USE OF EPIDEMIOLOGICAL TOOLS TO DIFFERENTIATE THE …isopb.mpob.gov.my/pdfFile/6th/P4-UseOfEpidemiological... · 2016. 3. 18. · The purpose of this study was to present a proposal

1

USE OF EPIDEMIOLOGICAL TOOLS TO DIFFERENTIATE THE A BILITY OF VARIOUS OIL PALM MATERIALS TO RESPOND TO THE BUD RO T DISEASE UNDER FIELD CONDITIONS

Edwin F. Restrepo1,3; Edwin A. Navia 1; Rodrigo A. Ávila1; Edison E. Daza1.

Abstract

The aim of this work is to present a proposal for evaluating the bud rot disease through epidemiological variables, disease progress rate and survival time, to differentiate the ability of oil palm materials to respond to the bud rot disease under field conditions.

An experiment was set up in a plantation of the Colombian Pacific Coast to evaluate the response of two E. guinnensis experimental materials and two interspecific hybrids, E. oleifera x E. guineensis, (Coari x La Mé and Coari x Pobé) to the bud rot disease. Monthly assessments of incidence and severity variables were made. The scale proposed by Cenipalma was used to estimate the severity index. The respective progress curves were generated and adjusted to monomolecular, logistic and Gompertz models. Incidence and severity rates for each material were estimated using simple linear regression. Statistical comparisons of the parameters were made using student's t-tests. Also, survival analyses were performed for each of the tested materials. Log-Rank statistics was used to compare the materials.

Severity progress rates of the interspecific hybrids, E. oleifera x E. guineensis (Coari x La Mé and Coari x Pobé), were significantly lower with respect to E. guineensis materials. No statistically significant differences were found between the severity progress rates of the two interspecific hybrids. However, the survival analysis showed significant differences between the hybrid materials. The Coari x Pobé material had the longest survival time.

Considering that the horizontal or partial resistance does not prevent the plants from getting infected, but slows down the rate at which the disease progresses between or within the plants, it may be inferred that it is possible that the two hybrids (Coari x La Mé and Coari x Pobé) evaluated in this research work, may be expressing a horizontal or partial resistance in response to the disease.

1 CENIPALMA, Bogota. 3 Corresponding author E-mail: [email protected]

2

Introduction

Meunier and Boutin (1975) were the first researchers to report the resistance of the interspecific hybrid, E. oleifera x E. guineensis, to the bud rot disease. The first signs of resistance of the interspecific hybrid to the bud rot disease were observed in the "La Arenosa" plantation, located in the region of Turbo, Colombia, where almost one hectare of interspecific hybrid cross between E. oleiferas from Suriname and African pisiferas E. guineensis Jacq. planted, survived the spear rot, while all the E. guineensis materials around were destroyed (Meunier et al., 1976).

According to Meunier et al., (1976) the hybrid has a high, but not total resistance to the spear rot. Indeed, several cases were reported in hybrid palms planted in 1963 at the La Arenosa plantation, where a few individuals spontaneously recovered and others died.

The resistance of the E. oleifera x E. guineensis hybrid to the bud rot disease has been reported by other authors. Hartley (1977) mentions that one of the advantages of the interspecific hybrid is its resistance to the bud rot disease. In addition, he pointed out that hybrids from a cross between Colombian E. oleiferas and pisiferas E. guineensis Jacq., were planted in 1968 in La Arenosa plantation, located in the region of Turbo, Colombia. Six years later, a large number of E. guineensis palms around the area were dead, while the hybrids had not yet been affected.

Van de Lande (1993) pointed out that the hybrid E. oleifera x E. guineensis planted in 1978 on one-hectare plot, at the Victoria plantation in Suriname, seemed to be resistant to the spear rot. Most of the palms around that plot were affected by or dead from the disease.

Amblard et al. (1995) mentioned that the interspecific hybrid had a very good tolerance to the bud rot in Latin America. In all places where the disease was present and the hybrid was planted, very few palms were affected and mortality was exceptional.

