Reactions of Oil Palm (Elaeis guineensis Jacq) Progenies to Fusarium Wilt Disease Caused by Fusarium oxysporum f.sp. Elaeidis under Natural Infection

The oil palm (Elaeisguineensis Jacq) is used worldwide in commercial agriculture for the production of palm oil, palm kernel oil and palm wine. It produces more oil per plant than any other oil-producing crop in the world. Production is constrained by several factors among which pests/diseases are of utmost importance. Vascular wilt (VW) caused by Fusarium oxysporum is the most devastating disease infecting this crop. Its soil-borne ecology has made the use of fungicides to manage this disease too expensive and inpragmatic. There is need for concerted research in the breeding and selection of wilt-tolerant progenies as an essential step in the management of Fusarium wilt disease. The study aims to assess the incidence and severity of vascular wilt among tested oil palm progenies, to evaluate the reduction in yield caused by the disease in the susceptible progenies and to identify the wilt-tolerant, high-yielding progenies. The study was carried out at Pamol Plantations Limited (PPL) in Ndian Estate (Ndian Division), in the Southwest Region of Cameroon. Three field trials were evaluated for tolerance/susceptibility to Fusarium wilt. Each trial consisted of 15 oil palm progenies replicated 4 times. Each progeny had 25 oil palm stands in each replicate. Hence, a total of 1500 oil palm stands were assessed. The experimental design was a randomized complete block (RCB) with trial codes: Trial 2001/1, planted in 2001; Trial 2001/2, planted in 2002; Trial 2001/3, planted in 2003. Each trail had an area of 12 ha, with a plant density of 143 palms·ha ⁻¹. Wilt incidence, severity, index, and yield were evaluated on 45 progenies from the 3 trails after identifying Fusarium oxysporum from oil palm plant part. Data was subjected to analysis of variance, Fischer’s least significant difference test (LSD) for mean separation. Identification of Fusarium was based on descriptive analysis. Incidence of VW in the 3 trials ranged from 1% - 39%. Also, 45% of infected plants were from progeny 676 while 1% was from progenies 689, 693, 694 and 710. Disease severity was from 0.9 in progeny 686 to 4.55 in 676. Wilt index ranged from 131 for progeny 694 and 710 to 495 for progenies 705. Out of the 45 progenies evaluated, 27 were tolerant (1 < 100) and 18 susceptible (1 ≥ 100). Within the tolerant progenies, 4 were significant (1 < 20) while 5 out of 18 were significantly susceptible (1 ≥ 185). Mean yield reduction of the susceptible progenies was 34.8% while in the tolerant progenies, it increased by 9.5% when compared to their controls. Progenies 702, 703 and 709 are recommended for planting based on the level of tolerance to Fusarium wilt disease and yield.

• Progenies
• Tolerant
• Susceptible
• Vascular Wilt
• Fusarium oxysporum
• Oil Palm

1. Introduction

The genus Elaeis has two species of economic importance in the Arecaceae: The African oil palm (Elaeis guineensis Jacq.) which is native to West Africa and the American oil palm (Elaeis oleifera), native to Tropical Central America and South America [1] . This plant is used in commercial agriculture for the production of palm oil, kernel oil and palm wine [2] . The oil palm is very profitable because it produces more oil per land area than any other oil-producing crop, such as soybean [3] . In addition, since the oil palm has an average production life span of about 25 years, productivity is combined with a perennial oil source, unlike annual oil seed crops such as soya, making this plant the highest in total world’s production of vegetable oils [4] .

Approximately 77% of palm oil produced worldwide is used for human consumption making it an indispensable source of edible oil [5] and the remaining 23% is used in manufacturing biodiesel, drugs, cosmetics, polish, and soap detergent [6] . Palm oil is nutritious and useful for bone, joint and skin health, source of medium-chain fatty acids and healthy unsaturated fats. It is a well-balanced fat, with 39% oleic acid (omega-9) and 10% linoleic acid (omega-6) which helps to lower blood cholesterol levels in the body. It is the richest vegetable oil source of Tocotrienols—potent forms of Vitamin E that strengthens the immune system and protects skin cells from toxins and UV radiation [7] . From its reddish-orange hue, this oil is also a good source of β-carotene, a nutrient found in sweet potatoes, carrots, and other orange foods that are useful as a precursor to vitamin A (retinol) in the body. In traditional medicine, palm oil is used as an ingredient for the cure of ailments such as headaches, pains, rheumatism, cardiovascular diseases and arterial thrombosis [8] . Healthwise, palm oil intake has no impact on body weight changes or Body Mass Index (BMI) [9] .

