La superficie plantada con Gmelina arbórea (melina) en Ecuador se ha incrementado en

la última década, actualmente esta especie forestal es afectada por la enfermedad

“marchitez vascular y pudrición del fuste”, que está matando miles de árboles en el país.

= Fusarium sp.3, T4 = Fusarium sp.4, y T5 = agar-agar (control). Se empleó un diseño

completo al azar (DCA) y las plantas se evaluaron a los 155 días después de inoculadas.

Los tratamientos Fusarium sp.1 y Fusarium sp.2 ocasionaron los mayores volúmenes

aparentes de necrosis (2.31 cm3 y 2.43 cm3), y generaron síntomas leves de enfermedad,

concluyentes. Se hace necesario continuar investigando el papel de Fusarium spp. en la

patogénesis de melina.

Palabras clave: Patogenicidad, postulados de Koch, volumen aparente de necrosis

Ecuador, it has become an important item for the country's economy, with a

planted area until 2015 of approximately 11458 ha, which represented 21.9% of

the 52395 ha, planted with other economically important forest species (teak,

balsa, pine, others) registered in the country (MAGAP (2016).

However, in the last five years, a complex and aggressive disease has been

affecting commercial plantations of G. arborea in Ecuador, manifesting itself with

a premature and gradual decline in the vigor of the trees, accompanied by

discoloration of the leaf system (chlorosis) and stunted growth. It can be observed

in some trees that excrete dark brown exudates from the trunk, with a strong odor

of decaying matter, indicating internal rotting of the trunk (Saltos-Sampedro,

Due to the presence of signs at field level and characteristics of the disease, the

phytosanitary problem detected in melina seems to be associated with fungal

microorganisms. Studies conducted by Macías-Moncayo (2019) demonstrated

the presence and pathogenicity of the ascomycete fungus Ceratocystis fimbriata,

associating it as the cause of the disease. However, periodic visits to THE

plantations report diseased trees with symptoms different from those previously

are occurring at the same time in G. arborea forests, probably caused by different

circumference of the tree. The symptomatology begins with the wilting of the

leaves and subsequent drying, until they finally fall to the ground of the

plantation. Scientific literature reports that this type of symptomatology is

associated with G. arborea trees in Costa Rica, being caused by the fungus

Deuteromycete Fusarium sp., whose sexual phase is Nectria sp. (ascomycete),

(Arguedas, 2004; Murillo-Gamboa et al., 2016).

In this sense, Saltos-Sampedro (2019), Macías-Moncayo (2019), and Belezaca-

Pinargote et al. (2021) in independent research works, constantly isolated

Fusarium spp. strains from xylem tissues of diseased melina trees, so their

participation in the etiology of the disease needs to be clarified. This paper shows

Table 2. Arbitrary five-category scale proposed by Salas-Rodríguez et al. (2016) to

assess stem rot disease severity in G. arborea.

10 mL of PDA culture media + 0.2 mL of an antibiotic mixture (50 µg/mL penicillin

and 25 µg/mL streptomycin), (Parkinson, 1994; Massimo et al., 2015; Belezaca-

Pinargote et al., 2018), and left to incubate for 96 hours at 24±2

the fungi developed in the culture medium were identified with the help of

dichotomous taxonomic keys, based on morphology (Von Arx, 1981; Barnett &

Hunter, 1987).

Activation of previously isolated Fusarium spp. strains. Strains were reactivated

in Petri dishes containing 10 mL of potato, dextrose, agar (PDA) culture medium

plus 0.2 mL of an antibiotic mixture (50 µg/mL penicillin and 25 µg/mL

streptomycin), under aseptic conditions, and then incubated for 8 days at 24±2

by means of an inclined cut with a sterile scalpel. A colony segment (0.5 cm disk)

of the selected phytopathogen was carefully applied inside the wound, and once

the fungus was inside the plant, the wound was covered with parafilm tape.

Control plants were inoculated under the same conditions as above, with the

difference that instead of inoculating the pathogen, a segment of agar-agar

(innocuous) was applied inside the wound and the wound was closed with

parafilm tape (Massimo et al., 2015).

The plants were watered periodically according to their requirements. The

experiment was established for 155 days (5 months and 4 days), during which

time observations were made on the health status of the inoculated plants, with

Necrotic lesions were measured in three dimensions (height, width and depth) to

estimate the apparent area of necrosis, expressed in cm3 (Zauza et al., 2004).

was used, consisting of five treatments: T1 = melina plants inoculated with

Fusarium sp.1, T2 = melina plants inoculated with Fusarium sp.2, T3 = melina

plants inoculated with Fusarium sp.3, T4 = melina plants inoculated with Fusarium

sp.4, T5 = uninoculated melina plants (control). For each treatment, 17 melina

plants were used (replicates).

Statistical analysis. The quantitative data obtained were analyzed using

descriptive statistical tools: mean, standard deviation, standard error, coefficient

of variation, etc. To establish the existence or not of significant statistical

differences between treatments, the data were analyzed under the analysis of

variance scheme (ANOVA) with a significance level of 95% (P < 0.05), after

Symptomatology of the disease. Trees of G. arborea in early stages of the disease

show a slight chlorosis, and loss of turgor in leaves at the ends of upper branches,

with wilting characteristics. Due to vascular blockage and gradual disease

trees, vigor decreases significantly compared to healthy neighboring trees, mainly

due to wilting of the photosynthetic area. Once the leaf area is compromised, as

a survival mechanism, diseased trees emit numerous epicormic shoots on the

stem, stimulated by the need for photosynthesis. However, as vascular plugging

continues to impede the ebb and flow of nutritional substances, the tree

eventually dies (Figure 1). In diseased trees it is common to observe the presence

Figure 1. Evolution of vascular wilt disease and stem rot in melina trees: A = First

Generation of multiple epicormic shoots on the stem. C = Death of the foliar

system of the tree.

Since the introduction of G. arborea in THE production systems in the mid-1980s,

the species had not presented complex phytosanitary problems, but in the last

symptomatology, similar to that reported in other economically important forest

species in the region, such as Schizolobium parahybum (Geldenhuis et al., 2004;

Belezaca-Pinargote et al., 2011), Acrocarpus fraxinifolius (Belezaca-Pinargote et

Tectona grandis (Belezaca-Pinargote et al., 2018; Vera et al., 2019; Belezaca-

Pinargote et al., 2020), whose disease appeared early in the past decade and

The behavior of G. arborea trees against the disease is not uniform, generally the

manifestation of the initial symptoms are difficult to detect, since chlorosis and

loss of turgor occurs when the xylem and bascular tissues of the trees are

irremediably compromised and necrotic, both radially and tangentially.

Defoliation, death of growth buds and drying of branches are observed in

advanced stages of the disease. The presence of natural and/or anthropogenic

wounds on the trunk is common, with abundant exudation of dark brown fluids,

with a strong odor of decomposing organic matter.

Incidence and severity of the disease. In the 2-year-old plantation, an average of

10 diseased trees and 2 dead trees per plot (500

results show that disease incidence was 24.1%, 7.1%, and 21.3% for the 2-, 2.3-,

and 4-year-old melina plantations, respectively (Table 3).

three replicates, with their respective standard error.

Most of the diseased trees in the 2-year-old plantation were classified in scales 2

and 4, which indicates that 9.52% of the trees were found with the presence of

the disease, in a state of medium progress, and 7.14% were dead (scale 5). While

in the 2.3 year old plantation, diseased trees were located in scale 2 with 7.14%.

In the 4-year-old plantation, trees with different levels of disease were detected