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Introduction
Plant quality refers to its ability of plants to adapt and develop under climatic and edaphic conditions of plantation sites, and it depends on the genetic characteristics of the germplasm and the techniques used for its reproduction in nursery. Nursery management practices are reflected on plant quality. In addition, produced plants should develop specific morphological and physiological attributes. These attributes provide the plant with the ability to adapt, obtain an optimum development and aptitude to survive under the climatic and edaphic conditions of the plantation sites (Ramirez & Rodríguez, 2004, Rodríguez, 2008).
To achieve plants with optimal morphological and physiological characteristics, it is necessary to develop cultural techniques from the nursery, such as the type of substrate, the container, the quality of the seed, the nutrition diet, and a proper management of fertilization, irrigation, weed control, pests and diseases. These are the main components that influence the production of plant of high quality and a proper price (Sáenz et al., 2010; Bierchler et al., 1998).Fertilization is the most important practice, because it directly influences the growth of the aerial and root system of the plants, modifying the content of nutrients in their tissues and the amount of available reserves, enhancing the rooting in the plantation site, increases the percentage of survival, and inducing greater resistance to water stress and low temperatures (Grossnickle, 2000, Landis, 2000; Andivia et al., 2012).
In Mexico, several researches have been carried out to determine the plant quality in nursery (Peñuelas y Ocaña, 2000; Prieto et al. (2003); Rodríguez, 2008; Prieto et al., 2009; Orozco et al., 2010; Sáenz et al., 2014; Rueda et al., 2014; Muñoz et al., 2015; Sáenz et al., 2017). Plant quality is determined based on morphological and physiological variables. By the one hand, morphological characteristics include plant height, diameter of the stem or neck, size, shape and volume of the root system, height/diameter ratio of the neck, stem/root ratio, foliage color and health, dry weight of stems, foliage and roots. On the other hand, physiological characteristics consider resistance to cold conditions, number of necessary days on which the main bud begins its growth, mitosis index, water potential, nutritional and carbohydrate content, tolerance to drought, net photosynthesis, mycorrhization and capacity to emit new roots (Gomes et al., 2002; Prieto et al., 2009).
Determination of plant quality in non-timber forest species of arid zones in Mexico is a little explored research field. Currently there are no studies in this regard. Likewise, there is a lack of a methodology to improve the plant quality in nursery. Hence it is important to conduct studies on the determination of plant quality on arid-zone species, in order to guarantee the survival and development of commercial plantations. In the production of nursery plant of this type of species highlights the “cortadillo” Nolina cespitifera Trel. (Asparagaceae Juss.) (Tropics, 2017 ), native and endemic species of xerophilous scrub and grassland of northeastern Mexico (Castillo & Sáenz, 1993, García & Galván, 1995). Currently, anthropogenic activities, the inadequate management of this resource, prolonged droughts, rainstorms and high temperatures, has caused the reduction of its natural populations and therefore the degradation of the ecosystem where it growths. Under this scenario, natural populations of N. cespitifera could be rehabilitated hardly on their own (Castillo et al., 2015a, Castillo et al., 2015b).
Therefore, it is necessary to carry out actions to mitigate the environmental damage caused by anthropic activities, such as the rehabilitation of degraded ecosystems, through the establishment of commercial plantations. This requires the massive propagation of high-quality plant of N. cespitifera in nursery, that is to say, producing plants with excellent genetic, morphological and physiological characteristics, which were able of supporting the transplant stress, guaranteed the success of the plantations and/or reforestations, increased their survival rate and allowed faster growth under adverse climatic and edaphic conditions after planting (Ramírez & Rodríguez, 2004; Prieto et al., 2009). Unfortunately, the rehabilitation programs of this species in its area of distribution have not been successful because the plants produced in the nursery have not had the adequate quality to resist the stress after planting. The objective of the present study was determining the plant quality of cortadillo (Nolina cespitifera Trel.) under chemical and biological fertilization, through the analysis of morphological and physiological variables and indexes.