Severe drought (8 - 10 months), infertile soil and disease are the major factors that limit oil palm yields [4] . Vascular wilt, otherwise known as Fusarium wilt, is among the most serious diseases affecting oil palm yield in Africa. The disease is caused by a soil-borne fungus, Fusarium oxysporum Schl. f.sp. elaeis [10] . Wardlaw first observed the disease in Zaire in 1964 and thereafter, it has also been recorded in Nigeria, Ivory Coast, Republic of Benin and Cameroon. This disease has not been reported in Malaysia, which is one of the world-leading exporters of palm oil [11] . Colhoun [12] suggested that climatic differences, notably the lack of prolonged dry season in Malaysia, could be a significant factor in disease expression. Palm oil production from South-East Asia, notably Malaysia, has increased steadily over recent years. In contrast, production in much of Africa has fallen due in part to diseases, with VW being considered as the most serious [13] . The significance of the disease in Africa with particular reference to Cameroon cannot be over-emphasized. The disease is fatal in the acute form of field-planted palms causing high economic losses in mature oil palm plantations. In the chronic form, it retards vegetative growth and prevents the production of fruit bunches. It is more severe in replanted estates, where incidence of up to 40% has been recorded in field-planted palms in some Pamol plantations, in Cameroon [14] . The causal organism of the disease is widely distributed in tropical soils, thereby creating practical difficulties to chemical control measures. Systemic fungicides like Benomyl can be used with limited success to treat infected oil palm fields, but such treatment would be too expensive over large areas [15] . Other measures to manage this disease include sanitation, use of resistant cultivars, clean propagation materials and oil palm seeds should be treated with hot water. Also, it is essential to lime the soil and use nitrate nitrogen fertilizer [16] . Oil palm is a cross-pollinated crop with a long generation time, thereby posing a lot of challenges in achieving a sustainable high yield and quality [16] . The complexity of the disease calls for concerted research in the breeding and selection of wilt-tolerant progenies as one essential step in the control of Fusarium wilt [17] . The objectives of the study, therefore, were to assess the incidence and severity of vascular wilt among tested oil palm progenies, to evaluate the reduction in yield caused by the disease in the susceptible progenies and to identify the wilt-tolerant, high yielding progenies.

Oil palm improvement, through the use of high yielding, wilt-tolerant planting material, would increase the oil yield per hectare [18] . The study is also important in that the strict use of wilt-tolerant seeds in areas with a disease history of wilt would go a long way in minimizing losses due to the disease to no more than one percent [19] . In addition, differences in tolerance among the tested progenies with regards to vascular wilt disease would enable conclusions to be drawn as the choice of planting materials for wilt-infested zones. The most tolerant progenies would be reserved for breeding and seed production programmes.

2. Methodology

2.1. Study Site

The study was carried out at PPL, Ndian Estate (Ndian Division), Southwest Region of Cameroon. Ndian Estate with 8000 hectares of palm is one of the three estates of PPL, and it is composed of three camps: Mana. Bulu and Makepe Camps. It has an average monthly temperature of 26.5˚C and an average monthly rainfall of 12.9 mm [20] . The area is about 6165 Km², has an equatorial maritime climate and a dominant lowland topography. It lies between Latitudes 4˚17' - 5˚26' and Latitudes 8˚35' - 9˚26' with an altitude of 1,764m above sea level [21] . Rainfall is ranged between 2500 mm - 4000 mm with maximum between July and October, mean annual temperature between 16˚C and 26˚C and soil types include: dark brown alluvial, lateralitic and silty alluvium which are good for plantation agriculture especially the oil palm and cocoa [22] ( Figure 1 ). Fusarium wilt occurs in many parts of Cameroon, but the disease is more prevalent in Ndian Division, where incidence of up to 40% has been recorded in some old fields.

Figure 1

Figure 1. Location of the study site in Ndian Division, Southwest region, Cameroon. Source: [21] .

Three field trials were carried out to determine the tolerance/susceptibility to Fusarium wilt. Each trial consisted of 15 oil palm progenies replicated 4 times. Each progeny had 25 oil palm stands in each replicate. Hence, a total of 1500 oil palm stands were assessed in each trial, that is, 15 progenies × 25 oil palm trees × 4 replicates = 1500 oil palm trees. The experimental design was a randomized complete block (RCB) and the trial codes were: Trial 2001/1, planted in 2001; Trial 2001/2, planted in 2002 and Trial 2001/3, planted in 2003 making a total of 45 progenies ( Table 1 ). Each trail had an area of 12 ha, with a plant density of 143 palms·ha⁻¹. The basic layout of the palms was 9 m × 9 m triangular.

Table 1

Table 1. List of 45 progenies planted for the three years.

Progeny Codes	Parents
710	12/0516T × 12/12630T
694	13/2548D × 12/12640P
683	52/1340D × 13/2068D
679	13/0837T × 52/1340D
685	13/2068D × 12/12440P
693	52/1424T × 12/1402D
698	13/2959T × 12/0719D
689	13/2959T × 52/1239D
685	13/2068D × 12/12440P
680	13/0837T × 13/2068T
674	52/1340D × 13/0837T
684	13/2548D × 12/12640T
707	52/5334D × 12/10516T
706	13/1572T × 12/12539T
685	13/2068D × 12/12440P
686	52/1340D × 12/12640P
683	52/1340D × 12/12640P
709	12/12539D × 13/1302T
713	13/1302T × 52/11505T
703	13/3021D × 52/5334D
699	13/2548D × 12/1402D
708	13/3021D × 12/10516T
702	52/1533D × 12/12539D
675	12/1514T × 52/1340D
701	12/0719D × 12/12440P
696	13/2548D × 12/1402D
672	52/1340D × 13/2068D
711	12/2630T × 13/3021D
692	13/3217T × 52/0424T
700	13/3217T × 52/0635T
704	13/2065T × 13/3021D
691	52/2601T × 12/1239D
695	12/1402D × 13/3217T
682	52/1514T × 53/0230T
681	52/0230T × 13/2068T
690	12/3217T × 13/2548D