Zambrano (2004) reported that the E. oleifera x E. guineensis hybrid resulting from the cross between E. oleiferas of Brazilian origin (Coari) and parents of Yangambi and La Mé origin, planted in 1991 at La Cabaña Plantation, located in the Eastern Zone of Colombia, had a high tolerance to the bud rot after 11 years of assessment, with only two palms affected by the disease. In another trial conducted in 1998 in the same plantation, it was found that in just six years of records, the commercial material E. guineensis Jacq. already had 33.2% of cumulative incidence of bud rot, while the five hybrid crosses, E. oleifera x E. guineensis , remained unaffected by the disease (Zambrano, 2004).

Louise et al. (2007) mentioned that the interspecific hybrid E. oleifera x E. guineensis shows good tolerance to the bud rot complex. They also pointed out that with the resurgence of the complex, some producers became interested again in those hybrids. Palmeras del Ecuador was the first plantation to start the industrial planting of the Coari x La Mé hybrid in 1999. 1.5% of cumulative losses from the bud rot complex were recorded in that plantation at the end of 2005, while E. guineensis Jacq. planted in 2000 reported losses of 8.6% (Louise et al., 2007).

3

Chinchilla et al. (2008) pointed out that the resistance/tolerance to the bud rot disease was one of the clearest advantages of the interspecific hybrid, E. oleifera x E. guineensis. On the other hand, a trial conducted in 1993 in Changuinola (Panama) to compare the response of various materials to spear rot and bud rot diseases showed that during eight years of assessment, OxG hybrids and E. oleifera materials showed the least incidence of the diseases, while Deli x AVROS was the most susceptible among the materials evaluated (Chinchilla et al., 2007).

Durand-Gaselin et al., (2010) mentioned that the resistance in the interspecific hybrid is not total. There have been a few cases of but rot. In adult palms, annual losses of up to 1% should not affect total production, as it had happened in the eastern region of Ecuador. In addition, they pointed out that it was likely that more cases would occur in young palms. This was very important because these palms could be replaced; therefore, the number of palms per hectare was not affected.

Bastidas et al. (2011) reported that after 32 years, OxG hybrids planted in 1977 at El Mira Experimental Station, located around the municipality of Tumaco, Colombia, show tolerance to the bud rot complex, with low levels of incidence.

As it could be inferred from the above information, there was yet consensus reached about the type of response of the interspecific hybrid materials E. oleifera x E. guineensis to the bud rot disease. Some researchers pointed out that the interspecific hybrid are tolerant to the bud rot (Zambrano, 2004; Louise et al., 2007; Bastidas et al., 2007). Other researchers said that the hybrid were resistant to the disease (Meunier et al., 1976; Van de Lande, 1993; Durand-Gaselin et al., 2010). In addition, most of these researchers pointed out that very few interspecific hybrid palms were affected by the bud rot.

The purpose of this study was to present a proposal for evaluating the bud rot disease using epidemiological variables that, on one hand, should differentiate the ability of various oil palm materials responding to the bud rot disease under field conditions and, on the other hand, elucidate the kind of response of the hybrids to the presence of the pathogen.

Materials and Methods

Location

Two experiments were conducted in the municipality of Tumaco, in the Pacific Coast of Colombia, to evaluate the response of various oil palm materials to the bud rot disease. The first trial was set up in June 2007 at the Palmas del Mira plantation, and the second trial was started in April 2010 at the Central Manigua plantation.

Experimental design

A completely randomized experimental design with four treatments was used in the Palmas del Mira plantation. The treatments consisted of two Elaeis guineensis experimental materials called Patuca and Pepilla and two interspecific hybrid materials of E. oleifera x E. guineensis (Coari x La Mé and Coari x Pobé).

4

A completely randomized experimental design with four treatments was used in the Central Manigua plantation. The treatments consisted of two interspecific hybrid materials, E. oleifera x E. guineensis, (Manicoré x La Mé 2T and Manicoré x La Mé 10T).

In order to assess the potential for response of various oil palm materials to the bud rot disease, it was decided to not manage the disease in any way in both experiments. Monthly censuses were performed from the first day of planting in order to identify new cases of bud rot. The severity was graded in each diseased palm based on the scale developed for this purpose by Cenipalma (Martínez & Torres, 2008) (Table 1).

Table 1. Bud rot severity scale.

