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Effects of mite (mononychellus tanajoa) and mealybug (phenacoccus manihoti) infestation on the mineral status of a cassava clone
Agriculture, Ecosystems and Environment, 18 (1986) Elsevier Science Publishers B.V., Amsterdam -Printed
73-81 in The Netherlands
73
Short Communication TANAJOA) AND EFFECTS OF MITE (MONONYCHELLUS MEALYBUG (PHENACOCCUS MANIHOTI) INFESTATION ON THE MINERAL STATUS OF A CASSAVA CLONE
D.K.G.
AYANRU’
‘Department ‘Department (Accepted
and V.C. SHARMA’
of Microbiology, University of Benin, Benin City (Nigeria) ofphysics, University of Benin, Benin City (Nigeria)
for publication
11 June 1986)
ABSTRACT Ayanru, D.K.G. and Sharma, V.C., 1986. Effects of mite (Mononychellus tanajoa) and mealybug (Phenacoccus manihoti) infestation on the mineral status of a cassava clone. Agric. Ecosystems Environ., 18: 73-81. Folithion-sprayed and unsprayed plants of a cassava (Manihot esculenta Crank) clone (TMS/U 30395) were evaluated monthly for infestations by mites, Mononychellus tanajoa (Bunda) and mealybugs, Phenacoccus manihoti (Mat-Ferr.).The plants were sampled for mature lamina, stem and tuber parenchyma tissues and analysed for nine mineral elements - N, P, K, Ca, Mg, Na, Fe, Mn and Zn. Concentrations of P and K in all the tissues sampled varied from 0.09 to 0.38 and from 0.25 to 1.46%, respectively, and were significantly lower (P < 0.01) in tissues of severely pest-infested (unsprayed) cassava than in those of healthy (sprayed) plants. Also, diminished values of Fe, Mn and Zn in roots and stems, and of Mg and N in leaves of post-infested plants were found. However, contents of Ca in all tissues, Mg and Na in roots and N in roots and stems of pest-infested and defoliated plants were considerably higher than those in tissues of healthy stands. The physiological bases for the pest-induced elemental concentration inbalances are discussed.
INTRODUCTION
Part of the dietary inadequacies of cassava products include their low mineral and other nutrient contents. These often necessitate supplementation of cassava products used in human and animal nutrition with essential nutrients for good results (Vitti et al., 1971; Montiila, 1977; Oke, 1978). Cassava pests are among the major causes of poor tissue quality. Of the numerous cassava pests, the cassava mealybug (CM), Phenucoccus munihoti (Mat-Ferr.), and the green spider mite (CGM), Mononycheilus tunujou (Bonda), which occur together on cassava, are the worst in the African tropics (Herren, 1981). Yield reductions on cassava caused by these pests have been determined (Nyira, 1976; Nwanze, 1982). Also, the identity of both pests on Nigerian cassava has been confirmed (Akinlosotu and Leuschner, 1981). 0167-8809/86/$03.50
o 1986 Elsevier
Science
Publishers
B.V.
74
Stress symptoms on cassava induced by CM and CGM may affect tissue quality, including levels of HCN (Ayanru and Sharma, 1984) and, presumably, those of mineral elements and other constituents. Critical tissue concentrations for deficiencies and toxicities for some mineral nutrients in cassava are known (Okeke et al., 1982; Howeler et al., 1982), but the extent to which CM and CGM cause elemental inbalances or otherwise in cassava has not been well documented. In this study, therefore, we report on the changes in the concentrations of some mineral elements in leaf, stem and root tissues of a cassava clone infested by CM and CGM. MATERIALS
AND METHODS
Plant growth A cassava (Manihot esculenta Crantz) clone (TMS/U 30395), selected by the Root Tuber Research Institute, Umudike, Nigeria, was planted by stem cuttings in field plots at Ugbowo, Benin City, on 12 July 1982. Plants were spaced 1 m apart on 12-m-long X a-m-wide rows. The rows were paired (insecticide-sprayed vs. non-sprayed). Rows of nonexperimental cassava plants that served as guards separated one set of paired row from another. The paired rows were replicated four times in each of three blocks, to provide a randomized block design. The chemical and textural characteristics of soil samples from field plots of the experiment have already been described (Ayanru and Sharma, 1984) - a coarse-textured sandy loam with mean pH, organic matter, base saturation, total N, and available P values of 5.16, 2.15%, 84%, 0.87% and 15.45 ppm, respectively. A compound fertilizer, containing 15-15-15 kg of N-Pz05-KzO, respectively, was used by row application at the rate of 200 kg ha-’ on 12 Aug. 1982. Fenitrothion (as Folithion - 200 g 1-l a.i.) (Bayer Leverkusen, Germany), was formulated at 300 ml 100 1-l water, and sprayed on plants in only one of each paired rows at monthly intervals (12 Aug. 1982-12 March 1983). A shoulder-mounted handoperated knapsack sprayer (Wambo Gartenbau, Hamburg, Germany) was used. Pest infestation ratings Using the evaluation system of the IITA (1979), plants were rated monthly for infestation symptoms of the cassava green spider mite (CGM), Mononychellus tanajoa (Bunda), on a scale ranging from 1 (no symptoms) to 5 (severe symptoms). Similar ratings were made simultaneously for incidence of the cassava mealybug (CM), Phenacoccus manihoti (Matt-Ferr.), using the inverted scale of 1 (severe infestation) - 5 (no infestation) recommended by Atu and Okeke (1981). For comparison, however, the numbering system of the CM scale is reversed here 1 (no infestation) - 5 (severe infestation).
