Myocardial bridges and coronary distribution in dairy cattle from Brazil Northeast

Revista Agrária Acadêmica

Agrarian Academic Journal

Volume 4 – Número 4 – Jul/Ago (2021)

doi: 10.32406/v4n4/2021/31-42/agrariacad

 

Myocardial bridges and coronary distribution in dairy cattle from Brazil Northeast. Pontes miocárdicas e distribuição coronariana em bovinos leiteiros do Nordeste brasileiro.

 

Vinícius Lima Brito1, Kethelyn Freitas de Lima1, Anielly Mirelly de Assunção Ramalho1, Jadson Vieira de Melo1, Júnior Mário Baltazar de Oliveira2, Amara Maria de Sousa Barbosa1, Emanuela Polimeni de Mesquita1, Daniela Oliveira1*

 

1 Laboratory of Animal Anatomy and Pathology, Federal University of Agreste of Pernambuco, Garanhuns, Brazil. Av. Bom Pastor, s/n, Boa Vista, Garanhuns, PE, Brazil. 55292-270, (87) 37645500, ramal 5573. E-mail: daniela.oliveira@ufape.edu.br
2- University Center Unifavip, Caruaru, Brazil.

 

Abstract

 

This study evaluated the distribution and possible variations of the coronary arteries and the presence of myocardial bridges in dairy cattle from Northeastern Brazil. Thus, healthy hearts were analyzed according to many variables. Left coronary artery originate the rami paraconalis, circumflexus et subsinuosus. Ramus subsinuosus and right coronary artery showed a short subepicardial path. Lengths of the main branches showed statistical differences only in relation to age group and weight of the animal. Myocardial bridges had a prevalence of 55% and were more frequent over the ramus paraconalis. Veterinary medicine is able to provide experimental models to expand the necessary study to understand pathophysiology and clinical relevance of the bridges.

Keywords: Blood circulation. Myocardium. Cardiovascular system. Bovine.

 

 

Resumo

 

Este estudo avaliou a distribuição e possíveis variações das artérias coronárias e a presença de pontes miocárdicas em bovinos leiteiros do Nordeste do Brasil. Assim, corações saudáveis foram analisados de acordo com muitas variáveis. A artéria coronária esquerda origina os rami paraconalis, circumflexus et subsinuosus. O ramus subsinuosus e a artéria coronária direita apresentavam trajeto subepicárdico curto. Os comprimentos dos ramos principais apresentaram diferenças estatísticas apenas em relação à faixa etária e ao peso do animal. As pontes miocárdicas tiveram prevalência de 55% e foram mais frequentes sobre o ramus paraconalis. A medicina veterinária é capaz de fornecer modelos experimentais para expandir o estudo necessário para entender a fisiopatologia e a relevância clínica das pontes.

Palavras-chave: Circulação sanguínea. Miocárdio. Sistema cardiovascular. Bovino.

 

 

Introduction

 

According to the OECD-FAO (Food and Agriculture Organization of the United Nations) Brazil stands out in world livestock production and, together with the United States and the European Union, will be responsible for approximately 60% of the world meat exports in 2029 (OECD-FAO, 2020). Substances necessary for the production of meat and milk (nutrients, hormones, etc.) circulate through the blood to the muscles and the udder, respectively (GETTY, 1986; DYCE et al., 2010). The circulatory system, therefore, is directly related to animal production.

The heart is compared to a large and powerful pump that drives blood to all tissues in the body. Thus, the heart, similar to any other tissue, also needs to have its own blood supply, receiving the equivalent of 15% of the cardiac output of the left ventricle (DYCE et al., 2010). The right and left coronary arteries, which emerge right after the aortic bulb, are responsible for this distribution, occupy the sulcus coronarius and present different paths and distributions according to each species (GETTY, 1986; FRANDSON et al., 2017).

According to König et al. (2011), angiology is the branch of science dedicated to the study of the shape, structure, topography and functioning of blood vessels. Thus, knowing and better understanding the distribution of cardiac vessels, especially coronary arteries and their branches, allows a better understanding of the blood supply in this organ, as well as possible pathologies that can be established on these, such as myocardial infarction and atherosclerosis (SIERVULI et al., 2014).

Myocardial bridge is the term used to describe the muscle bands that overlap the segments of the epicardial coronary arteries (ZHAO et al., 2019). A potential relationship is reported between myocardial bridges and some cardiac changes such as ischemia (TARANTINI et al., 2016), myocardial fibrosis (BRODSKY et al., 2008) and coronary spasm (TERAGAWA et al., 2003).

