1.Introduction

Potatoes (Solanum tuberosum L.) are of great economic and social importance both nationally and worldwide. The potato production cycle is mainly vegetative, with the tubers produced serving as an organ of asexual reproduction, the food part of the plant and a raw material for industrial processing [1]. In recent years, its worldwide production has risen from 328,616,920 tons in 2010 of 18,167,194 hectares to 370,436,581 on 17,340,986 ha in 2019 [2], making it the fourth most important crop after maize, wheat and rice. In Cameroon, potato cultivation has been introduced in certain agro-ecological zones since the 19th century and it occupies a very privileged place among marketed tubers. In 2019, 363,556 tons of potatoes were produced in an area of 21, 471 ha in nine out of ten Cameroonian regions [3]. Therefore, importance of potato's to the national economy, total production remains below the optimal potential. Several factors contribute to yield losses, such as the use of local varieties with low production potential, the unavailability of quality tuber seeds, pest and disease attacks. Among parasitic attacks, late blight is the most destructive and dreaded disease by potato growers [4]. It is caused by the Oomycete Phytophthora infestans (Mont.) [5]. This Oomycete is able to attack all organs of an infected plant. Yield losses caused by this disease can reach 100% in less than three weeks. Potato crops can be completely destroyed when conditions are conducive to the pathogen's development [6]. Chemical control, with the use of contact or systemic fungicides, remains the main measure for controlling potato late blight [4]. However, the management of these diseases with these fungicides is generally limited due to the development of resistance by populations of the pathogen or vector agents [7]. The reduced efficacy of metalaxyl and maneb against late blight, has been demonstrated in Cameroon [8, 9]. It is therefore necessary to intensify genetic control, in which many programs are based on the introduction of resistance genes [10], with the aim of selecting varieties with good agronomic value and resistance to pests and diseases. These programs are based on the introduction of a specific, single-gene resistance [11]. Similar genes have also been identified in other species of Solanum tuberosum, such as S. bulbocstanum [12, 13], S. berthaultii [14], S. phureja [15] or S. michoacanum [16].

Indeed, plants naturally develop resistance to biotic and abiotic stresses by activating preformed defenses and induced mechanisms. The triggering of the hypersensitive response (HR) of host plants following pathogen attack leads to the activation of induced mechanisms that are associated with local changes at the site of infection [17]. The hypersensitive response is one of the most effective forms of plant defense, causing an accumulation of antimicrobial compounds such as phenolics and phytoalexins, and an increase in the activity of peroxidases and polyphenol oxidase enzymes involved in defense responses [18, 19-21]. The hypothesis tested in this work is that the so-called improved and local varieties of potato grown in Cameroon possess little-known characteristics and may respond differently to infection by P. infestans in the field through the natural activation of defense mechanisms.  The aim of this study was to determine the natural response of potato varieties to P. infestans infection.  

2.   Materials and methods

2.1. Study site

The experiment was carried out in fields in the locality of Babadjou (623307 N and 628303 E). This locality belongs to agro-ecological zone 3, known as the Western Highlands zone of Cameroon. Rainfall is monomodal, ranging from 1,700 to 2,000 mm/year. The soil is ferralitic hydromorphic [22]. The research was conducted during the rainy season (between March and June) in 2023.

2.2.  Experimental design and culture condition

A Fisher completely randomized Block Design (CRBD) with three replicates was used to screen potatovarieties. Each block consisted of 12 experimental units delimited by a distance of 1 m and 2 m between blocks. Planting was carried out manually, with an equivalent tuber seeding rate of 1.2 t/ha and an average density of 50,000 plants per hectare. Plant spacing was 60 cm x 30 cm, and planting depth 7 to 10 cm. A mixture of fertilizers (urea 130 kg/ha, triple superphosphate 400 kg/ha and potassium sulphate 200 kg/ha) was applied to the soil before sowing to restore fertility [23]. Manual weeding was carried out every two weeks, starting 21 days after sowing (DAS). No phytosanitary treatments were applied, in order to encourage the natural infection of the plots by disease and to be able to judge the behavior of the varieties during vegetation. The size of the experimental plot was 164 x 10 m.

