Plant height

When plant height of the four coffee varieties was assessed and compared with respect to the control plants, the inoculation of the CMgrp consortium gave as a result plants with greater height (Figure 1). For this variable, the effect among both inoculants was different, above all, with respect to the inoculated coffee variety. The inoculant R. aggregatus had a minimum effect in this variable in the varieties Garnica and Catuaí (Figure 1).^{Adriano-Anaya et al., 2011} inoculated the var. Bourbon with Rhizophagus intrarradices cultivated in transformed roots, but no effect was observed in this variable.

*Different letters in the same figure indicate significant differences (Tukey’s P ≤ 0.05) test. Consortium = CMgrp (Glomus claroides, Rhizophagus diaphanus, and Paraglomus albidum).

Figure 1: Plant height of coffee varieties (a) Garnica, b) Catimor, (c) Caturra, and (d) Catuaí inoculated with two mycorrhizal inoculants Rhizophagus aggregatus and the consortium compared with the control plants at 335 days after sowing (DDS).  

^{Ibarra-Puón et al. (2014)} tested the same AMF but in Coffea canephora (Robusta), where plant height increased when compared to control at 140 days after inoculation. These results may indicate a certain preference of AMF species for coffee species although the influence in the form of the inoculant, production could be a factor to study in a near future. Furthermore, the time factor could also have an influence in the results observed.

The effect of the mycorrhizal inoculants on coffee with respect to height has been documented with different AMF consortia. ^{Del Aguila et al., 2018}, applied nine mycorrhizal consortia in coffee plants of the var. Caturra although the species in the consortia were not reported. The increase in this variable may be related to obtaining phosphorus by the inoculants.

Dry biomass

The dry biomass variable was also influenced by the mycorrhizal inoculation, above all, when it was inoculated with the CMgrp consortium with weight fluctuating from 1.4-5.45 g for all the varieties. The only one where the effect was lower, although significantly, was observed on the var. Catuaí (Figure 2).

*Different letters in the same figure indicate significant differences (Tukey’s P ≤ 0.05) test. Consortium = CMgrp (Glomus claroides, Rhizophagus diaphanus, and Paraglomus albidum).

Figure 2: Dry biomass in coffee plants varieties (a) Garnica, (b) Catimor, (c) Caturra, and (d) Catuaí with two mycorrhizal inoculations (1) Rhizofagus aggregatus and (2) the consortium, compared with the control plants at 335 days after sowing (DDS).  

Dry biomass is one of the most measured growth and development variables in coffee to analyze the mycorrhizal effect as biofertilizer (^{Ibarra-Puón et al., 2014}) because it allows calculating the variation among genotypes, environment and management - factors that generate modifications in biomass accumulation (^{Di Benedetto and Tognetti, 2016}).

^{Aguirre-Medina et al., 2011} observed that Rhizophagus intrarradices inoculation did not show variation in this variable in coffee plants var. Oro Azteca even when dry root, stem, and leaf dry weight were evaluated from 60-210 DAS.

On the other hand, ^{Adriano-Anaya et al. (2011)} assessed the effect of Rhizophagus intraradices in coffee plants var. Bourbon at 112 days after inoculation when they evaluated dry root weight and leaves, finding increments from 118-141% compared to the control plants. In both studies, mycorrhizal fungus efficiency as biofertilizer was observed in growth depending on the variety of coffee and mycorrhizal inoculant.

Leaf phosphorus content

Inoculation of the AMF had effect on increasing total phosphorus content, having differential results in function of the inoculant source and coffee variety. The values with greater phosphorus content were observed in the var. Catimor, which increased with the AMF inoculation with 0.16 mg kg^-1 (R. aggregatus) and 0.15 mg kg^-1 (CMgrp) even in the non-inoculated treatment (Figure 3).

*Different letters in the same figure indicate significant differences (Tukey’s P ≤ 0.05) test. Consortium = CMgrp (Glomus claroides, Rhizophagus diaphanus, and Paraglomus albidum).

