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Isolation and Identification of Storage Fungi from Citrus Sampled from Major Growing areas of Punjab, Pakistan.

Byline: Nosheen Akhtar, Tehmina Anjum and Rasheda Jabeen

Abstract

Stored citrus fruits were collected from cold storage houses of major citrus growing areas of the Punjab, Pakistan and storage fungi were isolated from the sampled fruits. The fungal isolates were identified as Aspergillus niger, A. flavus, A. fumigatus, A. terreus, Penicillium verrucosum, Rhizopus arrhizus, R. stolonifer, A. parasiticum, Fusarium oxysporum, P. citrinum, A. awamorii, Alternaria alternata, F. solani and Mucor sp. based on morphological characteristics. The frequency of occurrence of each fungal species was determined; P. italicum was found the most frequent with the highest occurrence of 29.75% among all isolates, followed by the A. niger (14.87%), while Dreshlera sp. having the least occurrence (0.82%). Hence, P. italicum was chosen for the molecular characterization among its different geographically distinct isolates through random amplified polymorphic DNA (RAPD) technique.

The UPGMA based dendrogram showed three distinct groups, which coincide with the geographical locations from where the isolates were collected. The total variation of 23% among the isolates confirmed that the isolates are of the same species and the source of variation can be due to the environmental factors. The variation can also be contributed by switching off and switching on of some genes under certain environmental conditions. 2013 Friends Science Publishers

Keywords: Citrus; Fungi; Penicillium italicum; RAPD; Random primers

Introduction

Citrus is one of the most important winter fruit crops of the world and has grown commercially in more than 100 countries across six continents (Terol et al., 2007). They contain several phytochemicals including vitamin C with disease preventing and life sustaining functions (Dillard and German, 2000). Pakistan is ranked 10th in citrus production worldwide (Sabir et al., 2010). Moreover, huge economic losses occur throughout the world due to post harvest diseases. In Pakistan, about 40% of total citrus produced is wasted during storage in post-harvest process (Naseer,2010), and is frequently reduced by fungal pathogens attack (Liu et al., 2007). Storage fungi can reduce the shelf life and acceptability of fresh produce.

Blue mold, caused by Penicillium italicum, is generally severe postharvest disease of citrus, which costs the loss up to 25% of the total production worldwide (Palou et al., 2007; Montesinos-Herrero et al., 2009). Mold growth in citrus fruit leads to the production of the hazardous mycotoxins (Moss, 2008). Taxonomic relationships of fungal species have been clarified by applying many phenotypic and genotypic approaches (Varga et al., 2000).

The molecular markers including biochemical protein markers and DNA markers are extremely valuable tools for weighing genetic similarity and determining species individualities. Among the DNA molecular markers, random amplified polymorphic DNA (RAPD) typically are more eminent due to high variability and reproducibility with an added advantage of no prior knowledge of DNA sequence for the fingerprinting of any genomic DNA. Analysis of genetic diversity among closely related species is crucial step towards understanding the fungal populations.

The objectives of this investigation were to characterize storage fungi isolated from stored citrus fruit of different storage houses in Punjab using morphological characteristics and to find the most occurring storage fungi among the storage fungi and to assess the diversity among these isolates through RAPD-PCR technique to show genetic variability within and between these isolates.

Materials and Methods

Sample Collection

Samples of citrus fruits were collected from different cold storage houses in eight major citrus growing areas of Province Punjab, Pakistan. These samples were placed in separate sterile plastic bags; transferred to the laboratory and kept in refrigerator at 4oC till further analysis. These regions were selected on the basis of their fruit production importance.

Isolation and Identification of Storage Fungi

Isolation of storage fungi from each of the collected fruit sample was carried out by using the technique of Baiyewu et al. (2007). A small portion of disease tissue were cut with sterile scalpel and placed on previously prepared Malt extract agar and Potato dextrose agar medium plates and incubated at 25+-1oC for 7 days. The developing fungal colonies were counted to calculate percentage frequency and further characterized on morphological basis by using the most documented keys and literature for fungal identification (Samson and Varga, 2007). Percentage frequency of individual isolated fungal species was determined by using the method described by Giridher and Ready (1997) as:

Finding Genetic variation in all Isolates

According to the percentage of occurrence, P. italicum was selected for genetic analysis as a most abundant blue mold fungus on citrus during storage. Genetic variation of eight morphologically similar but geographically distinct P. italicum isolates was carried out using RAPD analysis.

