Abstract: Background and Objective: Indonesia is rich in non-rice carbohydrate sources including tubers and seeds, but the achievement of consumption these kind of food has only reached 5%. One of these tubers is purple sweet potato. This study aimed to examine the effect of administration of Arbuscular Mycorrhizal Fungi (AMF) and Organic Fertilizer (OF) on the growth and production of purple sweet potatoes. Materials and Methods: Purple sweet potato seeds were sown in the form of plant stems. This study used factorial Randomized Block Design (RBD) consisting of 2 factors with 4 replications. The first factor is the dose of AMF and the second factor is OF. The agronomical parameters observed included stem length, number of leaves, number of branches, number of flowers as well as weight, diameter, number and length of tuber. All variables were analyzed with one-way analysis of variance (ANOVA). Results: The results showed that the administration of 20 and 30 g of AMF supplemented with 50 g of OF (m2p1 and m3p1, respectively) significantly increased stem length, number of leaves, number of branches, tuber weight, diameter and length. Statistical analysis showed a highly significant increase in potato yield for inoculated plants compared with non-inoculated controls. Conclusion: Hence, it can be concluded that application of Arbuscular Mycorrhizal Fungi in combination with organic fertilizer were able to improve the plant growth and the tuber yield of purple sweet potato.
INTRODUCTION
Sweet potato is an alternative food and used as a substitute for rice. This plant can be grown in various soil conditions and in various heights and climates. One of the popular sweet potato varieties is purple sweet potato (Ipomoea batatas var. Ayamurasaki) which contains anthocyanin, a source of antioxidants1. Purple sweet potato has a high nutrient content, so it can replace the cereals such as rice. In addition, its development, production and utilization are promising, which is in line with the food diversification program in Indonesia. As many as 89% of sweet potato production in Indonesia is used as food with a consumption rate of 7.9 kg/capita/year. The rest is used as industrial raw materials (sauces) and animal feed2.
The challenges often experienced in the production of horticultural crops including purple sweet potato in organic farming are the slow rate of phosphorus (P) and nitrogen (N) mineralization obtained from organic fertilizers3, causing slow absorption of nutrients by plants, especially when plants are still small. To overcome this condition, useful microorganisms are used and one useful microorganism that is often used is Arbuscular Mycorrhizal Fungi (AMF) which play an important role in absorbing nutrients4. These fungi are considered as biological fertilizer because they provide water, nutrients and protection against pathogens for plants5. The extraradical mycelia of these fungi take nutrients from the soil, transfer nutrients to the intraradical mycelia inside the plant roots and cross the plant-fungal interface6.
The application of compost as an Organic Fertilizer (OF) in agricultural and horticultural practices has provided benefits including increasing soil structure and fertility7, which consequently stimulated plant growth through various complex mechanisms. It was reported that plant growth due to response to compost substance depends on the host, compost substrate and the presence or absence of AMF propagules8. The AMF serve to expand the surface area of roots that absorb nutrients up to 100-1000 times9. The role of AMF is to take nutrients from the soil and change them in a form that can immediately be absorbed by plants. Colonization of AMF also suppresses pathogenic microorganisms10.
The AMF association varies in structure and function but most of AMF interaction is between the roots of most higher plants and zygomycetes fungi originating from the genus Glomales11. It is estimated that more than 80% of terrestrial plants have this type of association, including many important plants in the fields of agriculture and horticulture11,12. Until now, little information has been obtained regarding the effect of the introduction of AMF on purple sweet potato plants. Therefore, this study aimed to evaluate the administration of AMF and OF on the growth response and production of purple sweet potatoes.
MATERIALS AND METHODS
The research was conducted on the local farm from April-August, 2018. The beds used to plant purple sweet potatoes had a length of 10 m with a width of 1 m and a height of 30 cm. The distance between beds was 50 cm. Purple sweet potato seeds in the form of plant stems (25 cm each) were planted about two-thirds of the stem in the soil and watered every day. Seedlings were planted horizontally with all shoots pointing in one direction. In one planting groove, one stem was planted with leafy stems protruding above the beds. On each bed, there were 2 rows with a distance of about 30 cm. The methods used here were adopted from previous research with a modification13.
