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Journal of Plant Science and Research

Research Article


An Investigation on Changes in BiochemicalContents in Mealy Bugs Infested Mulberry Foliage

Mahadeva A*

Residential Coaching Academy, Babasaheb Bhimrao Ambedkar University, India


Corresponding author: A Mahadeva, Residential Coaching Academy, Babasaheb Bhimrao AmbedkarUniversity, Vidya Vihar, Rae Barely Road, Lucknow - 226 025, India; E-mail: kdevarasu@gmail.com


Citation: Mahadeva A. An Investigation on Changes in Biochemical Contents in Mealy Bugs Infested Mulberry Foliage. J Plant Sci Res. 2016;3(2): 153.


Copyright © Mahadeva A, 2016. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Journal of Plant Science & Research | ISSN: 2349-2805 | Volume: 3, Issue: 2


Submission: 05/07/2016; Accepted: 15/07/2016; Published: 20/07/2016


Abstract


The occurrence of pink mealy bugs (Maconellicoccus hirsutus Green) on mulberry (Morus sp.) considerably reduces the leaf yield and inturn damages its quality. Hence, an attempt was made to know the changes in biochemical constituents and photosynthetic pigments in mealy bugs infested mulberry foliage. The pest infested mulberry showed a variation in their contents. The nutritive status of the pest infested mulberry leaves may be altered adversely, feeding such leaves to the silkworm may alter the growth and development of the larvae in turns affect the quality and quantity silk production.


Keywords: Biochemical constituents; Mealy bugs; Mulberry; Photosynthetic pigments

Introduction


Mulberry (Morus sp.), the only food plant of silkworm Bombyxmori L. is of great importance to sericulture industry. The pink mealybug (Maconellicoccus hirsutus Green) is one of the major pests ofmulberry, causing severe damage and recurring loss in the leaf yieldof about 3000-6000 kg/hectare/year [1]. The pest occurs in bothirrigated and rain fed gardens causing a characteristic disease - tukra.The feeding behavior (sucking) of mealy bugs results in the curlingand crinkling of leaves of apical shoots, swelling and twisting ofapical internodes. As a result, the shoots become brittle and the leavesbecome dark green in colour and deformed. The pest is found toinhabit the folds and knots of the crumpling [2]. The morphologicalchanges in the tukra affected plant includes arrest of linear growthof the stem, followed by petiole thickening. The lamina of the leafwas found markedly reduced and distorted, ultimately leading topremature leaf fall [3]. Immature and mature mealy bugs are found inclusters on the stalks under overlapping leaf- sheath, below the nodeand spread up and down to the other internodes and buds. The largeamount of honey dew secretion by mealy bugs hosts a sooty mouldfungus and acts a vital role in virus transmission [4]. Cell sap sucking nature of the mealy bugs leads to stunted, yellowing and thin canesof mulberry and ultimately deprived of essential nutrients in theinfested plant parts. The present study was taken up to determine theimpact of mealy bug’s infestation on the biochemical constituents andphotosynthetic pigments in the leaves of some popular indigenousmulberry varieties.


Materials and Methods


The healthy and mealy bugs infested leaves were collected fromsix mulberry varieties i.e. M5, MR2, Mysore local, S36, S54 and V1. Theleaves were oven - dried and processed to analyze the biochemicalconstituents viz., free amino acids [5], total soluble proteins [6],reducing sugars [7], soluble sugars and starch [8], and total phenols[9]. The fresh leaves of healthy and mealy bug infested one were used toestimate the photosynthetic pigments (chlorophyll and carotenoids)[10,11]. Student’s t-test were followed for statistical analysis.


Results and Discussion


The six biochemical components i.e., free amino acids, totalsoluble proteins, total soluble sugars, total reducing sugars, starch and total phenols, and photosynthetic pigments viz., total chlorophyll,chlorophyll - a, chlorophyll - b, chlorophyll - a/b ratio andcarotenoids showed variation in the mealy bugs infested mulberryleaves compared to the healthy ones.