Figure 3: Leaf phosphorus content of coffee varieties (a) Garnica, (b) Catimor, (c) Caturra, and (d) Catuaí inoculated with two mycorrhizal inoculants (1) Rhizophagus aggregatus and (2) the consortium compared with control at 335 days after sowing (DDS).  

^{Ibarra-Puón et al. (2014)} reported that phosphorus concentration in coffee plants was 0.014% higher in the treatments inoculated with Rhizophagus intraradices (0.045%) at 140 days after transplant (DAT), compared with the control group (0.031%).

In papaya cultivation, ^{Quiñones-Aguilar et al. (2012)} mentioned that the AMF hyphae are capable of capturing and transporting soil phosphorus towards higher parts of the plants in poor soil or without fertilizer, which could explain the increase.

^{Perea-Rojas et al. (2018)} studied the importance of the AMF consortium in phosphorus transformation and absorption processes in coffee plants, finding greater leaf phosphorus concentration in the var. Garnica in treatments of plants inoculated with the mycorrhizal consortium and phosphorus solubilizing fungi. This study showed that despite the availability of this element in soil, the presence of the AMF was determinant to translocate phosphorus to the plant parts.

^{Aguirre-Medina et al. (2011)} measured an increase in phosphorus at 150 DAS in coffee var. Oro Azteca inoculated with Rhizophagus intraradices although this effect was not constant throughout the measurements from 60-210 DAS.

Mycorrhizal colonization

The highest colonization percentages were obtained with the CMgrp consortium, which fluctuated from 15.44% (in var. Catuaí) to 34.32% (in var. Garnica); the latter was the variety that best responded to the inoculation with the CMgrp consortium. Although the colonization percentages were lower than those obtained with the mycorrhizal consortium, R. aggregatus originated significant values of 9.7% in the var. Garnica and 23.5% in the var. Catimor - the variety with the best response to inoculation with R. aggregatus (Table 2).

Several studies have shown the mycorrhizal dependence on coffee plants, above all on less fertile soils. ^{Tristão et al. (2006)} mentioned that for these plants mycorrhizal symbiosis is extremely important, especially in soils where conditions are unfavorable - hydric stress, high salt content, degraded and contaminated soils.

Efficiency of the different inoculants is one of the parameters that should be considered when selecting them for their use in coffee plants, taking into account different examples, such as Gigaspora margarita (^{Tristão et al., 2006}), Rhizophagus intraradices (^{Ibarra-Puón et al., 2014}), and mycorrhizal consortia (^{Del Aguila et al., 2018}).

Despite mycorrhizal colonization percentage is one of the most measured variables, it does not guarantee an increase in the plant morphological and physiological variables. An example that supports this argument may be observed in ^{Aguirre-Medina et al. (2011)} where at 90 DAS, the colonization percentage in the treatments with Glomus intraradices did not go beyond 18%; however, the increase in dry biomass compared with the control was 307 and 116% in phosphorus content.

Current data reported by ^{Del Aguila et al. (2018)} highlighted mycorrhizal colonization from 13-31.3% and increments with respect to the control for the dry biomass variable (root and leaf) 566%; whereas ^{Adriano-Anaya et al. (2011)} obtained colonization percentages from 6.6-16.3% in inoculated plants and increments of 41.3% (root) and 17.3% (leaves) compared to the control for the dry weight variable. The previous results are justified because growth, development, and yield of the cultivation depend on mycorrhizal efficiency. To this respect, ^{Aguirre-Medina et al. (2011)} quoted that the initial establishment of the AMF in coffee plants may be slow, which is why its effect on plant development promotion responds in the same manner.