DNA Extraction

The total genomic DNA was extracted by using CTAB method (Doyle and Doyle, 1991) form the fungal mat and ground to fine powder with Fermentas glass beads. The freshly prepared pre-warmed (65oC) extraction solution was added to the powdered fungal mass in new autoclaved Eppendorf (1.5 mL) tubes and incubated at 65oC. An equal volume of solution Choloform isoamyl alcohol (24:1) was added and centrifuged at 10,000 x g to separate the phases.

Aqueous supernatants were transferred to new tubes and 2/3 volume of cold isopropanol was added. The sample was centrifuged and transparent DNA pellets were obtained. After washing, the pellets were air dried and resuspended in50 uL of Tris HCl EDTA (TE) buffer.

Estimation of Quantity and Quality of DNA

The quantity and quality of extracted DNA was determined by Techne Spec gene Spectrophotometer (140801-2, UK). The concentration was calculated on assumption that absorbance of 1 at 260 nm is equivalent to 50 mg/mL double stranded DNA or 40 mg/mL single stranded DNA (Sambrook et al., 1989). The quantity of DNA was calculated by the following equation:

DNA Con (ug/mL) - Absorbance at 260 nm xDilution factor x50

The quality of the DNA was also estimated through 1% agarose gel electrophoresis in which DNA bands were compared with the 1kb DNA markers showing the concentrations of DNA in ng/uL. Hence, the DNA concentration was maintained to 25 ng/uL for polymerase chain reaction (PCR) amplifications.

Random Amplification of Polymorphic DNA Analysis

The RAPD analysis is a valuable tool for studying DNA polymorphism in different fungal isolates for exploring phylogenetic relationships among them. RAPD analysis was carried out by following the method described by Ranganath et al. (2002).

Random Primer Screening

A set of 20 primers procured from School of Biological Sciences (SBS) Genetech Co. Ltd-Beijing, China were used in RAPD analysis for the initial screening (Table 1). Majority of these primers produced clear, distinct and reproducible polymorphic bands in different isolates of P. italicum. The primers were diluted up to 100 picomole concentration before use in RAPD analysis. PCR reactions were carried out in 25 uL volume containing PCR Buffer (10X), 2.5 mM MgCl2, 0.2 mM of each dNTP, and 0.6 U DNA polymerase (Enzynomics, Korea). PCR conditions and separation of RAPD-PCR fragments were done according to Messner et al. (1994). The amplifications were carried out in Techne-412 thermal cycler with temperature profile as initial denaturation at 94oC for 5 min and then primers were subjected for denaturation at 94oC for 1 min, annealing at 25oC for 1 min and final extension at 72oC for 5 min to a total of 40 cycles.

Statistical Analysis

RAPD profiles were recorded by visually comparing RAPD amplification profiles and scoring the presence or absence of each band for each primer (Halmschlager et al., 1994). The bands obtained from 2% agarose gel electrophoresis were combined in a binary matrix in two - discrete - characters - matrix (0 and 1 for absence and presence of RAPD - markers, respectively). In order to assess over all distribution of genetic diversity, data was analyzed by using MINITAB software (MINITAB, 2004).

Results

In the present study, different fungi associated with the deterioration of citrus fruit during cold storage were isolated from the collected fruit samples. A total of sixteen fungal species belonging to seven different genera included were isolated and identified on the basis of their cultural and morphological characteristics which are revealed in detail in Table 1. The frequency of occurrence of each isolate of fungi which showed that P. italicum was the most frequently isolated fungus with the highest occurrence of 29.75% among all isolates, followed by the Aspergillus niger (14.87%), A. flavus (9.09%), A. fumigatus (7.43%), A. terreus and P. verrucosum (5.78%), Rhizo pus arrhizus (4.95%), R. stolonifer (4.13%), A. parasiticus and Fusarium

Table 1: Morphological Characteristics of Different Storage Fungi Isolated from Stored Citrus Fruit

Name of fungus###Colony diameter Colony Texture Obverse###Reverse###Character of hyphae###conidiophore###conidia