2.3. Assessment of the agronomic parameters

Agronomic parameters including stem collar diameter, plant height, and number of leaves were evaluated at 3, 6 and 9 weeks after sowing (WAS). Stem collar diameter was determined using a caliper at 5 cm above ground level; height was determined using a meter, and leaves were determined for each variety by exhaustive counting. The parameters were measured for six plants per plots. Also, the tuber emergence rate was evaluated at 2, 3 and 4 days after sowing (DAS) and the percentage of tuber emergence was determined according to the formula:

TEr (%) = NTEr/NTS [4].

TEr = Tubers emerged (%); NTEr  = Number of tubers emerged; NTS = Number of tubers sown.

2.4.         Evaluation of epidemiological parameters

In the vegetation phase, the evaluation of plant infection by disease focused on its incidence and severity. Disease incidence or expansion rate is the frequency with which the disease appears on plants in a plot; it will be determined at 6; 8; 9 weeks after sowing (WAS) and expressed as a percentage according to the formula:

I (%) = n/N x 100 [24].

I (%) = Disease incidence; n = Number of infected plants in the plot; N = Total number of plants in the plot.

Disease severity or intensity of disease infection in the plants of each plot. It is estimated on the basis of the proportion occupied by characteristic disease symptoms in the aerial parts of the plants. It was also determined at 6; 8 and 9 WAS and then calculated as a percentage (%) according to the formula proposed by Tchoumakov and Zaharova [24]:

S (%) = ∑ (ab)/N x 100

S (%) = Severity of infection; a = Number of diseased plants; b = Degree of infection corresponding to diseased plants; N = Total number of diseased plants.

The degree of infection is graded according to the standard 0 to 4 scale [4]. Where 0 = [1 to 20 %]; 1 = [20-40 %]; 2= [40-60%]; 3 = [60-80 %]; 4 = [80-100 %]

2.5.    Biochemicals markers analysis

Tubers and leaves of the 12 potato varieties (4 months old) on which late blight was observed, were collected for determination of total phenols, proteins and certain antioxidant enzymes.

2.5.1.   Determination of content of total phenolic compound

Extraction and quantitative measurement of the total phenolic compounds were performed as described by Tene et al., [25]. Total phenolic compounds were extracted twice using 80% methanol. One gram of fresh potato leaves was ground in 3 mL of 80% methanol at 4˚C. After 5 min of agitation, the ground material was centrifuged at 10,000 g for 5 min at 4˚C. The supernatant was collected, and the pellet was re-suspended in 5 mL of 80% methanol followed by agitation for 5 min. After the second centrifugation at 4˚C, the supernatant was collected and mixed with the previously collected supernatant to constitute the phenolic extract. The concentration of phenolic compounds was determined spectrophotometrically at 725 nm according to the method of Singleton and Rossi [26], using the Folin-Ciocalteu reagent. Total phenolic content was expressed as mg equivalent of gallic acid per g of fresh weight.

2.5.2.   Determination of the content of total protein

To determine the total native protein content, extraction was performed as described by Tarafdar and Marschner [27] with some modifications. Potato leaves (1 g) and tubers (1 g) were ground with polyvinylpyrrolidone (PVP) under cold conditions. The sample material was mixed in 0.75 ml of Tris-maleate buffer (0.1 M) [0.5 M Tris-base, 0.3 M ascorbic acid, EDTA (0.1% w/v), Triton X-100 (0.1% v/v), LiCl (17% w/v) and pH 7.2].

The samples were incubated for 40 min at 4°C and then centrifuged at 4500 rpm (Thermo Fisher Scientific centrifuge) for 15 min at 4°C. The collected supernatant was used as the crude extract.