Studies on the variation in the anatomical distribution of the coronary arteries and myocardial bridges are still scarce in dairy cattle from northeastern Brazil (RODRIGUES et al., 1999; CORREIA-OLIVEIRA et al., 2013, 2014). Therefore, given the importance of this study, this research evaluated and described the path and possible variations in the distribution of coronary arteries and the presence of myocardial bridges in cattle from a dairy region in northeastern Brazil.

 

Material and methods

 

All methodology adopted for the development of the present research was submitted and approved by the Ethics Committee on the Use of Animals (CEUA) of the Federal Rural University of Pernambuco (UFRPE), Recife-PE, under protocol number 028/2019.

Twenty-two hearts of 17 females and five bovine males aged between two days and nine years, weighing between 30 and 620 kg were studied. The animals came from necropsies performed at the Animal Pathology Sector of the Animal Anatomy and Pathology Laboratory (LAPA) at UFAPE and sent to the Animal Anatomy Sector of the same laboratory. Age, gender, weight and breed were recorded on the necropsied animal’s record. The breeds recorded in the chart were Holstein (eight), Gir x Holstein (five), other crossbred (seven), Brown-Swiss (one) and Guzerá (one). The main cause of death was related to locomotor problems (fractures, traumas, muscle rupture, among others) and reproductive problems (uterine rupture and torsion, dystocia).

The hearts were removed by sectioning the vessels at the base. Subsequently, the specimens were washed, and the clots removed before being fixed in a 10% formaldehyde solution, where they remained until dissected. Then, the coronary arteries and their branches were evidenced from the origins in the aorta, with the use of appropriate dissection instruments, until their macroscopically visible terminations.

The main branches of the coronary arteries and whenever myocardial bridges were observed, the lengths were measured with the aid of a digital caliper and a flexible ruler, as well as the location (topography and vasculotopy) of each of them in each studied heart was recorded and documented.

All information obtained was recorded and reported using the Veterinary Anatomical Nomenclature (INTERNATIONAL, 2017).

Measurements of the length of the branches of the coronary arteries and the bridge of the bovine ramus paraconalis were tabulated in an Excel spreadsheet. Initially, a logarithmic transformation was carried out in order to homogenize the variances of the groups. After that, the normality of the data was tested by the Shapiro-Wilk test. Then, a comparison was made of the data obtained when measuring branches of the coronary arteries and the bridge of the ramus paraconalis, with dependent variables: sex, breed, age and weight. For parametric analysis, Student’s t test and Scheffe test were used and for non-parametric analysis, Kruskal Wallis and Mann-Whitney tests were used. Subsequently, a correlation analysis was performed between the length of the structures using Pearson’s or Spearman’s Correlation (depending on the distribution of the variables) (SAMPAIO, 2015). The IBM SPSS Statistics 23.0 program was used to perform the aforementioned statistical calculations. The level of significance was set to 5.0% for all analyses.

 

Results

 

Left coronary artery

 

It originated on the left side of the aorta and after a short course, in the sulcus coronarius, it was divided into two branches, the ramus interventricularis paraconalis (ramus paraconalis) and the left ramus circumflexus. The left ramus circumflexus continued in the sulcus interventricularis subsinuosus, where it became known as the ramus interventricularis subsinuosus (ramus subsinuosus). An extra branch (diagonal branch) was found in four hearts, with the same origin as the rami paraconalis and circumflexus, which runs above the left ventricle, on the auricular surface (Figure 1A).

The ramus paraconalis coursed through the sulcus paraconalis and emitted one to two subepicardial branches, mainly towards the left ventricle, although in a few cases it was also observed over the right ventricle. The ramus paraconalis deepened in the myocardium close to the apex of the heart. In only one case did this occur a few centimeters (3.7 cm) from the origin of the branch. On the contrary, in most of the analyzed hearts, the ramus subsinuosus runned a short path and soon entered the myocardium (Figure 1B), justifying subepicardial lengths much smaller than the ramus paraconalis. Even so, the short ramus subsinuosus also emitted a subepicardial branch, found in four specimens.

 

Figure 1 – A. Auricular surface of the bovine heart. Note the bifurcation of the left coronary artery in rami interventricularis paraconalis (RIP) et circumflexus (RC) and among them the emergence of the diagonal branch (DB). B. Bovine heart atrial surface. The ramus interventricularis subsinuosus (RIS) originates from the ramus circumflexus (RC), which courses a short distance before going deeper into the myocardium. Source: the authors.

 

The left ramus circumflexus surrounded the sulcus coronarius to the sulcus subsinuosus and emitted subepicardial branches still on the auricular surface and/or in the region between the auricular and atrial surfaces (marginal region, ramus intermedius) (Figure 2A). When the branches were located in the marginal region, they presented themselves as two long branches with a certain parallelism (Figure 1B) or a branch that soon divided into several others, directed to the margin and the apex.

