Mycorrhiza: Bio-fertilizer for the future

As different factors like lower-fertility, arsenic contamination, pollution of air and water coupled with draught and attack of pathogens put a dent on harvest Professor Dr Md. Amin Uddni Mridha of Chittagong University comes up with bio-fertilizers and methodology of Mycorrhizal fungi application to overcome the problem and ensure food security with a good yield.
An agricultural scientist of Plant Pathology and Microbiology, especially Mycorrhizal Technology Dr Mridha recently talked to this writer. A pioneer of mycorrhizal research in Bangladesh, he has identified more than 40 different types of endomycorrhiza and 25 different types of ectomycorrhizal fungi used for producing bio-fertilizers that could successfully help crops survive odds and bring forth increased yield.
Dr Mridha also spoke of methodology he recently developed with Arbuscular Mycorrhizal Fungi to reduce the arsenic contamination in crops in collaboration with scientists from USA under a project financed by USDA. Study on biodiversity of wood decay fungi helped him record a number of plant diseases, mainly in medicinal plants, and evolve method for their sustainable management with biopesticides.
Mycorrhizas are highly evolved non-pathogenic symbiotic association between roots of most vascular plants and certain specialized soil fungi (Basidiomycetes, Ascomycetes and Zygomycetes) that colonize the cortical tissues of roots during periods of active plant growth both in natural environment and in cultivation, he said.
Dr Mridha came up with the following findings and suggestions regarding the application of bio-fertilizer producing mycorrhizal fungi.
Plant growth in low-fertile or acid soil: The beneficial effects of Vesicular-Arbuscular Mycorrhizas (VAM) used in bio-fertilizers to plant growth, especially in soils of low fertility, are well documented, said the professor.
In the tropics, many crops are grown in infertile acid soils, where low levels of available phosphorus frequently limit their establishment. In such soils, an efficient mycorrhizal association can increase phosphorus uptake and crop yield.
In addition to enhanced P (phosphorus) uptake, VAM fungi often enhance acquisition of relatively immobile micronutrient cations, particularly Zn (zink) and Cu (copper). Vesicular-arbuscular mycorrhizas are also important for N (nitrogen) uptake to stimulate the growth and nutrition of plants and are of great ecological importance with regards to N-nutrition of plants, especially non nitrogen-fixing species.
“In mycorrhiza laboratory of Chittagong University we have studied the influence of mycorrhizal inoculation in growth improvement of a large number of agricultural crops, horticultural crops, ornamental plants, forest plants, tea, rubber and other plantation species. In most of the cases we have recorded higher growth,” said Dr Mridha.
“During these study we have studied the biodiversity of a large number of Arbuscular Mycorrhizas (AM) fungi belonging to six different identified genera. Out of the 126 species recorded all over the world we have recorded more than 40 different species from our soils in our laboratory for the first time working last 15 years. The fungi recorded in our laboratory have not been reported earlier from Bangladesh,” he maintained.
Transfer of carbon and nutrients: Vesicular-Arbuscular Mycorrhizas play an important role in the direct transfer of carbon from one plant to another. Nutrient transfer can occur between plants of the same species or between different species and, even in some cases, from trees to herbaceous plants. The plant roots are interconnected by mycorrhizal hyphae through which the nutrients move from one plant to another. Vesicular-Arbuscular Mycorrhizas can mediate interplant transfer of P and N. When there are legumes and non-legumes growing in N deficient soil, this flow of N will likely be from legume to non-legume and may be of considerable significance to the N-economy of the non-legume. The interplant nutrient transfer technology may be useful for Bangladesh agriculture. The implementation of Rhizobium technology available in our country needs mycorrhizal fungi for P nutrition, which is needed as energy of Rhizobium bacteria for better fixation of N from the atmosphere.
Tolerance against attack of root pathogens: Several studies have demonstrated, the potential of using VAM for establishment and growth of different micropopagated species after transplanting. Many reports have shown that VAM can decrease the severity of diseases caused by root pathogenic fungi, bacteria and nematodes. The VAM appear to decrease plant susceptibility to disease, or increase tolerance against the attack of root pathogens.
“In our laboratory we have recorded plants previously inoculated with fungal symbionts as exhibiting an increased resistance to fungal root diseases like wilts and rots," Dr Mridha said.
Reports have also indicated that VAM increase plant tolerance to salinity, thereby increasing yield in saline soils. The VAM can help plants to become established in nutrient deficient soils or degraded (eroded) habitats and can assist plant establishment in coal waste, eroded desert and disturbed soils, he said.
Land-rehabilitation and fertility: Land rehabilitation induces the mediation of soil aggregation -- a process known to be carried out by VAM fungi. Vesicular-arbuscular mycorrhizal fungi can improve plant-water relations in many situations. Through maintaining the uptake of slowly diffusing nutrients under water stress situations the VAM fungi can help plants cope with drought stress.
Mycorrhizal fungi play a significant role in the regulation of soil biological activity because of their abundance throughout the uppermost soil layer. It is interacting with other beneficial soil microbes to improve the soil fertility where soil biological activities are reduced because of burning and shifting cultivation. In last fifteen years of mycorrhizal studies it has been established that mycorrhizal inoculation enhance plant growth in degraded soil, saline soils, water stress condition, flooded soils etc.
Methodology to reduce the arsenic contamination in crops: More than 30 million people are already facing the problem of arsenic contamination in our country. The ground water contaminated with Arsenic poses significant risk to animal and human health through soil-crop transfer, through food crops like vegetables and cereals where arsenic entere the food chain. Arsenic poisoning causes skin pigmentation, development of warts, ulcers, cancer etc. To reduce the arsenic contamination in crop plants a number of experiments conducted under USDA financed project indicated that using mycorrhizal fungi could reduce the arsenic uptake by the crops.
We have also developed technology by which soil arsenic can be reduced by hyper accumulated plant like Pteris vitata.
Use of VAM fungi in agricultural management: Propagation of inocula for large-scale inoculation is a major problem in popularizing VAM fungi for use in agricultural management because of fungi are obligated symbionts and cannot be multiplied artificially. Although the fungi cannot be cultured in the laboratory, large-scale production techniques under field condition for VAM fungi have been developed in mycorrhiza laboratory in Chittagong University and the inoculum is available for distribution among the farmers.
Dr Mridha said, “The inoculum production technology developed in our laboratory is very useful and unique because we have developed this technology with our own mycotrophic plants available in our country only. The inoculum is ready for distribution among the farmers.”
Use of mycorrhiza needed to improve agricultural productivity: The reduction of water and air pollution from the leaching loss of chemicals and reduction of soil erosion because of mycorrhizal association can improve the soil health and environmental conditions. It is now recognized that VAM can be harnessed in order to improve productivity in agriculture, fruit culture, and forestry by reducing the input of fertilizers and/or by enhancing plant survival, thus offsetting ecological and environmental concerns, observed Dr Mridha.
For this reason, mycorrhizal research and its practical use as a low input technology for managing soil fertility and plant nutrition in the country is drawing increasing attention, he maintained.
Abdullah Al Mahmud is Staff Reporter, Chittagong Bureau of The Daily Star.