Provision of mycorrhizal fungi and organic fertilizers: The AMF were administered into planting holes (10 cm deep with a diameter of 2 cm). Organic fertilizers (OF) were given after one week the seedlings were planted. The amount of AMF and OF used were as follows:
| m0p0 | = | Without AMF and OF |
| m1p0 | = | AMF 10 g |
| m2p0 | = | MF 20 g |
| m3p0 | = | AMF 30 g |
| m0p1 | = | OF 50 g |
| m1p1 | = | AMF 10 g+OF 50 g |
| m2p1 | = | AMF 20 g+OF 50 g |
| m3p1 | = | AMF 30 g+OF 50 g |
Experimental design: The study used a completely randomized design with a 4×2 factorial pattern. One potato seedling was added into a planting hole in a sandy loam soil containing AMF, with each treatment being performed in quadruplicate. Observations were made every month starting from one month old seedlings to harvest and parameters observed were stem length, number of leaves, number of branches, number of flowers, weight, diameter, number and length of tuber. The observations and measurements of stem length, number of leaves, number of branches, number of flowers were conducted every month until harvesting. The weight, diameter, number and length of tuber were measured after harvesting.
Data analysis: Statistical analysis was performed by using Excel. All variables were analyzed with one-way analysis of variance (ANOVA). If the p-value is less than 0.05 then this indicates a significant influence between treatment and groups. The graphs were generated by using Excel and Statistica v13.
RESULTS
This study evaluated 8 agronomical characters of purple sweet potato after inoculation of AMF and provision of OF. The 8 characters were stem length, number of leaves, number of branches number of flowers, weight, diameter, number and length of tuber.
Length of stems: The response of AMF application to the length of purple sweet potato stems can be seen in Fig. 1. Statistical analysis showed that there was a significant influence between treatment and between groups (p = 0.00) in length of the stems. The increasing of stems length was observed since the 1st month after administration of AMF and OF and also AMF without OF, compared to control (without AMF and OF).
Number of leaves: The response of AMF application to the number of leaves of purple sweet potato is shown in Fig. 2. There was a significant influence between treatment and groups (p = 0.00) in number of leaves. The m3p1 gave best response, although the administration of any given amount of AMF with OF increased the number of the leaves compared to plants without OF. The leaves number was observed to increase significantly from the 3rd month.
Number of branches: The response of AMF application to the number of branches of purple sweet potato is shown in Fig. 3. There was a significant influence between treatment and groups (p = 0.00) in number of leaves and m3p1 gave the best response. However, m2p0, m3p0 and m2p1 also increased the number of branches significantly.
Number of flowers: The response of AMF application to the number of flowers of purple sweet potato is shown in Fig. 4. There was a significant influence between treatment and groups (p = 0.047) in number of flowers and m1p1, m2p1 and m3p1 increased the ability of plants to flower.
| Fig. 1: | Response of AMF administration and provision of OF to the length of purple sweet potato stems |
m0p0: Without AMF and OF, m1p0: AMF 10 g without OF, m2p0: AMF 20 g without OF, m3p0: AMF 30 g without OF, m0p1: Without AMF+OF 50 g, m1p1: AMF 10 g+OF 50 g, m2p1: AMF 20 g+OF 50 g, m3p1: AMF 30 g+OF 50 g, OF: Organic fertilizer, AMF: Arbuscular mycorrhizal fungi |
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| Fig. 2: | Response of AMF administration and provision of OF to the number of leaves of purple sweet potato stems |
m0p0: Without AMF and OF, m1p0: AMF 10 g without OF, m2p0: AMF 20 g without OF, m3p0: AMF 30 g without OF, m0p1: Without AMF+OF 50 g, m1p1: AMF 10 g+OF 50 g, m2p1: AMF 20 g+OF 50 g, m3p1: AMF 30 g+OF 50 g, OF: Organic fertilizer, AMF: Arbuscular mycorrhizal fungi |
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Weight of tubers: The response of AMF application to the weight of tubers can be seen in Fig. 5. The ANOVA result provided a p-value 0.030 for treatment. The p-value value (0.500 ) for the group indicated that there were no significant differences between groups. Administration of m1p1, m2p1 and m3p1 increased the weight of tubers significantly. The best response for the weight of tubers was obtained by m3p1 which produced 4.3 kg tubers per plant compared to the control (m0p0) which produced only 1.7 kg tubers per plant.