Degree Description 0 No lesions. Spear looks vigorous and healthy 1. Lesions covering from 0.1 to 20% of the spear area. 2 Lesions covering from 20.1 to 40% of the spear area. 3 Lesions covering from 40.1 to 60% of the spear area. 4 Lesions covering from 60.1 to 80% of the spear area. 5 Lesions covering from 80.1 to 100% of the spear area.

Each palm detected with the disease was considered as a new case, and became a part of the monthly incidence report of the corresponding material. The state of the youngest spear of each palm was assessed, recording the degree of severity based on the scale mentioned above. Removed palms were recorded in order to run an analysis about the dynamics of removals in each of the tested materials.

Evaluated variables and data analysis

Incidence and severity progress rates

Cumulative incidence curves were built using monthly incidence data. These curves allowed us to observe the trend of the disease in each group of palms. The index of disease severity was calculated using the following formula:

Where:

:

n: Number of plants affected by the disease.

S: Degree of severity (Cenipalma's severity scale)

N: Total number of plants evaluated

5

The value obtained was equivalent to the average degree of severity of the bud rot in each of the evaluated palms. As with the incidence, cumulative severity curves were generated for later analysis.

Cumulative incidence and severity data were linearized using the equations corresponding to the logistic growth, gompertz and monomolecular models. Y0 and slope of line parameters were estimated through simple linear regression, and were interpreted as the initial amount of disease and the rate of progress of the disease, respectively. The selection of the best fitted model was made using the concordance correlation coefficient (CCC), which ranges from 0 to 1 (Madden et al., 2007).

Statistical comparisons of rates of progress were made using student's t-tests. The null hypothesis of equal rates of progress of the different materials evaluated was used.

Survival analysis

In order to analyze the dynamics of removals in each of the materials, comparisons were made using the survival analysis technique. This analysis was performed only for the Palmas del Mira plantation trial.

Survival curves were generated using InfoStat software (University of Cordoba - Argentina). The presence or absence of statistically significant differences between the materials evaluated was determined by calculating the LogRank parameter for the survival time variable, with a probability of 0.05.

Results

Palmas del Mira Plantation

Incidence progress rate.

Disease progress curves of the four evaluated materials were generated using the cumulative incidence of bud rot data recorded over a period of 1812 days from the date of planting (Figure 1).

The first cases of bud rot appeared 99 days after planting (d.a.p.) in palms of the four materials being evaluated. Cumulative incidence curves showed a similar trend in all materials during the first 435 days. At this time, cumulative incidence values of the hybrid materials (Coari x La Mé and Coari x Pobé) were 57% and 67%, respectively, while the values for E. guineensis Jacq. materials (Patuca and Pepilla) were 64 and 69%, respectively (Figure 1).

471 d.a.p., the speed of occurrence of new cases began to decline in hybrid materials, while in E. guineensis Jacq. materials the speed of occurrence began to decline 810 d.a.p. At that time, the disease stabilized in the Patuca and Pepilla materials, reaching incidences of 96 and 99%, respectively. Hybrid materials had a maximum cumulative incidence of 66% (Coari x La Mé) and 76% (Coari x Pobé) (Figure 1).

6

Figure 1. Incidence progress curves for four oil palm materials evaluated at Palmas del Mira Plantation.

Table 2 shows the concordance correlation coefficients calculated for logistic, gompertz and monomolecular models for each material being evaluated. The highest values reported for the four materials correspond to the logistic model, suggesting that this model was the one that allowed the best fit with respect to the observed values of incidence over time.

Table 2. Concordance correlation coefficients calculated for incidence recorded in four oil palm materials evaluated at Palmas del Mira Plantation.

The slope of the regression line built with linearized values, according to the logistic model, was taken as the disease progress rate in the four materials. These values are shown in Table 3.

Model Coari x LaMé Coari x Pobé Patuca Pepilla

Logistic 0,89 0,83 0,96 0,86

Gompertz 0,26 0,151 0,155 0,073

Monomolecular 0,86 0,82 0,90 0,74

7

Table 3. Final cumulative incidence and incidence progress rate (r) in four oil palm materials evaluated at Palmas del Mira plantation.