Gender and breed did not influence the measures of length of the branches of the left coronary artery, according to the statistical analysis (p <0.05) observed in Tables 1 and 2.

 

Table 1 – Means and standard deviation of the length of the branches of the bovine coronary arteries and the ramus paraconalis bridge by sex.
Structure
Sex
Male
Female2
Right coronary artery
9.20 ± 7.10
9.20 ± 2.18
Ramus subsinuosus
3.56 ± 2.20
3.81 ± 2.70
Ramus paraconalis
12.90 ± 3.84
16.31 ±3.88
Ramus circunflexus
13.63 ± 3.88
15.53 ± 3.57
Ramus paraconalis bridge
3.66 ± 2.29
2.16 ± 0.98
1 n=5; 2 n=15; different letters on the same line indicate a difference by Student’s t test (p < 0.05)

 

Table 2 – Mean and standard deviation of the length of the branches of the bovine coronary arteries and the ramus paraconalis bridge by breed.
Breed
Crossbred1
Purebred2
Right coronary artery
8.30 ± 2.18
10.25 ± 3.78
Ramus subsinuosus
2.20 ± 0.69
5.65 ± 4.34
Ramus paraconalis
14.30 ± 4.47
16.27 ± 3.63
Ramus circumflexus
13.22 ± 4.45
17.00 ± 4.29
Ramus paraconalis bridge
2.36 ± 0.84
3.05 ± 2.30
1 n=11; 2 n=9; different letters on the same line indicate a difference by Student’s t test (p < 0.05)

 

On the other hand, when the length averages were compared in terms of age (Table 3) and weight (Table 4), significant differences were found (p <0.05). The rami paraconalis et circumflexus showed greater lengths in older animals (above 18 months). Animals weighing less than 100 kg obtained shorter lengths in the rami subsinuosus et circumflexus, while the ramus paraconalis was shorter in individuals weighing up to 300 kg.

 

Table 3 – Mean and standard deviation of the length of the branches of the bovine coronary arteries and the ramus paraconalis bridge by age.
Structure
Age
under 18 months
above 18 months
Right coronary artery**
8.08 ± 2.33
10.60 ± 3.37
Ramus subsinuosus**
3.80 ± 4.32
3.65 ± 1.83
Ramus paraconalis**
12.94 ± 3.99A
17.97 ± 1.63B
Ramus circunflexus**
12.04 ± 3.81A
18.47 ± 2.32B
Ramus paraconalis bridge*
2.08 ± 0.69
3.40 ± 2.16
1 n=12; 2 n=8; *Student’s t test; **Mann-Whitney test; different letters on the same line indicate statistical difference (p < 0.05)

 

Table 4 – Means and standard deviation of the length of the branches of the bovine coronary arteries and the ramus paraconalis bridge by weight.
Estruturas
Weight
under 100 kg1
 100-300 kg2
above 300 kg3
Right coronary artery**
7.33 ± 0.91A
13.52 ± 6.27B
12.80 ± 3.17B
Ramus subsinuosus**
2.44 ± 1.13A
5.02 ± 2.26AB
6.71 ± 3.33B
Ramus paraconalis**
11.21 ± 0.75A
12.80 ± 7.08A
19.35 ± 3.35B
Ramus circumflexus**
10.70 ± 0.97A
16.27 ± 5.10B
19.01 ± 1.48B
Ramus paraconalis bridge*
2.37 ± 0.26A
1.10 ± 0.00A
3.35 ± 2.23A
1 n=7; 2 n=4; 3 n=9; * Parametric analysis; ** Non-parametric analysis; different letters on the same line indicate statistical difference (p < 0.05) 

 

Right coronary artery

 

The right coronary artery originated on the right side of the aorta, it coursed through the space between the right auricle and the pulmonary trunk until it reached the sulcus coronarius, where it proceeded towards the auricle (Figure 2B). From that point on, it either entered the myocardium or extended until close to the sulcus subsinuosus and may emit subepicardial branches towards the right ventricle on the atrial surface or in the right marginal region, in some specimens.

 

Figure 2 – A. Left margin of the bovine heart. In this region, the ramus circumflexus (RC) can send the ramus intermedius (RI), generally parallel. B. The right coronary artery (RCA) after emerging from aorta follows the sulcus coronarius and sends small branches. Source: the authors.

 

There was no statistical difference (p <0.05) regarding sex, breed and age range in the length of the right coronary artery (Tables 1, 2 and 3). Individuals over 100 kg had significantly greater lengths of this vessel (p <0.05), as shown in Table 4.