75
Sample processing and analysis At 3-monthly intervals after propagation, standard tissue preparations for analysis (Grier, 1966) were carried out. Samples were analysed for nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sodium (Na) by the Nigerian Institute for Oil Palm Research (NIFOR), near Benin City, and for iron (Fe), manganese (Mn) and zinc (Zn) by the International Institute of Tropical Agriculture (IITA), Ibadan. Tissues were analysed for Fe, Mn and Zn only from plants sampled at 9 months. RESULTS
Plant age and tissue type effects Variations in the concentrations of N, P, K, Ca, Mg and Na in all the tissues analysed as affected by plant age showed similar patterns of increases with increased age of source plants. Thus, concentrations of these elements in tissues at 9 months increased consistently over their respective concentrations at 6 months, as did their values at 6 months relative to those at 3 months. Elemental concentrations also differed for the different tissues. Stem tissues contained the highest amounts of Fe, while for all the other elements studied the highest concentrations occurred in leaf tissues, followed by stem and tuber tissues in decreasing order. Pest incidence Mean monthly CGM and CM infestation severity ratings on the test plants are presented in Fig. 1. Incidence of both pests on sprayed plants was rated less than 1.50 for trace infestations throughout the 9-month growth period. On the unsprayed plants, symptoms of the pests increased rapidly from Aug. and Oct. 1982 to their peak values rated as severe in Nov. 1982-April 1983 and Jan.-April 1983, respectively, for CGM and CM. Unsprayed plants were completely defoliated by the pests between Feb. and April 1983. Consequently, mature lamina samples were not available for analysis from unsprayed plants sampled on 12 April 1983. Elemental concentrations at 3 months Concentrations of P and K in all tissues and of Mg in leaves of plants with only traces of CGM infestations were significantly higher (P < 0.01) than those in corresponding tissues of unsprayed and CGM-infested stands. On the other hand, leaves of unsprayed plants contained enhanced Ca contents (>70% in leaves) as compared with amounts in leaves of sprayed plants.
76
”
0 Atq Sep. Ott NW Dec. Jan Rating month (Aug -Dee 1982 and
Feb Mar. Jan - Apr
Apr 1983
)
Fig. 1. Cassava green spider mite (CGM) and mealybug (CM) mean monthly infestation severity ratings on folithion-sprayed (0) and unsprayed (. ) field stands of test clone TMS/U 30395. The rating scale for CGM and CM is 1 (no infestation)-5 (severe infestation).
Concentrations at 6 months Concentrations of P and K in all tissues and of N and Mg in leaves of sprayed plants were higher (P < 0.01) than those in paired tissues of unsprayed plants. The reverse was the case for Ca in all tissues of unsprayed cassava which contained augmented values (>70% in leaves) than those in tissues of unsprayed stands. Similarly, the concentrations of N, Mg and Na in roots of unsprayed plants were more than those in root tissues of sprayed cassava .
Concentrations at 9 months The ratios between the concentrations of corresponding elements N, P, K, Ca, Mg and Na in tissues of healthy (sprayed) and heavily pest-infested (unsprayed) plants were similar at 9 months to those at 6 months. However, N content in stems of infested cassava at 9 months was higher (P < 0.05) than that in healthy plants. Also, stem and tuber’ tissues of severely pest-infected cassava were significantly depleted (P < 0.01) of Fe, Mn and Zn, when compared with values in paired tissues of undefoliated plants. DISCUSSION
The discernable ferences in plant
patterns of elemental concentrations age and tissue types reported may
in relation to difbe species specific.
66.67** 56.52** 82.22**
‘The percentage difference (increase or decrease) = 1% probability levels, respectively. ZMeans of four, 3-plant-sample, replications.