Material and Methods
Under conditions of shade mesh nursery in the Saltillo Experimental Field (at 1,790 masl) of the INIFAP, the effect of the chemical and biological fertilization on the plant quality of cortadillo plant was evaluated. An experiment was established where the treatments indicated in Table 1 were applied. Germination trays were used for cortadillo seeds according to the methodology developed by Castillo et al. (2018). When the seedlings had three weeks of germination, they were transplanted in black polyethylene bags (5 x 15 cm). Black soil was used as substrate. A period of two weeks was left for plant establishment in the pot (5 x 15 cm) and treatments were subsequently applied. A completely randomized experimental design was used with 12 plants as an experimental unit. The plants were treated and maintained in nursery from May to November 2017.
Table 1 Treatments of chemical and biological fertilization applied to cortadillo plants (Nolina cespitifera Trel.) to accelerate their growth under nursery conditions.
| Number | Treatment | Monthly dose |
|---|---|---|
| T1 | 17-17-17 | 6 g/L water |
| T2 | Urea | 10 g/L |
| T3 | Mixture of mineral coal and microorganisms | 2 g/ plant |
| (Trichoderma spp. and Bacillus spp.) | ||
| T4 | Control | |
| T5 | Mycorrhiza INIFAP | 44 propagules) |
| T6 | Trichoderma sp. | 3 mL de 1 X 1012/L of water |
| T7 | Bacillus sp. | 3 mL de 1X 109/L of water |
| T8 | 18-18-18 | 6 g/L) |
| T9 | Gravel-based cover |
When the plants reached 6 months of growth under the nursery condition, morphological and physiological variables for each plant were evaluated and with these values, plant quality indexes were obtained.
The morphological variables considered to determine the quality of the plant in the cortadillo were: height of the aerial part (cm), root length (cm), fresh and dry weight of the biomass from aerial part and root (g). Prior to its measurement, the plant was removed from the polyethylene bag, applying a watering to facilitate the removal of the substrate. Then the bag was cut with a knife in order to avoid damage to the root system and obtain the plant without root ball. The plants were labeled and transferred to the laboratory to record the data for each of the variables mentioned above.
The height of the aerial part of the plant was taken from the base of the stem to highest leaf, and measured using a graduated ruler of 30 ± 0.01 cm. The diameter reading was made with a digital Vernier. The root length was obtained with a graduated rule of 30 ± 0.01 cm. To the determination of the fresh (wet) biomass from the aerial part and the root, both parts were separated (aerial and root) with a scalpel and the weight was recorded with a digital scale of each of the parts. Once the fresh weight was obtained, both parts of the plant were packed in brown paper bags with their respective treatment record, and were placed in a drying oven for a period of 72 hours at 70 °C to remove moisture; then the dry weight of each part of the plant (aerial and root) was recorded.
With the data of the variables evaluated, the following indices or relationships of plant quality were determined:
Robustness index (IR) o Ratio height/diameter of the root neck height
It relates the height (cm) and the root neck diameter (mm) of the plant. When there are low values, they are associated with better plant quality, since it is more robust and high values indicate that the plant is less strong and slender due to the disproportion between height and diameter; it is generally recommended that this index was less than six (Prieto et al., 2003). It was estimated with the following formula:
Relation between height: length of the root
It is a parameter of importance because it can be predicted since plantation. There must be a balance in the proportion between the aerial part and the root system of the plants. It was calculated with the formula:
It is determined with the percentage of dry weight in relation to the water content in the plants, which expresses its level of pre-conditioning (Prieto, 2004). Among higher was the content of lignin in its tissue, the cell walls of the plant will be better reinforced and will have greater resistance to physical damage, as well as to attacks of microorganisms by limiting the penetration of destructive enzymes (Petisco et al., 2005). It was calculated with the formula:
Dry air biomass / dry root biomass ratio
It refers to the proportion of the aerial biomass with respect to the biomass of the root. It reflects the development of the nursery plant. A relation between 1.5 and 2.5 reflects an optimum balance; relations greater than 2.5 indicate disproportion between the aerial and radical parts (Prieto et al., 2011). It was calculated with the formula:
Determination of plant quality ranges
With the data matrix generated which included the morphological variables and the values of the indexes of 108 plants, the plant quality ranges were determined in each of them with the R Project 2016 Program, and variance analysis were conducted to evaluate differences in ranges, with a significant level of 95% (p ≤ 0.05).