Material Final Cumulative Incidence (%)

r

Coari x La Mé 83 0,0024 a Coari x Pobé 86 0,0020 a

Patuca 100 0,0060 a Pepilla 96 0,0020 a

The comparison of progression rates among the four materials was made using student's t-tests. Comparison results showed no statistically significant differences between the four progression rates, suggesting that the rate of occurrence of bud rot was similar in all four materials (Table 3).

Severity progress rate.

The disease Index was calculated based on the degree of severity. This index was used to generate severity progress curves corresponding to 1812 days after planting (Figure 2).

Figure 2. Severity progress curves for four oil palm materials evaluated at Palmas del Mira Plantation.

8

Figure 2 showed that the severity of the bud rot disease remained below 20% (Degree 1 in Cenipalma's scale) in E. guineensis Jacq. materials, during the first 330 d.a.p. In the case of the two hybrid materials, severity remained below the same value for a longer period of time (435 d.a.p. in Coari x La Mé and 471 d.a.p. in Coari x Pobé.). The increase from 20% to 40% in severity (Degree 1 and 2) of the Patuca and Pepilla materials required 135 and 107 days, respectively. In contrast, in Coari x La Mé material this process took 633 days and in Coari x Pobè it took 1006 days (Figure 2).

Severity progress curves showed that E. guineensis materials, Pepilla and Patuca, exceeded 80% of severity (Degree 5) between 734-782 days, respectively. At the end of the period of observation (1812 d.a.p.) both hybrid materials had a severity of less than 55% (severity degree 3). A similar situation occurred much earlier in the two E. guineensis Jacq., materials (547 days) (Figure 2).

Table 4 showed the concordance correlation coefficients calculated for logistic, gompertz and monomolecular models for the material being evaluated. Contrary to what was observed in the incidence progress curve, the severity curve fitted to two different models of growth. Hybrid materials fitted to the monomolecular model and E. guineensis Jacq., materials fitted to the logistic model.

Table 4. Concordance correlation coefficients calculated for the severity recorded in four oil palm materials evaluated at Palmas del Mira Plantation.

The comparison of progress rates was made based on the transformation of the estimated rates from the linear regression, as the progress curves of the materials evaluated fitted to two different models. The transformation was used to calculate the rho parameter and t-test statistical comparisons were performed with the corresponding values (Table 5).

When comparing severity progress rates, it was found that hybrid materials showed progress rates significantly lower compared with those of E. guineensis Jacq., materials (Table 5).

Although no significant differences were found between incidence and severity progress rates of the hybrid materials, it was important to mention that the Coari x Pobé hybrid showed the lowest rates, compared to the rates of the Coari x La Mé hybrid (Tables 3 and 5).

Model Coari x LaMé Coari x Pobé Patuca Pepilla

Logistic 0,94 0,92 0,95 0,92

Gompertz 0,90 0,57 0,21 0,15

Monomolecular 0,98 0,97 0,93 0,89

9

Table 5. Final cumulative incidence and severity progress rate estimated in four oil palm materials evaluated at Palmas del Mira plantation.

Survival analysis

The analysis showed marked differences between the materials evaluated with respect to survival time of palms. Figure 3 shows the Kaplan-Meier survival curves, which indicate the proportion of palms removed over time from each group of materials.

Versión Estudiantil Versión Estudiantil Versión Estudiantil Versión Estudiantil Versión Estudiantil Versión Estudiantil Versión Estudiantil Versión Estudiantil

Versión Estudiantil Versión Estudiantil Versión Estudiantil Versión Estudiantil Versión Estudiantil Versión Estudiantil Versión Estudiantil































0 165 329 494 659 824 988 1153 1318 1483 1647 1812

Tiempo de Supervivencia (Días)

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,80

0,90

1,00

SU

PE

RV

IVE

NC

IA

Coarí x LaMé

Coarí x Pobé

Patuca

Pepilla

0,66

0,83

0,05

0,03

Curvas de Supervivencia (Kaplan-Meier)

Material

Final

Cumulative

Severity (%)

Final

Degree of

severity

rho

Coari x La Mé 52,2 3 0,00024 a

Coari x Pobé 44,0 3 0,00017 a

Patuca 98,0 5 0,00063 b

Pepilla 96,0 5 0,00052 b

Survival curves Kaplan-Meier

SU

RV

IVA

L

Survival Time (Days)

10

Figure 3. Survival curves for four oil palm materials evaluated at Palmas del Mira Plantation.

