Search

Description of the subject. Maize (Zea mays L.) is a major staple food providing nutrients for humans and animals worldwide. In Sub-Saharan Africa, maize is stored to ensure food resource availability throughout the year. However, stored-product pests such as the maize weevil, Sitophilus zeamais (Motsch.) (Coleoptera; Curculionidae) can cause huge grain losses. Objectives. This study aimed to assess the oviposition preference of Sitophilus zeamais over maize varieties commonly cultivated in Senegal and the effect of grain morphophysical and biochemical characteristics on their susceptibility to the maize weevil. Method. Twenty-five S. zeamais pairs (M/F) were placed in the center of an arena at equal distance of small heaps of maize grains (30 g) from nine maize varieties. Adult abundance, damaged grains, grain weight loss, and progeny were confronted to grain characteristics (phenolics and ferulic acid content, hardness, brightness, color and size of grains). Results. Susceptibility to the maize weevil varied significantly among maize varieties. Synth-9243 was the most susceptible variety with greatest damaged grains (10.5 ± 2.3%), grain weight loss (2.3 ± 0.6%), and progeny (17.3 ± 3.8 adults). The least susceptible varieties were Across-Pool, SWAN, Obatampa, and Tzee-Yellow. Grain characteristics such as phenolics and ferulic acid content were negatively related to susceptibility, but other constituents may have antixenosis or antibiosis effects. In addition, grain brightness may also have a visual effect deterring oviposition. Conclusions. The most repellent and less favorable varieties for S. zeamais were Tzee-Yellow, Across-Pool, Obatampa and SWAN, that presented high content of phenolics and ferulic acid, hardness and brightness of grains.

Limitations of Bt rice in the entomological rice cropping context in sub-Saharan Africa and Madagascar. A review. In sub-Saharan African countries and Madagascar, rice crops host many insect species, which have been inventoried and studied for almost 40 years. Management of these rice pests using synthetic chemical pesticides is not common practice. In Asia, genetically modified rice varieties (Bt rice) resistant to some insects were engineered in the 1990s. In 2009, two Bt rice varieties were authorized to be marketed in China. Bt rice is not grown in African countries. We therefore decided to analyze the published literature on Bt rice and to compare the findings with the current insect pest situation in African rice fields. The activity spectrum and the efficacy of Bt toxins represent the first limitation encountered in the use of currently available Bt rice varieties. For instance, the effect of Bt toxins against Diptera (Diopsidae) species is unknown, since these species only occur in Africa. On the African continent and in Madagascar, it would be essential to enhance or promote taxonomic, biological and ecological knowledge concerning rice pests and to more accurately measure the impact of various insect species on crop yields. The broad range of rice insect pests, including insect vectors of disease, the risk of target insects developing resistance to Bt toxins and the lack of economic assessments suggest that, with the current state of knowledge in Africa, it would be inappropriate to introduce currently available Bt rice varieties there.

Plants possess a broad array of defenses that could be actively expressed in response of pathogenic organisms or parasites but also following beneficial saprophytic microorganisms recognition. Specifically, there are compounds derived from these organisms and called elicitors that are perceived by the plant to induce a locally or systemically expressed resistance. The understanding of the physiological and biological basis of these induced immunity mechanisms have greatly advanced over the past years but a deeper investigation of the mechanisms underlying the perception of elicitors is essential to develop novel strategies for pest control. The application of chemical and biological stimulators of plant immune defenses in conventional agriculture is expected to increase within the next years. Because of their organic origin and as they provide means for conferring plant protection in a non-transgenic manner, elicitors of plant immunity have a huge potential as biocontrol products. Through this review, we want to illustrate the diversity of compounds identified as stimulators of the plant immune system and describe the mechanisms by which they could be recognized at the plasma membrane level.

Applications of molecular markers in bread wheat breeding for pest and disease resistance. The development in recent years of DNAmarkers offers the possibility of developing new approaches to improving the efficiency of selection strategies. The molecular markers are becoming essential tools in bread wheat (Triticum aestivum L.) breeding since they offer alternative solutions to many breeding problems resulting from the traditional phenotypic markers that are difficult and/or time-consuming to select by plant breeders. Availability of tightly linked molecular markers can now be used in markerassisted selection (MAS) programs, specially for disease and pest resistance gene where it is possible to infer the gene by the marker without depending on the natural pest or pathogen occurrence or waiting for its phenotypic expression. Moreover, these markers have potential importance in facilitating selection procedure, particularly for pyramiding two or more different genes aiming at a more durable and broad- spectrum resistance. Breeding for disease and pest resistance gene can contribute to improving quality yield in wheat plants by carrying out indirect selection through molecular markers linked to the traits of interest. We first provide a brief description of main molecular markers technologies currently being employed. Next, we review some of the current and potential uses of molecular markers in breeding for disease and pest resistance genes in bread wheat

Hessian fly, Mayetiola destructor (Say), is one of the most destructive pest of wheat (Triticum species) worldwide. In Morocco, damage caused by Hessian fly can result in total crop loss if high infestations occur during early stages of crop development. Genes that confer resistance to Hessian fly provide the most efficient and economical means of crop protection against this damaging insect. To date, 27 resistance genes (HJ-H27) have been reported in wheat; among these, 11 are very effective in Morocco. In this study, we have utilized amplified fragment length polymorphism (AFLP) analysis in conjunction with near-isogenic lines (NILs) and bulked segregant analysis (BSA) to identify molecular markers linked to Hessian fly resistance genes in bread wheat. Two pairs of NILs were used as source of DNA, one differing for H5 resistance gene and the other for H22 resistance gene. Using 42 primers combinations, 4200 selectively DNA fragments were analyzed throughout the wheat genome, with an average of 100 bands per combination and per pair of NILs. This technique appeared to be promising, since 28 polymorphic bands were detected, among which 13 associated to H5 locus and 15 to H22 locus.

Contribution of plant genetic resources to varietal selection of tropical food legumes. Thanks to their high content of proteins in the dry seeds and to their ability to fix symbiotically the air nitrogen, the food legumes are a key component of the cultural systems in the tropics. Unfortunately these plants are very often characterized by their low and unstable yields. This is explained, in particular, by their susceptibility to diseases, pests and other abiotic constraints (cold, heat, poor soils, etc.). In order to overcome these obstacles, the genetic improvement of food legumes must be undertaken on the basis of very large varietal collections, including wild and cultivated forms of the studied species or other related species. The analysis of the genetic organization of these collections, as well as their characterization and agronomic evaluation constitute essential steps, guiding the works of varietal selection. The present study synthesizes the results obtained by our laboratory in several cultivated species, mainly in the genera Phaseolus and Vigna, secondarily in the genus Cajanus.