopy Retention And Its Relationship With Field Resistance To Green Spider Mite

Three field trials were conducted at IITA, Ibadan, Nigeria between 1993 and 1995 to identify a rapid method of screening cassava (Manihot esculenta Crantz) cultivars for canopy retention and to determine the association between canopy retention and resistance to green spider mite (Mononychellus tanajoa Bondar) in cassava. Three methods (I, II and III) were used to assess canopy retention in 70 cultivars. Method I involves visual estimation and it takes the longest time; method II involves visual estimation and it takes the shortest time; and method III involves taking measurements and it takes a longer time than method II, but with a much shorter time than method I. Method II was the best method for screening cassava cultivars for canopy retention during dry periods. The cultivars showed significant (P &lt; 0.01) differences for canopy retention, stay green ability, mite population density and damage scores, but not for relative water content. Canopy retention was positively correlated (P &lt; 0.01) with stay green ability at the peak of the dry season (January). Generally, canopy retention and stay green ability were inversely associated (P &lt; 0.01) with mite density in March 1994 and 1995, and with damage during the dry season (December to March 1994 and 1995, respectively). It is proposed that cassava cultivars which are tolerant to drought may also be resistant to M. tanajoa and that the genetic potential of cassava to retain many green leaves during the dry season may be a major factor of resistance to M. tanajoa.Trois essais en champs ont \ue9t\ue9 men\ue9s \ue0 l ' IITA \ue0 Ibadan au Nigeria entre 1993 et 1995 pour identifier une m\ue9thode rapide de criblage des cultivars de manioc (Manihot esculenta Crantz) pour la r\ue9tention foliaire et la capacit\ue9 de rester vert, et de d\ue9terminer la relation entre la r\ue9tention foliaire et la resistance \ue0 l ' acarien vert du manioc (Mononychellus tanajoa Bondar). Trois m\ue9thodes (I, II et III) ont \ue9t\ue9 utilis\ue9es pour \ue9valuer la r\ue9tention foliaire chez 70 cultivars. La m\ue9thode I implique l'estimation visuelle et elle prend le temps plus long; la m\ue9thod II implique l'estimation visuelle et elle prend le temps plus court; et la m\ue9thode III implique les mesures et elle prend un temps plus long que celui de la m\ue9thode II, mais beaucoup plus court que celui de la m\ue9thode I. La m\ue9thode II a \ue9t\ue9 la meilleure m\ue9thode de criblage des cultivars de manioc pour la r\ue9tention foliaire pendant les p\ue9riodes s\ue8ches. Il y avait des diff\ue9rences significatives (P &lt; 0,01) entre les cultivars pour la r\ue9tention foliaire, la capacit\ue9 de rester vert, la densit\ue9 des acariens et des d\ue9g\ue2ts caus\ue9s par des acariens mais pas pour la teneur relative en eau. Des corr\ue9lations positives ont \ue9t\ue9 not\ue9es entre la r\ue9tention foliare et la capacit\ue9 de rester vert au pic de la saison seche (Janvier). En g\ue9n\ue9ral, la r\ue9tention foliaire et la capacit\ue9 de rester vert \ue9taient invers\ue9ment associ\ue9es (P &lt; 0,01) \ue0 la densit\ue9 des acariens en Mars 1994 et 1995, et avec des d\ue9g\ue2ts caus\ue9s par l'acarien pendant la saison s\ue8che (de D\ue9cembre \ue0 Mars 1994 et 1995). Il ressort de ces r\ue9sultats que les cultivars de manioc qui sont tol\ue9rants \ue0 la s\ue9cheresse semblent aussi r\ue9sistants \ue0 M. tanajoa et que le potentiel g\ue9n\ue9tique du manioc \ue0 retenir ses feuilles pendant la saison s\ue8che peut \ueatre un facteur majeur de r\ue9sistance au M. tanajoa

Restriction of virus movement into axillary buds is an important aspect of resistance in cassava to African cassava mosaic virus