There were positive and significant correlations (p <0.05) between the lengths of all branches of the left coronary artery and the right coronary artery, with the highest correlations (p <0.001) found between the right coronary artery and the ramus paraconalis and between the ramus paraconalis and the left ramus circumflexus (Table 5).

 

Myocardial bridges

 

Myocardial bridges had a prevalence of 55%, were found in 12 of the 22 dissected hearts. When present, there were one to two bridges in each heart and the majority was over the ramus paraconalis (Figure 3A). Only two specimens were over the ramus subsinuosus (Figure 3B) and in one heart there were bridges in both branches. When observed only over the ramus subsinuosus, the two hearts had two bridges over the same vessel, although one was visually thinner in width and thickness than the other.

 

Figure 3 – A. Bovine heart auricular surface. The left coronary artery ramus interventricularis paraconalis presents a myocardial bridge in the middle third, after the emission of two large branches. B. In two specimens, ramus interventricularis subsinuosus (RIS) had a myocardial bridge. Source: the authors.

 

All bridges were found in the region of the middle third of the vessel it covered. No myocardial bridges were observed over the right coronary artery or over the left ramus circumflexus. Over a division of the ramus paraconalis on the left ventricle, a bridge was found, the only occurrence observed over branches of the main rami of the coronary arteries.

There were no statistical differences in the length of the myocardial bridges over the ramus paraconalis in all the evaluated items (sex, breed, age and weight). The lengths of the evaluated bridges did not show significant correlation with any of the lengths of the left coronary artery branches or the right coronary artery (Tables 1 to 5).

 

Discussion

 

The dairy region of Pernambuco, a northeast state in Brazil, provided the animals for this study, so the main bovine breeds used in this study have such aptitude, such as Holstein and crossbred (Gir x Holstein and others). Although articles dealing with bovine cardiac vascularization are scarce, the most studied breeds are of double aptitude or beef cattle, such as Gir, Guzerá and Indubrasil (SEVERINO; BOMBONATO, 1992), Canchim (SANTOS et al., 2000 and 2011), Nellore (SEVERINO; BOMBONATO, 1992; MARTINS et al., 2008), crossbred (SHINJO et al., 2004; CORREIA-OLIVEIRA, 2013 and 2014) and half-breed (SEVERINO et al., 1997), which reinforces the importance of the contribution of the current research.

The nomenclature used to describe the studied bovine coronary arteries followed the most recent Nomina Anatomica Veterinaria (INTERNATIONAL, 2017). However, it was noticed that some branches found were not listed in the current official nomenclature, such as the diagonal branch of the left coronary artery and the collateral branches of both coronary arteries. The diagonal branch was previously found (CORREIA-OLIVEIRA et al., 2014) in seven (7/30) crossbred Gir x Holstein cattle. In the studied hearts, four (4/22) had this branch. The literature does not name branches in the right coronary artery in ruminants, citing them only as collateral (GETTY, 1986; CORREIA-OLIVEIRA et al., 2013 and 2014). Martins et al. (2008) also noticed this scarcity of nomenclature to describe the other branches of coronary arteries in cattle and had to rely on other articles to complement the description.

In all hearts described, the left coronary artery gave rise to the rami paraconalis, circumflexus et subsinuosus, while the right coronary artery was limited to the sulcus coronarius, as observed by other authors (BORELLI; FERNANDES-FILHO, 1970; CORREIA-OLIVEIRA et al., 2013). Coronary arterial dominance is determined according to the artery that gives rise to the posterior interventricular artery (SANTOS et al., 2021), which corresponds to the animals’ ramus subsinuosus in terms of location. These authors described the dominance of human coronary arteries as predominantly right (52.6%) (SANTOS et al., 2021), unlike the studied cattle, which had 100% dominance of the left coronary artery. Of the domestic species, cats can have dominance in any of the coronaries, but it is known that ruminants and canines have left dominance, and pigs and horses, right (INTERNATIONAL, 2017). However, Borelli and Fernandes-Filho (1970) reported 6 cases (4%) in which the right coronary artery gave rise to the right ramus circumflexus and the ramus subsinuosus in five cattle of European origin (10%) and one zebu (1%).

No differences were found between the sexes regarding the lengths of the right coronary artery or the branches of the left coronary artery, as well as Correia-Oliveira et al. (2013). Among the measures taken by these authors (CORREIA-OLIVEIRA et al., 2013) in bovine coronary arteries, the similarity in the lengths of the right coronary artery and rami paraconalis et circumflexus with the current study stands out, but the authors describe significantly longer lengths for the ramus subsinuosus. The cattle from northeastern Brazil showed a short subepicardial path of the ramus subsinuosus and only in two hearts did this branch remain superficially beyond the middle third of the sulcus interventricularis subsinuosus. It should be noted that in both studies, the animals evaluated had the same aptitude (dairy), age groups consistent and allocated in mountainous geography, with no external reasons at first glance for the difference in myocardial development in this region of the evaluated hearts.

