<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE article  PUBLIC "-//NLM//DTD Journal Publishing DTD v3.0 20080202//EN" "http://dtd.nlm.nih.gov/publishing/3.0/journalpublishing3.dtd"><article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" dtd-version="3.0" xml:lang="en" article-type="research article"><front><journal-meta><journal-id journal-id-type="publisher-id">AS</journal-id><journal-title-group><journal-title>Agricultural Sciences</journal-title></journal-title-group><issn pub-type="epub">2156-8553</issn><publisher><publisher-name>Scientific Research Publishing</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="doi">10.4236/as.2018.98068</article-id><article-id pub-id-type="publisher-id">AS-86748</article-id><article-categories><subj-group subj-group-type="heading"><subject>Articles</subject></subj-group><subj-group subj-group-type="Discipline-v2"><subject>Biomedical&amp;Life Sciences</subject><subject> Earth&amp;Environmental Sciences</subject></subj-group></article-categories><title-group><article-title>
 
 
  Biology and Physiology of &lt;I&gt;Colletotrichum acutatum&lt;/I&gt; Strains Causing Strawberry’s Anthracnose
 
</article-title></title-group><contrib-group><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Rababe</surname><given-names>Es-Soufi</given-names></name><xref ref-type="aff" rid="aff1"><sup>1</sup></xref><xref ref-type="corresp" rid="cor1"><sup>*</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Mohammed</surname><given-names>L’bachir El Kbiach</given-names></name><xref ref-type="aff" rid="aff1"><sup>1</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Tomader</surname><given-names>Errabii</given-names></name><xref ref-type="aff" rid="aff1"><sup>1</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Rabah</surname><given-names>Saidi</given-names></name><xref ref-type="aff" rid="aff2"><sup>2</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Alain</surname><given-names>Badoc</given-names></name><xref ref-type="aff" rid="aff3"><sup>3</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Ludovic</surname><given-names>Chaveriat</given-names></name><xref ref-type="aff" rid="aff4"><sup>4</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Patrick</surname><given-names>Martin</given-names></name><xref ref-type="aff" rid="aff4"><sup>4</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Ahmed</surname><given-names>Lamarti</given-names></name><xref ref-type="aff" rid="aff1"><sup>1</sup></xref></contrib></contrib-group><aff id="aff1"><addr-line>Laboratory of Plant Biotechnology, Biology Department, Faculty of Sciences, Abdelmalek Essaadi University, Tetouan, Morocco</addr-line></aff><aff id="aff3"><addr-line>Unité de Recherche &amp;amp;OElig;nologie, Axe Molécules d’Intérêt Biologique (MIB), University of Bordeaux, Villenave-d’Ornon, France</addr-line></aff><aff id="aff4"><addr-line>Artois University, UniLasalle, EA7519-Unité Transformations and Agro-Ressources, Béthune, France</addr-line></aff><aff id="aff2"><addr-line>Department of Matter and Life Sciences, High Normal School, Martil, Morocco</addr-line></aff><author-notes><corresp id="cor1">* E-mail:<email>rababeessoufi@gmail.co(RE)</email>;</corresp></author-notes><pub-date pub-type="epub"><day>09</day><month>08</month><year>2018</year></pub-date><volume>09</volume><issue>08</issue><fpage>974</fpage><lpage>990</lpage><history><date date-type="received"><day>19,</day>	<month>July</month>	<year>2018</year></date><date date-type="rev-recd"><day>17,</day>	<month>August</month>	<year>2018</year>	</date><date date-type="accepted"><day>20,</day>	<month>August</month>	<year>2018</year></date></history><permissions><copyright-statement>&#169; Copyright  2014 by authors and Scientific Research Publishing Inc. </copyright-statement><copyright-year>2014</copyright-year><license><license-p>This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/</license-p></license></permissions><abstract><p>
 
 
  Seven 
  <em>Colletotrichum acutatum</em> strains isolated from strawberries were cultivated on various culture media and tested 
  <em>in vitro</em> and 
  <em>in vivo</em> on 
  <em>Fragaria x ananassa</em> for anthracnose symptoms. PDA caused an optimum growth of all isolates, MEA, ML and Strawberry allowed a good but not optimal growth. Czapeck, Sabouraud and the organic medium from potato gave the lowest growth rate of all isolates. PDA allowed a good sporulation of isolates follow-up by strawberry, MEA; in contrast, ML, Czapeck and Sabouraud gave a low sporulation. The fungal development is maximal at 25
  &amp;degC and 27
  &amp;degC for all the isolates studied. No growth was observed at 5
  &amp;degC and 37
  &amp;degC. The studied strains developed at all pH values. They didn’t develop at 0.6, 0.65 and 0.7 aw but mycelial growth was perfect at 1 and 0.95 aw. The 
  <em>in vitro</em> test of the pathogenicity caused by 
  <em>C. acutatum</em> strains on strawberry’s leaves showed an increasing percentage of infection with time and different infection rates among 
  <em>C. acutatum</em> strains, strain Ca6 having a pathogenic power very high compared to the other isolates. After 
  <em>in vivo</em> inoculation and incubation of the seedlings, all isolates caused severe symptoms related to anthracnose on leaflets and petioles of the studied strawberry plants.