Finally, with the table of plant quality of cortadillo, and with the data organized by means of tables in Excel ©, the plant quality was determined in each of the treatments evaluated. The variance analysis used the procedure Proc means in SAS version 9.1 (Statistical Analysis System, 2003) and a comparison of means with the Tukey test (p ≤ 0.05) was accomplished.
Results and Discussion
Determination of plant quality ranges
With the generated data matrix which included the morphological variables and the values of the indices of 108 plants, the plant quality ranges were determined in each of them with the R Project 2016 Program. Analysis of variance indicated that the ranges are statistically different (p ≤ 0.05), that is, as independent populations (Table 2).
Table 2 Plant quality ranges considered for cortadillo (Nolina cespitifera Trel.)
| Variable | Plant quality and Range | |
|---|---|---|
| High | Low | |
| Height | ||
| Root neck diameter (mm) | ≥ 5 | <5 |
| Root length (cm) | ≥ 20 | <20 |
| Dry biomass of the aerial part (g) | ≥ 0.15 | <0.15 |
| Dry biomass of the root (g) | ≥ 0.20 | <0.20 |
| Height / Root neck diameter or Robustness Index (IR) | ≤ 5 | > 5 |
| Relationship height: root length | ≥ 1 | <1 |
| Ratio of dry aerial biomass / dry biomass root | ≤ 2.5 | > 2.5 |
| Lignification index (IL) | ≥ 25 | <25 |
Determination of plant quality by treatment
The results of the evaluated variables in each treatment were compared with the range values shown in the Table 2, In Table 3, the results and plant quality (A or B) from each variable are shown within treatments, where it is observed that, for the variable height, in T3 = Mixture of mineral coal and microorganisms (2g / plant), T6 = Trichoderma sp. (3 mL of 1 X 1012 / L of water), T7 = Bacillus sp. (3 mL of 1X 109 / L of water) was determined a high-quality plant (greater than 20 cm). Currently, there are no reports on the effect of the use of microorganisms in cortadillo under nursery conditions. However, in agricultural species, positive effects have been observed, that is, there was an accelerated induction of growth, and therefore a greater reflection in the height in treated plants, as mentioned by Cortés et al. (2015) who found a higher response in height in cocoa plants in nursery stage treated with different bio-inoculants. An action to improve the quality in the less favored treatments in this study, is leaving more time the plants in the nursery or adjusting the doses of fertilization.
Table 3 Determination of plant quality by fertilization treatment in cortadillo (Nolina cespitifera Trel.)
| Treatment | Root neck Diameter (mm) | Height (cm) | Root Length (cm) | Aerial dry biomass (g) | Dry root biomass (g) | Relationship Height/ Diameter | Relationship Height/ Long. Root | Ratio Air Dry Biomass / Dry biomass root | Lignification Index |
|---|---|---|---|---|---|---|---|---|---|
| T1 | 3.40 B | 15.67 B | 16.06 B | 0.11 B | 0.10 B | 4.57 A | 1.03 A | 1.32 A | 25.91 A |
| T2 | 2.71 B | 12.08 B | 10.75 B | 0.06 B | 0.04 B | 4.57 A | 1.44 A | 1.65 A | 33.71 A |
| T3 | 4.61 B | 21.70 A | 23.15 A | 0.18 A | 0.21 A | 4.77 A | 0.99 B | 1.04 A | 22.78 B |
| T4 | 4.65 B | 14.72 B | 23.07 A | 0.16 A | 0.18 B | 3.33 A | 0.64 B | 0.99 A | 26.40 A |
| T5 | 6.84 A | 19.70 B | 18.45 B | 0.15 A | 0.15 B | 3.93 A | 1.08 A | 1.17 A | 21.11 B |
| T6 | 3.87 B | 20.51 A | 22.29 A | 0.15 A | 0.15 B | 5.40 B | 0.94 B | 1.09 A | 23.94 B |
| T7 | 4.11 B | 21.18 A | 25.09 A | 0.17 A | 0.17 B | 5.12 B | 0.89 B | 1.04 A | 24.88 B |
| T8 | 3.43 B | 14.90 B | 15.95 B | 0.09 B | 0.07 B | 4.38 A | 1.22 A | 1.77 A | 25.68 A |
| T9 | 3.49 B | 16.23 B | 19.32 B | 0.11 B | 0.13 B | 4.73 A | 1.80 A | 1.01 A | 26.02 A |
In the case of the root neck diameter variable, in all the treatments it was determined a low quality plant (less than 5 mm). Such result may be possible due to the size of the container used (5 x 15 cm), as mentioned by NeSmith & Duval (1998), and Xu & Kafkafi. (2001). The development of the plant can be influenced by the size of the container, which restricts the prolongation of the root, effect that could induce minor development of the diameter of the root neck. Therefore, in order to improve the quality of this variable, the use of containers with a larger diameter is required, so that the plant had more lateral growth space, which is the place of initial growth of the cortadillo.