The proteins were quantified using the Bradford [28] method. One mL of Bradford reagent was added to each mL of extract. The absorbance was measured at 595 nm using a UV-VIS 1605 Shimadzu spectrophotometer. BSA was used as the standard. Total protein contents were expressed in mg eqBSA/g fresh weight.

2.5.3. Evaluation of enzymes activities

Polyphenoloxidase (PPO) activity was quantified in the total native protein extract as described by Van Kemmenn and Broumer [29] using catechol as a substrate. The enzyme activity was expressed as ΔA 330/min/g protein. POX activity in the total native protein extracts was determined according to the method described by Rodriguez and Sanchez [30].  The enzyme activity was expressed in ΔA 420/min/g protein. Phenylalanine ammonia-lyase (PAL) activity was assessed according to the method was described by Okey et al., [31] using phenylalanine as substrate. The enzyme activity was expressed as ΔA 290/min/g protein.

2.6.  Yield assessment

To assess tuber susceptibility to late blight, the harvest from each elementary plot was sorted and classified into three categories: yield in terms of the number of tubers and weight of infested tubers (tubers with one or more mildew spots); marketable yield (healthy tubers with a size greater than 28 mm); total yield (infested tubers + marketable tubers + waste) [4].

2.7.  Statistical analysis

Data were subjected to one-way analysis of variance (ANOVA) using R software version 4.0.1. The data tested followed a normal distribution (Shapiro-Wilk test; P ˃ 0.05) as did homogeneity of variance (Levene test; P ˃ 0.05). The multiple comparison of means in the case of growth and yield parameters were determined and the Tukey HSD test followed the analysis of variance when, significant differences (P ˂ 0.05) for any of the factors were detected. Means of biochemical parameters were grouped for comparison using the Scott and Knot [32] test. Principal component analysis (PCA) and clustering of each parameter were run for the effect of agronomic parameters, biochemical compounds in potato leaves and tubers.

3. Results

3.1. Tuber emergence rate

The results showed that the tuber emergence rate varied between the varieties (Table 1).  At 2 WAS, emergence rate was 23.5% for Moremeking variety and 77.5% for Manate blanc variety. At 4 WAS, the Moremeking variety had an emergence rate of 55.0% and the Manate blanc variety an emergence rate of 100% (Table 1). A significant difference was recorded at 2 WAS (F-value = 12.96; P < 0.001), 3 WAS (F-value = 72.68; P < 0.001) and 4 WAS (F-value= 10.91; P = 0.000129).

Table 1. Variation in emergence rate by variety

3.2. Stem diameter

Observations of the changes in stem diameter showed variation over time and variety (Table 2). A significant difference was observed at 3 WAS (F-value = 4.61; P < 0.001). At this time, the largest stem diameter was obtained by the Manate blanc variety (1.16 ± 0.11 cm) and the smallest by the Mogbing variety (0.26 ± 0.11 cm).  At 9 WAS (F-value = 24.80; P < 0.001), Dosa recorded the largest stem diameter (2.96 ± 0.49 cm), followed by Panamera (2.64 ± 0.33 cm).

Table 2. Variation in stem diameter by variety

3.3. Plant height

The evolution of plant height showed variety-dependent variation at 3 (F-value = 1.21; P ˃ 0.306), 6 (F-value= 4.53; P = 0.000108) and 9 (F-value= 3.99; P = 0.000376) WAS (Table 3). At 6 WAS, the highest plant height was obtained by the Pamela variety (13.0±1.22 cm) and the lowest by the Moremeking variety (4.6±1.52 cm). On the other hand, at 9 WAS, the Desiree variety (37.8±6.22 cm) recorded the highest height than the Wouzang variety (18.4±3.66 cm).

Table 3. Variation in plant height by variety

3.4. Number of leaves

The number of leaves increased over time and variety (Table 4). A significant difference between varieties were recorded for parameters. At 9 (F-value= 10.41; P ˂ 0.001) WAS, the Manate blanc variety produced the highest number of leaves (23.8±2.49 leaves), followed by Panamera (23.00±3.00 leaves), Pamela (14.4±3.3 leaves) and Bamso (14.8±2.17 leaves) varieties.