Penicillium###5-6 cm###bluish###yellow###septate, hyaline###smooth walled###ellipsoidal to cylindrical

italicum###green###brown

Penicillium###2.5-3.5 cm###velvety###or grey green yellowish###septate, hyaline###two-stage branched,###globose to subglobose

verrucosum###almost floccose###brown###rough walled

Penicillium###2-3 cm###blue green###bright###septate, hyaline###smooth###walled,###globose to subglobose,

citrinum###yellow###matulae and phailides###sooth walled

###present

Aspergillus###5-6 cm###powdery###black###Off-white conidial head radiate, broad, long, thick###globose ,###irregularly

niger###conidia###matulae###and walled, brownish###roughened,

###phailides present

Aspergillus###6-7 cm###powdery###yellow###Pale brown conidial head radiate,###hyaline, long, rough###globose to subglobose,

flavus###green###walled,###finely roughened to

###echinulate

Aspergillus###7 cm###bluish###Greyish###Vesicle###pyriform, clavate vesicle, thick###Smooth, globose to

fumigatus###green###uniseriate###walled###subglobose

Aspergillus###6-7 cm###velvety###or orange###uncolored###matulae present, conidial###smooth###walled,###globose###to###slightly

terreus###almost floccose brown###to###heads columnar,###with###ellipsoidal,###smooth

###brown###hemispherical vesicle###walled

Aspergillus###5-6cm###green###green###matulae and phailides smooth###walled,###cylindrical to ellipsoidal,

awamorii###present###vesicle subglobose###coarsely roughened

Aspergillus###5-6 cm###green###colorless###Uniseriate,###vesicle roughened, matulae###echinulate and coarsely

parasiticus###spherical###absent###spiny

Rhizopus###cottony###white###brown###Hyphae branched and sporangiophore short,###spoangiospores ovoid to

arrhizus###aseptate, rhizoids present columella globose###more or less globose,

###dark in color

Rhizopus###fluffy###greyish###yellow###columella subglobose to sporangiophore###sporangia pale to brown,

stolonifer###brown###oval###subglobose rigid,###straight, sporangiospore

###thick walled

Mucor sp.###full plate###cottony###white###to Brownish###Columella###obovoid, Sporangiophore short###Sporangia brownish to

###yellow###ellipsoidal, with truncate branches,###recurved###grey, spores ellipsoidal to

###base###and encrusted wall###subglobose

Fusarium###4.6-6.5 cm###sparce###to white###purple###Macroconidia present###septate,###fusiform,

oxysporum###floccose###moderately###curved,

###pointed at both ends

Fusarium###4.5-6.5###floccose###whitish###cream###macroconidia present###curved, short, with blunt

solani###apical and pedicellate

###basal cells

Alternaria###6-7 cm###dark brown###Hyphae branched and conidiophore simple,###conidia formed in long

alternata###blackish,###septate, brown in color straight and curved###chain, ovoid, obclavate

###and dark brown in color

Dreshlera sp.###4-5.5 cm###dark brown yellow###to conidiophore , conidia###simple and branched###Cylindrical or ellipsoidal,

###to black###brown###septate with round ends.

oxysporum (3.3%), P. citrinum, A. awamorii and Alternaria alternata (2.47%), F. solani and Mucor sp. (1.65%) with Dreshlera sp. having the least occurrence of 0.82% (Table2).

The morphological characteristics of P. italicum such as colonies on Malt Extract Agar (MEA) medium were 5-6 cm in diameter after 7 days. The colonies were bluish green in color with velvety and floccose and reverse side of the colony is yellow to brown. The microscopic characteristics such as septate and hyaline hyphae; conidiophores smooth walled and conidia ellipsoidal to cylindrical in shape smooth walled and blue in color were observed. The cultural and microscopic characteristics of P. italicum seen in the present study were correlated to those as described by Singh et al. (1991).

Eight geographically distinct isolates of P. italicum were collected during this study and subjected to further characterization by using RAPD-PCR technique (Table 3). A total of 20 RAPD decamers (Table 4) were used for testing the genetic variability among eight isolates of P. italicum of which two primers (Primer SBSA08 and SBSA15) did not show any amplification and hence dropped in the initial screening of the random primers. Remaining 18 random primers produced easily scorable and reproducible banding patterns, which were designated in genetic coefficient matrix in Minitab 16 software for further analysis. Total amplified polymorphic bands ranged from approximately 200 bp to 2000 bp sizes in the RAPD profile. There was a low percentage of polymorphism in different isolates of P. italicum. The most probable reason is that the isolates are of single species, which was correspondingly seen by their similar morphology. The average number of polymorphic bands perceived per primer was 8.22.