Loss of palms of Patuca and Pepilla materials was constant during the entire assessment period, and began 252 and 353 days after planting, respectively. The curves show steps with large risers in the proportion of the surviving palms and short time periods between removal events, suggesting that in these two materials, the disease caused a rapid loss of palms during the first 1000 days of evaluation. At this time, the survival ratio was 0.15 in Patuca and 0.11 in Pepilla. From that moment onward, the events became less frequent, which was clearly associated with a fewer number of palms exposed to the disease (Figure 3).

On the other hand, hybrid palms had higher survival rates than E. guineensis Jacq., materials. In Coari x Pobé and Coari x La Mé hybrids, the loss of palms was not constant throughout the entire evaluation period and began 330 and 471 days after planting, respectively. The curves showed steps with short risers in the proportion of the surviving palms and long time periods between removal events, suggesting that the disease caused a slow loss of palms in these two materials (Figure 3).

At the end of the evaluation period (1812 d.a.p), survivals of 0.03 and 0.05 were recorded for Pepilla and Patuca materials, respectively; while for Coari x Pobé and Coari x La Mé hybrid materials the survival values were 0.83 and 0.66, respectively (Figure 3).

Table 5 shows the survival values recorded at the end of the evaluation period, LogRank values from the analysis of survival curves, and the statistical significance test for differences in survival curves. The comparison between the curves of the four materials showed statistically significant differences in survival times. Independent analyses were run to determine specific differences between pairs of curves, as the LogRank test was pure significance and dis not provide information on the magnitude of the differences between groups (Bland & Altman, 2004).

Statistically significant differences were found in the survival times between the two hybrid materials, where Coari x Pobé showed the longest survival time, which means that the number of surviving palms throughout the evaluation time was significantly higher. On the contrary, no statistically significant differences were found in that variable when comparing the two E. guineensis Jacq., materials. On the other hand, when comparing survival times of two hybrid materials with respect to the two E. guineensis Jacq., materials, it was found that hybrids showed survival times significantly higher than those of E. guineensis Jacq., materials.

Central Manigua Plantation

Incidence progress rate

11

Disease progress curves for the four materials were generated using cumulative bud rot incidence data recorded over a period of 732 days from the date of planting (Figure 4).

Cumulative incidence curves showed a different trend in all materials during the first 116 days. At this time, cumulative incidence values of the Manicoré x La Mé 2T and Manicoré x La Mé 10T hybrid materials were 10% and 17%, respectively (Figure 4).

152 d.a.p. until the end of the evaluation period, incidence curves of both hybrid materials showed a similar tendency. The cumulative incidence 732 d.a.p. for Manicoré x La Mé 2T and Manicoré x La Mé 10T materials was 22% and 29%, respectively (Figure 4).

Table 5. Final survival values, LogRank statistics and probability for survival analysis in four oil palm materials affected by bud rot at the Palmas del Mira Plantation.

Severity progress rate

Figure 5 shows a similar trend in the progress trend for both hybrid materials: Manicoré x La Mé 2T and Manicoré x La Mé 10T. In addition, the severity of the bud rot remained below 20% (Degree 1 in Cenipalma's scale) throughout the evaluation period.

Discussion

Cumulative incidence curves of the disease in Patuca, Pepilla, Coari x La Mé and Coari x Pobé materials, evaluated at the Palmas del Mira Plantation, showed that all materials were affected by the bud rot. From a statistical perspective, the incidence progress rate analysis showed no differential reaction among the four materials evaluated, suggesting that the variable did not allow differentiating the ability of these oil palm materials to respond to the disease, even among those more genetically distant. During the first stage of emergence of new cases of bud rot, the tendency of the four curves was similar and remained unaltered until the impact exceeded 60%. A slight differentiation in the trends of progress of the

Material Survival LogRank value p

Coari x LaMé 0,66

Coari x Pobé 0,83

Patuca 0,05

Pepilla 0,03

Coari x LaMé 0,66

Coari x Pobé 0,83

Patuca 0,05

Pepilla 0,03

Coari x LaMé 0,66

Patuca 0,05

208,710 0,00000

4,795

0,002

113,030

0,02853

0,96602

0,00000

12

disease began only after this proportion was exceeded, showing that cases became less frequent from this point forward.