 
</p></abstract><kwd-group><kwd>Anthracnose</kwd><kwd> Strawberry</kwd><kwd> &lt;I&gt;Colletotrichum acutatum&lt;/I&gt;</kwd><kwd> Environmental Factors</kwd><kwd> Pathogenicity</kwd></kwd-group></article-meta></front><body><sec id="s1"><title>1. Introduction</title><p>Strawberry plant, Fragaria x ananassa, is one of the most widespread horticultural crop in the world. In Morocco, it was first introduced in the fifties, but its culture started toward the end of the seventies in two irrigated perimeters of the Loukkos and Souss-Massa. Ten years later the culture extended to the perimeter of the Gharb and then the area of Souss [<xref ref-type="bibr" rid="scirp.86748-ref1">1</xref>] . The climate in these regions allows the growth of strawberry in greenhouses but commercial fields are ideal for the development of a large number of diseases like anthracnose. The latter is regarded as an economically important disease affecting different hosts in the world caused by different species of Colletotrichum [<xref ref-type="bibr" rid="scirp.86748-ref2">2</xref>] [<xref ref-type="bibr" rid="scirp.86748-ref3">3</xref>] . Three species have been reported as causal agents of strawberry’s anthracnose: C. acutatum J. H. Simmonds, C. gloeosporioides (Penz.) Penz. &amp; Sacc., and C. fragariae A. N. Brooks [<xref ref-type="bibr" rid="scirp.86748-ref4">4</xref>] [<xref ref-type="bibr" rid="scirp.86748-ref5">5</xref>] .</p><p>C. gloeosporioides and C. acutatum are distributed on a large number of hosts in the world, whereas C. fragariae has a range of hosts very close [<xref ref-type="bibr" rid="scirp.86748-ref6">6</xref>] . Anthracnose causes up to 80% of death in nurseries and more than 50% loss of performance in the strawberry fields [<xref ref-type="bibr" rid="scirp.86748-ref7">7</xref>] . It has been defined as one of the most serious diseases in the commercial production of strawberry fruit. Colletotrichum acutatum is the most frequently species reported of the genus. It is today known as especially destructive on strawberry fruit [<xref ref-type="bibr" rid="scirp.86748-ref8">8</xref>] . It causes mainly black spots on fruit and can also attack crowns, roots and leaves [<xref ref-type="bibr" rid="scirp.86748-ref9">9</xref>] [<xref ref-type="bibr" rid="scirp.86748-ref10">10</xref>] [<xref ref-type="bibr" rid="scirp.86748-ref11">11</xref>] .</p><p>Environmental factors such as relative humidity, pH and temperature have been reported to have a profound influence on the virulence of a variety of fungi. The optimum temperatures for growth were often found between 25˚C and 30˚C; because of high temperatures the mycelial growth become weak and, in some cases, the mortality of fungi can occur. Several studies have been conducted on the effects of environmental factors on the growth of C. acutatum [<xref ref-type="bibr" rid="scirp.86748-ref12">12</xref>] .</p><p>In this context, the aim of this study was to examine the behavior of seven isolates of Colletotrichum acutatum by changing the medium composition, temperature, pH and water activity and to study the disease severity caused by these isolates on Fragaria x ananassa in vitro and in vivo.</p></sec><sec id="s2"><title>2. Materials and Methods</title><sec id="s2_1"><title>2.1. Fungal Material</title><p>Seven isolates of Colletotrichum acutatum (Ca1, Ca2, Ca3, Ca4, Ca5, Ca6 and Ca7) have been isolated from strawberry plants which has been collected from strawberry’s fields of Loukkos (Larache, Morocco) naturally affected by anthracnose, purified in Laboratory of Plant Biotechnology, Faculty of Sciences, Tetouan. They have been cultivated on PDA (Potato Dextrose Agar) medium for 7 to 10 days at 25˚C in the dark, and successive subculturing were made up within a total purification of strains.