Table 4. Number of leaves by variety

3.5. Incidence of late blight

Observation of the evolution of disease incidence showed variation over time and according to variety (Fig. 1). Late blight incidence ranged from 7.60% to 90% at 9 WAS. During this period, Dosa, Manate violet and Cipira varieties had the lowest incidence (7.60, 9.67 and 13.42% respectively), while Panamera, Mogbing and Wouzang varieties had the highest (73, 80.20 and 90% respectively).

Figure 1. Incidence of potato late blight according to variety.

3.6. Severity of Potato late blight

The evolution of severity showed a variation over time and according to variety (Fig. 2). Significant differences were observed (P ˂ 0.05) for each period (3, 6 and 9WAS). At 9 WAS, the varieties Cipira, Mondiale, Dosa and Manate violet varieties showed the lowest severity (2, 7, 9 and 11% respectively), while the Banso, Moremeking and Wouzang varieties showed the highest severity (27, 23 and 11% respectively).

Figure 2. Severity of potato late blight according to variety.

3.7. Variation of biochemical parameters of potato varieties under late blight control

3.7.1. Variation of biochemical parameters in screened potato leaves

The screened potato varieties showed variability in the biochemical parameters assessed in their leaves (Table 5). With regard to phenols, the Bamso variety produced the lowest phenolic compound content (2.13 ± 0.32 µg/g FW) and the Manate violet variety the highest phenolic compound content (5.29 ± 1.52 µg/g FW). In terms of protein, Pamela (8.63 ± 0.18 µg/g FW), Panamera (7.75 ± 1.54 µg/g FW) and Mondiale (7.03 ± 1.36 µg/g FW) varieties had the highest levels. PAL enzyme activity was higher in Manate blanc variety (182.72 ± 59.87 ΔA 290/min/mg) than in Wouzang (182.46 ± 72.32 ΔA 290/min/mg) and Mogbing (182.72 ± 59.87 ΔA 290/min/mg) varieties. POX activity is high in Mondiale variety (1.85 ± 0.85 ΔA 420/min/mg) and PPO in Panamera variety (5.45±0.69 ΔA 330/min/mg).

Table 5. Variation of biochemical markers in screened potato leaves

3.7.2. Variation in biochemical parameters in screened potato tubers

In potato tubers, the production of biochemical markers varied among varieties (Table 6). Protein content was higher in Mondiale (5.03 ± 1.13 µg/g FW), Manate blanc (4.74 ± 0.97 µg/g FW) and Pamela (4.64 ± 1.46 µg/g FW) varieties than in Panamera (2.69 ± 0.60 µg/g FW) and Moremeking (2.79 ± 1.21 µg/g FW) varieties. PAL activity was higher in Mondiale (439.51 ± 81.59 ΔA 290/min/mg), Mogbing (335.80 ± 54.84 ΔA 290/min/mg) and Moremeking (311.11 ± 46.41 ΔA 290/min/mg) varieties than in all other varieties. In terms of PPO activity, the Panamera variety (3.44 ± 0.70 ΔA 330/min/mg) had a high PPO content compared with all the other varieties, which produced statistically the same PPO content.

Table 6. Variation of biochemical markers in screened potato tubers

3.8. Variation in yield by variety under late blight control

A significant difference (P ˂ 0.05) was observed between the yield parameters of the different varieties (Table 7). The highest number of apparently healthy tubers was obtained by the Dosa variety (27.67 ± 7.79 tubers), followed by the Manate Blanc variety (20.67 ± 4.93 tubers) compared with the Panamera variety (5.83 ± 1.47 tubers). The highest number of diseased tubers was also recorded in the Dosa and Manate Blanc varieties (4.00 ± 2.53; 3.17 ± 2.04 respectively). The highest commercial yield (42.00 ± 2.51 t/ha) was obtained in Cipira variety. The highest non-commercial yield was recorded for the Dosa variety (3.69 ± 1.53 t/ha). Total yields in tons per hectare were 42.09 ± 2.52 t/ha for Cipira and 10.46 ± 2.74 t/ha for Pamela variety. 