Biochemical components (Table - 1)


Table 1: Biochemical changes (dry weight) in the mealy bugs - infested mulberry leaves.


Free amino acids: The free amino acid contents were decreasedin the pest - infested leaves of M5, MR2, Mysore local and S54 varieties.But, it was significant in the leaves of M5 variety. The reduction wasnegligible (0.73 %) in leaves of Mysore local and maximum (14.79%) in M5. But, there were no alteration in the free amino acids in theleaves of S36 and V1 variety due to pest attack.


The mulberry leaves are quite rich in amino acid content andtherefore satisfy the amino acid requirements of silkworm [12]. Inmulberry leaves, the number of amino acids available is twenty. Therewas an increase in total free amino acids in mealy bugs (M. hirsutus)infested mulberry varieties viz., M5, MR2, BC259, Tr4, S13 (indigenous),Kosen, Ichinose and Goshoerami (exotic) [13].


Total soluble proteins


The total soluble proteins were significantly decreased in thetukra affected leaves of MR2 variety (2.33 %). The total solubleproteins increased significantly in the leaves of M5 (2.39 %) and V1varieties and non-significantly in the S36 (4.26 %) variety. The totalsoluble proteins were not altered in the leaves of Mysore local and S54varieties due to mealy bugs - infestation.


The protein content in the mulberry leaves shown a major role insilk production by silkworm. The protein was reduced (10.50 %) inKajli and increased (40.00 %) in mealy bug affected Kanva-2 variety[14]. Similarly, decreased protein content was observed in tukraaffected mulberry varieties of M. macroura and M. nigra by [15].An increased total protein due to mealy bug infestation in M5 andDD varieties [16]. The mechanical damage caused by insect duringinfestation will alter the physiological activity in the host. This altered function may lead to the variation in synthesis or mobilization of proteins to the damaged tissues/area in order to resist insect bite. This may leads to variation in the total crude protein contents in host[17,18].


Total reducing sugars


Alteration was noticed in the total reducing sugars of M. hirsutusinfested mulberry leaves compared to healthy one. There was asignificant reduction in the leaves of M5, MR2, Mysore local, S36 and V1varieties. A maximum (22.22 %) reduction was found in the leaves ofMysore local and minimum (2.56 %) in the leaves of S36 variety. Therewas a negligible (0.78 %) increase in the leaves of S54.


There was a significant increase in the tukra affected M.macroura. In M. cathayana and M. nigra, it was unaltered. Alterationin the reducing sugars may be due to reduction in leaf lamina andmalformation of leaves in pest affected plants resulting in lessproductivity [15].


Total soluble sugars


There were changes in the total soluble sugars of mealy bugsinfested mulberry leaves. The total soluble sugars reduced significantlyin the leaves of M5 (5.95%) and non-significantly in V1 (3.57 %)variety. But, no alteration was noticed in the total soluble sugars ofpest attacked leaves of MR2, Mysore local, S36 and S54 varieties.


The Sugar content was decreased marginally in mealy buginfested 3 mulberry varieties (M. australis, M. cathayana and M.nigra) and noticed increase in sugar in M. macroura variety [15].The four indigenous (Berhampore, S30, S31 and S36) and six exotic(Kosen, M. multicaulis, Philippine, Okinawa-2, Tsukasaguwa andItalian) mulberry varieties shown a variation in sugar content dueto mealy bugs infestation [20]. There was increased sugar content inBerhampore, Okinawa-2 and Philippine varieties. Whereas, it wasdecreased in Italian, Kosen, M. multicaulis, S30, S36 and S41 varieties.No difference was observed in Tsukasaguwa [20]. An increasedsoluble sugar was observed in mealy bugs infested leaves of M5,MR2, BC259, S13, Kosen, Goshoerami. However, in Tr4 and Ichinose,it was decreased [13]. Similar variation was also noticed in leaf rollerinfested mulberry leaves [18].