_ _ 0.53 0.42 0.03
1.93 0.13 0.76
0.03
1.36 0.10 0.25 0.14 0.22
Sprayed
Sprayed - Unsprayed
0.46 0.39 0.03
0.36 0.25 0.16
& Na
0.23 0.15 0.09
1.77 0.22 1.29
6-monthold plants harvested on 12 Jan. 1983 N 0.67 1.21 _ 80.60** P 0.19 0.11 + 42.11** K 1.19 0.83 + 30.25**
0.00
0.02
0.02
Na
0.02
1.29 0.15 0.38 0.13 0.20
Unsprayed
Sprayed
Difference (%)’
Sprayed
Unsprayed
Stem (bark and wood)
cassava
Tuber pulp
in tissues from 3- and 6month-old
3-monthold plants harvested on 12 Oct. 1982 N 0.53” 0.58 _ 9.43 P 0.14 0.09 + 35.71** K 0.75 0.50 + 33.33** 2 0.15 0.10 0.16 0.09 _+ 10.00 6.66
Element (%)
Elemental concentrations
TABLE I
x
15.22* 7.69 0.00
9.04 40.91** 41.09**
50.00
5.43 33.33** 34.21** 10.00 7.69
0.85 1.26 0.09
2.85 0.25 1.34
0.04
2.12 0.21 0.63 0.33 0.47
Sprayed
0.62 2.15 0.08
2.08 0.17 1.03
0.04
1.98 0.13 0.48 0.25 0.59
Unsprayed
-+ +
+ + +
+ + + _+
70.64 27.06** 11.11
26.64** 32.00** 23.13**
0.00
7.07 38.10** 23.81** 46.81** 78.79
Difference (%)
100; differences with * or ** are significant at the 5 or
-_
_ + +
_
+ + _
Difference (%)
Leaf (mature lamina)
Cassava, harvested over lo-20 months of growth, is known to accumulate mineral nutrients over extended growth periods (Orioli et al., 1967). Also, mineral contents of the aerial parts of cassava have been reported to be several times those of roots (Solorzano and Bornemisza, 1976). Tissues of pest-infested cassava were depleted in P and K at 3 months, when only CGM symptoms were recorded (Fig. 1; Table I). This suggests that, for late cassava plantings (July-Ott.), levels of these elements may be substantially diminished by CGM, with serious outcome. Cassava tuber yield at 12 months is associated with P and K contents of tissues at 3 months (Okeke et al., 1982). As the needs of cassava for P are higher than for most other crops (Edwards et al., 1977), depletions of this element and perhaps of others in young and old cassava plants may partly account for known tuber yield reductions caused by CGM. Concentrations of Ca were more in tissues of infested than uninfested plants (>70% in leaves at 6 months). Sufficiency levels of Ca in cassava have not been adequately ascertained. However, as its content in relation to that of K and perhaps other elements may be critical, the drastically enhanced values, as found in this study, may have serious adverse consequences for cassava tuber yield and quality. Pushpadas and Aiyer (1976) have shown that, in cassava, high Ca decreases starch and crude protein contents at low K. Roots of cassava stressed by CGM and CM contained enhanced Na contents. The mechanism by which this occurs in cassava is unknown. Although in some crops, Na may substitute for K (Harmer and Benne, 1945), its value as a cassava nutrient has not been determined. Nevertheless, its accumulation in tubers of cassava may have serious implications in dietary value of the crop, and in cell membrane permeability and water transport systems. Zinc and Mn are among elements known to be highly toxic to plants. However, the concentrations of both elements reported for all the plants are much lower than critical deficiency values found in cassava by Howeler et al. (1982). Therefore, it seems that the presence of the pests may further aggravate a situation of potential deficiencies for both minerals in cassava grown in the study location. The upsurge of N and Mg in roots and their diminution in pest-stressed leaves (Tables I and II) may be traced to retranslocation phenomenon about which little is known. These elements and some others have been shown to be readily demobilized from senescing leaves to other tissues (Devlin, 1966). Indeed, Ayanru and Sharma (1983, 1984) reported that stress in cassava arising from CGM and CM incidence may deplete chlorophylls, induce other changes associated with senescence, demobilize HCN and perhaps other nitrogenous substances from leaves to roots. Similar works on retranslocation and accumulation of N and other minerals in tissues have also been reported (Leopold and Kriedemann, 1975). Depletion of minerals in pest-infested cassava may be traced partly to the
1.37 0.14 0.95 0.80 0.34 0.19 6.25 2.25 0.90
1.03* 0.29 1.28 0.50 0.18 0.10 12.25 3.50 3.63 + + _ _ + + +
_ 33.01** 51.72* 25.78** 60.00** 88.89** 90.00** 48.98** 35.71** 75.21**
Difference
(%)I 3.29
0.15 1.03 1.77 0.97 0.04 11.75 5.56 2.70
sprayed
Sprayed - unsprayed
2.91 0.28 1.39 1.45 0.97 0.04 24.75 7.50 4.83
Unsprayed
cassava
Sprayed
Stem
significant at the 5 or 1% probability levels, respectively. 2Means of four replications. ‘Completely defoliated plants with no lamina samples.
’% increase or decrease in sprayed over unsprayed =
Wwm) Mn6w-n) Wppm)
Na (%)
Mg 6)
Ca (%)
N (%I p (%I K (%)
Unsprayed
Sprayed
Elements Tuber
Concentrations of some elements in tissues of g-month-old
TABLE II
+ + +
+ + ~
_
x
0.38 1.46 2.53 1.31 0.09 12.50 60.00 42.03
3.29
Sprayed
-3 -
Unsprayed
100; differences with * or ** are
13.06* 46.43** 25.90** 22.07** 0.00 0.00 52.52** 25.87** 44.67**
Difference (%)
Leaf
80
feeding and defoliation effects of the bugs. A drop in transpiration normally accompanies the activities of phytophagous bugs on the host (Kloft, cited by Miles, 1968). The rate of transpiration, and hence of upward translocation of salts through vessels, is thought to create favourably steep gradients of elemental concentrations across the root and exert an indirect effect on salt accumulation (Leopold and Kriedemann, 1975). Apart from the upward flow of xylem sap theory on nutrient accumulation, a sortingout mechanism may also be involved (Leopold and Kriedemann, 1975). Furthermore, defoliation and other stress situations are believed to cause a reduction in accumulation of certain inorganic substances by diminishing the quantity of photosynthates reaching the root system (Meyer et al,, 1960). The results of this study show that great inbalances in the concentrations of some mineral elements are elicited in cassava infested by CGM and CM. Because minerals are important in enzyme systems and other roles, the degree of pest-induced elemental inbalance reported here could have serious growth effects. Less severe debilitation of cassava grown in fertile soils and known clonal differences in rates of recovery from attack by the pests (IITA, 1980) can perhaps be traced to varied levels of elemental depletions or augmentations. This suggestion might be a potential basis for clonal selection for resistance against the pests, which merits further investigation.