Continued

694	12/0719D × 52/2608T
678	12/1514T × 13/0837T
684	13/2548D × 12/12649P
697	52/0635T × 13/2548D
673	13/0837T × 12/1514T
677	52/0230T × 52/1340D
676	52/0230T × 12/1514T
712	12/12539D × 52/11505T
705	12/0719D × 52/6117T

2.2. Fusarium Wilt Assessment

For each trial, all palm entries in each progeny were inspected for fusarium wilt symptoms. During this operation, the following records were made:

$\begin{array}{l}\text{Incidence}\text{of}\text{wilted}\text{trees}\text{in}\text{each}\text{progeny}\\ =\frac{\text{Number}\text{of}\text{trees}\text{showing}\text{wilt}\text{symptoms}}{\text{Total}\text{number}\text{of}\text{trees}\text{in}\text{the}\text{progeny}}\times 100\%\end{array}$ (1)

Symptoms of fusarium wilt were observed in ten randomly selected trees in each progeny. A wilt index of 0 to 5, adopted from Flood et al. [23] was used to express severity of disease in each progeny.

0) No symptoms.

1) Slight necrosis/chlorosis on one or two leaves tips—usually oldest leaves.

2) Necrosis/chlorosis over one quarter of leaves of plant and some shortening of the younger leaves.

3) Severe necrosis/chlorosis over one half of the leaves of the plant and some shortening of the younger leaves.

4) Severe necrosis/ chlorosis over three quarters of the leaves of the plant. Extensive leave desiccation and stunting.

5) Dead plant.

Vascular wilt disease severity = Number of plants were counted per severity score on a scale of 1-5.

$\bar{\text{X}}\text{ISSAP}=\left({\displaystyle {\sum }_{s=1}^5\left(SXs\right)}\right)/\left({\displaystyle {\sum }_{s=1}^5\left(Xs\right)}\right)$ as described in Njock, 1994 and Oben et al, 2021). Where:

$\bar{\text{X}}\text{ISSAP}$ = Mean index of severity considering all plant units;

S = Severity class (1-5);

Xs = Number of plant units scored in severity class (1-5);

AP = Consider all plants units. (2)

The performance of each progeny with respect to fusarium was defined by an index (I) whose value is an inverse proportion to the tolerance of the progeny under consideration [19] . Thus, to each progeny corresponds an index (I) obtained by the following formula:

$\begin{array}{l}\text{Index rating}\left(\text{I}\right)\text{for each progeny}\\ =\frac{\text{Percentage of wilted plants in a progeny}}{\text{Average percentage of wilted plants in all progenie}}\times 100\end{array}$

The lower the rating (I), the higher the tolerance of the progeny under consideration. Thus, by the end of the fusarium wilt assessment, progenies were classified in relation to each other in order to increase susceptibility to wilt.

Each breeding parent was attributed to the mean of the indices of the crosses in which it is inscribed a value (Ig). The Ig value indicate that parent’s “combining ability”, that is the parent’s capacity to transmit to its progeny either a certain tolerance if the figure is less than 100, or susceptibility if the Ig value is more than 100. Classification of parent’s as regards tolerance or susceptibility of the wilt was based on their Ig value [24] .

2.3. Vegetative Measurement

For each progeny, the following vegetative measurements were carried out for 10 randomly selected trees as described by Corley [25] .

A graduated pole was used to measure the height of each palm. Measurements were made from ground level to the base of frond 41 in meter to one decimal place.

The existence of gradient in leaf sizes according to the ages of the leaves means that samples must be taken from leaves of the same rank to enable comparison between different samples. Leave 17 was chosen because it is mature and functionally assessable [15] . In order to determine leaf 17, leaves 1 and 9 were first determined. Leaves 1, 9, and 17 are located on the same spiral. Leaf 1 is the first fully opened leaf surrounding the spear. Leaf 9 is directly below leaf 1, while leaf 17 is directly below leaf 9. Leaf length was measured in meters to one decimal place from the lowest spine to the leaf tip, with the aid of a plastic measuring tape. Relative leaf area was calculated as follows:

$\begin{array}{l}\text{Leaf area}=\text{length of the longest leaf}\times \text{width of the leaflet}\\ \times \text{number of leaflets}\times \text{frond shape factor}\left(0.573\right)\end{array}$

They were measured directly with a measuring tape in centimeters to one decimal place. For tall palms, measurements were made at breast height. For stunted palms, measurements were made at 5 cm from the base of the lower frond.