Mycorrhizal efficiency

The CMgrp consortium promoted the greatest mycorrhizal efficiency percentage in the four coffee varieties with intervals from 333% in var. Catuaí to 1670% in var. Caturra, compared to non-treated plants (control). The fungus R. aggregatus, originated values from 13% (in var. Garnica) to 610% (in var. Caturra) (Table 2). The beneficial response of the AMF is defined as effectiveness; this capacity promotes plant growth and is determined by the species diversity used and origin of its isolation (^{Trejo et al., 2011}). Coffee plants establish mycorrhizal symbiosis naturally; their efficiency depends on the fungus species, plant (variety), environment, substrate (^{Rivera, 2010}), and soil (nutrient content, mainly phosphorus) (^{Gadea and Peña, 2013}).

In this study, the var. Caturra obtained the greatest mycorrhizal percentage, which was reflected in the highest values for coffee plants for the variables plant height (4.79 cm), dry biomass (4.73 g) and average values in phosphorus content (0.13 mg kg^-1) (Figures 1, 2, 3). With these results, we may conclude that the mycorrhizal CMgrp consortium promoted growth, development, and phosphorus absorption in plants.

Assessing mycorrhizal efficiency in this research study was relevant because the best symbiosis plant-fungus (Garnica-CMgrp and Caturra-CMgrp) was found between two mycorrhizal inoculants and four coffee varieties of economic importance for Mexico. To this respect, ^{Tristão et al. (2006)} mentioned that in coffee plant production, locating the mycorrhizal fungi that show elevated efficiency, greater competitiveness, and soil adaptation is a priority.

Available phosphorus by mycorrhization

The greatest available phosphorus percentages (260-1651%) by mycorrhization for the four coffee varieties were obtained with the CMgrp consortium. The inoculant R. aggregatus also originated important percentages (24-614%); both inoculants responded better in the var. Caturra (Table 2). The mycorrhizal inoculants used in this research study favored phosphorus translocation since the content of this element in leaves was greater than in the inoculated plants (Figure 3).

The available phosphorus percentage variable by mycorrhization was determined to find the most efficient fungi for a host to increase its efficiency in nutrient absorption, consequently reducing inorganic fertilizers in field. ^{Balota et al. (2011)} mentioned that inoculated plants with mycorrhizal fungi showed greater efficiency in the use of phosphorus in root, which means greater P capture and its transference. ^{Rivera (2010)} quoted that to achieve an effective mycorrhization in coffee plants and in soils, it was necessary to inoculate an efficient arbuscular mycorrhizal fungus. Therefore, searching for the best plant-fungus symbiosis is necessary to guarantee growth and develop healthy and vigorous plants.

Plant health

Table 3 shows the E_m, Index and the varieties Garnica, Catimor, and Caturra with the lowest harm indices - showing values close to 0 according to the scale from 0.14 +/- 0.24 established - when they were inoculated with the CMgrp consortium. Although the var. Catuaí had values closer to 1 with the CMgrp, it showed differences when compared with the control. Evidently, the effect of a monospecific inoculant, as R. aggregatus, reported lower E_m indices than the control. The E_m indices for chlorosis did not report differences in the var. Catuaí, which showed a similar health tendency as the other varieties and the mycorrhizal inoculants.

The subjective scales were used as a tool to assess some variables without destroying the plants; similar classes or scales have been adopted in mycorrhizal symbiosis studies (^{Sieverding, 1991}; ^{Rosendahl and Rosendahl, 1991}; ^{Raghavendra-Kumar et al., 2018}; ^{Ren et al., 2018}).

This study normalized the data obtained in the subjective scale, which allowed developing the E_m Index that demonstrated a similar tendency to quantitative data (Figures 1, 2, 3); the results showed that the production of coffee plants inoculated with the CMgrp consortium experienced less harm by P. costarrisensis, which has also been demonstrated by several authors who pointed out that the presence of mycorrhizal fungi granted plants tolerance or resistance to harm by pathogens (^{Plouznikoff et al., 2019}; ^{El-Sharkawy et al., 2018}; ^{Trejo Aguilar et al., 2018}). The data obtained in this study show that not all the varieties responded to the mycorrhizal inoculation, so other coffee varieties should be assessed in future studies.