Greener Journal of Agricultural Sciences

Vol. 10(2), pp. 95-102, 2020

ISSN: 2276-7770

Copyright ©2020, the copyright of this article is retained by the author(s)

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Effect of Stictococcus vayssierei Richard (Hemiptera: Stictococcidea) on growth and yield of cassava (Manihot esculenta Crantz)

 

 

Patrice Zemko Ngatsi1*, Bekolo Ndongo1, Désiré Anaba Manga1, Eric Biyo’a Ndongo1, Champlain Djieto-Lordon2

 

 

1Department of Plant Biology, Plant Pathology Laboratory, University of Yaoundé 1, Yaoundé, Cameroon

2 Department of Plant Animals, University of Yaoundé 1, Yaoundé, Cameroon

 

 

 

ARTICLE INFO

ABSTRACT

 

Article No.: 031020048

Type: Research

 

 

Cassava cultivation faces many constraints including various pathogens and pests. Among the pests of cassava, the African Root and Tuber Scale (ARTS) Stictococcus vayssierei (Hemiptera: Stictococcidea) is a sap-sucking insect that colonizes tubers and roots of cassava plants in humid Central Africa. Infestation by this pest affects plant physiology and severely reduces the productivity, causing 60 to100% yield losses in the field. The objective of this study is to evaluate the harmful effect of S. vayssierei on cassava yield in the field. The experiment was carried out using a completely randomized Fisher's blocs design with four replicate on six cassava varieties, four of which were improved and two local. During 12 months with a sampling interval of three months, the number of scale insects per plant, growth parameters, incidence and severity of the most important diseases, as well as yield were evaluated. As result, at 12 months after planting (MAP), the highest fresh shoot weight (2.69 ± 0.43 kg) as well as of fresh tuber yield (23.8 t ha-1) were obtained with the local variety Douma; at opposite, the Excel variety produces the lowest fresh shoot weight (1.69 ± 0.15 kg) and yield (14.1 t.ha-1). The average number of scale insects per plant (ARTS/P) was greater with the Excel variety (90.12 ARTS/P) and lowest on the 96/0023 variety (58.14 ARTS/P). In addition to ARTS infestation, two biotic constraints, namely cassava mosaic disease (CMD) and cassava anthracnose disease (CAD), appeared in the plots, with varying incidence and severity. Finally, it appeared that S. vayssierei through damage to cassava plants leads to a decrease in the productivity of cassava varieties, especially on improved varieties.

 

Accepted:  15/03/2020

Published: 22/06/2020

 

*Corresponding Author

Ngatsi PZ

E-mail: ngatsipatrice@ gmail.com

Phone: (237) 675974551

 

Keywords: Scale insect; Manihot esculenta; growth; yield

 

 

 

List of Abbreviations:

 

ARTS: African Root and Tuber Scale

MAP: months after planting

CMD: cassava mosaic disease

CAD: cassava anthracnose disease

ARTS/P: number of scale insects per plant

 


 

 

INTRODUCTION

 

The African Root and Tuber Scale (ARTS), Stictococcus vayssierei Richard, is one of the most harmful arthropod pests in cassava agro-systems in semi-humid forest regions in the Congo Basin (CNRCIP, 1989; Hanna et al., 2004). Probably because of its underground habitat, S. vayssierei is a cryptic polyphagous agricultural pest first reported in the early 1980 (Nonveiller, 1984; Dejean and Matile-Ferrero, 1996; Ambe et al., 1999; Ngeve, 2003; Tata Hangy et al., 2006). There are 16 plant species belonging to 13 families from which it draws sap from the roots to feed (Tindo et al., 2009).

Cassava (Manihot esculenta Crantz) is a shrub of the family Euphorbiaceae (Westphal, 1985). It is an important source of carbohydrates for more than 800 million humans across the African, American and Asian continents (Liu et al., 2011). Cassava is grown mainly for its starchy tuberous roots (20-40%), which represent an important part of industrial starch and daily food for many human and animal populations worldwide (Jose et al., 2008; Graziosi and Wyckhuys, 2017). However, its cultivation is constraint by the infestation of root scales in Central Africa. In case of severe infestations, heavy starvation of sap can lead to leaf drop, wilting, tip dieback, and eventually death of seedlings (Ngeve, 2003; Williams et al., 2010) reducing both biomass and yield, resulting in losses ranging from 60% to 100% in plantations and posing a major threat to cassava production in Central Africa (Ngeve, 2003; Hanna et al., 2004; Lema et al., 2004; Tata-Hangy et al., 2006). Yield reduction is often the result of damage caused during the vegetative phase of the plants. It injects toxic saliva into the plant tissue when removing its food resource; this saliva affects plant tissues and can sometimes transmit various pathogens including viruses and fungi in many economically important root and tuber plants (Richard, 1971; Mutsaers et al., 1981; Tindo et al., 2006). In addition, large sap collections can increase the plant's susceptibility to disease. Therefore, the objective of this work was to evaluate the harmful effect of S. vayssierei on cassava yield in the field.