The RAPD profiles produced with the primers (SBSA06, SBSA07, SBSA11, SBSA12, SBSA13, and SBSA18) and banding pattern are shown in Fig. 1. The ladder 100 bp was run as markers on

Table 2: Frequency of occurrence of fungi isolated from stored citrus fruit

Fungi isolated###% Frequency of occurrence

Penicillium italicum###29.75

P. verrucosum###5.78

P. citrinum###2.47

Aspergillus niger###14.87

A. flavus###9.09

A. fumigatus###7.43

A. terreus###5.78

A. awamorii###2.47

A. parasiticus###3.3

Rhizopus arrhizus###4.95

R. stolonifer###4.13

Mucor sp.###1.65

Fusarium oxysporum###3.3

F. solani###1.65

Alternaria alternata###2.47

Dreshlera sp.###0.82

Table 3: Qualitative and quantitative spectrophotometric analysis of extracted DNA

P. italicum Spectrophotometric reading of Ratio###Conc. of Extracted

isolates###Extracted DNA###260/280 DNA (ug/ml)

###at 260 nm at 280 nm

Pi.Lhr###1.504###1.332###1.13###60

Pi Mul###0.812###0.866###0.94###29

Pi Fsd###0.046###0.056###0.82###1.0

Pi Chn###1.479###1.303###1.13###59

Pi Jhg###0.084###0.080###1.04###3.0

Pi Bhk###0.163###0.175###0.93###6.0

Pi Sh###0.001###0.001###1.00###4.5

Pi Sgd###0.123###0.117###1.06###5.0

both sides along with the negative control in which only water was used instead of DNA that indicates the credibility of the reaction mixture having no amplified band.

A dendogram based on UPGMA analysis indicated that the eight isolates formed three major groups GI, G2 and G3 confirming some level of genetic variation among the isolates of P. italicum (Fig. 2). The similarity coefficient ranged from 0 to 0.23 indicating that there is no 100% similarity occurs among any two isolates. Group 1 was further divided in to three subgroups containing five isolates naming Pi Lhr, Pi Mul, Pi Jhg, Pi Bhk and Pi Sdg. G2 consisted of two isolates, Pi Fsd and Pi Chn while G3 consisted of only one isolate, Pi Sh.

The first subgroup consisted of two isolates collected from Lahore and Multan, which were 3% distant from each other while this subgroup is 9% distant from the second subgroup containing two isolates collected from Jhang and Bhakar regions of Punjab. There is much similarity seen in isolates collected from Jhang and Bhakar, which are 1% distant from each other. This subgroup was 5% distant from the third subgroup which contained only one isolate collected from Sargodha cold storage house. G2 is 2% distant from G1, while G3 was 4% and 6% distant from G1 and G2, respectively.

Discussion

This study showed that a number of storage fungi of genera Aspergillus, Penicillium, Rhizopus, Fusarium, Alternaria, Dreschlera, and Mucor are associated with the spoilage and loss of citrus fruit during storage in Pakistan. The most abundant of all these fungi was P. italicum. Several Penicillium species were frequently established on citrus fruits and cause storage rot commonly referred as blue and green mold (Filtenborg et al., 1996). Bukar et al. (2009) who reported that six genera of fungi namely Penicillium sp., Aspergillus sp., Fusarium sp., Rhizopus sp., Alternaria sp. and Mucor sp. were associated with massive deterioration of citrus fruit. Similarly, Niji et al. (1997) reported that A. niger was associated with the decay of citrus fruit. P. digitatum, R. stolonifer and A. niger have also

Table 4: Random twenty decamers used in initial screening, their accessions, sequences, number of polymorphic bands, percentage of polymorphic products and size of bands produced by each primer

Name###Sequence ( 5'- 3' )###nmol###Total no. of Bands###No. of poly morphic bands###%age of polymorphic bands###Size of bands (bp)

