ISSN e:2007-4034 / ISSN print: 2007-4034

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Vol. 27, issue 1 January - April 2021

ISSN: ppub: 1027-152X epub: 2007-4034

Scientific or technological note

Comparative analysis of floral volatiles between the ‘Hass’ variety and Antillean race avocado

http://dx.doi.org/10.5154/r.rchsh.2020.05.012

Campuzano-Granados, Álvaro J. 1 ; Cruz-López, Leopoldo 1 *

  • 1El Colegio de la Frontera Sur (ECOSUR), Grupo de Ecología de Artrópodos y Manejo de Plagas. Carretera Antiguo Aeropuerto km 2.5, Tapachula, Chiapas, C. P. 30700, MÉXICO.

Corresponding author: lcruz@ecosur.mx

Received: May 26, 2020; Accepted: October 03, 2020

This is an open-access article distributed under the terms of the Creative Commons Attribution License view the permissions of this license

Abstract

Mexico is the world’s leading producer of ‘Hass’ avocado and the Antillean race avocado is grown in the south of the country. Avocado plant flowers produce a great variety of volatile compounds, which act as chemical signals to attract herbivores and pollinating insects, in addition to providing information for taxonomic purposes. The research aim was to identify and compare the floral volatiles between the ‘Hass’ and Antillean race avocado. Floral volatiles were captured by solid-phase microextraction, and identification was made by gas chromatography coupled to mass spectrometry (GC-MS). Thirty-five compounds were identified as constituents of the flower aromas; most were monoterpenes and sesquiterpenes. α-Pinene, sabinene, β-pinene, (E)-linalool oxide, benzyl nitrile, lavandulol, methyl salicylate, α-copaene, β-gurjunene and γ-muurolene were only found in ‘Hass’ avocado flowers. The differences can help classify the two types of avocados analyzed into different races. Eventually, this information could be used to find out if these volatile compounds influence the interactions of avocado with its pollinating insects and herbivores.

KeywordsPersea americana; taxonomy; solid-phase microextraction; gas chromatography-mass spectrometry; terpenes

Introduction

Mexico is considered the center of origin of the Mexican avocado (Persea americana Mill) race, although the Antillean race is also cultivated in the south of the country (Can-Alonzo et al., 2005). Likewise, Mexico is the world’s leading producer of ‘Hass’ avocado, with a volume of 2 million 29 thousand tons in 2017 (Servicio de Información Agroalimentaria y Pesquera [SIAP], 2019).

Avocado floral volatiles provide chemical signals to phytophagous and pollinating insects to locate food sources, habitats and oviposition sites (Bruce, Wadhams, & Woodcock, 2005; Sanders & van Doorn, 2004), in addition to providing taxonomic information on the species (Kim, Ha, Kim, Chang, & Kim, 2014). The chemical composition of these volatiles depends on the species, variety, physiological state and circadian rhythm of the plants (Kolosova, Sherman, Karlson, & Dudareva, 2001; Niinemets, Loreto, & Reichstein, 2004). In Mexico, avocado flowering periods depend on race, variety, climatic conditions and elevation. For example, the ‘Hass’ avocado flowering period is 85 days at 12 to 17 °C, and decreases to 15 days at 28 to 33 °C (Sanders & van Doorn, 2004). This period is similar to that of the Antillean race; however, it is shorter in temperate zones (Can-Alonzo et al., 2005).

In the state of Chiapas, Mexico, the commercial ‘Hass’ avocado is mainly grown in the uplands, and the Antillean race avocado is cultivated in the subtropical Soconusco (coast) region. There is little information on the aroma chemistry of the different phenological stages among avocado races and varieties. Therefore, the aim of this study was to identify and compare the floral volatiles of the ‘Hass’ and Antillean race avocados. This information could be useful for taxonomic purposes, and could eventually be used to find out if these volatile compounds influence the interactions of avocado with its pollinating and herbivorous insects.

