A Model for the Development of the Rhizobial and Arbuscular Mycorrhizal Symbioses in Legumes and Its Use to Understand the Roles of Ethylene in the Establishment of these two Symbioses

We propose a model depicting the development of nodulation and arbuscular mycorrhizae. Both processes are dissected into many steps, using Pisum sativum L. nodulation mutants as a guideline. For nodulation, we distinguish two main developmental programs, one epidermal and one cortical. Whereas Nod factors alone affect the cortical program, bacteria are required to trigger the epidermal events. We propose that the two programs of the rhizobial symbiosis evolved separately and that, over time, they came to function together. The distinction between these two programs does not exist for arbuscular mycorrhizae development despite events occurring in both root tissues. Mutations that affect both symbioses are restricted to the epidermal program. We propose here sites of action and potential roles for ethylene during the formation of the two symbioses with a specific hypothesis for nodule organogenesis. Assuming the epidermis does not make ethylene, the microsymbionts probably first encounter a regulatory level of ethylene at the epidermis–outermost cortical cell layer interface. Depending on the hormone concentrations there, infection will either progress or be blocked. In the former case, ethylene affects the cortex cytoskeleton, allowing reorganization that facilitates infection; in the latter case, ethylene acts on several enzymes that interfere with infection thread growth, causing it to abort. Throughout this review, the difficulty of generalizing the roles of ethylene is emphasized and numerous examples are given to demonstrate the diversity that exists in plants

Taxonomic Significance of Some Vernacular names of Okra Accessions (Abelmoschus Spp.) in Ghana

The aim of this study was to examine the folk criteria used by farmers to name their local okra varieties and also to assess the taxonomic significance of vernacular names in the identification and classification of these okra varieties in Ghana. Forty two okra accessions and their vernacu-lar names were obtained from PGRRI, Bunso for the study. The various vernacular names of okra accessions were taxonomically analysed by determining their linguistic meanings, their folk criteria and their folk classification. The folk classification of the different okra accessions were then compared with numerical classification of the same set of accessions of another study based on their quantitative and qualitative morphological characteristics. Based on the taxonomic analyses, the 42 vernacular names of okra accessions in Ghana consisted of languages like Twi, Ewe, Dagbani and Krobo and were also based on folk criteria such as morphology, fruit charac-ters, names of persons or locality, maturity periods and culinary properties. Folk classification of the 42 okra accessions produced 8 different taxonomic groupings which contrasted with numerical classification of the same set of okra accessions. Thus, vernacular names of okra accessions in Ghana could not be used as the sole criterion in the identification and estimation of okra diversity because of the low degree of consistency between the two different methods of classification