SBSA01###CAG GCC CTT C###111.3###40###11###28%###250-1000

SBSA02###TGC CGA GCT G###108.4###39###7###17%###200-1500

SBSA03###AGT CAG CCA G###110.1###39###15###38%###200-700

SBSA04###AAT CGG GCT G###107.6###45###10###7%###300-1000

SBSA05###AGG GGT CTT G###106.5###29###5###17%###300-900

SBSA06###GGT CCC TGA C###109.9###37###5###14%###200-1200

SBSA07###GAA ACG GGT G###105.9###34###13###38%###400-1800

SBSA09###GGG TAA CGC C###108.1###46###6###13%###200-1400

SBSA10###GTG ATC GCA G###107.6###39###15###38%###270-1500

SBSA11###CAA TCG CCG T###110.4###41###9###22%###200-1600

SBSA12###TCG GCG ATA G###107.6###42###18###43%###400-1900

SBSA13###CAG CAC CCA C###112.2###63###7###11%###340-2000

SBSA14###TCT GTG CTG G###108.2###14###6###43%###350-800

SBSA16###AGC CAG CGA A###108.3###10###2###20%###300-1500

SBSA17###GAC CGC TTG T###109.3###11###3###27%###900-1500

SBSA18###ACG TGA CCG T###107.6###50###2###4%###200-1400

SBSA19###CAA ACG TCG G###108.7###47###7###15%###250-1100

SBSA20###GTT GCG ATC C###109.3###45###5###11%###200-1100

Fig. 1: RAPD profile of eight isolates (1-8 shown in Table 3) of P. italicum produced by random primers (SBSA06, SBSA07, SBSA11, SBSA12, SBSA13, and SBSA18. Molecular weight markers (M in bps) are indicated on the both sides (100 bp DNA ladder, cat # DM001), -ve sign shows the well with negative control in PCR reaction

Fig. 2: UPGMA cluster analysis based dendogram depicting the genetic relationship among different P. italicum isolates been isolated from orange fruits (Akintobi et al., 2011). Al- Hindi et al. (2011), showed that more than 90% of citrus fruit were under fungal decay. Numbers of Aspergillus species have been reported such as A. niger, A. fumigatus, A. nidulans, A. variecolour and A. candidus. Fusarium spp were also the most commonly associated fungi in citrus fruits (Tournas and Katsoudas, 2005).

The morphological characteristics of P. italicum of the lab cultured isolates collected from different citrus producing districts of Punjab in Pakistan were closely related. This morphological study was not sufficient in examining the diversity among these isolates. Therefore, with the advent of modern approaches including molecular and genetic marker studies, these isolates were further characterized by the RAPD fingerprinting technique. Dupont et al. (1999) reported that the molecular markers reveal comparatively significant level of similarities among twelve Penicillium species whereas morphological characterization exhibited moderate level of similarities. Variations on genetic material cannot be studied morphologically, while RAPD technique may overcome such type of problems and is very effective for microbial species characterizations (Tiwari et al., 2011). The results shown in dendogram are completely compatible with the geographical locations and belts from where the isolates have been collected.

Lahore and Multan are distant but fall in the same belt in citrus producing areas of the Punjab. Lahore, Multan, Bhakar, Jhang and Sargodha fall in the same geographical belt, whereas Chiniot and Faisalabad render a separate region. Consequently the collected isolates from different regions form distinct groups showing a range of variability as seen by UPGMA results. Sahiwal being more close to southern Punjab showed more variation i.e., 23% compared to other isolates. Here another point of concern cannot be negated that the mutation frequencies fluctuate considerably along the genomic nucleotide sequences such that mutations focus at certain positions called hotspots. Mutation hotspots in DNA reflect the effect of the environmental factors in which the organism prevail (Rozin and Pavlov, 2003).

These mutations are largely due to the point mutations, insertions, deletions, inversions and translocations in the chromosomes, which cause the variability in the genome that is easily detected through the fingerprinting process using various molecular marker tools such as RAPD.

The citrus producing belt is in extreme danger from P. italicum due to its most occurrences in storage conditions. Therefore, suitable integrated control measure should be taken to reduce this threat. Most probably the bio-control measures are more efficient, environmental safe and cost effective in a country like Pakistan. Accordingly, the future studies should be focused on the use of environmentally safer control measures.

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Institute of Agricultural Sciences, Quaid-e-Azam Campus, University of the Punjab, Lahore-54590, Pakistan

For Correspondence: tehminaanjum@yahoo.com
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Author:Akhtar, Nosheen; Anjum, Tehmina; Jabeen, Rasheda
Publication:International Journal of Agriculture and Biology
Article Type:Report
Geographic Code:9PAKI
Date:Dec 31, 2013
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