</p><p>Their identification has been carried out by macroscopic and microscopic observations with the help of determination keys [<xref ref-type="bibr" rid="scirp.86748-ref11">11</xref>] [<xref ref-type="bibr" rid="scirp.86748-ref13">13</xref>] .</p></sec><sec id="s2_2"><title>2.2. Study of the Pathogenicity of the Isolates of Colletotrichum acutatum</title><sec id="s2_2_1"><title>2.2.1. Plant Material</title><p>Fourteen strawberry plants (Fragaria x ananassa (Weston)) Duchesne ex Rozier cultivar Camarosa (<xref ref-type="fig" rid="fig1">Figure 1</xref>) were conducted at the Laboratory of the Plant Biotechnology in Faculty of Sciences of Tetouan in pots containing black sandy soils from the origin field of the plants. The plants were watered daily.</p></sec><sec id="s2_2_2"><title>2.2.2. Preparation of the Inoculum</title><p>Conidial suspensions of the isolates were obtained by adding 10 ml sterile distilled water on Petri dishes containing 10 to 15 day culture of C. acutatum on PDA, and gently rubbing the colonies using a sterile Pasteur pipette. At the end of spore release, the suspension of spores was filtered using sterile gauze nylon, pore size 100 μm. Concentration was determined using a Malassez cell.</p></sec><sec id="s2_2_3"><title>2.2.3. In Vitro Leaves Inoculation</title><p>Young and healthy leaflets were harvested, carefully washed with distilled water and disinfected with a solution of sodium hypochlorite (2% w/v) for five minutes followed by three washes of 15 minutes in sterile distilled water. Leaves have been dried under an air stream in laminar flow hood. They have been filed on sterile Petri dishes (four leaflets per box) containing a double layer of sterile filter paper previously soaked in sterile distilled water. Central lesions were incised with a sterile scalpel in each leaflet [<xref ref-type="bibr" rid="scirp.86748-ref14">14</xref>] . Three Petri dishes per strain were used.</p><p>On each lesion 30 &#181;l of C. acutatum’s suspension (10<sup>4</sup> spores/ml) was added (<xref ref-type="fig" rid="fig2">Figure 2</xref>); Petri dishes were incubated in dark at ambient temperature. As a blank, leaflets were inoculated by 30 &#181;l sterile distilled water. The test was repeated three times.</p><p>The pathogenicity was recorded on the following scale:</p><p>0 = no visible disease symptom;</p><p>1 = less than 15% of leaflet’s surface is infected;</p><p>2 = 15% - 35% of leaflet’s surface is infected;</p><p>3 = 36% - 49% of leaflet’s surface is infected;</p><p>4 = 50% - 74% of leaflet’s surface is infected;</p><p>5 = more than 75% of leaflet’s surface is infected.</p><p>The percent of pathogenicity was calculated by the formula bellow (1):</p><p>PDI = Sumofallnumericnotes Totalleaflet ’ ssurface &#215; maximalenote &#215; 100 (1)</p></sec><sec id="s2_2_4"><title>2.2.4. Inoculation in Vivo</title><p>Inoculation of plants was made by spraying 300 ml of conidial suspension of each tested pathogen (1 pot/strain). Plants were then covered for 48 hours with black plastic bags sprayed inside with sterile water to maintain a high relative humidity, necessary for germination and direct penetration of conidia (without injury). Pots were subsequently transferred in greenhouse (temperature ranging between 25˚C to 28˚C) in photoperiod. The percent of the pathogenicity degree in petioles (PDP) and leaflets (PDL) was calculated by (2) (3):</p><p>% PDP = Numberofinfectedpetioles Totalnumberofpetioles &#215; 100 (2)</p><p>% PDL = Numberofinfectedleaflets Totalnumberofleaflets &#215; 100 (3)</p></sec></sec><sec id="s2_3"><title>2.3. Growth and Sporulation of the Isolates of Colletotrichum acutatum on Culture Media</title><p>The isolates of Colletotrichum acutatum have been grown on four mixed culture media (Potato Dextrose Agar (PDA), Yeast Malt (ML), Sabouraud and Malt Extract Agar (MEA)), a semi-synthetic (Czapek) and two organic culture media (Strawberry and Potato (400 g of organic matter + 16 g of agar in 1000 ml of distilled water)). Growth and sporulation of each isolate were studied.