Starch


The starch content was decreased in the mealy bugs infestedleaves of M5, Mysore local, S54 and V1 varieties. The reduction wasminimum (1.72%) in Mysore local and maximum (5.08%) in V1variety. The increase in the starch content was noticed in the leaves ofMR2 (5.66%) and S36 (2.78%) varieties.


Increased starch content was observed in the tukra affectedmulberry leaves of Kajli and Kanva-2 varieties [14]. There was avariation in the starch content of mealy bugs infested mulberryleaves of M. macroura, M. nigra, M. australis and M. cathayana [15].The variation in starch content was also observed due to leaf rollerinfestation mulberry leaves [18].


Total phenols


The pest-infested mulberry showed variation in the phenoliccontents. it was decreased significantly in the leaves of M5 (3.23%)variety. Mealy bug infested mulberry varieties (MR2, S36, S54, V1 andMysore local) shown an increase in total phenols. The increase wasnegligible (0.51%) in Mysore local and maximum (28.57%) in MR2pest attacked mulberry leaves.


There were no changes in the phenolic content in tender andcoarse leaves of M5 mulberry variety when they were attacked by mealybugs. The phenolic level was decreased in tukra affected leaves of M.macroura and M. nigra varieties. However, there was a significantincrease in M. australis and M. cathayana [15]. The accumulationof phenol depends upon the position of leaves in a mulberry twigin mealy bug infected C15 mulberry variety. The insect bite leads toaccumulation of more and more phenol in the affected leaves. It maybe due to altered phenolic metabolism in response to pest attack [21].The accumulation of phenolics in the host may inhibit the furtheradvancement of pathogenic organism [22]. The most importantphenolic compounds implicated in the defense mechanism of plantsagainst pathogens are coumaric acid, phloretin, umberlliferons,caffeic acid, chlorogenic acid and ferulic acid [23]. These may acts as anatural defense mechanism by host against the phytophagous insects[18,19].


The variation in biochemical components were observed inother cases like jassids [24], leaf roller [25], spiralling whitefly [26],thrips [27] and giant African snails [28] infested mulberry leaves.The disturbance in the host metabolism may lead to changes inbiochemical composition during the mechanical damages causedduring pest infestation [19]. The altered biochemical constituentslead to discrepancy in the nutritional components of mulberry foliagewhich is disadvantageous for the quality silk production [18].


Photosynthetic pigments (Table - 2)


Table 2: Changes in photosynthetic pigments (mg/g. fresh weight) of mealy bugs infested mulberry leaves.


The pest infested mulberry leaves of six popular indigenousvarieties showed significant changes in the photosynthetic pigments(total chlorophyll, chlorophyll - a, chlorophyll - b, chlorophyll - a/bratio and carotenoids).


There was a significant decrease in the total chlorophyll contentof the foliage of MR2, Mysore local, S36, S54 and V1 mulberry varieties.The reduction was minimum (9.73%) and maximum (29.16%) in the leaves of S54 and Mysore local varieties respectively. The totalchlorophyll content was increased (0.29%) non-significantly in theleaves of M5 variety.


The chlorophyll - a content was significantly decreased in the pestinfested leaves of M5, MR2, Mysore local and V1 and non-significantlyin the leaves of S36 and S54 varieties. It was minimum (1.92%) in theleaves of S54 and high (31.51%) in the Mysore local varieties. Therewas a significant reduction in the chlorophyll - b content of tukraaffected leaves of MR2, Mysore local and S54 varieties. The decreasewas negligible (1.32%) in the pest infested leaves of Mysore localbut high (80.00%) in the leaves of S54 variety. The chlorophyll - bcontent was increased significantly in M5, S36 and V1 varieties. Theincrease was in the range of 9.08% to 13.78% in the leaves of V1 andM5 varieties respectively. Depending upon the amount of chlorophyll- a and chlorophyll - b, the chlorophyll - a/b ratio showed variationin M. hirsutus infested mulberry leaves. The tukra affected leaves ofM5, MR2, Mysore local, S36, S54 and V1 mulberry varieties shown asignificant decrease in the chlorophyll - a/b ratio. The decrease wasminimum (0.52 %) and maximum (30.76 %) in the leaves of S54 and V1mulberry variety respectively due to mealy bugs attack.