There are records of myocardial bridges in 100% of analyzed hearts (SEVERINO et al., 1997; GULMEZ; SAH, 2021), however, in the current study the existence of this characteristic was demonstrated in 55% of the 22 hearts. In pigs, from a total of 60 hearts, the presence of myocardial bridges was reported in 36.36% of them (BOMBONATO et al., 1994). In humans, bridges were found in 40.3% of the studied hearts, mainly in specimens with left dominance (22.8%) (SANTOS et al., 2021). These authors emphasize that this frequency is not common in humans, and clinically may suggest that bridges may be less frequent in populations with the usual distribution of arterial dominance. The usual dominance in cattle is left, as observed in the current study and by Correia-Oliveira (2014), however, no reports were found on the presence of myocardial bridges in cattle with usual and unusual dominance.

Myocardial bridges have been reported in several species besides human (SANTOS et al., 2021), such as ruminants (CORREIA-OLIVEIRA, 2013, 2014; GULMEZ; SAH, 2021), pigs (BOMBONATO et al., 1994), mules (RIBEIRO et al., 2009), monkeys Cercopithecus aethiops sabeus (NIKOLIĆ et al., 2009), among others.

 The findings of the present study corroborate with the one that observed the vast majority (94.3%) of bridges over the left coronary artery branches (SEVERINO et al., 1997). In other studies, bridges were described in subdivisions of the main coronary branches in cattle in a significant amount (29 of 106) (SEVERINO et al., 1997), in six pigs (BOMBONATO et al., 1994), and only one bovine presented this characteristic in the current study.

In the evaluated hearts, all myocardial bridges were located predominantly in the middle portion (middle third) of the vessel. Santos et al. (2021) observed the same location in most vessels that had bridges, even more striking in hearts with left dominance. Bridges occur almost exclusively in the middle region of the left anterior descending coronary artery (corresponding to the ramus paraconalis of the animals) (ISHIKAWA et al., 2011).

The average length of the bovine myocardial bridges over the ramus paraconalis of this study (24.6 ± 15.3 mm) was similar to that found in sheep (24.9 ± 16.1 mm) (GULMEZ; SAH, 2021). In half-breed cattle, the bridges had an average length of 16.2 mm (SEVERINO et al., 1997) and in pigs, 7.5 mm (BOMBONATO et al., 1994)

Most of the myocardial bridges in pigs were found over the ramus subsinuosus (BOMBONATO et al., 1994). It is pertinent to take into account the distinct origin of the ramus subsinuosus between these two species (in ruminants it originates from the left coronary artery, and in swine, from the right). Likewise, there was a difference regarding the presence of bridges in the ramus circumflexus, which were present in pigs (3 on the right and 2 on the left), however, were absent in the present study.

One of the importance of studying the vascularization of the heart is to understand how functional structures are supplied, such as the conduction system. Both coronary arteries provide branches for the sinoatrial node and the trunk of the atrioventricular fascicle, with the right ventricular branch derived from the ramus subsinuosus of the left coronary artery and the rami septales derived from the right coronary artery being the most frequent vessels of these structures, respectively (MARTINS et al., 2008). Therefore, ​​cardiac angiology research may contribute to the physiological analysis, the interpretation of imaging tests and the clinical and surgical evaluation of the patient (human or animal).

Several authors (ISHIKAWA et al., 2011; NASR, 2014; ZHAO et al., 2019) report that in humans, myocardial bridges cause coronary heart disease by two distinct mechanisms, influenced by the anatomical characteristics of the bridge, related to artery compression during cardiac systole and increased coronary atherosclerosis due to stenosis of the artery near the myocardial bridge. They also report that the study of myocardial bridges assists in the treatment decisions of heart disease and in the clinical improvement of the patient. In Canchim cattle, the lesions found before the bridge, in the bridge and in the post myocardial bridge are similar to the lesions that precede the formation of the atherosclerotic plaque, although in the region of the bridge there are smaller lesions than in the other regions (SANTOS et al., 2011). By analogy to the microscopic findings of the pre-bridge coronary arteries, cattle have the same chance of developing atherosclerosis as humans (SHINJO et al., 2004). However, coronary artery diseases resulting from myocardial bridges should not occur in sheep in veterinary practice, as they observed bridges in 100% of the analyzed sheep hearts, with no detected coronary disease (GULMEZ; SAH, 2021).

