African Journals On-line
African Journal of Biotechnology

The molecular initiation and subsequent acquisition of disease resistance in plants

Emma Wanjiru Gachomo¹, Olusola Olusoji Shonukan² and Simeon Oloni Kotchoni^{3 *}

¹Institute for Plant Diseases, Nussallee 9, University of Bonn, D-53115 Germany.

²Department of Microbiology, Obafemi Awolowo University, Ile-Ife, Nigeria.

³Department of Plant Molecular Biology, Institute of Botany, Kirschallee 1, University of Bonn, D-53115 Germany.

*Corresponding author; Tel: +49-228739580, Fax: +49-228732689, E-mail:

[email protected]

Interactions between disease resistance (R) genes in plants and their corresponding pathogen avirulence (Avr) genes are the key determinants of whether a plant is susceptible or resistance to a pathogen attack. Evidence has emerged that these gene-for-gene interactions in the perception of pathogenic invasions and development of acquired resistance in plants involve different molecular and hormonal transduction pathways, which are still poorly understood. It has become apparent that plants actively produce several phytohormones such as ethylene, jasmonate, salicylic acid, and reactive oxygen intermediates prior to upregulation of R genes. The physiological role of these molecules in plant resistance to pathogens is beginning to attract attention. The use of transgenic plants in recent attempts, including development of mutants with altered R genes, has provided new insights into the mechanisms involved in pathogen perception, signal transduction and subsequent resistance to disease in plants. This review tries to summarize current knowledge of pathogen-related genes in plants, and how they can be use to improve disease resistance in agronomically valuable plants. It also describes the molecular basis of defense mechanisms in plants under pathogen attack.

Key words: Avr, resistance gene, hypersensitivity, pathogenesis-related proteins, transgenic, plant-defense.

Variations in fatty acid proportions during desiccation of Telfairia occidentalis seeds harvested at physiological and agronomic maturity

Nkang A*, Omokaro D, Egbe A and Amanke, G

Department of Botany, University of Calabar, Calabar, Nigeria.

*Corresponding author; E-mail: [email protected]

The effect of desiccation on lipid content, fatty acid composition and the antioxidative enzymic capacity was investigated in seeds of Telfairia occidentalis, harvested at physiological and agronomic maturity. Seeds were dried at 5 and 28 ^oC, environments that induced different drying and metabolic rates. Desiccation of seeds was associated with decreased antioxidative enzymic capacity (of peroxidase and polyphenoloxidase), and thus increased likelihood of free radical attack and decreased viability (germinability). Agronomically mature seeds contained predominantly saturated fatty acids (tridecanoic), with very low levels of the major fatty acids of edible oilseeds (palmitic, stearic or the unsaturated C18 fatty acids). There was increased accumulation of the mono-unsaturated (oleic) and polyunsaturated (linoleic) fatty acids when seeds were dried at 28 ^oC and moisture contents have reduced to about 42 % or lower. In contrast, seeds dried at 5 ^oC maintained high levels of saturated fatty acids and lower levels of monounsaturated or polyunsaturated fatty acids. Results suggest the need to develop different post-harvest protocols for seed storage, and for processing T. occidentalis to ‘improve’ the seed fatty acid profile as an oilseed for human and animal food.

The use of a novel phage-based technology as a practical tool for the diagnosis of tuberculosis in Africa

Tracy Seaman¹, Andre Trollip¹, Richard Mole², Heidi Albert^1*

¹Biotec Laboratories Ltd., c/o National Health Laboratory Service, PO Box 9066, Cape Town 8000, South Africa.

²Biotec Laboratories Ltd., Ipswich, United Kingdom.

*Corresponding author; Tel: +27 (0)21 425 1541 / +27 (0)82 902 8199, Fax: +27 (0)21 425 9857, E-mail: [email protected]

Sub-Saharan Africa has experienced a significant increase in tuberculosis cases in recent years, fuelled by high rates of TB-HIV co-infection in the region.  The diagnosis of tuberculosis is based largely on clinical assessment, sputum smear microscopy and chest radiography. Although smear microscopy is useful for detecting the most infectious cases, a significant portion of cases are negative on sputum smears, making diagnosis more difficult.  New tests are urgently needed.  The FASTPlaqueTB test, a bacteriophage-based method, has been evaluated in several studies in Africa and elsewhere. Studies in South Africa and Pakistan reported that between half and two-thirds of smear-negative culture-positive TB cases were detected by the FASTPlaqueTB test within 2 days. This suggests a beneficial role for this test in the early diagnosis of clinically suspected smear-negative cases. The same technology has been applied to develop a rapid test to indicate multi-drug resistant TB, FASTPlaqueTB-MDRi.  This test gave equivalent results to conventional drug susceptibility methods, but with more rapid results.  The tests are simple to perform and require no specialised equipment, making the technology suitable for widespread implementation.

Key words: Tuberculosis, bacteriophage, diagnostic test, phage amplification technology, multi-drug resistance, drug susceptibility test.

Relationship between genetic similarity and some productive traits in local chicken strains

Bahy Ahmed Ali^1*, Mohamed Morsy Mohamed Ahmed¹, Osama Mahmoud Aly²

¹Nucleic Acid Research Dept., Genetic Engineering& Biotechnology Research Institute (GEBRI), Mubarak City For Scientific Research & Technology Applications, Alexandria, Egypt.

²El-Sabhiah Poultry Research Station, Alexandria, Animal Production Research Institute- El-Dokki - Cairo, Egypt.

*Corresponding author; E-mail: [email protected]

Random amplified polymorphic DNA (RAPD) technique was applied to detect genetic similarity between five local chicken strains that have been selected for eggs and meat production in Egypt. Based on six oligonucleotide primers, the genetic similarity between the egg-producing strains (Anshas, Silver Montazah and Mandarah) ranged from 72.4 to 85.4%.  While the genetic similarity between the two chicken strains selected for meat production (Baheij and El-Salam) is 86.9%.

Key words: Chicken, local strains, RAPD-PCR, genetic similarity.

Genetic diversity in cowpea [Vigna unguiculata (L.) Walp.] varieties determined by ARA and RAPD techniques

Laïty Fall¹, Diaga Diouf^1*, Mame Arama Fall-Ndiaye ¹, François Abaye Badiane¹ and Mamadou Gueye²

¹Laboratoire de Biotechnologies Végétales, Département de Biologie Végétale, Faculté des Sciences et Techniques, Université Cheikh Anta Diop, Dakar, Sénégal

²Laboratoire de Microbiologie des sols ISRA-IRD, BP 1386, Dakar, Sénégal

*Corresponding author; E-mail: [email protected]

Cowpea, Vigna unguiculata (L.) Walp. presents phenotypical variabilities and in order to study the genetic diversity of cultivated Senegalese varieties, two experimental approaches were used. First, a physiological characterization based on nitrogen fixation was used to assess cowpea breeding lines. Inoculation with two Bradyrhizobium strains (NGR234 and ISRA312), showed a difference in nitrogen fixation potential between the cowpea varieties. Diongoma is the highest nitrogen fixing variety, whereas Mouride is the lowest. The second approach employed genetic characterization based on DNA polymorphism to screen. Results suggest that random amplified polymorphic DNA (RAPD) technology can be used to reorganize the national germplasm in order to eliminate the putative duplicates, and to identify elite varieties.

Key words: Vigna unguiculata, nitrogen fixation, cowpea, molecular markers, RAPD.