</p></sec><sec id="s2_4"><title>2.4. Effect of Temperature on Mycelial Growth, Germination and Sporulation of the Isolates of Colletotrichum acutatum</title><p>Mycelial discs, from older cultures of ten days, were placed in Petri dishes of 70 mm containing the culture medium PDA. These plates were incubated in the dark at different temperatures (5˚C, 18˚C, 23˚C, 25˚C, 27˚C, 30˚C and 37˚C).</p></sec><sec id="s2_5"><title>2.5. Effect of pH on Mycelial Growth, Germination and Sporulation of the Isolates of Colletotrichum acutatum</title><p>The effect of pH on the development of Colletotrichum acutatum strains was tested at pH 4, 4.5, 5, 5.5, 6, 6.5, 7.5 and 8. The culture media PDA has been stamped, according to the desired pH, by different buffers (<xref ref-type="table" rid="table1">Table 1</xref>) [<xref ref-type="bibr" rid="scirp.86748-ref15">15</xref>] . Using a pH-meter, the pH was adjusted by addition of HCl and NaOH 1N [<xref ref-type="bibr" rid="scirp.86748-ref15">15</xref>] . Plates were incubated at 27˚C in the dark.</p></sec><sec id="s2_6"><title>2.6 Influence of the Water Activity on the Development of Seven Isolates of Colletotrichum acutatum</title><p>The water activity (aw) represents the availability in open water for the biochemical reactions for the development of microorganisms. Different values of activity of the water have been tested (1; 0.95; 0.90; 0.85; 0.80; 0.75; 0.70; 0.65 and 0.60) by the addition of glycerol in the culture medium PDA [<xref ref-type="bibr" rid="scirp.86748-ref15">15</xref>] [<xref ref-type="bibr" rid="scirp.86748-ref16">16</xref>] , which will attach a part of the water and make it unusable to microorganisms.</p></sec><sec id="s2_7"><title>2.7. The Studied Factors Were Tested on</title><sec id="s2_7_1"><title>2.7.1. The Mycelial Growth</title><p>For each medium, three Petri dishes were inoculated in their center by mycelial discs of 5mm diameter. After ten-day incubation at 25˚C in the dark, the growth</p><table-wrap id="table1" ><label><xref ref-type="table" rid="table1">Table 1</xref></label><caption><title> Different values and buffers of used pH</title></caption><table><tbody><thead><tr><th align="center" valign="middle"  rowspan="2"  >pH</th><th align="center" valign="middle"  colspan="2"  >Buffer</th><th align="center" valign="middle"  rowspan="2"  >Molecular weight</th><th align="center" valign="middle"  rowspan="2"  >20 mM (g/l)</th></tr></thead><tr><td align="center" valign="middle" >Common</td><td align="center" valign="middle" >Chemical</td></tr><tr><td align="center" valign="middle" >4</td><td align="center" valign="middle"  rowspan="2"  >Trizma (TrisHCl)</td><td align="center" valign="middle"  rowspan="2"  >2-amino-2-(hydroxymethyl)-1,3-propanediol, hydrochloride</td><td align="center" valign="middle"  rowspan="2"  >157.59</td><td align="center" valign="middle"  rowspan="2"  >3.152</td></tr><tr><td align="center" valign="middle" >4.5</td></tr><tr><td align="center" valign="middle" >5</td><td align="center" valign="middle"  rowspan="3"  >MES</td><td align="center" valign="middle"  rowspan="3"  >2-(N-morpholino)ethanesulfonic acid</td><td align="center" valign="middle"  rowspan="3"  >213.25</td><td align="center" valign="middle"  rowspan="3"  >4.265</td></tr><tr><td align="center" valign="middle" >5.5</td></tr><tr><td align="center" valign="middle" >6</td></tr><tr><td align="center" valign="middle" >6.5</td><td align="center" valign="middle" >PIPES</td><td align="center" valign="middle" >piperazine-N,N’-bis (2-ethanesulfonic acid)</td><td align="center" valign="middle" >302.4</td><td align="center" valign="middle" >6.048</td></tr><tr><td