The phyllotaxy of fronds in the crown of an oil palm tree shows that the fronds are spirally arranged around the stem. Each oil palm tree contains eight spirals of fronds [11] . Hence, the number of fronds in each tree was determined as follows:

$\text{Number of fronds}=\text{Number of fronds in one spiral}\times 8$ (4)

2.4. Harvest and Measurement of Yield

Harvesting of ripe bunches was done with a Malayan knife, attached to a pole of varying length. Bunches which had more than one loose fruits were considered ripe [4] . For each progeny, the bunch weight and number were determined and recorded. Bunches were weighed on a measuring scale, mounted on a tripod stand. Harvesting and recording of fresh fruit bunches were carried out in 10 to 12 days cycle, for 9 months. The harvesting process started in April and ended in December. The percentage decrease in yield of susceptible progenies (R) was compared to the yield of the tolerant check (control) as described by Corley et al. [25] as follows:

$R=\frac{C-W}{C}\times 100\%$. (5)

R = Relative yield reduction

C = Average yield in the tolerant check

W = Average yield in the susceptible progeny

2.5. Microbial Identification

1) Sterilization of laboratory materials and preparation of growth media

Detergents were used to wash glassware for the experiment. Inoculation needles, cork borers and scalpels were dipped into 70% ethanol and flamed to red hot using a Bunsen flame to effect sterilization. Glassware like beakers, pipettes agar plates were sterilized by heating at 120˚C for an hour in hot air oven while the laminar flow Hood was cleaned with cotton wool soaked in 70% ethanol. The UV-light of the lamina flow hood was put on for at least 2 hours and put off before plating of the various samples in semi-solidified agar. Media including Potato dextrose agar, nutrient agar, bacto-agar, carnation leaf agar were suspended individually in one litre conical flask containing distilled water in a water bath and heated for 20 minutes at 50˚C and later autoclaved at 121˚C for 20 minutes to effect sterilization before they were cooled and stored at 4˚C in a refrigerator until when needed.

2) Isolation and identification of Fusarium

3) Source of material for isolation

Equipment used was sterilized and growth media was prepared as described earlier. Leaf tissue from some randomly selected tolerant and susceptible progenies were examined with light microscopeFusarium isolates were identified by streaking sample portions on Peptone-pentachloronitrobenzene (PPA) a selective medium for isolation of Fusarium sp. and the other fungi, sub-cultured in potato dextrose agar (PDA). Single spores were plated and incubated on water agar for a day; in complete medium for seven days and on carnation leaf agar for 2 weeks. Pure fungal cultures raised were identified based on colony morphology and microscopic examination of their spores [26] .

All microscopic examination of fungal isolates was done by teasing a small portion of the material with a sterilized needle on a slide using lactophenol and covering with a cover slip before mounting on a microscope. Sub-culturing was done by cutting a 2 mm² portion of growing mycelium using a sterile needle and placing it centrally on a fresh plate containing PDA. All magnifications were done on X100 and or X400 depending on clarity of the micrographs.

Colony morphology, growth rates and presence of pigments was identified on PDA alongside microconidia (shape, size, number of septa, shape of basal and apical cells, presence of chlamydiospores, conodiogenous cells (monophylides and polyphylides) and spore type. Description of microconidia was done with the use of the mycological dictionary of Kirk et al. [27] , while Rayners mycological chart [28] and Hawsksworthet al. [29] terminologies were used in describing colony colours and nature of their edges, zonation and texture of aerial mycelium.

2.6. Data Analysis

Data on disease indices, number of bunches and the average bunch weight, were subjected to a two-way analysis of variance, followed by Fischer’s least significant difference test (LSD) for mean separation. A correlation analysis [30] was computed between disease incidence and disease severity of the susceptible progenies. Identification of fusarium was based on descriptive statistics.

3. Results

3.1. Wilt Incidence

The incidence of wilt in the three trials is given in Figures 2(a)-(c) as percentages of affected palms for each progeny. Trees which died as a result of the disease are taken into consideration.

The incidence of vascular wilt ranged from 3% to 45%, 1% to 8% and 1% to 39% in trials 2001/1, 2001/2 and 2001/3, respectively. The highest percentage of infected palms (45%) was recorded in progeny 676 ( Figure 2(a) ). On the other hand, only 1% of the palms of progenies 693, 689, 698, 710 and 694 showed external symptoms. No progeny had zero-rated incidence.

3.2. Disease Severity Rating (DSR)

Disease severity ratings (on scale of 1-5) ranged from 0.9 for progeny 686 to 4.55 for progeny 676 ( Table 2 ) with highest for progeny 676 (4.5) and the lowest with 0.9 for progeny 686.

Figure 2

(a)--(b)--(c)--Figure 2. (a) Incidence of Fusarium wilt in trial 2001/1. *Differs significantly from control at 5% level of probability, LSD0.05 = 20; **Differs significantly from control at 1% level of probability, LSD0.01 = 27. (b) Incidence of Fusarium wilt in trial 2001/2. *Differs significantly from control at 5% level of probability, LSD0.05 = 3.5; **Differs significantly from control at 1% level of probability, LSD0.01 = 4.8. (c) Incidence of Fusarium wilt in trial 2001/3. *Differs significantly from control at 5% level of probability, LSD0.05 = 17.8; **Differs significantly from control at 1% level of probability, LSD0.01 = 24.1.

Figure 2

(a)--(b)--(c)--Figure 2. (a) Incidence of Fusarium wilt in trial 2001/1. *Differs significantly from control at 5% level of probability, LSD0.05 = 20; **Differs significantly from control at 1% level of probability, LSD0.01 = 27. (b) Incidence of Fusarium wilt in trial 2001/2. *Differs significantly from control at 5% level of probability, LSD0.05 = 3.5; **Differs significantly from control at 1% level of probability, LSD0.01 = 4.8. (c) Incidence of Fusarium wilt in trial 2001/3. *Differs significantly from control at 5% level of probability, LSD0.05 = 17.8; **Differs significantly from control at 1% level of probability, LSD0.01 = 24.1.

