International Institute of Tropical Agriculture

About: International Institute of Tropical Agriculture is a nonprofit organization based out in Ibadan, Nigeria. It is known for research contribution in the topics: Population & Agriculture. The organization has 2638 authors who have published 4330 publications receiving 119041 citations. The organization is also known as: IITA.

Statistical properties of QTL linkage mapping in biparental genetic populations

Abstract: Quantitative trait gene or locus (QTL) mapping is routinely used in genetic analysis of complex traits. Especially in practical breeding programs, questions remain such as how large a population and what level of marker density are needed to detect QTLs that are useful to breeders, and how likely it is that the target QTL will be detected with the data set in hand. Some answers can be found in studies on conventional interval mapping (IM). However, it is not clear whether the conclusions obtained from IM are the same as those obtained using other methods. Inclusive composite interval mapping (ICIM) is a useful step forward that highlights the importance of model selection and interval testing in QTL linkage mapping. In this study, we investigate the statistical properties of ICIM compared with IM through simulation. Results indicate that IM is less responsive to marker density and population size (PS). The increase in marker density helps ICIM identify independent QTLs explaining >5% of phenotypic variance. When PS is >200, ICIM achieves unbiased estimations of QTL position and effect. For smaller PS, there is a tendency for the QTL to be located toward the center of the chromosome, with its effect overestimated. The use of dense markers makes linked QTL isolated by empty marker intervals and thus improves mapping efficiency. However, only large-sized populations can take advantage of densely distributed markers. These findings are different from those previously found in IM, indicating great improvements with ICIM.

Phosphorus in smallholder farming systems of sub-Saharan Africa: implications for agricultural intensification

Abstract: Current efforts in combating food insecurity in sub-Saharan Africa (SSA) focus on agricultural intensification. Given the high soil nutrient depletions, replenishing soil fertility is a major component of such efforts. One of the key nutrients limiting crop production is phosphorus (P). Overcoming P deficiency in smallholder farming in SSA faces many challenges, mainly because the causes of P deficiencies vary, and viable options to replenish soil P have limitations. In some areas, P deficiency is associated with a low P reserve, while in others, it results from a high soil P-adsorption capacity. Numerous studies have focused on developing approaches and strategies with potential to replenish soil P or improve its availability to crops. This paper highlights approaches and strategies that have been studied, including the use of soluble P fertilizers, phosphate rocks and organic resources. The contribution of soluble P fertilizers is mainly limited by their high cost, while most phosphate rocks are not mined. Replenishing P through organic resources is constrained by their often low P content and inadequate availability in smallholder farms. Optimizing the P use efficiency appears as the most plausible target pending an increased accessibility of P sources to farmers. Practices towards this optimization include strategic crop sequences and P allocation to crops, use of P-efficient genotypes, and targeting the residual P. Research is needed towards gaps in understanding processes governing benefits associated with these practices. Since P replenishment is fertilizer dependent, greater attention is required in enhancing the accessibility of P fertilizers to smallholder farmers.

Effect of plant nitrogen and silica on the bionomics of Sesamia calamistis (Lepidoptera: Noctuidae)

Abstract: The effects of nitrogen and silica application to maize plants on various aspects of the bionomics of the maize stem borer, Sesamia calamistis Hampson, were studied in the laboratory. Increasing nitrogen doses significantly increased larval survival (from 18.7% (control) to 37.3% at 2.25 g N/plant), larval weight (from 49.0 mg (control) to 99.5 mg at 2.25 g N/plant), and female fecundity (from 77 eggs per female (control) to 365 eggs per female at 1.69 g N/plant). A significant, positive relationship was found between moth fecundity and female pupal weight. Nitrogen had no effect on larval and pupal developmental time but increased adult longevity. Intrinsic rate of increase, rm, and the net reproductive rate, Ro, were positively related to leaf and stem nitrogen, while generation time, G, was negatively related. Silica had the opposite effect from nitrogen on larval survival. Increasing silica supply reduced ultimate larval survival from 26.0% (control) to 4.0% at 0.56 g Si/plant. Immature developmental time, larval and pupal weight, pupal survival, female fecundity, egg viability and adult longevity of S. calamistis were not affected by silica application.

Breeding tef [Eragrostis tef (Zucc.) trotter]: conventional and molecular approaches

Abstract: With 2 figures and 5 tables Abstract Tef [Eragrostis tef (Zucc.) Trotter] is an important food staple cereal crop in Ethiopia. Despite its importance in the Ethiopian agriculture, there are constraints that need to be addressed through scientific research. The major constraints are low yield of landrace cultivars under widespread cultivation, susceptibility to lodging and a lack of knowledge concerning the genetic control of agronomic traits. Conventional tef breeding efforts started in the late 1950s, and since then a total of 24 varieties have been developed and released. Yield gain from tef breeding has been linear with an average annual increase of 0.8%. Tef genomics has provided much molecular genetic information on important agronomic traits. More than 1500 PCR-based molecular markers have been developed and several genetic linkage maps based on intra- and inter-specific crosses have been constructed. Results from quantitative trait loci studies have provided information necessary for marker-assisted selection. Lodging is the number one cause of yield loss in tef. Recently, molecular breeding techniques and biotechnologies are being employed to understand the genetic control of lodging.