align="center" valign="middle" >7.5</td><td align="center" valign="middle" >MOPS</td><td align="center" valign="middle" >3-(N-morpholino)propanesulfonic acid</td><td align="center" valign="middle" >209.3</td><td align="center" valign="middle" >4.186</td></tr><tr><td align="center" valign="middle" >8</td><td align="center" valign="middle" >BICINE</td><td align="center" valign="middle" >N,N-bis(2-hydroxyethyl)glycine</td><td align="center" valign="middle" >163.2</td><td align="center" valign="middle" >3.264</td></tr></tbody></table></table-wrap><p>has been recorded by measuring the mycelial growth rate (G) (4)</p><p>G = Sumof2perpendiculardiameters 2 (4)</p></sec><sec id="s2_7_2"><title>2.7.2. The Sporulation</title><p>It was evaluated with the help of a Malassez cell. Conidia were obtained from ten-day cultures by placing 2 discs in a 5 ml tube containing 2 ml sterile distilled water and agitation on a vortex.</p></sec><sec id="s2_7_3"><title>2.7.3. The Germination</title><p>30 &#181;l of a suspension of 10<sup>4</sup> spores/ml was spread on the surface of Petri dishes containing 0.5 g agar/100 ml distilled water. The counting of the germinated spores was carried out on a total of 100 spores after 24-hour incubation at 25˚C. In each test, three Petri dishes were used and the experiment was repeated three times.</p></sec></sec></sec><sec id="s3"><title>3. Statistical Analysis</title><p>Before you begin to format your paper, Isolates development rates have been subjected to analysis of variance (ANOVA) using STATISTICA software for Windows V.6. The statistical significance of the results was determined by performing a test of Duncan’s multiple range (p &lt; 0.05).</p></sec><sec id="s4"><title>4. Results</title><sec id="s4_1"><title>4.1. Pathogenicity of Isolates of Colletotrichum acutatum</title><sec id="s4_1_1"><title>4.1.1. In Vitro</title><p>The percentage of infection on strawberries leaves increases with time and there is a difference in the rate of infection among different isolates (<xref ref-type="fig" rid="fig3">Figure 3</xref>). Strain Ca1 in the first 3 days does not show any spot on the leaves against the other strains where the percentages of infection vary between 5 (Ca2, Ca3 and Ca4) and 20% (Ca6). Strain Ca6 has a pathogenic power very high compared to the</p><p>other isolates. After 11-day incubation, strain Ca6 reached up to 95% infection, all inoculated leaves being infected (<xref ref-type="fig" rid="fig3">Figure 3</xref> and <xref ref-type="fig" rid="fig4">Figure 4</xref>). All leaflets inoculated with isolates showed symptoms typical of anthracnose symptoms with black spots at the surface of the leaflets (<xref ref-type="fig" rid="fig4">Figure 4</xref>).</p></sec><sec id="s4_1_2"><title>4.1.2. In Vivo</title><p>After the inoculation and incubation of the seedlings, all the isolates cause severe symptoms typical from anthracnose on leaflets and petioles. The severities of the disease for each isolate increase in the course of time. Isolate Ca6 is the most aggressive among other isolates on leaflets and petioles (Figures 5-7).</p></sec></sec><sec id="s4_2"><title>4.2. Effect of Culture Medium</title><p>All culture media have enabled the mycelial growth of Colletotrichum acutatum (<xref ref-type="fig" rid="fig8">Figure 8</xref>) with different means of development (<xref ref-type="table" rid="table2">Table 2</xref>). PDA remains the culture medium the most favorable for the mycelial growth of Colletotrichum acutatum, with a maximum enlargement of all isolates. MEA, ML and Strawberry have allowed a good growth but not optimal. Czapeck and Sabouraud have given an average growth of all isolates.</p><p>PDA has allowed a good sporulation of isolates follow-up by Strawberry, MEA while ML, Czapeck and Sabouraud have allowed low sporulation (<xref ref-type="table" rid="table2">Table 2</xref>).