Myocardial bridges are an interesting area of ​​study, as it is not clear whether they are a pathology, a variation or even a physiological protection strategy for certain clinical conditions (SANTOS et al., 2021). The literature is unanimous regarding the need to extend studies on the topic to understand the pathophysiology and clinical relevance of these bridges. In this way, veterinary medicine will be able to provide experimental models to expand knowledge on the subject.

 

Conclusion

 

Dairy cattle coronary arteries may present variation into their branches, especially the left one. The ramus interventricularis paraconalis had a higher incidence of myocardial bridges, which occurred in the middle third of the vessel. When observed in the subsinuous branch, they had thinner characteristics in width and thickness.

 

Acknowledgements

 

To CBG (Bovine Clinic of Garanhuns) – UFRPE, which assisted patients subsequently necropsied at LAPA and donated their hearts to this research.

 

Author’s Contributions

 

VLB, KFL, AMAR and JVM participated in its design, dissected the hearts, made the measurements, collected the animal data, tabulated the data and measures for statistical analysis, JMBO participated in the design of the study and performed the statistical analysis, AMSB participated in the collections and applied the specimen conservation techniques, EPM participated in the design of the study, in the writing and in the final revision of the manuscript, DO conceived of the study, and participated in its design, analysis and coordination and helped to draft the manuscript. All authors read and approved the final manuscript.

 

Competing Interests

 

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

 

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Retornado para ajustes em 13 de julho de 2021

Recebido com ajustes em 14 de julho de 2021

Aceito em 18 de julho de 2021

Germination of Corymbia citriodora on different substracts

Revista Agrária Acadêmica

Agrarian Academic Journal

Volume 4 – Número 4 – Jul/Ago (2021)

doi: 10.32406/v4n4/2021/23-30/agrariacad

 

Germination of Corymbia citriodora on different substracts. Germinação de Corymbia citriodora em diferentes substratos.

 

Maurício Hartmann1, Eder Marques2*

 

1- Agronomy student, UPIS Integrated Colleges. E-mail: mauriciohartmann92@gmail.com
2*- Agronomist, Full Professor II, UPIS Integrated Colleges, Fazenda Lagoa Bonita, BR 020 KM 12, DF 335 KM 4,8 – Planaltina, Brasília – DF. E-mail: eder.marques.08@gmail.com

 

Resumo

 

O objetivo do presente trabalho foi avaliar a germinação de sementes de eucalipto limão (Corymbia citriodora) em diferentes substratos. Foram testados: 1) substrato comercial, 2) areia, 3) areia + fibra de coco (2:1), 4) fibra de coco, 5) substrato + fibra de coco (2:1), 6) areia + substrato (2:1) e a testemunha (papel germitest).  Com base no experimento, observou-se que a germinação foi abaixo do esperado para a espécie, variando entre 57 e 74%, apesar de não haver diferença significativa entre os tratamentos quanto a este parâmetro. Os tratamentos que levaram a uma maior velocidade de germinação foram a testemunha (papel germitest), seguido pelo substrato comercial, fibra de coco, areia + substrato e substrato + fibra, sem diferença significativa, indicando ser os melhores para a germinação das sementes de C. citriodora. O substrato a base de fibra de coco é promissor, pois pode ser considerado um substrato alternativo e de baixo custo.

Palavras-chave: Eucalipto limão. Germinação de sementes. Substratos alternativos. Testes in vitro.

 

 

Abstract

 

The objective of the present work was to evaluate the germination of lemon-scented gum (Corymbia citriodora) on different substrates. The following were tested: 1) commercial substrate, 2) sand, 3) sand + coconut fiber (2: 1), 4) coconut fiber, 5) substrate + coconut fiber (2: 1), 6) sand + substrate (2: 1) and the control treatment (germitest paper).  Based on the experiment, it was observed that germination varied between 57 and 74%, although there was no significant difference between treatments. The treatments that led to a higher germination speed were the control (germitest paper), followed by the commercial substrate, coconut fiber, sand + substrate and substrate + fiber, with no significant difference, indicating that they are the best for the germination of C. citriodora seeds. The substrate based on coconut fiber is promising, as it can be considered an alternative and low-cost substrate.

Keywords: Alternative substrates. In vitro tests. Lemon-scented gum. Seed germination.

 

 

Introduction

 

Corymbia citriodora (Hook.) K.D. Hill and L.A.S. Johnson, belonging to the Myrtaceae family, is a medium to large tree species, reaching 25 to 50 m in height and 1.2 m in diameter at breast height, and occupying a prominent place in the segment of aromatic plants (BOLAND et al., 1991). Its taxonomy has been the subject of controversy, and it was previously classified as Eucalyptus. C. citriodora is composed of two subspecies: C. citriodora subsp. citriodora and C. citriodora subsp. variegata (HILL; JOHNSON, 1995).