Figure 2

(a)--(b)--(c)--Figure 2. (a) Incidence of Fusarium wilt in trial 2001/1. *Differs significantly from control at 5% level of probability, LSD0.05 = 20; **Differs significantly from control at 1% level of probability, LSD0.01 = 27. (b) Incidence of Fusarium wilt in trial 2001/2. *Differs significantly from control at 5% level of probability, LSD0.05 = 3.5; **Differs significantly from control at 1% level of probability, LSD0.01 = 4.8. (c) Incidence of Fusarium wilt in trial 2001/3. *Differs significantly from control at 5% level of probability, LSD0.05 = 17.8; **Differs significantly from control at 1% level of probability, LSD0.01 = 24.1.

Table 2

Table 2. Mean values of disease severity rating (on a scale of 1-5) for selected progenies in trial 91/1.

Progeny Code	Scale*					Disease severity Rating (DSR)	Disease Incidence (%)
	1	2	3	4	5
676	0	0	0	10	10	4.5	45
677	0	0	1	16	3	4.1	40
673	4	2	0	8	6	3.5	37
678	6	3	0	10	1	2.9	30
681	9	0	0	6	5	2.9	29
682	0	0	0	2	18	2.5	27
672	12	3	1	3	1	1.9	17
675	12	3	2	2	1	1.8	16
686	19	0	0	0	1	0.9	9
680	9	0	0	10	1	2.7	2.7

*The scale (1-5) is interpreted as follows: 1 = slight necrosis/chlorosis on one or two leaf tips, 2 = necrosis over one-quarter of palm leaves, 3 = severe necrosis/chlorosis over one-half of palm leaves and shortening of youngest leaves, 4 = severe necrosis/chlorosis over three-quarter of the plant, extensive leaf desiccation and stunting, 5 = plant death.

The validity of the two disease assessment methods (% infection and DSR), compared by correlation analysis showed significant positive correlation (r = 0.89).

3.3. Disease Index (I)

Disease index was used as an estimate wilt infection per progeny. The values of the indices obtained for the different progeny categories are presented in Table 3 .

Wilt indices ranged from 13 (progeny 710 and 694) to 495 (progeny 705). Based on the wilt index values obtained, the progenies were classified in relation to each other and in order of increasing susceptibility to wilt. Of the 45 progenies evaluated, 27 appeared tolerant (I < 100), while 18 were susceptible (I >100). Out of the 27 tolerant, 4 were significantly tolerant (I < 20) while 5 out of the 18 susceptible were significantly susceptible (I > 185).

In Table 4 , each parent was classified according to its combining ability, that is, its capacity to transmit to its progeny either a certain tolerance (Ig < 100) or a susceptibility which is generally appreciable (I > 100).

Reactions of the progenies to Fusarium wilt ranged in severity from no wilt symptom to death ( Table 5 ) Affected palms showed growth retardation ( Plate 1 ). Wilting of leaf margins, a paler green colour (chlorosis).

Plate 1 . Yellowing of leaves (chlorosis) in a susceptile progeny (714) is a characteristic sign of Fusarium Wilt. In some palms, browning of leaves was observed ( Plate 1 ). Browning of leaves caused by leaflet death in susceptible progeny.

Table 3

Table 3. Classification of oil palm progenies in increasing order of susceptibility to wilt.

Progeny Codes	Parents	Indices	Progeny Category
710	12/0516T × 12/12630T	13	Significantly Tolerant
694	13/2548D × 12/12640P	13
683	52/1340D × 13/2068D	16
679	13/0837T × 52/1340D	16
685	13/2068D × 12/12440P	22	Tolerant
693	52/1424T × 12/1402D	23
698	13/2959T × 12/0719D	23
689	13/2959T × 52/1239D	23
685	13/2068D × 12/12440P	25
680	13/0837T × 13/2068T	27
674	52/1340D × 13/0837T	27
684	13/2548D × 12/12640T	38
707	52/5334D × 12/10516T	38
706	13/1572T × 12/12539T	38
685	13/2068D × 12/12440P	45
686	52/1340D × 12/12640P	45
686	52/1340D × 12/12640P	49
709	12/12539D × 13/1302T	51
713	13/1302T × 52/11505T	51
703	13/3021D × 52/5334D	51
699	13/2548D × 12/1402D	68
708	13/3021D × 12/10516T	76
702	52/1533D × 12/12539D	76
675	12/1514T × 52/1340D	87
701	12/0719D × 12/12440P	89
696	13/2548D × 12/1402D	91
672	52/1340D × 13/2068D	92
711	12/2630T × 13/3021D	102	Susceptible
692	13/3217T × 52/0424T	114
700	13/3217T × 52/0635T	114
704	13/2065T × 13/3021D	127
691	52/2601T × 12/1239D	136
695	12/1402D × 13/3217T	136
682	52/1514T × 53/0230T	146
681	52/0230T × 13/2068T	157
690	12/3217T × 13/2548D	159
694	12/0719D × 52/2608T	159	Susceptible
678	12/1514T × 13/0837T	162
684	13/2548D × 12/12649P	181
697	52/0635T × 13/2548D	181
673	13/0837T × 12/1514T	200	Significantly Susceptible
677	52/0230T × 52/1340D	217
676	52/0230T × 12/1514T	444
712	12/12539D × 52/11505T	454
705	12/0719D × 52/6117T	495

Table 4

Table 4. Effects of fusarium wilt on aerial parameters of growth on tolerant oil palm progenies.