Respect to the root length variable, in T3 = Mixture of mineral coal and microorganisms (2 g / plant), T4 = Control, T6 = Trichoderma sp. (3 mL of 1 X 1012 / L of water) and T7 = Bacillus sp. (3 mL of 1X 109 / L of water) was obtained high quality plant (greater or equal to 20 cm) and the rest was of low quality. With these results, it is deduced that the quality response in root length cortadillo is associated to bio-inoculation. Although there are no references on the effect of bio-inoculation in cortadillo, this pattern is similar to that observed in other vegetal species (Quiñones et al., 2013). To improve the quality of this variable, it is necessary to use containers with greater length and the application of root growth promoter, such as phosphorus in chemical fertilization, to induce its development.
For the aerial dry biomass variable, it was found that in the T1 = 17-17-17 (6 g / L), T2 = Urea (10 g / L), T8 = 18-18-18 (6 g / L) and T9 = gravel based cover, the plant was of low quality (less than 0.15 g). As can be observed, lower quality for this variable was obtained with the non-bio-inoculated treatments, that is, the bio-inoculants allow greater biomass accumulation, as cited by Quiñones et al. (2013). The improvement of the quality of this variable may be reached through an increase of the growth area, early planting or longer plant time in the nursery and adjustment in chemical fertilizer doses.
In the root dry biomass variable, in all treatments it was found that the plant is of low quality (less than 0.20 g), except in T3 = Mixture of mineral coal and microorganisms (2 g / plant). This effect in quality may be possible due to the synergy that occurs between the coal, that acts as a cover and prevents the evaporation of water from the substrate, and on the other hand, Trichoderma as a root stimulant. This may be reflected in greater accumulation of biomass. The quality of this variable is improved with the increase of the area of root growth, and with the application or addition of products promoting root growth, such as phosphorus.
In the height / root neck diameter ratio, only in T6 = Trichoderma sp. (3 mL of 1 X 1012 / L of water) and T7 = Bacillus sp. (3 mL of 1X 109 / L of water), the plant was of low quality (greater than 5). Tis indicates that there is a disproportion between growth in height and diameter. This disproportion may be due to the fact that the bio-inoculated plants acquire more height in a short time, while the diameter does not develop. However, when using mycorrhiza, there is a good balance between height and diameter. This condition can be improved with the addition of root growth promoting products, such as phosphorus, and with an increase in the growth area, that is, a larger diameter of the containers used in the production of the cortadillo plant.
About the height / root length ratio, in T3 = Mixture of mineral coal and microorganisms (2 g / plant), T4 = Control, T6 = Trichoderma sp. (3 mL of 1 X 1012 / L of water) and T7 = Bacillus sp. (3 mL of 1X109 / L of water) the plant was determined with low quality (less than 1), which predicts low survival rates and reduced increases in planting sites. The same pattern was observed as in the previous relationship, except when mycorrhiza was used as bio-inoculant. As previously mentioned, the bio-inoculants stimulate the growth and development of the seedlings and is reflected in greater height, however, mycorrhiza as a bio-inoculant also contributes in other effects such as fertilization by incorporating phosphorus, which is a low- mobility nutrient, as cited by Álvarez-Sánchez et al. (2013) and Cabrales et al. (2016). This relationship can be improved with root or aerial pruning and the increase of the growth area.