REFERENCES Akinlosotu, T.A. and Leuschner, K., 1981. Outbreaks of two new pests (Mononychellus Nigeria. Trop. Pest Manage., 27: tanajoa and Phenacoccus manihoti) in southern 247-250. Atu, U.G. and Okeke, J.E., 1981. Evaluation of insecticides for control of cassava mealybug (Phenacoccus manihoti). Trop. Pest Manage., 27: 251-253. Ayanru, D.K.G. and Sharma, V.C., 1983. Chlorophyll depletion in leaves of field-grown cassava clones infested by cassava green spider mites (Mononychellus tanajoa (Bonda)) (Acarina:Tetranychidae). Trop. Agric. (Trinidad), 60(2): 85-88. Ayanru, D.K.G. and Sharma, V.C., 1984. Changes in total cyanide content of tissues from cassava plants infested by mites (Mononychellus tanajoa) and mealybugs (Phenacoccus manihoti). Agric. Ecosystems Environ., 12: 35-46. Devlin, R.M., 1966. Plant Physiology. Reinhold Publishing Corporation, New York, 564 pp. Edwards, D.G., Asher, C.J. and Wilson, G.L., 1977. Mineral nutrition of cassava and adaptation to low fertility conditions. In: Fourth Symp. Int. Sot. Trop. ROOT Crops, IDRC - 080e, Ottawa, Canada, pp. 124-130. Grier, J.D., 1966. Preparation of plant material for analysis. J. Assoc. Off. Anal. Chem., 49: 291-298. Harmer, P.M. and Benne, E.J., 1945. Sodium as a crop nutrient. Soil Sci., 60: 137148. Herren, H.R., 1981. IITA’s role and actions in controlling the cassava mealybug in Africa. IITA Res. Briefs, 2(4): l-4. Howeler, R.H., Edwards, D.G. and Asher, C.J., 1982. Micronutrient deficiencies and toxicities of cassava plants grown in nutrient solution. 1. Critical tissue concentrations. J. Plant Nutr. (USA), 5(8): 1059-1076.
81 I.I.T.A. (International Institute of Tropical Agriculture), 1979. Annu. Rep. 1979, Ibadan, Nigeria, 152 pp. I.I.T.A. (International Institute of Tropical Agriculture), 1980. Annu. Rep. 1980, Ibadan, Nigeria, 185 pp. Leopold, A.C. and Kriedemann, P.E., 1975. Plant Growth and Development, 2nd edn. McGraw-Hill, New York, 545 pp. Meyer, B.S., Anderson, D.G. and Bohning, R.H., 1960. Plant Physiology. D. Van Nostrand, Toronto, 541 pp. Miles, P.W., 1968. Insect secretions in plant. Annu. Rev. Phytopathol., 6: 137-164. Montilla, J.J., 1977. Utilization of the whole cassava plant in animal feed. In: 1st Int. Symp. Utah Agric. Expt. Station, Utah State University, Logan, pp. 98-104. Nwanze, K.F., 1982. Relationships between cassava root yields and crop infestations by mealybug, Phenacoccus manihoti. Trop. Pest. Management, 28(l): 27--32. Nyira, Z.M., 1976. Advances in Research on the economic significance of the green Exchange and cassava mite (Mononychellus tonajoa) in Uganda. In: The International Testing of Casaava Germplasm in Africa. Intern. Dev. Res. Centre (IDRC) Ottawa, pp. 27-29. Oke, D.L., 1978. Problems in the use of cassava as animal feed. Animal Feed. Sci. Technol., 3: 345-380. Okeke, J.E., Kang, B.T. and Obigbesan, G.O., 1982. Effects of fertilizers and plant age on distribution of nutrients in Nigerian Caasava (Munihot esculentu). Expt. Agric., 18: 403-411. Orioli, G.A., Mogilner, I., Bartra, W.L. and Senienchuk, P.A., 1967. Accumulation of DM, N, P, K and Ca in Manihot esculenta. Bonplandia, 2(13): 175-182. Pushpadas, M.V. and Aiyer, R.S., 1976. Nutritional studies on cassava (Manihotesdenta Crantz). 2. Effects of potassium and calcium on yield and quality of tubers. J. Root Crops (India), 2(l): 4241. Solorzano, V.N. and Bornemisza, E., 1976. Studies on cassava cultivation in Costa Rica. 2. Chemical composition and production of three cultivars. Turialba, 26(3): 261264. Vitti, P., Figueiredo, L.B. and Angelucci, E., 1971. (Dehydrated caasava leaves as human food) Folhas de mandioca desidratadas de. Tech01 Alim. (Brazil), 14: 117-125.
