Viviene Matiru

Potential of indigenous bradyrhizobia versus commercial inoculants to improve cowpea (Vigna unguiculata L. walp.) and green gram (Vigna radiata L. wilczek.) yields in Kenya

Limited information is available on reduced cowpea (Vigna unguiculata L. Walp.) and green gram (Vigna radiata L.Wilczek.) yields in Kenya. Declining soil fertility and absence or presence of ineffective indigenous rhizobia in soils are assumptions that have been formulated but still require to be demonstrated. In this study, soils were collected from legume growing areas of Western (Bungoma), Nyanza (Bondo), Eastern (Isiolo), Central (Meru) and Coast (Kilifi) provinces in Kenya to assess indigenous rhizobia in soils nodulating cowpea and green gram under greenhouse conditions. Our results showed that highest nodule fresh weights of 4.63 and 3.32 g plant−1 for cowpea and green gram were observed in one soil from Isiolo and another from Kilifi, respectively, suggesting the presence of significant infective indigenous strains in both soils. On the other hand, the lowest nodule fresh weights of 2.17 and 0.72 g plant−1 were observed in one soil from Bungoma for cowpea and green gram, respectively. Symbiotic nitrogen (N) fixation by cowpea and green gram was highest in Kilifi soil with values of 98% and 97%, respectively. A second greenhouse experiment was undertaken to evaluate the performance of commercial rhizobial inoculants with both legumes in Chonyi soil (also from Coast province) containing significant indigenous rhizobia [>13.5 × 103 Colony Forming Units (CFU) g−1]. Rhizobial inoculation did not significantly (P < 0.05) affect nodulation, biomass yield and shoot N content in cowpea and green gram compared with controls. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) of the 16S-23S rDNA intergenic spacer (IGS) region analysis of nodules revealed six groups of which only IGS Group IV corresponded with those from commercial inoculants applied, indicating a lower competitiveness of inoculated strains. In cowpea, IGS III was dominant in nodules of plants inoculated with Biofix and Rizoliq commercial inoculants, and the uninoculated control treatment (63.2, 60 and 52.9%, respectively). Similarly, in green gram, IGS Group III was dominant in nodules of plants inoculated with Biofix 704 and Rizoliq commercial inoculants, and the uninoculated control treatment (75, 73.7 and 61.1%, respectively). Our results suggest that the systematic inoculation of both legumes with current available commercial inoculants to improve biomass yields is not necessary in these regions of Kenya. Also, according to our study, it would make sense to promote the utilization of indigenous strains performing well with both legumes.

Fungal endophytes as promising tools for the management of bean stem maggot Ophiomyia phaseoli on beans Phaseolus vulgaris

Common bean, Phaseolus vulgaris, is an important food and cash crop in Africa. Its production is seriously affected by the bean stem maggot (BSM), Ophiomyia spp., which attacks seedlings. We evaluated the ability of eleven fungal isolates to colonize bean plants and the effects of inoculation on BSM feeding and oviposition, pupation, and adult emergence. All fungal isolates were able to colonize different bean plant parts (root, stem, and leaves), except isolates of Metarhizium anisopliae and Beauveria bassiana isolate ICIPE 273. Colonization was generally higher on the roots than on the stem and leaves and varied significantly between the fungal isolates. BSM feeding and oviposition were significantly reduced in all the fungus-inoculated bean plants which in turn affected pupation and adult emergence as compared to the control. Metarhizium anisopliae ICIPE 20 outperformed the other isolates in interfering with BSM lifecycle. Although M. anisopliae ICIPE 78 recorded a high number of punctures similar to the control, a significant reduction in the number of pupae and adult emergence was observed, suggesting possible BSM growth inhibition. This study clearly demonstrates that fungal endophytes can be considered as promising tools for the management of BSM in East Africa.

Rhizosphere ecology of lumichrome and riboflavin, two bacterial signal molecules eliciting developmental changes in plants.

Lumichrome and riboflavin are novel molecules from rhizobial exudates that stimulate plant growth. Reported studies have revealed major developmental changes elicited by lumichrome at very low nanomolar concentrations (5 nM) in plants, which include early initiation of trifoliate leaves, expansion of unifoliate and trifoliate leaves, increased stem elongation and leaf area, and consequently greater biomass accumulation in monocots and dicots. But higher lumichrome concentration (50 nM) depressed root development and reduced growth of unifoliate and second trifoliate leaves. While the mechanisms remain unknown, it is possible that lumichrome released by rhizobia induced the biosynthesis of classical phytohormones that caused the observed developmental changes in plants. We also showed in earlier studies that applying either 10 nM lumichrome, 10 nM ABA, or 10 ml of infective rhizobial cells (0.2 OD600) to roots of monocots and dicots for 44 h produced identical effects, which included decreased stomatal conductance and leaf transpiration in Bambara groundnut, soybean, and maize, increased stomatal conductance and transpiration in cowpea and lupin, and elevated root respiration in maize (19% by rhizobia and 20% by lumichrome). Greater extracellular exudation of lumichrome, riboflavin and indole acetic acid by N2-fixing rhizobia over non-fixing bacteria is perceived to be an indication of their role as symbiotic signals. This is evidenced by the increased concentration of lumichrome and riboflavin in the xylem sap of cowpea and soybean plants inoculated with infective rhizobia. In fact, greater xylem concentration of lumichrome in soybean and its correspondingly increased accumulation in leaves was found to result in dramatic developmental changes than in cowpea. Furthermore, lumichrome and riboflavin secreted by soil rhizobia are also known to function as (i) ecological cues for sensing environmental stress, (ii) growth factors for microbes, plants, and humans, (iii) signals for stomatal functioning in land plants, and (iv) protectants/elicitors of plant defense. The fact that exogenous application of ABA to plant roots caused the same effect as lumichrome on leaf stomatal functioning suggests molecular cross-talk in plant response to environmental stimuli.

Prevalence of gastric mucosal interleukin-1 polymorphisms in Kenyan patients with advanced gastric cancer.

According to data from the Nairobi Cancer Registry, gastric cancer is the fourth most common malignancy in adult males and the fifth most common in adult females. However, this may not represent the true situation because of under-reporting of cases. In the development of gastric cancer, environmental factors such as smoking, diet and, in particular, infection with H. pylori are significant. 1 Based on epidemiological studies, the International Agency for Research on Cancer (IARC) identified H. pylori as a ‘group 1 agent (definite carcinogen)’. 2 H. pylori infection can result in decreased acid secretion with subsequent mucosal atrophy and intestinal metaplasia. 1 Another precondition for mucosal atrophy is autoimmunity against parietal cells, which can mimic classic autoimmune gastritis with the presence of various autoantibodies in up to 40% of H. pylori-infected individuals. 1 The occurrence of intestinal metaplasia, for which a relationship with gastric cancer is strongly suggested, has been demonstrated in approximately 60% of patients with H. pylori infection. 1 The metaplasia may then progress to gastric cancer, especially to tumours of the intestinal type. 1