The carotenoids content was significantly decreased in the leavesof M5, MR2, Mysore local, S36, S54 and V1 varieties. The reduction wasminimum (0.53 %) in S54 and maximum (36.23 %) in the leaves ofMR2 variety. There was no alteration in the carotenoids content in thetukra infested leaves of S36 variety.


The chlorophylls are the essential catalysts of photosynthesisand occur universally as green pigments in all the autotrophicplant tissues. They occur in chloroplasts in relatively large amount.Level of chlorophyll content is one of the criteria for quantifyingthe photosynthetic rate. Chlorophyll estimates may be required torelate other biochemical changes in the plant tissues [29]. There wasa decrease (4.00 %) as well as increase (28.00 %) in the chlorophyllcontent in the mealy bugs infested leaves of Kajali and Kanva - 2varieties respectively [15]. There was a significant reduction in thetotal chlorophyll, chlorophyll - a, chlorophyll - b and chlorophyll - a/bratio in tukra affected M. cathayana. Increase in the total chlorophyll,chlorophyll - a, chlorophyll - b and chlorophyll - a/b ratio wassignificant in M. nigra, marginal in M. macroura and negligible inM. australis. Diseases affect not only the total chlorophyll contentbut also alters the ratio between chlorophyll - a and b. The feedingbehavior of the insect pests results in the reduction of pigment(s)and/of laminar area which decreases photosynthetic efficiency andthereby the productivity of the leaves. As a result of it, the nutritional level of mulberry leaves reduces [15], [18] & [20]. Total chlorophyll content was increased in Berhampore, Italian, Okinawa-2, Philippine, S36 and Tsukasaguwa varieties. Whereas, it decreased in Kosen, M. multicaulis, Philippine and S30. Negligible difference was observed in the S41 variety due to M. hirsutus infestation [16]. There were an changes in the photosynthetic pigments (total chlorophyll, chlorophyll - a, chlorophyll - b and carotenoids) in mealy bugs infested eight mulberry varieties viz., M5, MR2, BC259, Tr4, S13 (indigenous), Kosen, Ichinose and Goshoerami (exotic) [13]. The levels of total chlorophyll, chlorophyll - a, chlorophyll - b and carotenoids increased strikingly in the tukra leaves. The increase in chlorophyll content was equally contributed by both chlorophyll - a and chlorophyll - b. This increasemay be due to the failure of the pathogen to inhibit chlorophyllase,as in okra [30]. In all the mulberry varieties except Kosen and Tr4,chlorophyll - a/b ratio was lower in tukra leaves compared to that ofthe control. Thus, the intensity of pest attack, level of damage leads tothe variation in photosynthetic pigment in the mulberry leaves.


The alteration in the photosynthetic pigments was observed inmany cases where mulberry leaves were infested by various pestssuch as, jassids [24], leaf roller [25] spiralling whitefly [26], thrips[27] and giant African snails [28]. The photosynthetic activitiesadversely affect due to altered chlorophyll content [31] and whichleads to reduced protein synthesis [32]. Consequently the mulberryfoliage will be nutritionally inferior. Feeding such low nutritive, pestinfested mulberry to silkworms will have an adverse impact on theirgrowth and development, leading to cocoon crop failures [33,34]. Thediseased or/and pest infested mulberry leaves are nutritionally inferiorand not fit to feed the silkworm, because they are known to influencethe quality and quantity silk production. Necessary arrangementsmust be made to manage the pests and disease of mulberry plant as itis the only source of food for silkworms.


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