73-81 in The Netherlands
73
Short Communication TANAJOA) AND EFFECTS OF MITE (MONONYCHELLUS MEALYBUG (PHENACOCCUS MANIHOTI) INFESTATION ON THE MINERAL STATUS OF A CASSAVA CLONE
D.K.G.
AYANRU’
‘Department ‘Department (Accepted
and V.C. SHARMA’
of Microbiology, University of Benin, Benin City (Nigeria) ofphysics, University of Benin, Benin City (Nigeria)
for publication
11 June 1986)
ABSTRACT Ayanru, D.K.G. and Sharma, V.C., 1986. Effects of mite (Mononychellus tanajoa) and mealybug (Phenacoccus manihoti) infestation on the mineral status of a cassava clone. Agric. Ecosystems Environ., 18: 73-81. Folithion-sprayed and unsprayed plants of a cassava (Manihot esculenta Crank) clone (TMS/U 30395) were evaluated monthly for infestations by mites, Mononychellus tanajoa (Bunda) and mealybugs, Phenacoccus manihoti (Mat-Ferr.).The plants were sampled for mature lamina, stem and tuber parenchyma tissues and analysed for nine mineral elements - N, P, K, Ca, Mg, Na, Fe, Mn and Zn. Concentrations of P and K in all the tissues sampled varied from 0.09 to 0.38 and from 0.25 to 1.46%, respectively, and were significantly lower (P < 0.01) in tissues of severely pest-infested (unsprayed) cassava than in those of healthy (sprayed) plants. Also, diminished values of Fe, Mn and Zn in roots and stems, and of Mg and N in leaves of post-infested plants were found. However, contents of Ca in all tissues, Mg and Na in roots and N in roots and stems of pest-infested and defoliated plants were considerably higher than those in tissues of healthy stands. The physiological bases for the pest-induced elemental concentration inbalances are discussed.
INTRODUCTION
Part of the dietary inadequacies of cassava products include their low mineral and other nutrient contents. These often necessitate supplementation of cassava products used in human and animal nutrition with essential nutrients for good results (Vitti et al., 1971; Montiila, 1977; Oke, 1978). Cassava pests are among the major causes of poor tissue quality. Of the numerous cassava pests, the cassava mealybug (CM), Phenucoccus munihoti (Mat-Ferr.), and the green spider mite (CGM), Mononycheilus tunujou (Bonda), which occur together on cassava, are the worst in the African tropics (Herren, 1981). Yield reductions on cassava caused by these pests have been determined (Nyira, 1976; Nwanze, 1982). Also, the identity of both pests on Nigerian cassava has been confirmed (Akinlosotu and Leuschner, 1981). 0167-8809/86/$03.50
o 1986 Elsevier
Science
Publishers
B.V.
74
Stress symptoms on cassava induced by CM and CGM may affect tissue quality, including levels of HCN (Ayanru and Sharma, 1984) and, presumably, those of mineral elements and other constituents. Critical tissue concentrations for deficiencies and toxicities for some mineral nutrients in cassava are known (Okeke et al., 1982; Howeler et al., 1982), but the extent to which CM and CGM cause elemental inbalances or otherwise in cassava has not been well documented. In this study, therefore, we report on the changes in the concentrations of some mineral elements in leaf, stem and root tissues of a cassava clone infested by CM and CGM. MATERIALS
AND METHODS
Plant growth A cassava (Manihot esculenta Crantz) clone (TMS/U 30395), selected by the Root Tuber Research Institute, Umudike, Nigeria, was planted by stem cuttings in field plots at Ugbowo, Benin City, on 12 July 1982. Plants were spaced 1 m apart on 12-m-long X a-m-wide rows. The rows were paired (insecticide-sprayed vs. non-sprayed). Rows of nonexperimental cassava plants that served as guards separated one set of paired row from another. The paired rows were replicated four times in each of three blocks, to provide a randomized block design. The chemical and textural characteristics of soil samples from field plots of the experiment have already been described (Ayanru and Sharma, 1984) - a coarse-textured sandy loam with mean pH, organic matter, base saturation, total N, and available P values of 5.16, 2.15%, 84%, 0.87% and 15.45 ppm, respectively. A compound fertilizer, containing 15-15-15 kg of N-Pz05-KzO, respectively, was used by row application at the rate of 200 kg ha-’ on 12 Aug. 1982. Fenitrothion (as Folithion - 200 g 1-l a.i.) (Bayer Leverkusen, Germany), was formulated at 300 ml 100 1-l water, and sprayed on plants in only one of each paired rows at monthly intervals (12 Aug. 1982-12 March 1983). A shoulder-mounted handoperated knapsack sprayer (Wambo Gartenbau, Hamburg, Germany) was used. Pest infestation ratings Using the evaluation system of the IITA (1979), plants were rated monthly for infestation symptoms of the cassava green spider mite (CGM), Mononychellus tanajoa (Bunda), on a scale ranging from 1 (no symptoms) to 5 (severe symptoms). Similar ratings were made simultaneously for incidence of the cassava mealybug (CM), Phenacoccus manihoti (Matt-Ferr.), using the inverted scale of 1 (severe infestation) - 5 (no infestation) recommended by Atu and Okeke (1981). For comparison, however, the numbering system of the CM scale is reversed here 1 (no infestation) - 5 (severe infestation).