Originating in Australia, C. citriodora stands out for its economic value in the production of wood for various purposes, such as in the manufacture of furniture, firewood and charcoal. It is highly sought-after in light and heavy civil construction, in addition to presenting medicinal properties (CUNHA et al., 2019). The tree species is cultivated in more than 90 countries (CABI, 2015).

Eucalyptus species are the most planted trees in Brazil, has and they cover a current area of approximately 6.97 million hectares (IBÁ, 2020). Recent data on the area cultivated with C. citriodora in Brazil have not been accessed, but according to Kronka et al. (2002) it was around 85,000 ha, with greater concentration in the states of Minas Gerais and São Paulo.

The essential oil is found mostly in its leaves. The product of the distillation of leaves of C. citriodora, with an extremely pleasant odor and known as citronellal or as citronella, is an input of great demand in the market. It is part of the composition of products such as flavorings, soaps, toothpastes, detergents, candies, perfumes, deodorants, disinfectants, waxes, sachets and insecticides, etc. (BOLAND et al., 1991).

C. citriodora is known as lemon-scented gum, citron-scent gum, lemon gum tree or spotted gum. Its cultivation grows in Brazil, due to its characteristics of fast growth and edaphoclimatic adaptation, in addition to the silvicultural characteristics and the quality of its wood. These are other interesting features: good tolerance to pests and diseases (MORAIS et al., 2010), wood that can be applied for civil construction (NOGUEIRA et al., 2021) and calorific value acceptable for energy production (MARCHESAN et al., 2020).

Despite their widespread use, species of the genus Corymbia are considered difficult to propagate. With the exception of C. torelliana, for which rooting is viable, the other species are difficult to root. Rooting levels are usually below 5%, which has prevented its use in clonal propagation programs. In this way, C. citriodora commercial plantations have traditionally been established through seeds (SMITH et al., 2007; REIS et al., 2013). Recent studies showed that C. citriodora present genotypes adapted to different soil textures and the low additive genetic variance can limit the development of breeding populations (SOUZA et al., 2020).

According to Pierret and Moran (2011), the substrate is the medium that provides the support for the roots to proliferate. It is, therefore, on the substrate that the initial growth of the seedling will depend, since the root is the connection between it and the aerial part, which will develop in function of its physical, chemical and biological properties, since the conditions of humidity, temperature, light and wind are not limiting. Besides, the choice of substrate can also impact the cost of seedling production (CANTLIFFE, 1993).

Some works have already been carried out in order to verify the most suitable substrate for the production of C. citriodora seedlings. Steffen et al. (2011) studied the use of vermicompost as a substrate in the production of E. grandis and C. citriodora seedlings. Oliveira and co-workers (2014) evaluated the rice husk and coconut fiber. Later, Lopes et al. (2015) evaluated different formulations based on commercial substrate, sugarcane bagasse and coal dust. Ferreira and co-workers (2020) also studied the use of vermicompost and coconut fiber as a sustainable substrate in the production of seedlings of this plant. However, among these works accessed, the only one that evaluated the influence of the substrate on seed germination was that of Ferreira et al. (2020).

Given this context, the present study aimed to evaluate the effect of different substrates on the germination of Corymbia citriodora seeds.

 

Materials and methods

 

The study was conducted in the Federal District, central Brazil (15.58 ºS, 47.73 ºW), consisting of the Cerrado biome, during the month of September 2020. According to the Köppen classification, the location has a Tropical seasonal climate of megathermic savannah, with an average annual precipitation of 1,400 mm (CARDOSO et al., 2014).

The Corymbia citriodora seeds were donated by the IPEF (Forestry Research and Studies Institute). The crop identified by the donor is from 2018 and comes from Rio das Pedras – SP, from an ACS-AS (Altered Seed Collection Area – F1).

In the experiment, seven treatments were evaluated: T1 – Commercial substrate; T2 – Sand; T3 – Sand: coconut fiber (2: 1); T4 – Coconut fiber; T5 – Coconut fiber: substrate (2: 1); T6 – Sand: Substrate (2: 1) and T7 – Control (Germitest paper).

In each gerbox (11 x 11 x 3.5 cm) containing the treatments, 20 seeds were deposited, which were kept at room temperature (24-25 ºC) and light. As the seeds lost moisture, they were moistened. The readings of the experiment took place daily, where the number of seeds that germinated each day was recorded.