Progeny Code	No. of Fronds	Frond Length (m)	Palm Height (m)	Leaf Area (m2)	No. of Leaflets per Frond
693	30**	6.20	3.65	2.51**	214**
699	24**	5.40	5.10	10.37	348
688	32**	6.40	4.50	13.70	368
685	30**	3.95	3.15	12.60	274**
707	40	5.77	4.10	11.14	360
706	48	5.80	3.90	12.49	374
685	48	6.00	3.50	10.94	362
694	48	5.50	5.80	10.37	370
710	48	5.59	4.60	9.78	400
LSD0.05	11	3.10	2.60	4.10	58
LSD0.01	14	3.90	3.20	4.90	78
CV (%)	25.2	12.9	19.9	30.90	17.2

*Significantly different from control P = 0.05; **Significantly different from control at P = 0.001.

Figure 3

Plate 1. Oil palm plant showing symptoms of fusarium wilt. Table 5. Effects of Fusarium wilt on aerial parameters of growth on susceptible oil palm progenies. Progeny Code No. of Fronds Frond Length (m) Palm Height (m) Leaf Area (m 2 ) No. of Leaflets per Frond 676 28** 4.44* 2.90* 1.39* 310 677 28** 4.43** 2.80* 2.01* 278** 673 48 5.7 4.7 4.08 340 682 32 4.4 2.66** 4.08 290* 681 30 4.92 3.10 2.28 290* 678 32 5.29 3.35 5.31 357 705 40 5.65 3.3 7.68 320 712 32 4.59* 2.25** 2.07 299 685 (Control) 40 5.67 3.90 7.05 328 675 38 7.12 3.16 6.39 324 679 48 4.00* 4.50 5.36 312 LSD (0.05) 10 1.02 0.9 5.2 30 LSD (0.01) 12 1.8 1.2 8.3 38 CV (%) 20.3 17.5 24.8 50.7 9.0 The effect of disease on cell elongation (size) was more severe in diseased palms than in the tolerant progenies. In diseased palms, epidermal cell length and width were reduced by 12.7% and 13% respectively from the control.The mean palm height and frond length of the tolerant progenies ( Table 6 ) were not significantly different from the control palms. Table 6. Effect of Fusarium wilt on fruit yield of susceptible and tolerant oil palm progenies (trial 2001/1). Progeny Code Progeny Class Mean Bunch No. Mean Bunch Weight (kg FFB/progeny) % Yield Deviation from Control 683 Significant Tolerant 121 1681.5 +12.9 679 100 1596.9 +9.2 685 Tolerant Control 118 1462.8 0 680 Tolerant 95 1571.1 +7.4 674 101 1699.5 +16.2 684 113 1346.4 −7.9 686 154** 1748.9 +19.6 675 134 1803.7 +23.3 672 105 1366.8 −6.6 682 Susceptible 69** 619.4** −57.5 681 131 1233.3 −15.7 678 60** 835.6** −42.9 673 Significantly Susceptible 85* 1272.5** −13.0 677 117 1119.6* −23.5 676 73** 638.2** −56.4 LSD 0.05 27 342.3 LSD 0.01 38 CV (%) 6.2 *Significantly different from control P = 0.05 - 57.5; **Significantly different from control at P = 0.001.3.4. Effect of Fusarium Wilt on Fruit YieldFruit yield, expressed as a total weight of fresh fruit bunches (FFB) further discriminated between the relative impacts of wilt infection on the susceptible and tolerant progenies. In trial 2001/1, fruit yield was generally lower on the wilt-susceptible progenies compared to the tolerant ones ( Table 7 ). The mean yield reduction in susceptible progenies was 34.8% while in tolerant progenies, fruit yield was increased by 9.3%, when compared to tolerant control (685). The fruit yield of six tolerant progenies (683, 679, 680, 674, 686 and 675) in trial 2001/1 was higher than that of the tolerant control ( Table 7 ).

Table 5

Table 7. Impact of Fusarium wilt on fruit yield of susceptible and tolerant oil palm progenies (trial 91/2).

Progeny Code	Progeny Class	Mean Bunch No.	Mean Bunch Weight (kgFFB/progeny)	% Yield Deviation from Control
694	Significantly tolerant	119	1505.9	+8.3
685	Control	120	1381.3	0
693	Tolerant	134	1331.5	−3.6
698		113	1342.5	−2.8
689		73**	1041.8	−24.6
686		152**	1216.3	−11.9
699		107	1401.6	+1.5
696		134	1400.5	+1.4
692	Susceptible	98	1203.3	−12.9
700		75**	983.8*	−28.8
691		97	1240.8	−10.2
695		120	1381.3	0
690		73**	1058.9	−23.3
684		114	1570.1	+12.0
697		110	1493.7	+7.5
LSD0.05		28	348.9
LSD0.01		39	484.3
CV (%)		21.2	13.5

*Significantly different from control P = 0.05 - 57.5; **Significantly different from control at P = 0.001.