Table 7. Variation in yield by variety

3.9. Multivariate analysis

3.9.1. Principal component analysis

Principal Component Analysis (PCA) (Fig. 3) showed the closeness of potato varieties to growth parameters, biochemical parameters, disease incidence and severity, in potato leaves, tubers and yields. The visualized dispersion of the two main components (PC1 and PC2) explained 44.6 % of the total variation in the system and contained more information and graphically summarized genotypes performance about late blight infection. The varieties Bamso, Mogbing, Moremeking, Pamela, and Wouzang are closer to the incidence (Inc) and severity (Sev) of the disease with a trend away from the different biochemical markers of resistance assessed (Ph.L, Prot.L, PAL.L, POX.L, PPO.L, Ph.T, Prot.T, PAL.T, POX.T, PPO.T). On the other hand, the varieties Cipira, Desiree, Dosa, Manate blanc, Manate violet, Mondiale and Panamera are very close in terms of yield (NAHPT.P, NDPT.P, MY.ha, NMY.ha) and resistance markers.

Figure 3. Principal component analysis – biplot of evaluated parameters.

(LR: Lift Rate, DRC: Diameter at Root Collar , SH: Stem Height, NLP: Number of Leaves per Plant, Inc: Incidence, Sev: Severity, NAHPT.P: Number of apparently healthy potato tubers per Plant, NDPT.P: Number of Disease Potato Tubers per Plant, MY,ha : Marketable Yield in tons per hectare, NMY,ha : Non-Marketable Yield in tons per hectare, Ph,L : Total Phenol in leaves, Prot,L : Total Proteins in leaves, PAL,L : Phenylalanine ammonia-lyase in leaves, POX,L : Peroxidases in leaves, PPO,L : Polyphenol oxidases in leaves, Ph,T : Total phenols in Tuberbercules, Prot,T : Proteins in Tuberbercules, PAL,T: phenylalanine ammonia-lyase in Tuberbercules, POX,T: Peroxidases in Tuberbercules, PPO,T: Polyphenol oxidases in Tuberbercules).

3.9.2. Hierarchical clustering analysis of different parameters  

The classification of these varieties according to the different parameters studied using a cluster (5% dissimilarity) showed six groups (Fig. 4). The first group consists of a single variety (Wouzang), the second of Moremeking, Mogbing and Bamso, the third of Dosa and Manate blanc, the fourth of Panamera, the fifth of Cipira and Manate violet, and the sixth of Desiree, Mondiale and Pamela. Overall, this analysis revealed that Cipira and Manate violet are the most resistant varieties to late blight, while Wouzang, Moremeking, Mogbing and Bamso are the most susceptible.

Figure 4. Classification cluster of different varieties according to parameters.

4. Discussion

The emergence rates of potato tubers of the different varieties in the field were more or less high on all plots at 4 weeks after sowing (WAS). Moremeking and Pamela varieties had the lowest emergence rates (55% and 57% respectively), while the other varieties had emergence rates of over 80%. Significant variations of the same type were also observed by some researchers such as Giri et al., [33] who showed that the highest emergence rates were registered by the variety PRP 146871.20 followed by PRP 016567.6, CIP 303381.106, Desiree and the lowest emergence rate was found by local variety Jumli at 30 days after sowing. Observations of changes in collar diameter showed a variation over time in the different potato plant varieties. At 9 WAS, the Wouzang and Mogbing varieties had the smallest diameters. In terms of plant height, the results showed that plant heights vary from 18.4 to 37.8 cm for the Wouzang and Desiree varieties respectively. Results for the average number of leaves for each variety showed that the Manate blanc variety followed by the Panamera variety had the highest number of leaves, while the Bamso and Pamela varieties had the lowest. The variability observed in plant growth is thought to result from genetic variation among the potato genotypes tested [34]. Many authors have shown that growth parameters vary according to potato genotype [35-38]. These varieties are genetically different in their growth mode, which effects the number of leaves per plant, stem height and collar diameter.