Figure 4. Incidence progress curves for two oil palm hybrid materials evaluated at the Central Manigua Plantation.

13

Figure 5. Severity progress curves for two oil palm hybrid materials evaluated at the Central Manigua Plantation.

The fact that all the cumulative incidence curves fitted to the logistic model suggests that the emergence of new cases was due, in principle, to the high disease pressure from neighboring infected fields. In fact, 9315 hectares of oil palm lost to the bud rot disease in that area had already been reported in 2007 (Silva & Martinez, 2009). In general, all four evaluated materials showed a decrease in the rate of occurrence of new cases when the cumulative incidence rate exceeded 50%, possibly due to the decrease in the number of available palms to get infected.

The high proportion of Coari x La Mé and Coari x Pobé hybrid palms affected by the bud rot in this study is in contrast to the low proportions of affected palms that have been reported in hybrids evaluated in other works (Meunier & Boutin, 1975; Amblard et. al., 1995; Zambrano, 2004; Louise et al, 2007; Chinchilla et al, 2008; Durant-Gaselin et al, 2010; Bastidas et al, 2011).

The severity progress rate variable did allow discriminating between genetically distant materials; therefore, the two hybrids (Coari x La Mé and Coari x Pobé) showed significant lower values compared to those of E. guineensis Jacq. materials (Patuca and Pepilla). However, this variable was not discriminant when comparing genetically close materials, as no statistically significant differences were found between the two hybrids.

14

The fact that the severity progress curves for the Coari x La Mé and Coari x Pobé hybrids fitted to the monomolecular model, suggests that the severity progress rate is directly proportional to the apparently healthy plant tissue. Therefore, the absolute rate reached its highest value at the beginning of the epidemic and gradually declined over time. The availability of healthy tissue for a longer time may be an indication that hybrid materials had a delayed progress of lesions, compared to E. guineensis Jacq. materials.

Survival curves showed that the decrease in the number of palms in the field was constant in E. guineensis Jacq. materials (Patuca and Pepilla). This may be inferred from the way how the steps were formed with short ¨treads¨ and ¨risers¨ (time between removals and proportion of lost palms, respectively). About 700 d.a.p., 50% of palms had already been eliminated in both materials. It is very likely that the loss of palms was related to the high severity of the disease in these materials. In fact, just 547 d.a.p. palms had a severity level that exceeded 60% (degree 3) and a survival of 0.75. From this point to 824 d.a.p. survival curves showed high risers, suggesting substantial loss of palms in short periods of time.

After 824 d.a.p. it was observed a reduction in the height of the risers and an increase in the depth of the treads, suggesting a lower loss of palms in increasingly longer periods of time, which in turn, could be due to the fewer number of palms not yet affected by the disease.

In the case of hybrid materials (Coari x La Mé and Coari x Pobé) the situation was contrasting with respect to E. guineensis Jacq. materials (Patuca and Pepilla). Survival steps showed a tendency to have higher risers and deeper treads, suggesting fewer losses of palms in longer periods of time. This was particularly evident in Coari x Pobé materials, which showed the highest survival rate (0.83), even in the LogRank test, it was determined that their survival time was significantly longer than that of the Coari x La Mé material.

Unlike the incidence and severity progress rate variables, the survival time variable did allow discriminating between genetically close materials; thus, survival time for Coari x Pobé hybrid palms was significantly longer with respect to the Coari x La Mé hybrid.

The evaluation of the bud rot using epidemiological variables, disease progress rates and survival time, allowed differentiating the ability of oil palm materials to respond to the disease under field conditions; therefore, those materials that had a level of resistance significantly higher compared with the rest of evaluated materials could be identified.

It was important to note that the use of the previously described epidemiological variables had a limitation because, due to their population-based nature, these variables cannot be used for the selection of individual plants within the best materials identified by their high resistance. The rigorous selection of individual plants with the highest levels of resistance required the development of a bud rot evaluation test under controlled conditions or the use of resistance molecular markers. However, nothing had yet been published on this matter.