75
Sample processing and analysis At 3-monthly intervals after propagation, standard tissue preparations for analysis (Grier, 1966) were carried out. Samples were analysed for nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sodium (Na) by the Nigerian Institute for Oil Palm Research (NIFOR), near Benin City, and for iron (Fe), manganese (Mn) and zinc (Zn) by the International Institute of Tropical Agriculture (IITA), Ibadan. Tissues were analysed for Fe, Mn and Zn only from plants sampled at 9 months. RESULTS
Plant age and tissue type effects Variations in the concentrations of N, P, K, Ca, Mg and Na in all the tissues analysed as affected by plant age showed similar patterns of increases with increased age of source plants. Thus, concentrations of these elements in tissues at 9 months increased consistently over their respective concentrations at 6 months, as did their values at 6 months relative to those at 3 months. Elemental concentrations also differed for the different tissues. Stem tissues contained the highest amounts of Fe, while for all the other elements studied the highest concentrations occurred in leaf tissues, followed by stem and tuber tissues in decreasing order. Pest incidence Mean monthly CGM and CM infestation severity ratings on the test plants are presented in Fig. 1. Incidence of both pests on sprayed plants was rated less than 1.50 for trace infestations throughout the 9-month growth period. On the unsprayed plants, symptoms of the pests increased rapidly from Aug. and Oct. 1982 to their peak values rated as severe in Nov. 1982-April 1983 and Jan.-April 1983, respectively, for CGM and CM. Unsprayed plants were completely defoliated by the pests between Feb. and April 1983. Consequently, mature lamina samples were not available for analysis from unsprayed plants sampled on 12 April 1983. Elemental concentrations at 3 months Concentrations of P and K in all tissues and of Mg in leaves of plants with only traces of CGM infestations were significantly higher (P < 0.01) than those in corresponding tissues of unsprayed and CGM-infested stands. On the other hand, leaves of unsprayed plants contained enhanced Ca contents (>70% in leaves) as compared with amounts in leaves of sprayed plants.
76
”
0 Atq Sep. Ott NW Dec. Jan Rating month (Aug -Dee 1982 and
Feb Mar. Jan - Apr
Apr 1983
)
Fig. 1. Cassava green spider mite (CGM) and mealybug (CM) mean monthly infestation severity ratings on folithion-sprayed (0) and unsprayed (. ) field stands of test clone TMS/U 30395. The rating scale for CGM and CM is 1 (no infestation)-5 (severe infestation).
Concentrations at 6 months Concentrations of P and K in all tissues and of N and Mg in leaves of sprayed plants were higher (P < 0.01) than those in paired tissues of unsprayed plants. The reverse was the case for Ca in all tissues of unsprayed cassava which contained augmented values (>70% in leaves) than those in tissues of unsprayed stands. Similarly, the concentrations of N, Mg and Na in roots of unsprayed plants were more than those in root tissues of sprayed cassava .
Concentrations at 9 months The ratios between the concentrations of corresponding elements N, P, K, Ca, Mg and Na in tissues of healthy (sprayed) and heavily pest-infested (unsprayed) plants were similar at 9 months to those at 6 months. However, N content in stems of infested cassava at 9 months was higher (P < 0.05) than that in healthy plants. Also, stem and tuber’ tissues of severely pest-infected cassava were significantly depleted (P < 0.01) of Fe, Mn and Zn, when compared with values in paired tissues of undefoliated plants. DISCUSSION
The discernable ferences in plant
patterns of elemental concentrations age and tissue types reported may
in relation to difbe species specific.
66.67** 56.52** 82.22**
‘The percentage difference (increase or decrease) = 1% probability levels, respectively. ZMeans of four, 3-plant-sample, replications.