Axillary buds and bark samples of resistant, moderately resistant and susceptible (control) cassava genotypes either naturally infected under field conditions or experimentally inoculated by grafting were indexed for African cassava mosaic virus (ACMV). Virus detection was carried out using enzyme‐linked immunosorbent assay and polymerase chain reactions to determine the distribution of the virus within the plant and elucidate the genotypes response to virus movement. Significantly more bud and bark samples were positive for virus on the susceptible genotype TME 117 than resistant genotypes TMS 30001 and TMS 91/02319, or the moderately resistant genotype TMS 30572. Detectable virus concentration was significantly lower in the buds of moderately resistant and resistant genotypes than the susceptible control. Under field conditions, it was significant that more primary stem buds were infected than the buds of secondary and tertiary stems but such a gradient was not obvious with bark samples. Shoots that had asymptomic new leaves after the initial symptomatic leaves had no virus in their buds, but some of the bark samples from the same plants tested positive. A significant interaction was observed between year and stem type, and among year, genotype and stem type with respect to virus detection in bud and bark samples. Restriction of virus movement into axillary buds occurred in all the resistant and moderately resistant genotypes. This may explain ACMV‐infected stem cuttings of resistant genotypes producing healthy plants in subsequent generation

Dry matter content and post-harvest physiological deterioration as phenemarkers for characterization of improved clones of cassava

Postharvest Physiological Deterioration (PPD) is a devastating stress of cassava with a positive but undesirable relationship with dry matter (DM) content. The present study evaluated PPD susceptibility and DM among thirty-six improved genotypes of cassava to gain knowledge of their status for possible PPD management. In addition, PPD and DM were assessed as phene markers for estimating genetic distances (GD) among the 36 genotypes for breeding objectives. PPD was quantified using visual streaking evaluation and DM was by oven drying to a constant weight. The results obtained showed a high effect of individual root and genotype on PPD susceptibility and DM content among the assessed cassava genotypes. A weak positive relationship was observed between PPD and DM content (P&lt;0.0001, r = 0.32). Five and three phenetic groups were identified among the 36 cassava genotypes for PPD and DM, respectively. Genetic distances estimated ranged between 0.01 and 0.56 GD with an average of 0.17 GD and nine phenetic clusters were revealed among the 36 cassava genotypes. The factorial analysis employed revealed some useful demarcations among the PPD pheneticgroups while there was no clear cut demarcation for DM phenetic groups among the cassava genotypes. The information embedded in this study is useful in facilitating breeding for PPD with an attention to DM content. Furthermore, it would encourage the use of agronomic traits, in the absence of molecular tools, for genotypic characterization in plants.Keywords: Cassava, Genetic distance, phenetic groups, Postharvest physiological deterioration, and Dry matter conten

Gene Complementarity of Resistance to the Cassava Mosaic Disease among African Cassava Accessions

The cassava mosaic virus disease (CMD) is the most important disease of cassava in Africa, causing severe economic losses. The genetic stock, clone 58308, has been extensively used in breeding for resistance to the disease, but recently, other sources of resistance to the disease have been identified among the landraces and could be used in breeding to diversify resistance to the disease. In this study, the progenies of 70 segregating F1 crosses of some resistant and susceptible landraces, clone 58308 and its derivatives, were evaluated in 3 environments for their reaction to CMD to determine the mode of inheritance and allelic relationships among the various resistant accessions. The results indicated a polygenic mode of inheritance, with both resistant and susceptible accession contributing effective factors towards CMD resistance in their progenies. Effective factors contributed by the susceptible parents were recessive. Among the resistant accessions, the results further showed that the genes for resistance are nonallelic and not linked. Positive transgressive segregants were also detected in several crosses. Significant differences in the mean distribution of F1 progeny disease severity scores further revealed allelic differences among the various sources of resistance. These results imply that the resistant landraces are potential new sources of resistance, which could be used in a breeding programme, together with the resistant improved clones derived from clone 58308 to diversity resistance, while developing new genotypes with enhanced resistance to CMD