15

While the test under controlled conditions or the molecular markers associated with the resistance are being developed, we suggest the use of the disease severity assessment through the maximum severity level reached by each palm throughout the evaluation period for the selection of individual plants within the materials selected for their high resistance, so that those palms where the disease has progressed very little (degrees 1 or 2) can be finally selected.

Considering that horizontal or partial resistance does not prevent the plants from getting infected, but slows down the rate at which the disease progresses between or within plants (Tapiero, 1999; Ribeiro et al., 2001; Cooke et al., 2006), it may be inferred that it is possible that the interspecific hybrids Coari x La Mé, Coari x Pobé, Manicoré x La Mé 2T and Manicoré x La Mé 10T, evaluated at the Palmas del Mira and Central Manigua plantations, may be expressing horizontal or partial resistance in response to the presence of the bud rot disease.

To further generalize the hypothesis, it will be necessary to evaluate hybrids from crosses between parents of different origins, E. oleifera and E. guineensis, respectively. To achieve these objectives, Cenipalma, through its Oil Palm Biology and Breeding Research Program, has initiated a study whose general objective is to assess the response of various interspecific hybrids sold in Colombia to the bud rot disease.

Palms of the first backcross generation between the Coari x La Mé hybrid and La Mé as recurrent parent, evaluated at a plantation in the eastern part of Colombia, have showed a continuity in the expression of resistance to the bud rot disease in such a way that palms ranging from very susceptible to very resistant to the disease can be found (Jorge Zambrano, personal communication). The wide range of variation in the expression of resistance to the bud rot suggests that this resistance is likely to be controlled by several genes; therefore, it would be a horizontal or partial-type resistance, which would be consistent with the hypothesis outlined in this research study.

If it is fully confirmed that the interspecific hybrid, E. oleifera x E. guineensis has a horizontal or partial type resistance to the bud rot in regions where the disease pressure is high, it would have a very important implication in terms of the type of required management, because it would suggest the implementation of an integrated disease management strategy for these regions. Some researchers such as Ribeiro et al (2001) pointed out that quantitative resistance was suitable to be implemented within an integrated disease management program, as it increased the effects of other control methods. The core component of the integrated management program would be the use of oil palm materials with partial resistance to the bud rot (E. oleifera x E. guineensis interspecific hybrid), which should be accompanied by a good agronomic management program and a good phytosanitary management so that the interspecific hybrid can express and maximize its genetic potential (Figure 6).

16

Martinez and Torres (2009) recommend that any bud rot control measure must start before the disease progresses to severity 3, because this would increase the chances of recovery of the affected palm. Considering the characteristics exhibited by the hybrid materials evaluated in this study in terms of reduced severity, a control based on early detection of the disease and elimination of the affected tissue, would help maximize the expression of partial resistance of the hybrid material.

The implementation of the integrated disease management program, which is proposed in this study, would be supported by the fact that being a partial-type resistance, it most likely would be controlled by several genes; therefore, the expression of such resistance would depend on the type of agronomic management used and the environmental conditions of the plantation site. On the other hand, the integrated disease management should include the use of the E. oleifera x E. guineensis hybrid, because oil palm Elaeis guineensis Jacq. is generally very susceptible to the bud rot. In fact, in regions where the disease is more aggressive, almost all palms of that species have disappeared (Durand-Gasselin et al., 2010). In addition, the only known sources in E. guineensis Jacq. that have some degree of resistance to bud rot (Deli C07 and C65) have not yet been tested in regions where the bud rot is more aggressive, such as the region of Tumaco in Colombia and the region of San Lorenzo in Ecuador (Durand-Gasselin et al., 2010).

Finally, the verification of the hypothesis outlined in this study could become a very important finding for the oil palm sector in the Americas because, in theory, it is usually a durable resistance, which would make sustainable the oil palm cultivation in those regions where the disease pressure is high.

17

Figure 6. Integrated bud rot management program suggested for regions where the disease pressure is high.

Conclusions

Traditionally, the incidence had been used as a variable for rating the performance of the materials against the bud rot. However, the results of this research study indicated that not even the progress rate of that variable allowed discriminating between genetically distant

18

materials. On the contrary, the survival time and severity progress rate variables used in this study did allow discriminating between oil palm materials.

The survival time variable turned out to be an efficient discriminant, that it allows differentiating between genetically close materials. On the other hand, the disease progress rate variable was a fair discriminant, as it only allowed differentiating between genetically distant materials.