</p></sec><sec id="s4_3"><title>4.3. Effect of Temperature</title><p>All isolates didn’t develop at 5˚C and 37˚C (Figures 9-12). Mycelial growth is low at 30˚C, average at 18˚C, maximum at 25˚C and 27˚C for all the isolates studied (<xref ref-type="fig" rid="fig1">Figure 1</xref>0).</p><p>The seven isolates sporulate weakly at 18˚C and 3˚C. Sporulation is maximal at 25˚C and 27˚C and averages 23˚C for all the isolates studied (<xref ref-type="fig" rid="fig1">Figure 1</xref>1).</p><table-wrap id="table2" ><label><xref ref-type="table" rid="table2">Table 2</xref></label><caption><title> Effect of seven culture media on the mycelial growth (mm) after 10-day incubation and sporulation of Colletotrichum acutatum</title></caption><table><tbody><thead><tr><th align="center" valign="middle" >Culture medium</th><th align="center" valign="middle" >Mycelial growth (mm)</th><th align="center" valign="middle" >Sporulation (&#215;10<sup>4</sup>)</th></tr></thead><tr><td align="center" valign="middle" >Mixed medium</td><td align="center" valign="middle" ></td><td align="center" valign="middle" ></td></tr><tr><td align="center" valign="middle" >Potato Dextrose Agar (PDA)</td><td align="center" valign="middle" >70.00 &#177; 0.00 a</td><td align="center" valign="middle" >34.44 &#177; 0.86 a</td></tr><tr><td align="center" valign="middle" >Yeast Malt (ML)</td><td align="center" valign="middle" >66.31 &#177; 0.43 ab</td><td align="center" valign="middle" >19.03 &#177; 1.12 bc</td></tr><tr><td align="center" valign="middle" >Malt Extract Agar (MEA)</td><td align="center" valign="middle" >65.30 &#177; 0.93 ab</td><td align="center" valign="middle" >1.10 &#177; 0.29 d</td></tr><tr><td align="center" valign="middle" >Sabouraud</td><td align="center" valign="middle" >49.14 &#177; 0.47 bc</td><td align="center" valign="middle" >1.02 &#177; 0.18 d</td></tr><tr><td align="center" valign="middle" >Semi-synthetic medium</td><td align="center" valign="middle" ></td><td align="center" valign="middle" ></td></tr><tr><td align="center" valign="middle" >Czapeck</td><td align="center" valign="middle" >55.67 &#177; 1.09 c</td><td align="center" valign="middle" >1.50 &#177; 0.32 d</td></tr><tr><td align="center" valign="middle" >Organic medium</td><td align="center" valign="middle" ></td><td align="center" valign="middle" ></td></tr><tr><td align="center" valign="middle" >Strawberry</td><td align="center" valign="middle" >61.76 &#177; 0.98 b</td><td align="center" valign="middle" >26.78 &#177; 1.12 b</td></tr><tr><td align="center" valign="middle" >Potato</td><td align="center" valign="middle" >52.60 &#177; 0.43 bc</td><td align="center" valign="middle" >10.59 &#177; 0.62 c</td></tr></tbody></table></table-wrap><p>Averages of a column with the same letter are not significantly different between them at the threshold of 5%.</p><p>The conidia do not germinate at 5˚C and 37˚C. Conidial germination of all species studied is medium at 18˚C and 30˚C and maximal at 23˚C, 25˚C and 27˚C (<xref ref-type="fig" rid="fig1">Figure 1</xref>2).</p></sec><sec id="s4_4"><title>4.4. Effect of pH</title><p>All isolates studied developed at all pH values (Figures 13-16). The mycelial growth is maximum at pH 5 and 5.5.</p><p>All isolates of C. acutatum germinated perfectly at pH = 4.5, 5, 5.5 and 6, and sporulated perfectly at pH 5, 5.5 and 6, moderately to pH 4 and 4.5 and weakly to pH 7.5 and 8.</p></sec><sec id="s4_5"><title>4.5. Effect of the Water Activity</title><p>All isolates do not develop at aw 0.6, 0.65 and 0.7. The mycelial growth is perfect at aw 1 and 0.95, average at aw 0.85 and 0.90, and low at aw 0.75 and 0.8 (<xref ref-type="fig" rid="fig1">Figure 1</xref>7 and <xref ref-type="fig" rid="fig1">Figure 1</xref>8). Sporulation is perfect to aw 1, average at aw (0.9 and 0.95) and low at aw (0.75, 0.8 and 0.85) (<xref ref-type="fig" rid="fig1">Figure 1</xref>9). The germination is maximal at aw 1, average at aw (0.9 and 0.95) and low at aw (0.75, 0.8 and 0.85) (<xref ref-type="fig" rid="fig2">Figure 2</xref>0).