Respect to the dry aerial biomass/dry root biomass, in all treatments the obtained plant had high quality (less than or equal to 2.5).
For the lignification index, in T3 = Mixture of mineral coal and microorganisms (2 g / plant), T5 = Mycorrhiza INIFAP (44 propagules), T6 = Trichoderma sp. (3 mL of 1 X 1012/L of water) and T7 = Bacillus sp. (3 mL of 1X 109 / L of water) the obtained plant hadlow quality (less than 25). This value indicates that the productive cycle and the fertilization doses must be adjusted, and a decrease of water applied in the irrigation.
Means with the same letter, in the same column, are not significantly different according to Tukey’s test (p ≤ 0.05).
The plant growth time evaluated under nursery condition was close to 6 months (170 days), from which two clearly marked quality categories were derived (high quality and low quality), with height values higher than 20 cm for the first category. Castillo & Cano (2005) report that N. cespitifera requires 1.8 to 2 years in nursery to achieve plantation quality, which contrasts with the results obtained by requiring a third of the time with the application of treatments T3 = Mixture of mineral coal and microorganisms (2 g / plant), T6 = Trichoderma sp. (3 mL of 1 X 1012 / L of water), T7 = Bacillus sp. (3 mL of 1X 109 / L of water).
Table 4 shows that the treatment with the greatest impact on the obtaining of high-quality plant was the T3 treatment, which corresponds to the mixture of activated charcoal with microorganisms of the Trichoderma sp., followed by T6 in which Trichoderma sp. (3 mL of 1 X 1012 / L of water) was used. As observed, there is an association between the analyzed variables and the Trichoderma microorganisms, present in both treatments, since they promoted the plant quality. In relation to the response of T3, it can be assumed that the activated charcoal functioned as a cover or mulch in the pot, which could have increased the water availability for a longer time compared to treatments that did not have a barrier, except for T9 (Gravel cover), that expressed a high quality in the related variables and lignification index.
Table 4 Effect of treatment on the quality index in cortadillo plants
| Índice o Relación | Calidad Alta | Calidad Baja |
|---|---|---|
| Height | T3, T6 y T7 | T1, T2, T4, T5, T8 y T9 |
| Root neck diameter | - | T1, T2,T3, T4, T5, T6, T7, T8 y T9 |
| Root length | T3, T4, T6 y T7 | T1, T2, T5, T8 y T9 |
| Aerial dry biomass | T3, T4, T5, T6 y T7 | T1, T2, T8 y T9 |
| Dry root biomass | T3 | T1, T2, T4, T5, T6, T7, T8 y T9 |
| Root neck diameter: height ratio | T1, T2, T3, T4, T5, T8 y T9 | T6 y T7 |
| height / Root length | T1, T2, T5, T6, T8 y T9 | T3, T4 y T7 |
| Dry aerial biomass / Dry root biomass | T1, T2,T3, T4, T5, T6, T7, T8 y T9 | - |
| Index of lignification | T1, T2, T4, T8 y T9 | T3, T5, T6 y T7 |
Generally, using Trichoderma, beneficial effects such as the promotion of plant growth of seedlings are reported (Candelero et al., 2015), on the biocontrol of soil pathogens (Carretero et al., 2013, Núñez & Pavone, 2014) and on rooting effect (Bravo et al., 2016)
Conclusions
The results of the analysis of N. cespitifera plants indicate that it is possible to obtain high-quality plants with the use of a mixture of activated charcoal and microorganisms, such as Trichoderma sp. The use of containers with larger dimensions that those used is required (5 x 15 cm), in order tothe plants had a greater growth area, and adjustments are required in the chemical fertilization doses and / or combined with the biological fertilization treatments, to obtain cortadillo plants of higher quality, and therefore greater survival in the plantation sites.