Berhanu and Tewodros [39] reported a highly significant effect of environment and cultivar on the number of leaves per plant and potato plant height in eastern Ethiopia. Also, Bandjade [40] reported substantial variability in plant height between potato genotypes in northern Ethiopia. These differences in heights, leaf numbers and neck diameters between varieties may also be due to plant material quality, seed tuber size, environmental variations, agronomic practices, plant spacing [37, 41]. Observation of the evolution of plot infection rates by the disease shows variation over time and according to variety.

Incidences of late blight ranged from 7.60% to 90% at 9 WAS. The Dosa variety, Manate violet followed by the Cipira variety showed the lowest incidences compared with the other varieties, with the highest rates in the Panamera, Mogbing and Wouzang varieties. Significant differences were observed between degree of disease infection (severity) for each observation period (3; 6 and 9 WAS). At 9 WAS, the varieties Cipira, Mondiale, Dosa and Manate violet showed the lowest severity, while the varieties Banso, Moremeking and Wouzang showed the highest severity. Glen-Karolczyk et al., [42] demonstrated that, the intensity of infectious diseases in potato tubers is the result of a number of coinfluencing factors: environmental; agro-technical and biotic interactions between organisms that colonize the tubers.  According to principal component analysis, the variation in disease severity is correlated with the variation in the expression of biochemical markers involved in plant defense against pathogens. A decrease in disease severity is associated with an increase in the synthesis of biochemical compounds involved in plant defenses.

The potato leaves and tubers screened showed variability in the production of biochemical compounds. In leaves, the Banso variety produced the lowest phenolic compound content and the Manate violet variety the highest phenolic compound content in both leaves and tubers. Indeed, phenolic compounds constitute a very important group of secondary metabolites involved in pathogen resistance. According to Lorenc-Kukula et al., [43], phenolic compounds are present in potato flowers, leaves and tubers, imparting antimicrobial properties. In terms of protein, the varieties Pamela, Panamera and Mondiale have the highest protein content in the leaves. In tubers, the protein content was higher in the Mondiale variety, than in the Panamera variety. The variation in protein production in leaves and tubers is thought to be due to the level of infection by the pathogen. The Banso, Moremeking and Wouzang varieties were the most susceptible to the disease. Many authors stipulate that these proteins are encoded and cannot be expressed when the plant is stressed by pathogen infection or elicitors [44, 45]. PR proteins can inhibit pathogen growth and/or spore germination and act as antimicrobial agents, hydrolases and proteinase inhibitors [46]. With regard to oxidative enzyme activity, phenylalanine ammonia-lyase (PAL) was very high in the leaves of the Manate blanc variety than in the Wouzang and Mogbing varieties. POX activity was high in Mondiale and PPO in Panamera. In potato tubers, PAL activity was high in the Mondiale variety and PPO activity was high in the Panamera variety. Ngadze et al., [47] showed high PAL, PPO and POD activity conferring resistance to soft rot in S. tuberosum. PAL enhances cinnamic acid production [48] which can induce the expression of defense-related genes. PPO confers disease resistance to plants by hydroxylating monophenols to ortho-diphenols, which are toxic to pathogens [49]. De Ascensao and Dubery [50] demonstrated that peroxidase (POX) is linked to the host plant's defense response and is involved in strengthening the plant cell wall. The production of PPO and POX in screened potato varieties can prevent chemical and biological attacks by reinforcing physical barriers or by counter-attacking a microorganism through the strong generation of free radicals [51].