_ _ 0.53 0.42 0.03
1.93 0.13 0.76
0.03
1.36 0.10 0.25 0.14 0.22
Sprayed
Sprayed - Unsprayed
0.46 0.39 0.03
0.36 0.25 0.16
& Na
0.23 0.15 0.09
1.77 0.22 1.29
6-monthold plants harvested on 12 Jan. 1983 N 0.67 1.21 _ 80.60** P 0.19 0.11 + 42.11** K 1.19 0.83 + 30.25**
0.00
0.02
0.02
Na
0.02
1.29 0.15 0.38 0.13 0.20
Unsprayed
Sprayed
Difference (%)’
Sprayed
Unsprayed
Stem (bark and wood)
cassava
Tuber pulp
in tissues from 3- and 6month-old
3-monthold plants harvested on 12 Oct. 1982 N 0.53” 0.58 _ 9.43 P 0.14 0.09 + 35.71** K 0.75 0.50 + 33.33** 2 0.15 0.10 0.16 0.09 _+ 10.00 6.66
Element (%)
Elemental concentrations
TABLE I
x
15.22* 7.69 0.00
9.04 40.91** 41.09**
50.00
5.43 33.33** 34.21** 10.00 7.69
0.85 1.26 0.09
2.85 0.25 1.34
0.04
2.12 0.21 0.63 0.33 0.47
Sprayed
0.62 2.15 0.08
2.08 0.17 1.03
0.04
1.98 0.13 0.48 0.25 0.59
Unsprayed
-+ +
+ + +
+ + + _+
70.64 27.06** 11.11
26.64** 32.00** 23.13**
0.00
7.07 38.10** 23.81** 46.81** 78.79
Difference (%)
100; differences with * or ** are significant at the 5 or
-_
_ + +
_
+ + _
Difference (%)
Leaf (mature lamina)
Cassava, harvested over lo-20 months of growth, is known to accumulate mineral nutrients over extended growth periods (Orioli et al., 1967). Also, mineral contents of the aerial parts of cassava have been reported to be several times those of roots (Solorzano and Bornemisza, 1976). Tissues of pest-infested cassava were depleted in P and K at 3 months, when only CGM symptoms were recorded (Fig. 1; Table I). This suggests that, for late cassava plantings (July-Ott.), levels of these elements may be substantially diminished by CGM, with serious outcome. Cassava tuber yield at 12 months is associated with P and K contents of tissues at 3 months (Okeke et al., 1982). As the needs of cassava for P are higher than for most other crops (Edwards et al., 1977), depletions of this element and perhaps of others in young and old cassava plants may partly account for known tuber yield reductions caused by CGM. Concentrations of Ca were more in tissues of infested than uninfested plants (>70% in leaves at 6 months). Sufficiency levels of Ca in cassava have not been adequately ascertained. However, as its content in relation to that of K and perhaps other elements may be critical, the drastically enhanced values, as found in this study, may have serious adverse consequences for cassava tuber yield and quality. Pushpadas and Aiyer (1976) have shown that, in cassava, high Ca decreases starch and crude protein contents at low K. Roots of cassava stressed by CGM and CM contained enhanced Na contents. The mechanism by which this occurs in cassava is unknown. Although in some crops, Na may substitute for K (Harmer and Benne, 1945), its value as a cassava nutrient has not been determined. Nevertheless, its accumulation in tubers of cassava may have serious implications in dietary value of the crop, and in cell membrane permeability and water transport systems. Zinc and Mn are among elements known to be highly toxic to plants. However, the concentrations of both elements reported for all the plants are much lower than critical deficiency values found in cassava by Howeler et al. (1982). Therefore, it seems that the presence of the pests may further aggravate a situation of potential deficiencies for both minerals in cassava grown in the study location. The upsurge of N and Mg in roots and their diminution in pest-stressed leaves (Tables I and II) may be traced to retranslocation phenomenon about which little is known. These elements and some others have been shown to be readily demobilized from senescing leaves to other tissues (Devlin, 1966). Indeed, Ayanru and Sharma (1983, 1984) reported that stress in cassava arising from CGM and CM incidence may deplete chlorophylls, induce other changes associated with senescence, demobilize HCN and perhaps other nitrogenous substances from leaves to roots. Similar works on retranslocation and accumulation of N and other minerals in tissues have also been reported (Leopold and Kriedemann, 1975). Depletion of minerals in pest-infested cassava may be traced partly to the
1.37 0.14 0.95 0.80 0.34 0.19 6.25 2.25 0.90
1.03* 0.29 1.28 0.50 0.18 0.10 12.25 3.50 3.63 + + _ _ + + +
_ 33.01** 51.72* 25.78** 60.00** 88.89** 90.00** 48.98** 35.71** 75.21**
Difference
(%)I 3.29
0.15 1.03 1.77 0.97 0.04 11.75 5.56 2.70
sprayed
Sprayed - unsprayed
2.91 0.28 1.39 1.45 0.97 0.04 24.75 7.50 4.83
Unsprayed
cassava
Sprayed
Stem
significant at the 5 or 1% probability levels, respectively. 2Means of four replications. ‘Completely defoliated plants with no lamina samples.
’% increase or decrease in sprayed over unsprayed =
Wwm) Mn6w-n) Wppm)
Na (%)
Mg 6)
Ca (%)
N (%I p (%I K (%)
Unsprayed
Sprayed
Elements Tuber
Concentrations of some elements in tissues of g-month-old
TABLE II
+ + +
+ + ~
_
x
0.38 1.46 2.53 1.31 0.09 12.50 60.00 42.03
3.29
Sprayed
-3 -
Unsprayed
100; differences with * or ** are
13.06* 46.43** 25.90** 22.07** 0.00 0.00 52.52** 25.87** 44.67**
Difference (%)
Leaf
80
feeding and defoliation effects of the bugs. A drop in transpiration normally accompanies the activities of phytophagous bugs on the host (Kloft, cited by Miles, 1968). The rate of transpiration, and hence of upward translocation of salts through vessels, is thought to create favourably steep gradients of elemental concentrations across the root and exert an indirect effect on salt accumulation (Leopold and Kriedemann, 1975). Apart from the upward flow of xylem sap theory on nutrient accumulation, a sortingout mechanism may also be involved (Leopold and Kriedemann, 1975). Furthermore, defoliation and other stress situations are believed to cause a reduction in accumulation of certain inorganic substances by diminishing the quantity of photosynthates reaching the root system (Meyer et al,, 1960). The results of this study show that great inbalances in the concentrations of some mineral elements are elicited in cassava infested by CGM and CM. Because minerals are important in enzyme systems and other roles, the degree of pest-induced elemental inbalance reported here could have serious growth effects. Less severe debilitation of cassava grown in fertile soils and known clonal differences in rates of recovery from attack by the pests (IITA, 1980) can perhaps be traced to varied levels of elemental depletions or augmentations. This suggestion might be a potential basis for clonal selection for resistance against the pests, which merits further investigation.
