Arbuscular Mycorrhizal Biofertilizers Sources in the Potato (Solanum Tuberosum) Plant show Interactions with Cultivars on Yield and Litter-bags Spectral Features

Four strains of Arbuscular Mycorrhizal (AM) biofertilizer fungi, combined with two potato cultivars, were in-field tested in a four-replicate arrangement in a factorial experiment. As far as general combinability is concerned, cv. Agria was more responsive to different inocula (yield +5.56%, P 0.02) and to two strains in particular (+8%). On the other hand, the results with Innovator, a cultivar that yields 33% less than Agria, showed a significant reduction in the number of tubers for three AM strains, thus proving a clear genetic Biofertilizer * Cultivar interaction. The study of hay litter-bags has shown a high NIR spectral fingerprint for the Cultivar factor (81%), while the Inoculation factor showed a higher spectral fingerprint in Agria (76%) than in Innovator (65%). The Substrate Induced Respiration predicted from the NIR-SCiO spectra of the litter-bags was significantly increased after inoculation (+6.3%, P 0.04), but appeared lower for Agria (-5.4%) vs. Innovator (P 0.05), with a non-significant interaction. The obtained results show that the adaptation of the AM strains to the genetics of potato cultivars is a first step toward reducing chemical inputs, with consequent benefits for the environment, but without an excessive reduction in yield. The litter-bag technique can therefore be recommended for a simplified monitoring of the complicated plant-mycorrhizosphere relationship.


Introduction
In 1990, Reganold et al. 1 pointed out that sustainability in agriculture was afflicted by serious problems: "high energy costs, groundwater contamination, soil erosion, loss of productivity, depletion of fossil resources, low farm incomes and risks to human health and wildlife habitats". Thirty years later, progress in agriculture has increased crop yields to face the rapidly growing human population, which is increasing at a rate of 70 million per year. However, the greater use of chemical fertilizers and pesticides, as a result of the spread of animal husbandry and therefore of the increased leaching of excreta, has led to a greater pollution of the environment, through poisoning of the air, soil and water, which in turn has led to the accumulation of toxic residues in food, as well as the development of the resistance of pests. As a result, less invasive remedies, such as reduced tillage, organic farming and botanical insecticides have been introduced 2 . Moreover, since much of humanity is fed inadequately and many food productive systems have been pushed beyond safe boundaries, a radical transformation in modern agriculture, evolving from the BAU paradigm 3 , is being pursued. Sustainability in intensive crop production requires a reduction in chemical inputs, and biofertilizers are therefore being encouraged, with benefits for the environment, but without an excessive reduction in yield, in the search for an optimum economic vs. a maximum system 4,5 .
Many experiments have shown that Arbuscular Mycorrhizal (AM) biofertilizer fungi can overcome the nutrient limitations on plant growth by enhancing nutrient acquisition. Furthermore, their benefits ranges from stress alleviation to bioremediation in soils polluted with heavy metals 6 . Biofertilizers may also enhance the protection of plants against pathogens and increase plant diversity 7 .
Potato plants are known to be sensitive to water stress and have a low P uptake, due to their rarefied root hair system. Therefore, AM fungi can alleviate abiotic stress caused by low levels of P and/or a partially localized water deficit 8 . An economic potato yield can only be achieved through a suitable irrigation and through fertilization, provided that a critical Olsen-P concentration of 46 mg/kg is attained to achieve a maximum production of 90% 9 .

Results
Divergent results were obtained for the two cultivars ( Table 1). The average effect of size on the yield of Agria amounted to +5.56% (P 0.02), with differences in favor of the C (Septoglomus constrictum ) biofertilizer, with as much as +7% in the number of tubers. On the other hand, the Innovator cultivar responded negatively to the biofertilizers, and the tubers were reduced (-11.82%, P 0.01), as was the yield (-5.62%, P 0.07).
The two dimensions of the letter-bags are highlighted in Figure 1,

Discussion
The preliminary results from this experiment confirm the luxuriating effects albeit of an emersion of a  According to Rai 23 , inoculation of the Kufri Lalima and Kufri Sindhuri with Glomus mosseae and G. fasciculatum potato cultivars increased yields by 4.2 and 5.5%, respectively.
The biofertilizer dose can be under the Mitscherlich law. Three biofertilizers were compared in one potato cv., Kufri Sindhuri 24 , at doses of 250, 500, 750 g ha -1 . One product was identified as the best to increase all the growth, yield and quality parameters.
The optimum concentration was found to be the minimum one, that is, 250 g ha -1 . Both the mycorrhizal products produced adverse effects on all the growth and yield parameters at much higher concentrations. The Authors suggested that AM should be used as a supplement, along with commonly used fertilizers, to increase the growth and yield.
According to Sakha et al. 25

Conclusion
The main result of this experiment is that a possible AM * cultivar interaction, which had previously been shown for corn 14 , has been confirmed. Thus, the adaptation of AM strains to the genetics of potato cultivars can be considered a first step toward reducing chemical inputs, with benefits for the environment, but without an excessive reduction in yield.
The litter-bag technique may be recommended for a simplified monitoring of the complicated plant-mycorrhizospher relationship, preferably combined with a foliar pH measurement.