Materials and methods

‘Hass’ avocado flowers were collected in orchards located in the municipalities of Margaritas (16° 18’ 1” N and 91° 57’ 18” W) and Comitán de Domínguez (16° 16’ 58.3” N and 92° 1’ 59.7” W), Chiapas, Mexico, which have an average temperature of 19.5 °C and an elevation of 1,600 masl. The Antillean race flowers were collected from trees in Canton Texcuntic, municipality of Frontera Hidalgo (14° 47’ 41.13” N and 92° 11’ 14.5” W) and in the municipality of Tuxtla Chico (14° 54’ 21” N, 92° 13’ 43.4” W), Chiapas, where the average temperature is 27 °C and the elevation is 92 masl. The collections were carried out between November and December 2018. These two types of avocado were selected due to their commercial importance in the region.

The volatiles were captured using the solid-phase microextraction technique. For this, 100 g of flowers were placed in 12 mL glass vials. The vial inlet was covered with aluminum foil and a 65 µm thick polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber (Supelco®, Mexico) was inserted into it, for a period of 16 h. The procedure was similar for the ‛Hass’ and Antillean avocado flowers, and five replications were performed in both cases.

The identification of the volatiles captured by the PDMS/DVB fiber was performed in a gas chromatograph (CP-3800, Varian, USA) coupled to a selective mass detector (Saturn 2200, Varian, USA). A methyl silicon column (DB5-MS) of 30 m in length by 0.25 mm in inner diameter, with helium as carrier gas, was used for the determination. The samples were injected in splitless mode and the temperature program used was: initial temperature of 50 °C (2 min) to a final temperature of 280 °C (2 min), with an increase of 15 °C per min. The volatile analysis was performed with the Saturn GC/MS Workstation software. Preliminary identification of the compounds was made by comparing retention time and mass spectrum with the NIST 2002 spectral library; later, they were confirmed with the synthetic standards. The relative abundance of the components was calculated considering the peak area of all of them.

Statistical analysis

Peak areas of floral compounds identified in ‘Hass’ and Antillean avocado were subjected to a principal component analysis (PCA), in which the correlation matrix was used to determine the compounds with the highest incidence in the two varieties. Differences in volatiles between varieties were tested by constructing confidence ellipses (α = 0.05). Confidence ellipses around the centroids allow observing the variation within the groups: similar correlation matrices denote a similar shape, while those having a common mean must overlap. Before the PCA, data were rescaled to have zero mean and one standard deviation, which reduces the influence of variables with very high or low magnitudes, in addition to normalizing the data (McCune & Grace, 2002). The statistical analysis was conducted with the R v3.6.3 software (R Core Team, 2020).

Results and discussion

Thirty-five volatiles were identified in ‘Hass’ and Antillean avocado flowers, which are mostly monoterpenes and sesquiterpenes. The average values of the percentage compositions are shown in Table 1, where linalool was the most abundant compound (30 %) in the Antillean race, while in ‘Hass’ the most abundant was (E)-β-ocimene (20 %).

Table 1. Mean relative abundance (± standard error) of ‘Hass’ and Antillean avocado floral volatiles.

