Table_1_Phylogeny and mycotoxin profiles of pathogenic Alternaria and Curvularia species isolated from date palm in southern Tunisia.docx

Date palm (Phoenix dactylifera L.), is a widely cultivated crop across North Africa, with about 300 thousand tons of fruits produced per year, in Tunisia. A wide range of fungal pathogens has been associated with leaf spots of date palm, Alternaria species being the most frequently reported. Symptomatic leaves of Deglet Nour variety were randomly collected in six localities in Tunisia. We used a polyphasic approach to identify 45 Alternaria and five Curvularia strains isolated from date palm, confirming their pathogenicity. Sequencing of allergen Alt-a1, glyceraldehyde-3-phosphate dehydrogenase (gpd) and calmodulin genes allowed us to group 35 strains in Alternaria Section, and 10 strains in Ulocladioides section. Based on sequencing analyses of Internal Transcribed Spacer, gpd and elongation factor genomic regions, all Curvularia strains were identified as Curvularia spicifera. All Alternaria and Curvularia species tested on date palm plantlets proved to be pathogenic, fulfilling Koch’s postulates. Although no significant differences were observed among the species, the highest mean disease severity index was observed in A. arborescens, while the lowest corresponded to C. spicifera. The capability of these strains to produce mycotoxins in vitro was evaluated. None of the A. consortialis strains produced any known Alternaria mycotoxin, whereas more than 80% of the strains included in Alternaria section Alternaria produced variable amounts of multiple mycotoxins such as alternariol, alternariol monomethyl ether, altenuene, tenuazonic acid and tentoxin. Curvularia spicifera strains produced detectable traces of fumonisins B. This work reports a first comprehensive multidisciplinary study of mycotoxigenic Alternaria species and C. spicifera associated with leaf spot disease on date palm.

海枣（Phoenix dactylifera L.）是北非广泛种植的作物，在突尼斯年产量约30万吨果实。多种真菌病原均与海枣叶斑病相关，其中链格孢属（Alternaria）物种为最常被报道的致病菌。研究人员从突尼斯6个地区随机采集了Deglet Nour品种的病叶，采用多相分类法对分离得到的45株链格孢及5株弯孢霉（Curvularia）菌株进行鉴定，并验证了其致病性。通过对过敏原Alt-a1、甘油醛-3-磷酸脱氢酶（glyceraldehyde-3-phosphate dehydrogenase, gpd）及钙调蛋白基因进行测序，将35株菌株归入链格孢组（Alternaria Section），10株归入类乌洛拉组（Ulocladioides section）。基于内部转录间隔区（Internal Transcribed Spacer, ITS）、gpd及延伸因子基因组区域的测序分析，所有弯孢霉菌株均被鉴定为螺旋弯孢霉（Curvularia spicifera）。将所有受试链格孢及弯孢霉菌株接种至海枣幼苗后，均表现出致病性，符合科赫法则（Koch’s postulates）。尽管各物种间未观察到显著差异，但树状链格孢（A. arborescens）的平均病情严重指数最高，而螺旋弯孢霉（C. spicifera）的指数最低。本研究评估了这些菌株的体外产真菌毒素能力：协同链格孢（A. consortialis）菌株均未产生任何已知的链格孢属真菌毒素；而链格孢组（Alternaria section Alternaria）中超过80%的菌株可产生含量不等的多种真菌毒素，包括交链孢酚（alternariol, AOH）、交链孢酚单甲醚（alternariol monomethyl ether, AME）、细皱青霉素（altenuene, ALT）、细交链孢菌酮酸（tenuazonic acid, TA）及腾毒素（tentoxin）；螺旋弯孢霉菌株可产生可检测到的伏马菌素B（fumonisins B）痕量。本研究首次针对与海枣叶斑病相关的产毒链格孢属物种及螺旋弯孢霉开展了综合性多学科研究。