In addition, several studies have shown that good plant health has a significant impact on production yield [52, 53]. This study showed that the number of apparently healthy tubers differed between the varieties. Dosa variety followed by the Manate Blanc variety had the highest number of tubers per plant. Habtamu et al., [54] showed that the number of tubers per plot depends mainly on the number of stems per plot, the total number of runners that tuberize. Total yields in tons per hectare varied according to the variety and the commercial yield was obtained from Cipira variety. The highest commercial yields were observed in the Cipira, Dosa and Manate violet varieties, while the lowest yields were observed in the Banso, Moremeking, Pamamera, Pamela and Wouzang varieties. The variation in total yield of potato genotypes at different locations may be due to the responses of genotypes and environmental factors. Glen-Karolczyk et al., [42] demonstrated that hydrothermal conditions prevailing during the growing season are the main determining factor in plant yield, in particular, root vegetables with a long growing season and high water demand. This suggestion is in line with other authors who have shown that yield differences between genotypes are attributed to both the inherent yield potential of genotypes and the growing environment, as well as to genotype x environment interactions [55]. Similarly, other researchers have also shown that marketable yield varies significantly with variety, location and genotype x environment interactions [56, 57]. Also, genotype variation in non-marketable yield may be due to the following factors adaptability, crop maturity and the inherent ability of potato genotypes to produce non-marketable tubers per plant [54]. The result of the non-marketable yield of potato varieties in the present work is consistent with the findings of Hammerschmidt and Kuc [58], who reported that the interaction effects of the growing environment and genotype significantly influence non-marketable tuber yield. Habtamu et al., [54] also reported similar significant differences between genotypes in phenological and growth characteristics, tuber yield, tuber physical characteristics and internal quality from the evaluation of 16 potato genotypes in eastern Ethiopia. Indeed, the expression of a given trait can be the result of interaction between genetic factors and the plant environment.

Principal component analysis and cluster carried out on all the agro-morphological variables of the potato lines showed that, out of the eight descriptors adopted, two proved to be the most discriminating according to Fisher statistic (F) values greater than 10: yield parameters and epidemiological parameters. The varieties Cipira, Desiree, Dosa, Manate blanc, Manate violet, Mondiale and Panamera are very similar in terms of yield and resistance markers. They are more resistant to late blight, while the Wouzang, Moremeking, Mogbing and Bamso varieties are the most susceptible. Infection of potato plants by the disease triggers the activation of natural defense mechanisms, which vary from variety to variety [59]. The triggering of this resistance by P. infestans infection reinforces the plant's innate defense mechanism [60].

5.   Conclusions

At the end of the study, it was found that the vegetative conditions and development of the lines differed in the field. Desire and Dosa were the variety that performed the best vegetative state. As for varietal behavior with regard to late blight, the expression of tolerance varied significantly between the different varieties tested. Manate and Cipira were the most tolerant to late blight, while Wouzang, Mogbing, Moremeking and Pamela were the most susceptible. With regard to yield there was considerable variability between the lines, for all yield parameters. Cipira varieties, with 42.09 t.ha^-1, were the most productive, while Pamela varieties were the least productive. This study revealed significant variability among released potato varieties in their tuber yield and resistance to late blight. This suggests a greater chance of using these genotypes to improve resistance, tuber yield and other important agronomic traits in the crossing program.

Authors’ contributions

Ousman abdraman collect data in field and write the first draft of manuscript, Sylvere Landry Lontsi Dida collect data, writing and editing, Alain Heu collect data in field and read, Patrice Zemko Ngatsi formal analysis and editing, Paul Martial Tayo Tene make lab experimentation and editing^,, Landry Thierry Voukeng Dongmo, Benoit Constant Likeng Li-Ngue, Joseph Martin Bell read and editing.

Acknowledgements

The authors are sincerely thankful to the IFDD for their funding and the Laboratory of Phytoprotection and Genetic Resources Valorization, Biotechnology Center, Faculty of Science of University of Yaounde I for biochemical assays.

Funding

This research received fund from the IFDD.

Availability of data and materials

All data will be made available on request according to the journal policy.

Conflicts of interest

The authors declare that they have no conflicts of interest.

References