| Fig. 3: | Response of AMF administration and provision of OF to the number of branches of purple sweet potato stems |
m0p0: Without AMF and OF, m1p0: AMF 10 g without OF, m2p0: AMF 20 g without OF, m3p0: AMF 30 g without OF, m0p1: Without AMF+OF 50 g, m1p1: AMF 10 g+OF 50 g, m2p1: AMF 20 g+OF 50 g, m3p1: AMF 30 g+OF 50 g, OF: Organic fertilizer, AMF: Arbuscular mycorrhizal fungi |
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| Fig. 4: | Response of AMF administration and provision of OF to the number of flowers of purple sweet potato stems |
| m0p0: Without AMF and OF, m1p0: AMF 10 g without OF, m2p0: AMF 20 g without OF, m3p0: AMF 30 g without OF, m0p1: Without AMF+OF 50 g, m1p1: AMF 10 g+OF 50 g, m2p1: AMF 20 g+OF 50 g, m3p1: AMF 30 g+OF 50 g, OF: Organic fertilizer, AMF: Arbuscular mycorrhizal fungi |
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Diameter of tubers: The response of AMF application to the diameter of tubers is shown in Fig. 6. The ANOVA result provided a p-value 0.001 for treatments indicating that there was a significant difference between treatments. The p-value for the group of 0.002 showed significant differences between groups. Administration of m3p1 and m3p0 gave the best response.
Number of tubers: The response of AMF application to the number of tubers can be seen in Fig. 7. The ANOVA result provided a p-value 0.000 for treatment. This indicated a significant difference between treatments. The p-value for the group of 0.009 showed significant differences between groups.
| Fig. 5: | Response of AMF administration and provision of OF to tubers weight |
m0p0: Without AMF and OF, m1p0: AMF 10 g without OF, m2p0: AMF 20 g without OF, m3p0: AMF 30 g without OF, m0p1: Without AMF+OF 50 g, m1p1: AMF 10 g+OF 50 g, m2p1: AMF 20 g+OF 50 g, m3p1: AMF 30 g+OF 50 g, OF: Organic fertilizer, AMF: Arbuscular mycorrhizal fungi |
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| Fig. 6: | Response of AMF administration and provision of OF to the diameter of tubers |
m0p0: Without AMF and OF, m1p0: AMF 10 g without OF, m2p0: AMF 20 g without OF, m3p0: AMF 30 g without OF, m0p1: Without AMF+OF 50 g, m1p1: AMF 10 g+OF 50 g, m2p1: AMF 20 g+OF 50 g, m3p1: AMF 30 g+OF 50 g, OF: Organic fertilizer, AMF: Arbuscular mycorrhizal fungi |
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The number of tuber significantly reduced due to the addition of AMF. The higher the AMF concentration, the lower the number of tuber.
Length of tubers: The response of AMF application to the length of tubers can be seen in Fig. 8. The ANOVA result provided a p-value 0.000 for treatment. The p-value value for the group of 0.248 showed no significant differences between groups. Administration of m2p1 and m3p1 gave the best response.
Overall response of growth and production of purple sweet potato to the administration of AMF and OF: The results in Table 1 show that administration of m1p1 gave a very good response in increasing stem length, number of leaves, number of branches, number of flowers, tuber weight, tuber diameter, number and tuber length.
| Table 1: | Response of growth and production of purple sweet potato to the administration of AMF and OF |
m0p0: Without AMF and OF, m1p0: AMF 10 g without OF, m2p0: AMF 20 g without OF, m3p0: AMF 30 g without OF, m0p1: Without AMF+OF 50 g, m1p1: AMF 10 g+OF 50 g, m2p1: AMF 20 g+OF 50 g, m3p1: AMF 30 g+OF 50 g, +: The increase in parameters | |
| Fig. 7: | Response of AMF administration and provision of OF to the number of tubers |
| m0p0: Without AMF and OF, m1p0: AMF 10 g without OF, m2p0: AMF 20 g without OF, m3p0: AMF 30 g without OF, m0p1: Without AMF+OF 50 g, m1p1: AMF 10 g+OF 50 g, m2p1: AMF 20 g+OF 50 g, m3p1: AMF 30 g+OF 50 g, OF: Organic fertilizer, AMF: Arbuscular mycorrhizal fungi |
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The weight, diameter and length of tuber increased significantly when administered with m1p1, m2p1 and m3p1.
DISCUSSION
Current agricultural practices and intensification can decrease the abundance and diversity of AMF as well as soil fertility13-15. Therefore, inoculation of AMF may form a new mycorrhizal symbiosis which caused a beneficial effect on overall plant growth and development16. Organic matter in the form of organic fertilizer given to the soil serves as a carbon source for soil microbes17. Organic matter also increases soil porosity and reduced the mechanical barriers to AMF hyphal growth, so that hyphae can continue to grow near the roots of plants and infect them.