In trial 2001/2, the average yield reductions in the tolerant and susceptible progenies were 31.7% and 55.7%, respectively, when compared to the tolerant control (685). The fruit yield (weight of fresh fruit bunches) of three tolerant progenies (696, 699, 694) and 2 susceptible progenies (684 and 697) was higher than that of the tolerant control ( Table 8 ).

Table 6

Table 8. Impact of Fusarium wilt on fruit yield of susceptible and tolerant oil palm progenies (trial 2001/3).

Progeny code	Progeny Class	Mean Bunch No.	Mean Bunch Weight	% Yield Deviation from Control
710	Significantly tolerant	92	1200.5	−1.6
685	Control	106	1219.5	0
707	Tolerant	85	1373.3	+12.6
706		134	1555.6	+27.6
709		168**	1640.6*	+34.5
713		90	1270.8	+4.2
703		88	1709.5*	+40.2
708		87	1553.2	+27.4
702		137	1720.6*	+41.1
701		104	1501	+23.1
711	Susceptible	178**	856.5	−29.8
704		92	1393.8	+24.8
694		143**	1522.5	+24.8
712	Significantly susceptible	159**	1603.1	+31.5
705		145*	1410.2	+15.6
LSD0.05		34	401.9
LSD0.01		48	561.7
CV (%)		27.2	15.9

*Significantly different from control P = 0.05 - 57.5; **Significantly different from control at P = 0.001.

In trial 2001/3 the average yield increase in tolerant and susceptible progenies was 23.2% and 56.4%, respectively, when compared to the tolerant control (685). A total of 8 tolerant, high-yielding progenies (709, 703, 702, 707, 706, 713, 708 and 701) and 4 susceptible, high-yielding progenies (704, 694, 712 and 705) were identified ( Table 8 ).

Results from the variance analysis showed that the fruit yield (average weight of fresh fruit bunches) of three tolerant progenies (709, 703 and 702) was significantly higher than that of the tolerant control ( Table 8 ). These tolerant, high-yielding progenies; 709, 703 and 702 were derived from the cross: 12/12539D.

3.5. Isolation and Identification of Fusarium

From the colony characteristics on Potato dextrose agar, Fusarium isolate exhibited fast growth, producing abundant uniform mycelia and pale brown pigment. On CLA, it had abundant macroconidia that were medium in length, falcate, thin with characteristic 3 septa. The apical cell was hook shaped. Chlamydospores were abundant on the hyphae and microconidia were non-septate, oval in shape and formed on mono phialides ( Plate 2 ).

Detection of a range of disease-tolerant planting materials makes it possible to replace old plantings and establish new oil palm fields that will be high-yielding and disease-resistant.

References

1. Supriyono, R.A. (2018) Akuntansi Keperilakuan. Gadjah Mada University Press.

2. Ayompe, L.M., Schaafsma, M. and Egoh, B.N. (2021) Towards Sustainable Palm Oil Production: The Positive and Negative Impacts on Ecosystem Services and Human Wellbeing. Journal of Cleaner Production, 278, Article 123914. >https://doi.org/10.1016/j.jclepro.2020.123914

3. Ayelegun, T. and Ajewole, P. (2018) Effects of Length of Fermentation and Storage Media on Chemical Properties of Palm Oil. Biotechnology Journal International, 20, 1-7. >https://doi.org/10.9734/bji/2017/37393

4. Jacquenard, J.C. (1988) The Oil Palm. The Tropical Agriculturist/CTA. Gembloux Agricultural Press.

5. Nesaretnam, K. (2017) Palm Oil and Its Importance from Food Safety and Nutrition Perspective. Journal of Food Microbiology, 2, 4-11.

6. Ohimain, E.I., Daokoru-Olukole, C., Izah, S.C. and Alaka, E.E. (2012) Assessment of the Quality of Crude Palm Oil Produced by Smallholder Processors in Rivers State, Nigeria. Nigerian Journal of Agriculture, Food and Environment, 8, 28-34.

7. Ng, N. (2013) Some Quality Parameters of Crude Palm Oil from Major Markets of Douala, Cameroon. African Journal of Food Science, 7, 473-478. >https://doi.org/10.5897/ajfs2013.1014

8. Owoyele, B.V. and Owolabi, G.O. (2014) Traditional Oil Palm (Elaeis guineensis Jacq.) and Its Medicinal Uses: A Review. CellMed, 4, 16. >https://doi.org/10.5667/tang.2014.0004

9. Muhamad, N.A., Mustapha, N., Baharin, M.F., et al. (2018) Impact of Palm Oil versus Other Oils on Weight Changes: A Systematic Review. Food and Nutrition Sciences, 9, 915-936.

10. Kinge, T. (2019) Cultural Variability of Fusarium oxysporum f. sp. Elaeidis Isolates from Oil Palm in South Western Cameroon and Sensitivity to Four Plant Extracts. Plant Pathology&Quarantine, 9, 116-127. >https://doi.org/10.5943/ppq/9/1/10

11. Turner, P.D. and Gillbanks, R.A. (2003) Oil Palm Cultivation and Management. The Incorporated Society of Planters.

12. Colhoun, J (1981) Vascular Wilt Disease of Oil Palms. In: Nelson, P.E., Tousan, T.A. and Cook, R.J., Eds., Fusarium; Disease, Biology and Taxonomy, Pennsylvania State University Press, 21-28.

