Analysing natural diversity of Arbuscular Mycorrhizal Fungi in Coffee (Coffea arabica L.) plantations and application of mycrorrhizal technology in commercial cultivars of coffee plantlets in Nilgiris. Executive Summary
The genus Coffea belongs to the Rubiaceae family, which includes about 100 species. In several developing countries such as Africa, Asia and America, coffee was the significant source of income. It also influenced directly or indirectly in generating job opportunities in those countries. However, only two species are commercially cultivated, namely Coffea arabica L. and Coffea robusta L.
The beneficial effects of mycorrhizae on the nutritional status of plants and on the ability of these plants to withstand different environmental stresses have made these mycosymbionts a key factor for sustainable agriculture. These benefits vary depending on the AMF strains or ecotypes used for inoculation, which makes the selection of an effective AMF for predetermined edapho-climatic conditions a prerequisite for achieving the desired positive response from the association.
The use of efficient mycorrhizal inocula in coffee nurseries may be a promising technology for the production of healthy and vigorous coffee plantlets, thus increasing survival after field transplantation. Nevertheless, knowledge about the role and benefits of mycorrhizae in this important economic crop is still very sparse. The relevance of the symbioses in relation to environmental factors, such as drought, extreme temperatures and chemical toxicity stress conditions, is now of significant interest since agricultural lands are subject to changes in modern environmental conditions that threaten agricultural production and quality.
Significance of the study
Diversity of AMF in Coffee plantations may reveal the fertility of the soil in The Nilgiri District.
It is assumed that this investigation can increase the chance of supplementing or replacing the Phosphorus fertilizer by effective P-mobilizing AM fungal inoculum that symbiotically associated with coffee.
The selected AMF inoculum used to enhance the plant biomass, yield and Phosphorus content of the coffee cultivars. The AMF are soil microbes and cause no ecological pollution they can be used for soil reclamation.
Application of indigenous mass inoculum of AM fungi in soils of The Nilgiri district with other beneficial soil microbes which promote the growth of commercial plants.
Present study was undertaken with the following objectives:
1. Evaluation of the taxonomic diversity of AM fungal communities associated in coffee (Coffea arabica L.) plantations of The Nilgiri district
2. To study the percent root colonization, species richness and spore density of Arbuscular mycorrhizal fungi from rhizosphere soils of Coffee at different taluks of The Nilgiri district,
3. To identify the dominant native AM fungi and also to assess their mass inoculum production using Allium cepa L. as host in pot culture method,
4. To analyse the effectiveness of dominant indigenous AMF inoculum on root formation of coffee in the nursery condition
5. To determine AMF root colonization and its effect on growth, biomass and nutrition of Coffee (Coffea arabica L.) by pot culture method.
The significant findings of the present study are given below:
The study plant Coffea of the family Rubiaceae, exhibited AM fungal association. In Nilgiri district two varieties of coffee were identified namely Coffea arabica L. and Coffea robusta L. In Gudalur taluk and Pandalur taluk, the occurrence of Coffea robusta L. was reported. Hence, the study was restricted to four taluks namely Ooty, Coonoor, Kundah and Kothagiri. Coffee variety Coffea arabica L. from two different localities of four taluks were taken for further studies. AMF colonization in roots and the spore population in the rhizosphere soil samples of the coffee plant studied showed wide range of variation. Percent root colonization and mycorrhizal spore counts steadily increased in summer. Most commonly and highly colonised AMF spores were isolated from the rhizosphere soil samples of coffee plants of the eight localities of four taluks. These 10 spores come under four genera namely Acaulospora, Gigaspora, Glomus, and Scutellospora. Arbuscular Mycorrhizal Fungi belonging to genus Glomus were dominant when compared to all other genus. Coffee plants from Coonoor Taluk showed higher root colonization as well as the spore count when compared to other plants of different taluk. The physico- chemical properties of the soils varied considerably among samples particularly in the nutrient level. Edaphic characteristics of samples collected from study areas indicated that the soils were only acidic (pH 5.1 – 6.1) with no appreciable variations in available nutrients.