 

 

MATERIALS AND METHODS

 

Plant material

 

The cassava cuttings used in the study belong to six varieties (Table 1). Four improved (TMS 96/0023 and TMS 92/0057) and (8034 and Excel) obtained from the International Institute of Tropical Agriculture and Institute of Agricultural Research for Development of Nkolbisson collections respectively and known as tolerant to cassava mosaic and two local varieties named Douma and Miboutou susceptible to cassava mosaic based on field observations and locally grown by the farmers.


 

 

Table 1. Characteristics of cassava varieties used in this study

Varieties

Root Color

Maturity (months)

Behaviour against diseases and pests

Yield (t ha-1)

Origin

TMS 96/0023

White

12

Resistance to : cassava mosaic, Anthracnose tolerance to green mite

18-27

IITA-Nkolbison

Excel

Brown

12

Resistance to : cassava mosaic, Anthracnose tolerance to green mite

25-30

IRAD-Ekona

TMS 92/0057

Red

12

Resistance to : cassava mosaic, Anthracnose tolerance to green mite

21-30

IITA-Nkolbison

8034

White

12

Resistance to : cassava mosaic, Anthracnose tolerance to green mite

18-30

IRAD-Ekona

Miboutou

White

12

Sensitive to mosaic

nd

Local

Douma

Red

12

Sensitive to mosaic

nd

Local

IITA: International Institute of Tropical Agriculture; IRAD: Institute of Agricultural Research for Development; nd: not determined

 

 


Experimental design and cultural practices

 

The trial was conducted in a 3 year old fallow land naturally infested by the scale insect in the locality of Akonolinga (N 03°48.136' and E 012°15.518', altitude 671 m) in the Central region of Cameroon from March 2018. The fallow vegetation was cut and burnt in places when dry. This locality belongs to the agro-ecological zone V known as the bimodal rainfall zone with rainfall ranging from 1500 to 2000 mm per year. The cuttings (about 30 cm) of the six varieties of cassava were planted obliquely by pushing 2/3 into the soil using a completely randomized Fisher block design with four repetitions. Each block consisted of six sub-plots measuring 3 m x 4 m each, 1 m apart. The sub-plots have 15 cuttings at 1 m x 0.8 m spacing (12,500 plants ha-1) (IITA, 2000). Weeding was carried out at 2, 3, 5 and 9 months after planting (MAP). No chemical pesticides or fertilizers were applied during the growth of the cassava plants.

 

Parameters measured

 

Evaluation of agronomic parameters

 

Agronomic parameters were assessed at 3, 6, 9 and 12 months after planting (MAP). Stem diameter was measured using a caliper on three labelled plants. Fresh shoot weight (aerial biomass of stems, leaves) and tuber weight were measured on three randomly uprooting plants and weighed using a 200 and 250 precision balance with double graduation trademark Pesola. Tuber weights were extrapolated in tons per hectare to estimate the fresh tuber yield of the six cassava varieties using the formula of Kamau et al. (2011).


 

Yield (t ha-1) = tuber weight (kg/m²) x 10 000 m2/ha x 1 t/1000 kg.

 


 

Evaluation of ARTS density

 

Cassava root scales were counted on three plants randomly sampled in the subplots by uprooting plants. All life stages (first-instar nymphs L1, second-instar nymphs L2, adults, dead individuals) of the scale were counted on cassava stem, mother cuttings, tuberous and feeder roots of cassava at 3, 6, 9 and 12 MAP according to Ambe et al., 1999 and Ndengo et al., 2016a. Subsequently, the level of infestation was determined (Table 2) by visual estimation with a ranking on a scale index (Tertuliano, 1993).


 

Table 2. Scale insect infestation index

Index

Number of scale insects per plant

Description

1

1-25

Very low infestation

2

26-50

Low infestation

3

51-75

Average infestation

4

76-100

Heavy infestation

5

˃100

Very heavy infestation

 

 


Diagnosis, evaluation of the incidence and severity of diseases identified in the field

 

By removing nutrients, ARTS injects toxic saliva into the plant tissue, which can weaken the plant's defense system and promote the development of diseases. The visual diagnosis method through observations, precise comparisons of symptoms and their evolution in time and space (Renard and Foucart, 2008) has made it possible to follow the evolution of diseases in the field. Epidemiological parameters, i.e. disease incidence and severity, were assessed on plants in the field.