</p></sec></sec><sec id="s5"><title>5. Discussion and Conclusion</title><p>Colletotrichum acutatum strains cause symptoms related to the anthracnose in vitro and in vivo but the severity of the disease varies from an isolate to another, isolate Ca6 representing a high level of aggressiveness among the strains studied; the percent of pathogenicity has been affected to 92% after 11 days of the in vitro inoculation and 100% after 20 days of the in vivo inoculation. Peres et al., [<xref ref-type="bibr" rid="scirp.86748-ref17">17</xref>] have described that the symptoms caused by C. acutatum are mainly necrosis including burns on various types of tissues of the host such as leaves, petioles on a wide range of hosts. By comparing the pathogenicity of C. acutatum and C. fragariae on fruit, petioles and roots of Fragaria x ananassa, Tanaka et al., [<xref ref-type="bibr" rid="scirp.86748-ref18">18</xref>] have found that C. acutatum is less aggressive than C. fragariae against this host. Same results were found by Smith and Black [<xref ref-type="bibr" rid="scirp.86748-ref11">11</xref>] and McInnes et al., [<xref ref-type="bibr" rid="scirp.86748-ref19">19</xref>] who have noted the association of C. acutatum with lesions of the rhizomes. C. acutatum from strawberry can parasitize and cause diseases on other hosts [<xref ref-type="bibr" rid="scirp.86748-ref19">19</xref>] [<xref ref-type="bibr" rid="scirp.86748-ref20">20</xref>] [<xref ref-type="bibr" rid="scirp.86748-ref21">21</xref>] or, alternatively, survive on other cultures and on weeds without producing symptoms. Smith and Black [<xref ref-type="bibr" rid="scirp.86748-ref11">11</xref>] , Peres et al., [<xref ref-type="bibr" rid="scirp.86748-ref17">17</xref>] and Hyde et al., [<xref ref-type="bibr" rid="scirp.86748-ref21">21</xref>] have found that their studied Colletotrichum acutatum isolates haven’t caused leaf lesions on wounded inoculated leaves unlike two other Colletotrichum species whereas, in our study, all the isolates tested caused lesions on the strawberry leaves in vitro. C. acutatum isolated from almond and peach were demonstrated to be pathogenic on wounded and nonwounded fruit [<xref ref-type="bibr" rid="scirp.86748-ref22">22</xref>] ; artificial inoculations demonstrated that fruits of all host species except for the banana were susceptible to C. acutatum isolates from strawberry [<xref ref-type="bibr" rid="scirp.86748-ref23">23</xref>] .</p><p>Fungi generally require different pH and temperature conditions during the course of their development. These two factors influence the stages of their life cycle. The development of Colletotrichum acutatum changes with the environmental factors studied (culture medium composition, temperature, pH and aw).</p><p>Mycelial growth and sporulation of the strains are perfect in the culture medium PDA, followed by MEA and Strawberry. For ML, mycelial growth was good but the sporulation was very low as in the other culture media. PDA has been used as the base culture medium for the isolation, purification and growth of Colletotrichum species causal agents of grown strawberry’s anthracnose [<xref ref-type="bibr" rid="scirp.86748-ref5">5</xref>] [<xref ref-type="bibr" rid="scirp.86748-ref11">11</xref>] [<xref ref-type="bibr" rid="scirp.86748-ref24">24</xref>] [<xref ref-type="bibr" rid="scirp.86748-ref25">25</xref>] [<xref ref-type="bibr" rid="scirp.86748-ref26">26</xref>] . Variation of temperature also affects the development of C. acutatum strains; 5˚C and 37˚C cause no development of the fungus. Germination of strain Ca4 is perfect at other temperatures; germination of Ca1, Ca2, Ca5, Ca6 and Ca7 is maximal at 23˚C, 25˚C, 27˚C and 30˚C. Sporulation of all isolates is too low at 18˚C and 30˚C, average at 23˚C and maximum at 25˚C and 27˚C. Mycelial growth is maximum at 25˚C and 27˚C, average at 18˚C and 30˚C, and no growth is observed at 5˚C and 37˚C.