13. Nazies, M., Borakabah, S.S. and Loong, S.G. (2000) Potential of High Density Oil Alm Planting in Disease Environments. The Incoporated Society of Planters.

14. Oguntade, T., Becke, H.I., et al. (2021) Evaluation of Bacterial and Fungal Diseases of the Oil Palm (Elaeis guineensis Jacq) in Pamol Plantations, Ndian Division, Southwest Region, Cameroon. International Journal of Current Microbiology and Applied Sciences, 10, 200-215. >https://doi.org/10.20546/ijcmas.2021.1007.022

15. Pushparajah, E. (2000) Plantation Tree Crops in the New Millennium. The Way Ahead. The Incorporated Society of Planters, 217-225.

16. John Martin, J.J., Yarra, R., Wei, L. and Cao, H. (2022) Oil Palm Breeding in the Modern Era: Challenges and Opportunities. Plants, 11, Article 1395.

17. Renard, J.-L. and Quillec, G. (1983) Fusariose et replantation. Elements à prendre en consideration pour les replantations de palmier à huile en zone fusariée en Afrique de l’Ouest—Oléagineux, 38, 7. Conseil de I’IRHO, 235, 421-427.

18. de Franqueville, H. (1991) Former Savannah or Former Forest. Effect of Pathogen Isolate on the Performance of Oil Palm Families with Respect to Fusariu Wilt. Oleagineux, 46, 179-186.

19. Renard, J.L., Noiret, J.M. and Meuner, J. (1980) Sources and Ranges of Resistance to Fusarium wilt in the Oil Palms Elaeis guinensis and Elaeisis melanococca. Oleagineux, 35, 387-393.

20. Kamga, P.H. and Chaillard, F.C. (1987) Agronomical Research and the Development of Oil Palm Cultivation in Cameroon. Oleagineux, 42, 307-315.

21. Kimengsi, J. and Lambi, C. (2015) Pamol Plantations Plc: Prelude to a Looming Population Problem in Ekondo-Titi Sub-Division, South West Region of Cameroon. Journal of Sustainable Development in Africa, 17, 79-95.

22. BUCREP (2010) Rapport final 3ème recensement général de la population et de l’habitat au Cameroun. Répartition de la population résidant dans la province du Littoral par Département et par Arrondissement/District. Yaoundé, Cameroun, 45-47.

23. Flood, J., Cooper, R.M. and Lees, P.E. (1989) An Investigation of Pathogenicity of Four Isolates of fusarium Oxysporum from South America, Africa and Malaysia to Clonal Oil Palm. Journal of Phytopathology, 124, 80-88. >https://doi.org/10.1111/j.1439-0434.1989.tb04898.x

24. Renard, J.I., de franqueville, H., Diabate, S. and Ouvrier, M. (1993) Study on the Impact of Fusarium Wilt on FFB Production in Oil Palm. Oliagineux, 48, 495-503.

25. Corley, R.H.V. (2009) How Much Palm Oil Do We Need? Environmental Science&Policy, 12, 134-139. >https://doi.org/10.1016/j.envsci.2008.10.011

26. Leslie, J.F. and Summerell, B. (2013) An Overview of Fusarium. In: Brown, D.W. and Proctor, R.H., Eds., Fusarium Genomics, Molecular and Cell Biology, Caister Academic Press, 1-9.

27. Kirk, P.M., Cannon, P.F., Minter, D.W. and Stalpers, J.A. (2008) Dictionary of the Fungi. 10th Edition, CAB International. >http://bookshop.cabi.org/default.aspx

28. Rayner, R. (1970) Mycological Colour Chart. Commonwealth Mycological Institute and British Mycological Society.

29. Hawksworth, D.L., Kirk, P.M., Sutton, B.C. and Pegler, D.M. (1995) Ainsworth&Bisby’s Dictionary of the Fungi. 8th Edition, CAB International.

30. Gomez, K.A. and Gomez, A. (1984) Statistical Procedure for Agricultural Research—Hand Book. Wiley.

31. Meunier, F.J., Pascal, M. and Loubens, G. (1979) Comparaison de méthodes squelettochronologiques et considérations fonctionnelles sur le tissu osseux acellulaire d’un Osteichthyen du Lagon Néo-Calédonien. Aquaculture, 17, 137-157.

32. Toyoda, H., Hosoi, Y., Yamamoto, A., Nishiguchi, T., Maeda, K., Takebayashi, T., et al. (1991) Transformation of Melon (Cucumis melo L.) with Agrobacterium Rhizogenes. Plant Tissue Culture Letters, 8, 21-27. >https://doi.org/10.5511/plantbiotechnology1984.8.21

33. Mepsted, R., Flood, J. and Cooper, R.M. (1995) Fusarium Wilt of Oil Palm I. Possible Causes of Stunting. Physiological and Molecular Plant Pathology, 46, 361-372. >https://doi.org/10.1006/pmpp.1995.1028