REFERENCES Akinlosotu, T.A. and Leuschner, K., 1981. Outbreaks of two new pests (Mononychellus Nigeria. Trop. Pest Manage., 27: tanajoa and Phenacoccus manihoti) in southern 247-250. Atu, U.G. and Okeke, J.E., 1981. Evaluation of insecticides for control of cassava mealybug (Phenacoccus manihoti). Trop. Pest Manage., 27: 251-253. Ayanru, D.K.G. and Sharma, V.C., 1983. Chlorophyll depletion in leaves of field-grown cassava clones infested by cassava green spider mites (Mononychellus tanajoa (Bonda)) (Acarina:Tetranychidae). Trop. Agric. (Trinidad), 60(2): 85-88. Ayanru, D.K.G. and Sharma, V.C., 1984. Changes in total cyanide content of tissues from cassava plants infested by mites (Mononychellus tanajoa) and mealybugs (Phenacoccus manihoti). Agric. Ecosystems Environ., 12: 35-46. Devlin, R.M., 1966. Plant Physiology. Reinhold Publishing Corporation, New York, 564 pp. Edwards, D.G., Asher, C.J. and Wilson, G.L., 1977. Mineral nutrition of cassava and adaptation to low fertility conditions. In: Fourth Symp. Int. Sot. Trop. ROOT Crops, IDRC - 080e, Ottawa, Canada, pp. 124-130. Grier, J.D., 1966. Preparation of plant material for analysis. J. Assoc. Off. Anal. Chem., 49: 291-298. Harmer, P.M. and Benne, E.J., 1945. Sodium as a crop nutrient. Soil Sci., 60: 137148. Herren, H.R., 1981. IITA’s role and actions in controlling the cassava mealybug in Africa. IITA Res. Briefs, 2(4): l-4. Howeler, R.H., Edwards, D.G. and Asher, C.J., 1982. Micronutrient deficiencies and toxicities of cassava plants grown in nutrient solution. 1. Critical tissue concentrations. J. Plant Nutr. (USA), 5(8): 1059-1076.
81 I.I.T.A. (International Institute of Tropical Agriculture), 1979. Annu. Rep. 1979, Ibadan, Nigeria, 152 pp. I.I.T.A. (International Institute of Tropical Agriculture), 1980. Annu. Rep. 1980, Ibadan, Nigeria, 185 pp. Leopold, A.C. and Kriedemann, P.E., 1975. Plant Growth and Development, 2nd edn. McGraw-Hill, New York, 545 pp. Meyer, B.S., Anderson, D.G. and Bohning, R.H., 1960. Plant Physiology. D. Van Nostrand, Toronto, 541 pp. Miles, P.W., 1968. Insect secretions in plant. Annu. Rev. Phytopathol., 6: 137-164. Montilla, J.J., 1977. Utilization of the whole cassava plant in animal feed. In: 1st Int. Symp. Utah Agric. Expt. Station, Utah State University, Logan, pp. 98-104. Nwanze, K.F., 1982. Relationships between cassava root yields and crop infestations by mealybug, Phenacoccus manihoti. Trop. Pest. Management, 28(l): 27--32. Nyira, Z.M., 1976. Advances in Research on the economic significance of the green Exchange and cassava mite (Mononychellus tonajoa) in Uganda. In: The International Testing of Casaava Germplasm in Africa. Intern. Dev. Res. Centre (IDRC) Ottawa, pp. 27-29. Oke, D.L., 1978. Problems in the use of cassava as animal feed. Animal Feed. Sci. Technol., 3: 345-380. Okeke, J.E., Kang, B.T. and Obigbesan, G.O., 1982. Effects of fertilizers and plant age on distribution of nutrients in Nigerian Caasava (Munihot esculentu). Expt. Agric., 18: 403-411. Orioli, G.A., Mogilner, I., Bartra, W.L. and Senienchuk, P.A., 1967. Accumulation of DM, N, P, K and Ca in Manihot esculenta. Bonplandia, 2(13): 175-182. Pushpadas, M.V. and Aiyer, R.S., 1976. Nutritional studies on cassava (Manihotesdenta Crantz). 2. Effects of potassium and calcium on yield and quality of tubers. J. Root Crops (India), 2(l): 4241. Solorzano, V.N. and Bornemisza, E., 1976. Studies on cassava cultivation in Costa Rica. 2. Chemical composition and production of three cultivars. Turialba, 26(3): 261264. Vitti, P., Figueiredo, L.B. and Angelucci, E., 1971. (Dehydrated caasava leaves as human food) Folhas de mandioca desidratadas de. Tech01 Alim. (Brazil), 14: 117-125.