 

Evaluation of the incidence of identified diseases

 

Disease incidence was estimated from the frequencies of occurrence on plants in the experimental units and was calculated by the formula proposed by Tchumakov and Zaharova (1990):

 

I (%) = (n / N) × 100

 

I: incidence of disease; n: number of diseased plants; N: total number of plants

 

Evaluation of the severity of diseases

 

Disease severity was assessed on cassava plants in the experimental units according to the Rwegasira and Rey (2012) visual rating scale of 1-5 where 1=0; 2=1-5%; 3=5-30%; 4=30-60% and 5=60-100%. Thus the severity during development was given by the formula of Tchoumakov & Zaharova (1990) which is expressed as follows:

 

S (%) = ∑ (a.b)/N

 

S (%): severity of the disease; ∑(a.b): sum of the multiplication of the number of diseased plants (a) by the corresponding degree of infection (b) given as a percentage; N: total number of diseased plants.

 

Statistical analyses

 

The data collected for the various parameters studied were subjected to a one-way analysis of variance (ANOVA) using R software version 3.5.1. The multiple comparison tests of Tukey means at the 5% threshold followed the ANOVA when significant differences (p ˂ 0.05) were detected. The data are represented as means ± standard deviation of a minimum of three replicates (n = 3).

 

 

RESULTS

 

Agronomic parameters

 

Data for agronomic parameters measured at 3, 6, 9 and 12 MAP show that there is no significant difference (P ˃ 0.05) between varieties in mean stem diameter (

Table 3). On the other hand, fresh shoot weight and number of tubers per plant are highly significant (P ˂ 0.001) between varieties. The local variety Douma 2.69±0.43 kg produces the highest fresh shoot weight than the improved variety Excel 1.69±0.15 kg. The highest number of tubers 6.08±0.43 tubers is produced by the local variety Douma. A significant effect (P ˂ 0.05) was recorded between varieties with regard to yield. The highest yield was observed with the local variety Douma (23.8 t ha-1) followed by the improved variety 96/0023 (21.8 t ha-1). The Excel variety has the lowest yield (14.1 t ha-1).

 

Table 3. Agronomic growth and yield parameters of cassava varieties grown under the influence of Stictococcus vayssierrei

Varieties

Stem diameter average (cm)

Fresh shoot average (kg)

Number of tubers average

Yield (t ha-1)

92/0057

2.45±0.36a

2.01±0.11bc

4.67±0.52b

18.7±4.5ab

96/0023

2.39±0.29a

2.19±0.38abc

4.50±0.55b

21.8±5.9ab

Excel

2.09±0.22a

1.69±0.15c

4.17±0.98b

14.1±2.8b

8034

2.38±0.35a

2.46±0.25ab

5.17±0.75ab

17.7±5.7ab

Douma

2.55±0.17a

2.69±0.43a

6.08±0.49a

23.8±2.9a

Miboutou

2.29±0.24a

2.30±0.30ab

5.00±0.63ab

20.5±3.7ab

Pr(>F)

0.138ns

˂0.001***

0.0006***

0.0139*

P: 0 '***' 0.001 '**' 0.01 '*' 0.05; ns: not significant. Means followed by the same letter in the columns are not significantly different in the Tukey test (P ˂ 0.05).

 

 


Variation in the number of scale insects on the cassava varieties tested.

 

The number of root scales (ARTS) on cassava varieties as a function of time is recorded in Table 4. It can be seen that varieties 96/0023, 92/0057 and 8034 have an average number of scale insects between 50 and 75. On the other hand, the local’s varieties Miboutou, Douma and Excel have an average number of scale insects between 75 and 100. A very highly significant difference (P ˂ 0.001) is observed at 3, 6, 9 and 12 MAP. Overall, the improved variety Excel (90.12 ARTS/P) has the highest average number of scale insects, followed by the local variety Douma (83.27 ARTS/P). The improved varieties 92/0057 (65.54 ARTS/P) and 96/0023 (58.14 ARTS/P) have the lowest average number of scale insects.


