New cassava germplasm for food and nutritional security in central Africa

Open Access Journal; Published online: 01 Apr 2021Cassava is a key food security crop in Central Africa, but its production depends largely on the use of local farmers’ varieties characterized by inherently low yield which is compounded by generally high susceptibility to various growth and yield-limiting pests and diseases. Improved cassava genotypes have demonstrated the potential to substantially improve cassava’s contribution to food security and the development of the cassava industry and the improvement of nutrition status elsewhere in Western Africa. Eleven improved cassava genotypes were compared with a local landrace (LMR) used as a check under field conditions over two years in eight locations, grouped in four agro-ecologies in Cameroon. Pest and disease abundance/incidence and damage severity were evaluated. At harvest, root yield and carotenoid content were measured. Best linear unbiased predictors showed the lowest breeding value for LMR with the cassava mosaic virus disease (+ 66.40 ± 2.42) compared with 1.00 ± 0.02% for the most susceptible improved genotype. Two genotypes (I010040-27 and I011797) stood out for having higher predicted fresh root yield means which were at least 16 times greater compared with LMR. Predicted total carotenoid content was the highest (+ 5.04 ± 0.17) for improved genotype I070593 compared with LMR which showed the lowest (− 3.90 ± 0.06%) and could contribute to the alleviation of vitamin A deficiency from cassava-based food systems. Diffusion of high-yielding and nutritious genotypes could alleviate food and nutritional security in Central Africa

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

Reaction of cassava genotypes to the cassava mosaic disease in three distinct agroecologies in Nigeria

Nine cassava genotypes were grown at six representative sites in Nigeria for 3 years to study their response to cassava mosaic disease (CMD), investigate the influence of genotype × environment (G× E) interactions on their reactions to the disease, and identify genotypes with stability to the disease, using the Additive Main Effects and Multiplicative Interaction statistical model. Environments, genotypes and G × E interactions were highly significant (P < 0.01) for the disease. The G × E interactions accounted for 19.5% of the treatment sums of squares for CMD and influenced the relative ranking of genotypes across environments. The magnitude of the G × E interaction effect for CMD was larger than that of genotypes. Examination of the G × E interaction structure revealed specific areas where screening of cassava genotypes for resistance to CMD could be performed best. The study identified genotypes such as TMS 30001 and 63397 with resistance to CMD and CMD‐stable clone U/41044, which could be distributed to growers, and sites such as Ibadan and Ubiaja with high CMD severity for screening genotypes for reaction to CMD

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 < 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 < 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 < 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

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

Relationships between leaf trichome characteristics and field resistance to cassava green mite (Mononychellus tanajoa (Bondar)

Experiments were conducted at Ibadan, Nigeria to assess the effect of leaf trichome characteristics (pubescence intensity index, length, and orientation) on field resistance of cassava to the green spider mite, Mononychellus tanajoa (Bondar). There were significant (P < 0.01) differences in M. tanajoa density, damage score and leaf trichome characteristics among the cultivars. During the dry season (February, 1993 and 1994) and the early part of the rainy season (May, 1993), there were significant (P < 0.01) negative correlations between pubescence intensity index on the top leaves (leaf 3) and mite damage. Significant negative correlations were also obtained between trichome length and damage in the dry season (February, 1993) (P < 0.05), and between trichome orientation and mite damage in the rainy season (May, 1993) (P < 0.01). Correlation between pubescence intensity index and mite density on the top leaves was significant and positive only in the "middle" of the rainy season (August, 1993). A significant (P < 0.01) negative correlation was obtained between trichome orientation and mite density in the dry season (February, 1993). The results suggest that, during the dry season, a high pubescence intensity significantly reduces leaf damage by M. tanajoa through mechanical disturbance of movement and feeding. Trichome length is more important than trichome orientation in cassava resistance to M. tanajoa

Population dynamics of cassava green mite, Mononychellus tanajoa (Bondar) (Acari: Tetranychidae) as influenced by varietal resistance

The population dynamics of Mononychellus tanajoa as influenced by varietal resistance of cassava was determined over two cassava planting seasons (dry and wet season), using biweekly samples from 11 cassava genotypes in Ibadan, Nigeria. The population size of M. tanajoa and the damage scores were higher during dry than wet season. In 1993, there was a higher mite population and damage peak in January than in March, while in 1994, the peak occurred only in April. Mite population and damage generally varied significantly among genotypes and sampling dates, and decreased as the plant aged. High relative humidity rainfall, and low temperature inhibited the mite population growth. During dry season, the rate of mite increase was higher on the susceptible cassava genotype than on the resistant genotypes while situation was reverse in wet season. The study showed that varietal resistance of cassava had a significant effect on the population growth rates of M. tanajoa. January was the favourable period for screening cassava genotypes for resistance to M. tanajoa in Ibadan, Nigeria regions