1. VESICULAR ARBUSCULAR MYCORRHIZA Investigating the VAM root infection in soybean Felix Kariuki Karuga The University of Nairobi School of Biological Studies Chiromo Campus and Tropical Soil Biology and Fertility (TSBF), World Agroforestry Centre, ICRAF, Nairobi, Kenya

2. Introduction Mycorrhiza is the mutualistic symbiotic relationship between non-pathogenic soil borne fungi and the roots of the higher plants. Mycorrhiza is the mutualistic symbiotic relationship between non-pathogenic soil borne fungi and the roots of the higher plants. There are two types of mycorrhiza;- endomycorrhiza and ectomycorrhiza. There are two types of mycorrhiza;- endomycorrhiza and ectomycorrhiza. Mycorrhizal fungi derive enormous advantage from teaming up with mycotrophic plants e.g cassava, onions, rice, legumes eg soybeans. Mycorrhizal fungi derive enormous advantage from teaming up with mycotrophic plants e.g cassava, onions, rice, legumes eg soybeans.

3. Development of VAM fungi The first stage is the Pre-infection stage which has the resting spores fungal hyphae and root fragments with fungal structures. The second stage is the Primary infection stage which involves root penetration by the VAM fungi hyphae, this penetration occurs between epidermal cells and forms an appressorium. The first stage is the Pre-infection stage which has the resting spores fungal hyphae and root fragments with fungal structures. The second stage is the Primary infection stage which involves root penetration by the VAM fungi hyphae, this penetration occurs between epidermal cells and forms an appressorium.

4. Role of VAM in phosphorous uptake VAM fungi have most significant role of improving plant growth when little phosphate is present in the soil VAM fungi have most significant role of improving plant growth when little phosphate is present in the soil The mycelium absorbs the p and transports it to arbuscules where major transfer of p from the fungi takes place The mycelium absorbs the p and transports it to arbuscules where major transfer of p from the fungi takes place

5. Sites studied The study on VAM infection in soy bean was done in two sites which are Mituguu and Bungoma sites three teratments i.e C,P and P+L besides ten varieties in each site were looked at. The study on VAM infection in soy bean was done in two sites which are Mituguu and Bungoma sites three teratments i.e C,P and P+L besides ten varieties in each site were looked at. Mitunguu is in the central region of Kenya Mitunguu is in the central region of Kenya It’s a dry site and receives low amount of rainfall annually, in terms of mycorrhiza colonization It’s a dry site and receives low amount of rainfall annually, in terms of mycorrhiza colonization this site has the highest infection of mycorrhiza as compared to Bungoma site this site has the highest infection of mycorrhiza as compared to Bungoma site The Bungoma site is found in the western region of Kenya, it’s a wet site; receives high rainfall annually as likened to Mitunguu the water content is high in uppermost layers of the soil. The Bungoma site is found in the western region of Kenya, it’s a wet site; receives high rainfall annually as likened to Mitunguu the water content is high in uppermost layers of the soil.

6. Effects of p fertilization on VAM The treatments with p fertilization on both sites registered lowest VAM infection, this shows that the application of p fertilizer lowers the infection on both sites; The treatments with p fertilization on both sites registered lowest VAM infection, this shows that the application of p fertilizer lowers the infection on both sites; Though p fertilization inhibits the VAM infection, the low infection seen in these treatments is due to the p tolerant fungal species which are indigenous in the soil and they continue colonizing the soy bean roots Though p fertilization inhibits the VAM infection, the low infection seen in these treatments is due to the p tolerant fungal species which are indigenous in the soil and they continue colonizing the soy bean roots

7. Effects of lime on VAM The treatment with phosphorus and lime had high VAM infection than treatment with P fertilization. The treatment with phosphorus and lime had high VAM infection than treatment with P fertilization. Liming of the soil is associated with supply of ca and mg. Liming of the soil is associated with supply of ca and mg. High rate of liming reduces uptake of P. Besides indigenous VAM surviving in acidic soil are destroyed. High rate of liming reduces uptake of P. Besides indigenous VAM surviving in acidic soil are destroyed. Some species of VAM fungi do well in a wide range of soil Ph, e.g Glomus fasciculatum, Gigaspora margarita. Some species of VAM fungi do well in a wide range of soil Ph, e.g Glomus fasciculatum, Gigaspora margarita.

8. Effects of P and P+L on VAM in Bungoma

9. Effects of P and P+L on VAM in Mitunguu

10. Nodulation In the two sites studied we have the nodulation increasing from the control treatment with P+L having the high nodulation except in Meru of nodules as shown in the graphs. In the two sites studied we have the nodulation increasing from the control treatment with P+L having the high nodulation except in Meru of nodules as shown in the graphs. The dry site records highest percentage of nodules as likened to wet site, this is due to high colonization of VAM in this site, The dry site records highest percentage of nodules as likened to wet site, this is due to high colonization of VAM in this site, the nitrogen fixation by the rhizobia requires energy, VAM fungi plays a critical role in uptake of P this helps because the large surface area the legume can support sufficient photosynthates to symbionts, also the P demand for nitrogen fixing bacteria is met, and that’s why colonization of roots by VAM increases nodulation by rhizobia. the nitrogen fixation by the rhizobia requires energy, VAM fungi plays a critical role in uptake of P this helps because the large surface area the legume can support sufficient photosynthates to symbionts, also the P demand for nitrogen fixing bacteria is met, and that’s why colonization of roots by VAM increases nodulation by rhizobia.

11. Nodulation in Meru

12. Nodulation in Bungoma

13. Nodulation cont…….

14. Nodulation cont……

15. Importance of mycorrhiza; Protect plant from certain soil borne diseases and parasitic nematodes by producing antibiotics and altering root epidermis besides competing with fungal pathogens for infection site. Protect plant from certain soil borne diseases and parasitic nematodes by producing antibiotics and altering root epidermis besides competing with fungal pathogens for infection site. Sequestration of toxic metals in hyphal walls, lowering the concentration of metal plant is exposed to. Sequestration of toxic metals in hyphal walls, lowering the concentration of metal plant is exposed to. External hyphae of e.g. Glomus fasciculatum can take nitrogen and transport it to the rooting zone. External hyphae of e.g. Glomus fasciculatum can take nitrogen and transport it to the rooting zone. This helps the movement of nitrate ions to roots by mass flow or diffusion. This helps the movement of nitrate ions to roots by mass flow or diffusion. When fungal sheath of ectomycorrhiza cover absorbing roots, there is flux of water between soil and roots, this induces draught resistance. When fungal sheath of ectomycorrhiza cover absorbing roots, there is flux of water between soil and roots, this induces draught resistance.

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