The design used was the Completely Randomized Design (CRD) with four replications, composed of 20 seeds each, including the seven treatments mentioned. Based on the germination data, the average germination time (1), the germination speed (2) and the germination index (3) were calculated using the following equations (SANTANA; RANAL, 2004):

 

  • T = (days) average germination time (1)
  • V = (days-1) germination speed (2)
  • Germination index (%) = (3)

 

Where fi = number of seeds germinated on the i-th day; and xi = number of days counted from seeding to the day of reading.

The test data were subjected to analysis of variance (ANOVA), using the SISVAR 5.6 program (FERREIRA, 2014). The mean values of the germination and length parameters were compared using the Tukey test, at 5% probability.

 

Results

 

Based on the statistical analysis of the results, it was observed that the treatment that took least time to germinate was the one that used the germitest paper (control), followed by the commercial substrate, sand, sand + substrate (2: 1) and substrate + fiber (2: 1), with no significant difference between them (Figure 1). The treatments fiber and sand + fiber (2: 1) did not differ, with the longest germination times.

 

Figure 1 – Average germination time in days (Axis y) of Corymbia citriodora seeds on different substrates (Axis x). Means followed by the same letter do not differ statistically by the Tukey test (P <0.05).

 

Figure 2 – Germination speed in days-1 (Axis y) of Corymbia citriodora seeds on different substrates (Axis x). Means followed by the same letter do not differ statistically by the Tukey test (P <0.05).

 

Regarding the germination speed, which is the inverse of time, it is observed that the highest speed was precisely with the germitest paper (control treatment), followed by the commercial substrate, sand, sand + substrate (2: 1) and substrate + fiber (2: 1), also without significant difference. Following the same reasoning, the substrates on which the seeds germinated most slowly were sand + fiber (2: 1) and pure fiber (Figure 2).

The germination index was below what is expected for the species, and it was observed here at 57 to 74% (Figure 3).

 

Figure 3 – Germination index (Axis y) of Corymbia citriodora seeds on different substrates (Axis x). Means followed by the same letter do not differ statistically by the Tukey test (P <0.05).

 

The appearance of fungi was observed in all treatments, but mainly on paper and coconut fiber. Although not quantified, the genera observed were: Alternaria sp., Aspergillus sp., Fusarium sp. and Rhizopus sp.

 

Discussion

 

According to Ferreira and co-workers (2020), treatments with a lower proportion of coconut fiber (75% coconut fiber + 25% vermicompost and 65% coconut fiber + 35% vermicompost) germinated faster, on the fourth day; those with 85% coconut fiber + 15% vermicompost and only commercial substrate germinated on the fifth day, corroborating the results of the present study.

In the current study, low seed germination was observed (< 74%). According to Reis et al. (2013) the average germination of C. citriodora is 86%. The treatment in which less germination was observed was that of germitest paper, followed by substrate + fiber, sand, fiber, substrate + fiber and lastly the one with the highest index was sand + substrate, although they did not differ significantly. In a study by Ferreira et al. (2020) substrates with different proportions of vermiculite and substrate, germination was 100%.

The appearance of fungi was observed in all treatments, but mainly on paper (control treatment) and coconut fiber. Fungi may have affected germination. For the present experiment, no superficial disinfestation of the seeds was carried out, nor the sterilization of the substrates, since the intention was to simulate natural sowing conditions. Fungi can originate from the seed itself, since they also appeared in the control treatment (germitest paper). According to Santos et al. (2000), these fungi mentioned are common in the seeds of forest species, such as eucalyptus.

It is worth mentioning that the choice of substrate will be of fundamental importance in the production of seedlings, even interfering in their production cost (CANTLIFFE, 1993). In the germination speed, substrate + coconut fiber (2: 1) also stood out, which can be considered low-cost mixture. The same was observed by Oliveira et al. (2014), where a lower proportion of coconut fiber also stood out in the production of C. citriodora seedlings. Following the same reasoning, Ferreira et al. (2020) highlight that the alternative substrate for seedling production, composed of coconut fiber and vermicompost, was the most promising. Thus, in addition to being a good alternative for seedling production, it was also observed here that the coconut fiber substrate mixture is interesting for a better germination of this seed species.

 

Conclusions

 

It is concluded that the treatments that stood out with the highest germination speed were commercial substrate, sand, sand + substrate (2: 1) and substrate + fiber (2: 1). The substrate based on coconut fiber is promising, as it can be considered an alternative and low-cost substrate. Knowledge about the best substrate for the germination of Corymbia citriodora seeds can contribute significantly to the improvement of seedling production of this species.

 

Acknowledgments

 

The authors acknowledge the Forestry Science and Research Institute (IPEF), for donating the seeds of Corymbia citridiora used in this study.

 

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Aceito em 15 de julho de 2021