</p><p>Miles et al., [<xref ref-type="bibr" rid="scirp.86748-ref27">27</xref>] , Grahovac et al., [<xref ref-type="bibr" rid="scirp.86748-ref28">28</xref>] and Fernando et al., [<xref ref-type="bibr" rid="scirp.86748-ref29">29</xref>] have found that Colletotrichum acutatum has an optimal development at 25˚C &#177; 2˚C. These results are consistent with other studies that have evaluated the effect of the temperature on species of Colletotrichum from different hosts [<xref ref-type="bibr" rid="scirp.86748-ref4">4</xref>] [<xref ref-type="bibr" rid="scirp.86748-ref12">12</xref>] [<xref ref-type="bibr" rid="scirp.86748-ref13">13</xref>] [<xref ref-type="bibr" rid="scirp.86748-ref30">30</xref>] [<xref ref-type="bibr" rid="scirp.86748-ref22">22</xref>] . The comparison of the effect of temperature between C. acutatum strains isolated from avocado, banana, guava, papaya, mango and passion fruit shows that the optimum temperature for their development is 28˚C. None of the strains has grown at 8˚C and only the isolates from avocado, papaya and banana have developed at 36˚C [<xref ref-type="bibr" rid="scirp.86748-ref23">23</xref>] . Optimum germination of C. acutatum isolated from coffee has occurred at 21˚C - 29˚C [<xref ref-type="bibr" rid="scirp.86748-ref31">31</xref>] and its mycelial growth was maximal at 21˚C [<xref ref-type="bibr" rid="scirp.86748-ref31">31</xref>] [<xref ref-type="bibr" rid="scirp.86748-ref32">32</xref>] [<xref ref-type="bibr" rid="scirp.86748-ref33">33</xref>] .</p><p>The environmental pH plays an important role in the growth and differentiation of microorganisms. In the present work, pH variation has no remarkable effect on mycelial growth and germination of the seven strains studied: the mycelial growth, sporulation and germination of all strains reach an optimum at pH 5, 5.5, 6 and 6.5. Colletotrichum musae, the causal agent to anthracnose of banana tree, has an optimal development at pH 4.5 [<xref ref-type="bibr" rid="scirp.86748-ref34">34</xref>] .</p><p>The water activity has a remarkable effect on the mycelial growth, which is optimal at 0.95 and 1, medium at 0.75 - 0.90 and null between 0.60 and 0.70: C. acutatum, the agent of anthracnose of strawberry, requires water in order to develop.</p><p>The anthracnose caused by several species of the genus Colletotrichum and especially C. acutatum represents one of the major fungal diseases of Fragaria x ananassa. The disease manifests itself by small circular spots which merge to form large elliptical spots on fruit and leaves. Therefore the control against this disease for cultures of strawberry plants, devoid of phytopathogenic agents, is necessary in order to produce healthy fruit to meet the consumer’s requirement.</p></sec><sec id="s6"><title>Conflicts of Interest</title><p>The authors declare no conflicts of interest regarding the publication of this paper.</p></sec><sec id="s7"><title>Cite this paper</title><p>Es-Soufi, R., El Kbiach, M.L., Errabii, T., Saidi, R., Badoc, A., Chaveriat, L., Martin, P. and Lamarti, A. (2018) Biology and Physiology of Colletotrichum acutatum Strains Causing Strawberry’s Anthracnose. Agricultural Sciences, 9, 974-990. https://doi.org/10.4236/as.2018.98068</p></sec></body><back><ref-list><title>References</title><ref id="scirp.86748-ref1"><label>1</label><mixed-citation publication-type="other" xlink:type="simple">Mouden, N., Benkirane, R., Ouazzani Touhami, A. and Douira, A. 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