Considering that the horizontal or partial resistance does not prevent the plants from getting infected, but slows down the rate at which the disease progresses between or within the plants, it may be inferred that it is possible that the interspecific hybrids evaluated in this research study may be expressing a horizontal or partial resistance in response to the bud rot disease.

19

Literature cited

Amblard, P.; Noiret, J.M.; Kouamé, B.; Potier, F.; Adon, B. 1995. Performances comparées des hybrides interspécifiques et du matériel commercial E. guineensis OCL. Oléagineux corps gras lipides 2(5): 335-340.

Bastidas S., Peña E., Reyes R., Medina C., Villa A., y Tolosa W. 2011. Avances sobre las pruebas agronómicas para comprobar la tolerancia y productividad de los híbridos Elaeis oleifera x Elaeis guineensis al disturbio Pudrición del cogollo en la zona palmera occidental de Colombia. Informe técnico Corpoica. pdf.

Bland, J.M. y Altman, D.G. 2004. The logrank test. British Medical Journal 328: 1073.

Cooke, B. M.; Gareth, J. D.; Kaye, B. 2006. The epidemiology of plant diseases. Springer, Dordrecht. Pp. 139-157.

Chinchilla, C. 2008. The Many Faces of Spear Rots in Oil Palm: The Need for an Integrated

Management Approach. ASD Oil Palm Papers 32: 1-25.

Durand-Gaselin, T.; Corredor, J.; Sanz, J. I.; de Franqueville H.; Amblard. P. 2010. Visión futura del mejoramiento genético de la palma de aceite en Latinoamérica: varias resoluciones sobre cooperación en Colombia para mejoramiento del material de siembra. Palmas 31 (Tomo I Ed. Especial): 11-26.

Hartley, C. W. S. 1977. The oil palm. Longman Group Limited, London and New York. Pp. 731-784.

Louise, C.; Amblard, P.; de Franqueville, H.; Benavides, D.; Gallardo C. 2007. Investigaciones dirigidas por el Cirad sobre las enfermedades del complejo pudrición del cogollo de la palma aceitera en Latinoamérica. Palmas 28 (Tomo I Ed. Especial): 345-362. Madden, L.; Hughes, G. and Van den Bosch, F. 2007. The study of plant disease epidemics. APS Press, St. Paul. Pp. 1– 116.

Martínez, G.; Arias, N.; Sarria, G.; Torres, G.; Varón, F.; Noreña, C.; Salcedo, S.; Aya, H.; Ariza, J.; Aldana, R.; Martínez, L.; Moya, O.; Burgos, C. 2009. Manejo integrado de la pudrición del cogollo (PC) de la palma de aceite. Cartilla técnica No. 1 Cenipalma. 24 p.

Meunier, J.; Boutin D. 1975. L’Elaeis melanococca et l’hybride Elaeis melanococca x Elaeis guineensis. Premières données. Oléagineux 30(1): 5-8. Meunier, J.; Vallejo, G.; Boutin D. 1976. L’hybride Elaeis melanococca x Elaeis guineensis et son amélioration. Oléagineux 31(12): 519-525. Ribeiro do Vale, F.X.; Parlevliet, J.E. y Zambolim, L. 2001. Concepts in plant disease resistance. Fitopatologia Brasileira 26: 577 – 589.

20

Tapiero, A. 1999. Durable resistance to plant disease. Revista Corpoica (Colombia) 3 (1): 36-40.

Van de Lande, H. 1993. Studies on the epidemiology of spear rot in oil palm (Elaeis guineensis Jacq.) in Suriname. Ph. D. tesis. Wageningen Univ., Wageningen. 154 p. Zambrano, J. E. 2004. Los híbridos interespecíficos Elaeis oleifera H. B. K x Elaeis guineensis Jacq. Una alternativa de renovación para la zona oriental de Colombia. Palmas 25 (Tomo II Ed. especial): 339-349.

Documents

USE OF EPIDEMIOLOGICAL TOOLS TO DIFFERENTIATE THE …isopb.mpob.gov.my/pdfFile/6th/P4-UseOfEpidemiological... · 2016. 3. 18. · The purpose of this study was to present a proposal