Number Compound name RI Abundance (%)
Antillean ‘Hass’
1 α-Pinene* 927 0.00 0.39 ± 0.05
2 Sabinene 970 0.00 0.36 ± 0.36
3 β-Pinene* 977 0.00 0.43 ± 0.08
4 β-Myrcene* 985 0.93 ± 0.57 3.45 ± 0.07
5 Limonene* 1031 0.25 ± 0.08 0.49 ± 0.08
6 (Z)-β-Ocimene* 1034 1.45 ± 0.20 3.16 ± 0.81
7 (E)-β-Ocimene* 1045 9.99 ± 2.07 20.82 ± 3.92
8 (E)-Linalool oxide* 1078 0.00 0.30 ± 0.07
9 (Z)-Linalool oxide* 1093 3.98 ± 1.08 1.97 ± 0.40
10 Linalool* 1105 30.30 ± 6.05 0.43 ± 0.04
11 Perylene (isomer) 1117 24.36 ± 5.45 9.33 ± 4.76
12 Benzyl nitrile 1151 0.00 1.91 ± 0.63
13 Lavandulol 1170 0.00 0.43 ± 0.07
14 Butyl caproate 1193 7.65 ± 2.27 0.00
15 Methyl salicylate* 1206 0.00 2.74 ± 0.72
16 n-Tridecane* 1300 2.51 ± 1.45 0.36 ± 0.08
17 α-Copaene* 1362 0.00 2.41 ± 0.43
18 β-Cubebene* 1389 0.84 ± 0.20 1.94 ± 0.35
19 β-Gurjunene 1405 0.00 2.03 ± 0.60
20 β-Caryophyllene* 1443 3.62 ± 1.04 13.98 ± 1.22
21 γ-Muurolene 1447 0.00 0.55 ± 0.08
22 Valencene 1480 0.44 ± 0.10 1.58 ± 0.41
23 β-Guaiene 1494 1.04 ± 0.14 1.54 ± 0.34
24 n-Pentadecane* 1500 0.41 ± 0.20 2.40 ± 0.52
25 γ-Cadinene 1506 0.73 ± 0.30 12.85 ± 4.07
26 β-Cadinene 1535 1.45 ± 0.30 2.75 ± 0.58
27 Dendrasaline 1583 2.27 ± 1.21 1.34 ± 0.93
28 n-Hexadecane* 1600 0.29 ± 0.06 0.27 ± 0.04
29 8-Hexadecine 1663 0.00 0.53 ± 0.05
30 Cyclohexadecane 1669 0.00 2.57 ± 0.48
31 n-Heptadecane* 1700 0.85 ± 0.18 3.36 ± 0.53
32 n-Nonadecane* 1900 2.53 ± 0.81 2.77 ± 0.70
33 n-Icosane* 2000 1.85 ± 0.51 0.00
34 n-Heneicosane* 2100 1.54 ± 0.30 0.50 ± 0.05
35 n-Docosane* 2200 0.730.18 0.05 ± 0.01
RI = retention index.* Compounds confirmed with synthetic standards.

The PCA between the compounds of the two varieties explains 66.1 % of the total variability of the data, which denotes high eigenvalues (Table 2). Of the 35 compounds included in the model, 26 were significantly correlated with PC1, and 2 with PC2, which had the highest contribution percentage in the ranking (Table 2; Figure 1).

Table 2. Eigenvalues and correlation coefficients of the first two components (PC1 and PC2) in ‘Hass’ and Antillean avocado floral volatiles.

Compound Correlation
PC1 PC2
C1 0.9566* 0.0982
C2 0.9343* 0.1891
C3 0.8648* -0.3282
C4 0.7430* 0.4990
C5 0.6105 0.1005
C6 0.6517* 0.5577
C7 0.6840* 0.0915
C8 0.8248* -0.2656
C9 -0.5702 0.0141
C10 -0.8251* 0.0958
C11 -0.6115 -0.4225
C12 0.7247* -0.3634
C13 0.9117* 0.0157
C14 -0.7980* 0.0080
C15 0.8466* 0.3575
C16 -0.4690 0.4592
C17 0.9152* 0.0653
C18 0.6688* 0.1751
C19 0.7548* -0.2011
C20 0.8965* -0.0214
C21 0.8975* -0.2019
C22 0.7481* 0.5412
C23 0.4453 0.4676
C24 0.7716* -0.0187
C25 0.6807* -0.2620
C26 0.5736 0.2075
C27 -0.2147 0.6735*
C28 -0.0725 0.8191*
C29 0.9646* 0.0341
C30 0.9076* 0.0718
C31 0.8142* -0.3060
C32 -0.0228 -0.2417
C33 -0.8107* 0.3504
C34 -0.7999* 0.2285
C35 -0.8391* 0.2105
Eigenvalues 19.42 3.7
*Significant correlation (α = 0.05).