 

 

Table 4. Number of root scale insect on six cassava varieties

Varieties

3 MAP

6 MAP

9 MAP

12 MAP

Means±SD

92/0057

52.67±8.82cd

92.00±7.94bc

70.92±5.92cd

46.58±3.42c

65.54±2.34d

96/0023

47.50±3.49d

66.79±3.47e

68.13±4.28d

50.13±5.17c

58.14±1.93e

Excel

78.21±8.28a

113.67±7.63a

102.83±4.14a

65.75±4.58ab

90.12±3.84a

8034

66.17±7.19ab

82.25±9.42cd

74.39±6.70cd

59.56±4.70b

70.59±1.88cd

Douma

72.83±6.21ab

104.54±9.38ab

87.21±4.76b

68.49±2.91a

83.27±3.03b

Miboutou

62.33±6.46bc

73.71±7.36de

78.75±5.18bc

70.63±5.57a

71.36±3.96c

Pr(>F)

˂0.001***

˂0.001***

˂0.001***

˂0.001***

˂0.001***

P: 0 '***' 0.001 '**' 0.01 '*' 0.05; ns: not significant. Means followed by the same letter in the columns are not significantly different in the Tukey test (P ˂ 0.05).

 


 

Diseases observed during the experiment

 

Throughout the experiment, two diseases were recorded with varying incidence and severity following root scale infestation. These include cassava mosaic disease (CMD) observed only on local varieties and cassava anthracnose disease (CAD) causal agent (Colletotrichum gloeosporioides f. sp. manihotis) observed on the six cassava varieties tested.

 

Incidence and severity of cassava anthracnose

 

Observations of the evolution of cassava anthracnose during the experiment on a site naturally infested with ARTS allowed measuring the incidence and severity of the disease (Fig. 1).

The variation of these two parameters as a function of time shows that they differ from one variety to another with very highly significant differences (P ˂ 0.001). The incidence of anthracnose increases up to 6 MAP and no longer varies up to 12 MAP. At 3 MAP, the lowest incidence of 35.24% is observed on variety 96/0023 than on variety 92/0057 (68.56%). As regards severity at this period, the variety Miboutou recorded the highest value (9.14%). At 6 and 12 MAP, all cassava plants are attacked by the disease with an incidence of 100%. However, the severity during these periods varies from one variety to another. At 6 MAP, the Excel variety had the lowest severity (11.14%). At 9 and 12 MAP, variety 96/0023 recorded the lowest severity (19.28 and 29.38% respectively) than variety Miboutou (49.87 and 62.37% respectively).


 

 

                          

Fig. 1. Evolution of anthracnose as a function of time; a: Incidence; b: Severity.

 

 

 


Incidence and severity of cassava mosaic

 

The disease in the field was observed on two varieties, namely the Douma variety and the Miboutou variety (Table 5). The evolution of the incidence shows that it no longer varies from 6 MAP onwards. At 3 MAP, the Douma variety recorded an incidence of 36.65% against 41.87% for the Miboutou variety. The severity is higher in the Miboutou variety (32.93%, 67.44%, 77.45% and 83.68%) than the Douma variety (25.54%, 63.63%, 71.13% and 74.82%) at 3, 6, 9 and 12 MAP respectively.


 

 

Table 5. Evolution of incidence and severity of cassava mosaic disease as a function of time

Variétés

Incidence (%)

Severity (%)

3 MAP

6 MAP

9 MAP

12 MAP

3 MAP

6 MAP

9 MAP

12 MAP

92/0057

0 b

0 b

0 b

0 b

0 c

0 c

0 b

0 c

96/0023

0 b

0 b

0 b

0 b

0 c

0 c

0 b

0 c

Excel

0 b

0 b

0 b

0 b

0 c

0 c

0 b

0 c

8034

0 b

0 b

0 b

0 b

0 c

0 c

0 b

0 c

Douma

36.65 a

100 a

100 a

100 a

25.54 b

63.63 b

71.13 a

74.82 b

Miboutou

41.87 a

100 a

100 a

100 a

32.93 a

67.44 a

77.45 a

83.68 a

Pr(>F)

˂0.001***

˂0.001***

˂0.001***

˂0.001***

˂0.001***

˂0.001***

˂0.001***

˂0.001***

P: 0 '***' 0.001 '**' 0.01 '*' 0.05; ns: not significant. Means followed by the same letter in the columns are not significantly different in the Tukey test (P ˂ 0.05).

 

 

 


DISCUSSION

 

The cassava root scale is a biting-sucking insect that feeds on the resources available in cassava roots, causing loss of vigour and weakening of the plant (Johnson, 2009). Damage caused during its feeding is not limited to specific tissues near feeding sites, but affects the entire plant causing yield losses ranging from 60 to 100% in the field (Lema et al., 2004; Tata-Hangy et al., 2006).