The electrical conductivity (EC) was low to moderate (ECs 0.04 – 0.08) in the study sites. The organic matter was maximum in Ooty taluk study sites (OM 6.26 – 7.97%) and it was minimum in kothagiri taluk study sites (OM 2.32 – 3.10%). The physicochemical properties of the soils varied considerably among samples particularly in the nutrient level. The soil types were mostly red and brown fine loam. The available Nitrigen content of the soils in study localities were invariably high (0.21 – 0.32 ppm). Generally the soils were nutrient deficient particularly with moderate phophorus level (11.1 – 22.3 ppm), low to high level of potassium (50.5 – 335.5 ppm) and also with other micro nutrient contents. Relative amount of Zn (3.05 – 8.14 ppm), Ca (202.5 – 910.5 ppm), Fe (8.98 – 13.24 ppm), Mn (3.17 – 5.04 ppm) and Mg (54.0 – 90.5 ppm). Coffee plants which were collected from all the four study localities were positive for AM fungal colonization in roots and the species of AM colonizing roots showed wide range of variation. Per cent root colonization ranged from 52.2 – 70.2% in south west monsoon, 60.2 – 74.5% in North east monsoon, 30.5 – 63.7% in winter and 60.5 – 98.7% in summer. There was a certain degree of specificity among the different AM fungal species in those four different study sites with coffee plants. Per cent root colonization was as low as 30.5% at Chinnacoonoor site of Ooty taluk in winter and as high as 98.7% at Araihatty site of Coonoor taluk in summer. Most commonly occurring Ten AM fungal species were isolated from the rhizosphere soils of the coffee plants from the study areas. The occurrence of hyphae and vesicles was consistent during the entire study period, but arbuscules were absent during winter and summer seasons. Arbuscules were observed very low during south west monsoon and north east monsoon. The extra metrical phase of AM fungi differed greatly. AM fungal spores and sporocarps were isolated from the root zone soils of coffee collected separately from eight study localities. The total spore counts varied between 84 – 540 per 100 g soil in coffea arabica. Based on the frequency of occurrence, the AM fungal species identified were grouped as (dominant above 75%), (common 55-75%) and frequent (below 55%) forms accordingly. Acaulospora scrobiculata, Gigaspora margarita, Glomus aggregatum, G. fasciculatum, Glomus mosseae, and Scutellospara heterogama, was dominant forms. Acaulospora bireticulata and Glomus geosporum constitute common AM fungal forms. Glomus macrocarpum and Scutellaspora persica are AM fungal species identified may be considered as rare forms. Further Acaulospora scrobiculata, Glomus aggregatum, G. fasciculatum and Gigaspora margarita showed 100% frequency in all the study areas. The lowest number of spores 84 was regarded in root zone soil of coffee at Cinnacoonoor locality of Ooty study sites in winter, while the highest number of spores 540 at Araihatty locality of Coonoor study site in summer was recorded. Species richness, diversity index and species evenness were also recorded for all eight localities of four study sites. Among the ten, seven indigenous fungi were used for inoculum production. The bioassay was conducted using onion (Allium cepa L.) as the test plant to study the association efficiency and confirmation of the production of the AM fungal species. The native AM fungal isolates were used for inoculum production: Acaulospora scorbiculata, Gigaspora margarita, Glomus aggregatum, Glomus fasciculatum, Glomus geosporum, Glomus mosseae, and Scutellospora heterogama. The plant inoculated with Glomus aggregatum showed higher shoot (36.15g/plant) and root with bulb fresh weight (57.12g/plant) when compared to all other treatments. The shoot and root with bulb dry weight (3.95g/plant and 6.34g/plant respectively) was also found to be higher in plants inoculated with Glomus aggregatum. The maximum phosphorus content in shoot (5.62mg/plant) and phosphorus content in root with bulb (5.39mg/plant) was observed in Glomus aggregatum inoculated onion plants. Per cent root colonization and mycorrhizal spore counts were found to vary in all treatments. The onion plants inoculated with Glomus aggregatum showed significantly higher percent root colonization (96.2%), extrametrical spore number (560). Among the seven isolates of AM fungi tested in inoculum production, Glomus aggregatum was the most efficient strain followed by Glomus mosseae when compared to all other strains. A poly bag trial was conducted in Government Arts College, Ooty to study the influence of inoculation of different AM fungi on growth and biomass production of Coffea arabica in sand : soil of 1:1 ratio with pH 5.4. Seven dominant native AM fungi isolated from different coffee plants of The Nilgiri district were tested for their symbiotic efficiency against coffee plants. The growth, biomass and nutrient of coffee seedlings was influenced by different AM fungi were recorded. In general, inoculated plants showed increased plant height, number of leaves and biomass compared to control plants without am fungi inoculum. The growth, biomass and nutrient in 6 months, 10 months, 14 months and 18 months of seven different AM fungi inoculated plants were recorded. Among the seven inoculated treatments, the plants of 18 months growth inoculated with Glomus mosseae showed maximum shoot and root length (25.9 cm and 36 cm respectively), number of leaves (22 leaves) and fresh and dry biomass of shoot and root (19.55, 6.99, 8.18 and 3.54 g/plant respectively) which differed significantly from all other treatments. The plants growth and biomass was maximum in plants inoculated with Glomus mosseae followed by those inoculated with Glomus aggregatum. The lowest plant growth, biomass and nutrient were noticed in uninoculated control plants. Mycorrhizal inoculation resulted in significant increase in Nitrogen (26.25 mg/plant), Phosphorus (85.59 mg/plant) and Potassium (0.32 mg/plant) content in 18th month coffee plant. Highest N, P and K content was recorded in plants inoculated with Glomus mosseae which differed significantly from other treatments, followed by the plants inoculated by G. aggregatum. Inoculation with AM fungi greatly influenced the uptake of micronutrients such as Zn (0.64 mg/plant), Ca (0.34mg/plant), Mg (0.52 mg/plant) and Fe (0.85mg/plant). Least growth, biomass and nutrient were observed in plants inoculated with Scutellospora heterogama. The results of the present study clearly brought out that Glomus mosseae is the efficient AM fungi selected from screening, performed better in improving plant growth and nutrition. Conclusion:
This study clearly indicates that a proficient biological response of coffee plants towards different AM fungi, with G. mosseae conferring superior benefits compared to all other AMF inoculated plants. The results clearly indicate that AM fungal inoculation can significantly reduce synthetic fertilizer in seedling production. Inoculation of efficient AM fungal symbionts can be effectual in obtaining vigorous seedlings which could be used commercially.