Figure 1. Principal component analysis of the areas of the floral compounds found in ‘Hass’ and Antillean avocado. The intensity of the arrows in the biplot indicates the contribution percentage of each compound in the construction of the first two dimensions of the ranking chart. From 1 to 35 correspond to the compound number in Table 1. Confidence ellipses (α = 0.05).

The confidence ellipses indicate high heterogeneity in the analyzed samples, with the greatest variation in the ‘Hass’ variety samples. However, differences in volatile composition are evident between varieties, which are explained to a greater extent by PC1, which indicates a positive association with the ‘Hass’ variety and a negative one with the Antillean race. Similarly, a greater amount of compounds associated with the ‘Hass’ variety was observed (Figure 1).

The results of this work allow identifying the compounds that were more abundant in ‛Hass’ and Antillean avocado, or that are only found in one of them. In this sense, the volatiles α-pinene, sabinene, β-pinene, (E)-linalool oxide, benzyl nitrile, lavandulol, methyl salicylate, α-copaene, β-gurjunene and γ-muurolene were only found in the ‘Hass’ avocado flowers. These differences in floral volatiles can help to taxonomically classify the avocado races analyzed, as in the study by Kim et al. (2014), where they classified different species of chrysanthemums (Chrysanthemum) in Korea according to the composition of floral volatiles.

Differences in the volatile compounds of the two types of avocados may also help explain the preference of some herbivorous species for these crops. Such is the case of the avocado seed weevil Conotrachelus perseae, which has only been reported in the ‘Hass’ avocado crop in the Comitan region, Chiapas (Vázquez, Cruz-López, & Chamé-Vázquez, 2015), while the seed borer moth Stenoma catenifer has been reported in Antillean race crops (Vázquez, Cruz-López, Gómez, & Castillo, 2017) in the Soconusco region, Chiapas. The same may occur with the attraction of several species of pollinators that have been reported for avocado (Castañeda-Vildózola et al., 1999), as happens with the floral volatiles of several species of pumpkin (Curcubita) and Cirsium arvense flowers that attract herbivores and pollinators (Andrews, Theis, & Adler, 2017; Theis, 2006).

Conclusions

Thirty-five compounds were identified in ‘Hass’ and Antillean avocado flowers. The floral volatiles α-pinene, sabinene, β-pinene, (E)-linalool oxide, benzyl nitrile, lavandulol, methyl salicylate, α-copaene, β-gurjunene and γ-muurolene were only found in ‘Hass’ avocado. In addition, differences were observed between the two types of avocados in terms of the proportions of the compounds.

References

Andrews, E. S., Theis, N., & Adler, L. S. (2007). Pollinator and herbivore attraction to Cucurbita floral volatiles. Journal of Chemical Ecology, 33, 1682-1691. 10.1007/s10886-007-9337-7

Bruce, T., Wadhams, L., & Woodcock, C. (2005). Insect host location: a volatile situation. Trends in Plant Science, 10(6), 269-274. doi: 10.1016/j.tplants.2005.04.003

Can-Alonzo, C., Quezada-Euán, J. J., Xiu-Ancona, P., Moo-Valle, H., Valdovinos-Nuñez, G. R., & Medina-Peralta, S. (2005). Pollination of ‘criollo’ avocados (Persea americana) and the behavior of associated bees in subtropical Mexico. Journal of Apicultural Research, 44(1), 3-8. doi: 10.1080/00218839.2005.11101138