Results show that cassava varieties were infested differently by scale insects with variation in growth. The highest average shoot fresh weight was produced by the local variety Douma (2.69 ± 0.43 kg) compared to the improved Excel variety which produced the lowest shoot fresh weight (1.69 ± 0.15 kg). It could be hypothesized that infestation of the plants by scale insects feeding on the roots would reduce their growth. Prüter and Zebitz (1991) show that field infestation by sucking biting insect’s results in a reduction in leaf area, weight and average growth rate. The reduction in growth parameters is probably caused by the removal of carbohydrates. There are two other factors that are discussed as other possible causes of this reduction. One is a change in the well-source ratio in favour of sucking biting insects (Mallot and Davy, 1978), and the other is the excretion, with the saliva of sucking biting insects, of toxic or phytohormone-like compounds (Miles, 1987). In addition, damage caused by the scale insect at the root can impair the uptake of energy-dependent minerals and lead to a reduction in nutrient supply, thus indirectly affecting plant growth (Hawkins et al., 1986; Prüter and Zebitz 1991).

The average tuber number and yield are better for the local variety Douma 6.08±0.49 tubers and 23.8 t ha-1 respectively. In general, the improved varieties showed a low yield compared to the local varieties regardless of the damage observed. In addition, the yield of these varieties was not close to the yields expected from the experimental stations. This could be justified by the presence of scale insects that feed at the roots of the plants. Ndengo et al. (2016a) obtained similar results in the study on the influence of the population density of ARTS on the yield of cassava varieties in the Democratic Republic of Congo. These authors showed that local varieties were more tolerant to root scale attacks than improved varieties, resulting in higher yields. According to Schulthess et al. (1991), high densities of biting sap-sucking insects generally show adverse effects on crop yields.

The number of root scale insects on cassava varieties varies with time. This number is high at 6 and 9 MAP compared to 3 and 12 MAP. Indeed, Ndengo et al. (2016a,b) showed in their work that a high number of ARTS is observed at 6 MAP. On the other hand Lema et al. (2004) show that a peak of ARTS infestation on the different cassava genotypes is observed at 9 and 12 MAP. The improved variety Excel and the local variety Douma recorded the highest average number of scale insects than the improved variety 96/0023. This could be explained by the fact that the screened varieties do not have the same genetic heritage and therefore do not develop the same defense mechanisms influencing the root scale fixing behaviour.

All varieties were infested with varying incidence and a ranking according to the level of infestation in ARTS was established. Screening did not reveal any cassava varieties that were fully resistant to S. vayssierei. Infested varieties (TMS 96/0023 and TMS 92/0057), moderately infested varieties (Miboutou and 8034) and heavily infested varieties (Excel and Douma) were found. Le et al. (1991); Tertuliano (1993) showed that not all cassava varieties sifted in the field against the cassava mealybug (Phenacoccus manihoti) are fully resistant, but earlier partially resistant.

By removing its nutritive resource, ARTS injects into the plant tissues toxic saliva that can weaken the plant's defense system, hence the observation of certain diseases with variable incidence and severity. During the experiment, two of the most important diseases (Cassava Mosaic Disease and Cassava Anthracnose Disease) were observed at the site. The importance of CMD attack is related to the susceptibility of the local variety. According to the results of Fokunang et al. (2000), in field trials, the severity of Anthracnose and cassava mosaic disease depends on the susceptibility or resistance of the host plant. The incidence and severity of Cassava Anthracnose Disease on all screened cassava varieties ranged from 3 to 9 MAP. Maho (2017) shows in his work that improved and local varieties of cassava were severely attacked by Anthracnose. 

 

 

CONCLUSION

 

The damage caused by S. vayssierei is observable on the growth and yield of the cassava varieties used. In addition to feeding on the underground parts of the cassava plants, it causes loss of vigour, hence the low yields obtained. The improved Excel variety is the least productive and relatively more infested (90.12 ARTS/P). In addition to root scale infestation, two diseases were observed in the plots, with varying incidence and severity. These are cassava anthracnose observed on all varieties and cassava mosaic observed only on local varieties.

 

 

ACKNOWLEDGEMENTS

 

The authors are sincerely thankful to the International Institute of Tropical Agriculture and Institute of Agricultural Research for Development for planting material provision.

 

 

COMPETING INTERESTS

 

The authors declare that they have no competing interest.

 

 

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Cite this Article: Ngatsi PZ; Ndongo B; Manga DA; Ndongo EB; Djieto-Lordon C (2020). Effect of Stictococcus vayssierei Richard (Hemiptera: Stictococcidea) on growth and yield of cassava (Manihot esculenta Crantz). Greener Journal of Agricultural Sciences 10(2): 95-102.

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