The data showed that administration of AMF and OF and also AMF alone increased the length of stem significantly as compared to the control plant without AMF or OF.
| Fig. 8: | Response of AMF administration and provision of OF to the length of tubers |
m0p0: Without AMF and OF, m1p0: AMF 10 g without OF, m2p0: AMF 20 g without OF, m3p0: AMF 30 g without OF, m0p1: Without AMF+OF 50 g, m1p1: AMF 10 g+OF 50 g, m2p1: AMF 20 g+OF 50 g, m3p1: AMF 30 g+OF 50 g, OF: Organic fertilizer, AMF: Arbuscular mycorrhizal fungi |
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A research showed that plant grew higher significantly if inoculated with mycorrhizae18. This is because AMF produced auxins and gibberellins-like substances19. Inoculation of AMF increased the potato plant height20. The leaves number were observed to increase significantly in 3rd month after administration of m3p1. Provision of AMF and OF improved the absorption of N, P and K, which in turn increase the number of leaves of Arachis pintoi 13,21. A previous investigation showed that AMF can maintain and improve the P and N intake22. The increasing of the area absorption surface and N mineralization of organic matter will in turn increase the N uptake by AMF23. Some AMF can increase P uptake in media from organic materials24, indicated that AMF is not only infective but also effective.
Treatment m3p1 gave the best response in increasing the number of branches. As reported previously, inoculation of AMF increases the number of potato branches20. The number of branches per plant was significantly higher in AMF inoculated plantlets as compared to the plants without AMF25. Such increase was caused by the widening of the surface area absorption of P from the soil by extended fungal hyphae as it was directly proportional to the higher level of mycorrhizal colonization26. Provision of AMF and OF has been shown to increase the flower formation, compared to treatment with AMF alone13,21. In this study, treatments m1p1, m2p1 and m3p1 gave best response in increasing the number of flowers. A study showed that inoculation with AMF significantly enhanced the number of flowers per plant and per cluster of Pelargonium zonale27. Flower bud emergence was accelerated and number of flowers per plant increased when the rose plant was treated with AMF28.
It was observed that the m3p1 increased the weight of tubers by 2.5 times compared to the control (without AMF or OF) and m3p1 produced 4.3 kg tuber per plant and the control plants only produce 1.7 kg tuber per plant. The AMF promoting effect on potato tuber initiation was observed previously29,30. Inoculation of AMF Glomus etunicatum increased the tube weights of the five species of yam (Dioscorea spp.)31. Glomus dussii inoculation yielded significantly higher tuber weights32. Inoculation of AMF Acaulospora scrobiculata yielded higher tuber weight of Flemingia vestita33. Treatments m3p1 and m3p0 increased the diameter of the tubers. This showed that OF did not contribute significantly to tuber diameter. Commercial AMF inoculation increased the production of potato tubers34. Inoculation of AMF produced larger sized potatoes (10-20%) compared to controls34. There was an increase of 30-35% in the diameter of Libidibia ferrea inoculated with AMF related to non-inoculated control35.
The amount of tuber is inversely proportional to all other parameters of tuber (weight, diameter and length) after provision with AMF and OF. The tuber size at harvest is inversely proportional to the number of tubers36. The treatment m3p1 increased tuber length 1.7 times compared to control. A study showed that inoculation of AMF on yam increased the length of the tubers31. Inoculation of AMF Acaulospora laevis increased tuber length of Gloriosa superba25. Administration of AMF and OF gave a very good response in increasing stem length, number of leaves, number of branches, number of flowers, weight, diameter and tuber length, except tuber numbers.
Overall agronomic character of the purple sweet potato increased significantly when administered with m2p1 and m3p1. A study showed that after inoculation of AMF and all fertilization regimes, the plant biomass, height, leaves area and stems diameter increased significantly37. The AMF make plants more efficiently to acquire nutrients which in turn leading to the improvement of plant growth38. A research on Arachis pintoi showed that provision of AMF increased plant length, number of leaves and flowers13. Overall this study showed that AMF administration without the OF addition can be applied without a significant decrease in yield, thus further increasing profitability.
CONCLUSION
From this study it can be concluded that the administration of m2p1 and m3p1 gave the best response in increasing the weight, diameter and length of the tuber of purple sweet potato. In an overall assessment, provision of AMF and OF increased the growth and development parameters of the plants, therefore increased the production of purple sweet potato.
SIGNIFICANCE STATEMENT
This study discovers that Arbuscular Mycorrhizal Fungi (AMF) and Organic Fertilizer (OF) can be applied to improve the yields of purple sweet potato tubers. This study will help the farmers to use AMF and OF doses optimally so as to increase profit in the cultivation of purple sweet potatoes.
ACKNOWLEDGMENT
This research was funded by the Directorate of Research and Community Service, Ministry of Research and Higher Education of the Republic of Indonesia, Decree No. 3/E/KPT/2018, contract number 132/UN12.13/LT/2018.