Castañeda-Vildózola, A., Equihua-Martínez, A., Valdés-Carrasco, J., Barrientos-Priego, A. F., Ish-Am, G., & Gazit, S. (1999). Insectos polinizadores del aguacatero en los estados de México y Michoacán. Revista Chapingo Serie Horticultura, 5, 129-136. Retrieved from http://www.avocadosource.com/WAC4/WAC4_p129.pdf

Kim, S., Ha, T., Kim, J., Chang, D., & Kim, K. (2014). Classification of Korean Chrysanthemum species based on volatile compounds using cluster analysis and principal component analysis. Journal of the Korean Society for Applied Biological Chemistry, 57(6), 789-796. doi: 10.1007/s13765-014-4162-5

Kolosova, N., Sherman, D., Karlson, D., & Dudareva, N. (2001). Cellular and subcellular localization of S-adenosyl-L-methionine: Benzoic acid carboxyl methyltransferase, the enzyme responsible for bio- synthesis of the volatile ester methylbenzoate in snapdragon flowers. Plant Physiology, 126(3), 956-964. doi: 10.1104/pp.126.3.956

McCune, B., & Grace, J. (2002). Analysis of ecological communities. Oregon, USA: MjM Software Design.

Niinemets, U., Loreto, F., & Reichstein, M. (2004). Physiological and physicochemical controls on foliar volatile organic compound emissions. Trends in Plant Science, 9(4), 180-186. doi: 10.1016/j.tplants.2004.02.006

R Core Team. (2020). R: A language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing. Retrieved from https://www.R-project.org/

Sanders, M., & van Doorn, W. (2004). Book review. The avocado: botany, production and uses. Postharvest Biology and Technology, 31(2), 213-214. doi: 10.1016/j.postharvbio.2003.11.010

Servicio de Información Agroalimentaria y Pesquera (SIAP). (2019). Nuestro “Oro Verde”: El Aguacate. Retrieved September 18, 2019 from Retrieved September 18, 2019 from https://www.gob.mx/siap/articulos/nuestro-oro-verde-el-aguacate?idiom=es

Theis, N. (2006). Fragrance of Canada thistle (Cirsium arvense) attracts both floral herbivores and pollinators. Journal of Chemical Ecology , 32, 917-927. doi: 10.1007/s10886-006-9051-x

Vázquez, M., Cruz-López, L., & Chamé-Vázquez, E. (2015). First record of Conotrachelus perseae (Coleoptera: Curculionidae) in Comitán, Chiapas, Mexico. Florida Entomologist, 98(4), 1252-1253. doi: 10.1653/024.098.0439

Vázquez, M., Cruz-López, L., Gómez, J., & Castillo, A. (2017). Annual capture of two elachistidae moth species using Stenoma catenifer sex pheromone in criollo avocado (Persea americana) at Chiapas, Mexico. Southwestern Entomologist, 42(1), 91-101. doi: 10.3958/059.042.0106

Figures:

Figure 1. Principal component analysis of the areas of the floral compounds found in ‘Hass’ and Antillean avocado. The intensity of the arrows in the biplot indicates the contribution percentage of each compound in the construction of the first two dimensions of the ranking chart. From 1 to 35 correspond to the compound number in Table 1. Confidence ellipses (α = 0.05).

Tables:

Table 1. Mean relative abundance (± standard error) of ‘Hass’ and Antillean avocado floral volatiles.
Number Compound name RI Abundance (%)
Antillean ‘Hass’
1 α-Pinene* 927 0.00 0.39 ± 0.05
2 Sabinene 970 0.00 0.36 ± 0.36
3 β-Pinene* 977 0.00 0.43 ± 0.08
4 β-Myrcene* 985 0.93 ± 0.57 3.45 ± 0.07
5 Limonene* 1031 0.25 ± 0.08 0.49 ± 0.08
6 (Z)-β-Ocimene* 1034 1.45 ± 0.20 3.16 ± 0.81
7 (E)-β-Ocimene* 1045 9.99 ± 2.07 20.82 ± 3.92
8 (E)-Linalool oxide* 1078 0.00 0.30 ± 0.07
9 (Z)-Linalool oxide* 1093 3.98 ± 1.08 1.97 ± 0.40
10 Linalool* 1105 30.30 ± 6.05 0.43 ± 0.04
11 Perylene (isomer) 1117 24.36 ± 5.45 9.33 ± 4.76
12 Benzyl nitrile 1151 0.00 1.91 ± 0.63
13 Lavandulol 1170 0.00 0.43 ± 0.07
14 Butyl caproate 1193 7.65 ± 2.27 0.00
15 Methyl salicylate* 1206 0.00 2.74 ± 0.72
16 n-Tridecane* 1300 2.51 ± 1.45 0.36 ± 0.08
17 α-Copaene* 1362 0.00 2.41 ± 0.43
18 β-Cubebene* 1389 0.84 ± 0.20 1.94 ± 0.35
19 β-Gurjunene 1405 0.00 2.03 ± 0.60
20 β-Caryophyllene* 1443 3.62 ± 1.04 13.98 ± 1.22
21 γ-Muurolene 1447 0.00 0.55 ± 0.08
22 Valencene 1480 0.44 ± 0.10 1.58 ± 0.41
23 β-Guaiene 1494 1.04 ± 0.14 1.54 ± 0.34
24 n-Pentadecane* 1500 0.41 ± 0.20 2.40 ± 0.52
25 γ-Cadinene 1506 0.73 ± 0.30 12.85 ± 4.07
26 β-Cadinene 1535 1.45 ± 0.30 2.75 ± 0.58
27 Dendrasaline 1583 2.27 ± 1.21 1.34 ± 0.93
28 n-Hexadecane* 1600 0.29 ± 0.06 0.27 ± 0.04
29 8-Hexadecine 1663 0.00 0.53 ± 0.05
30 Cyclohexadecane 1669 0.00 2.57 ± 0.48
31 n-Heptadecane* 1700 0.85 ± 0.18 3.36 ± 0.53
32 n-Nonadecane* 1900 2.53 ± 0.81 2.77 ± 0.70
33 n-Icosane* 2000 1.85 ± 0.51 0.00
34 n-Heneicosane* 2100 1.54 ± 0.30 0.50 ± 0.05
35 n-Docosane* 2200 0.730.18 0.05 ± 0.01
RI = retention index.* Compounds confirmed with synthetic standards.
Table 2. Eigenvalues and correlation coefficients of the first two components (PC1 and PC2) in ‘Hass’ and Antillean avocado floral volatiles.
Compound Correlation
PC1 PC2
C1 0.9566* 0.0982
C2 0.9343* 0.1891
C3 0.8648* -0.3282
C4 0.7430* 0.4990
C5 0.6105 0.1005
C6 0.6517* 0.5577
C7 0.6840* 0.0915
C8 0.8248* -0.2656
C9 -0.5702 0.0141
C10 -0.8251* 0.0958
C11 -0.6115 -0.4225
C12 0.7247* -0.3634
C13 0.9117* 0.0157
C14 -0.7980* 0.0080
C15 0.8466* 0.3575
C16 -0.4690 0.4592
C17 0.9152* 0.0653
C18 0.6688* 0.1751
C19 0.7548* -0.2011
C20 0.8965* -0.0214
C21 0.8975* -0.2019
C22 0.7481* 0.5412
C23 0.4453 0.4676
C24 0.7716* -0.0187
C25 0.6807* -0.2620
C26 0.5736 0.2075
C27 -0.2147 0.6735*
C28 -0.0725 0.8191*
C29 0.9646* 0.0341
C30 0.9076* 0.0718
C31 0.8142* -0.3060
C32 -0.0228 -0.2417
C33 -0.8107* 0.3504
C34 -0.7999* 0.2285
C35 -0.8391* 0.2105
Eigenvalues 19.42 3.7
*Significant correlation (α = 0.05).