اتیولوژی پوسیدگی بنه‌ی زعفران در شهرستان خرم‌آباد | Etiology of corm rot of saffron in Khorramabad

Persian. زعفران (Crocus sativus L.) گیاهی چند ساله و از مهمترین محصولات زراعی است. زعفران یک چاشنی ارزشمند است و به دلیل کاربردهای دارویی و پزشکی فراوان، تقاضا برای مصرف آن افزایش یافته است. تنش­های زیستی از چالش­های کشت زعفران هستند و پوسیدگی بنه به عنوان تنشی زیستی، یکی از مخرب­ترین بیماری­های بخش­های زیرزمینی است. عوامل بیماری‌زای مختلفی از جمله قارچ‌ها بر رشد بنه تأثیر می‌گذارند و شناسایی این قارچ‌ها در کشت زعفران مهم است. مطالعه حاضر به منظور شناسایی قارچ­های همراه بنه­ی زعفران در شهرستان خرم­آباد و بررسی بیماریزایی آنها اجرا گردید. بدین منظور، بنه­های زعفران دارای علایم پوسیدگی از مناطق مختلف خرم­آباد (10 منطقه) در استان لرستان جمع­آوری و به آزمایشگاه منتقل شدند. جداسازی قارچ­ها با استفاده از محیط کشت جامد سیب­زمینی و دکستروز انجام گرفت. پس از تهیه کشت خالص جدایه­ها، مشخصات ریخت­شناسی و میکروسکوپی اسپورها و سایر اندام­های زایشی قارچ­ها روی محیط­های کشت برگ میخک آگار و سیب زمینی هویج آگار بررسی گردید. آزمون اثبات بیماریزایی جدایه­های قارچ­ها در شرایط گلخانه روی بنه­های زعفران و به روش غوطه­ور کردن در سوسپانسیون اسپور اجرا گردید. در مجموع 58 جدایه جمع­آوری و گونه­های Alternaria alternata، Fusarium solani، F. acuminatum و F. oxysporum جداسازی و بر اساس ویژگی­های مورفولوژیکی شناسایی شدند. گونه­ی  A. alternataبا 25 جدایه و گونه­ی F. acuminatum با 4 جدایه به ترتیب بیشترین و کمترین فراوانی را داشتند. بر اساس آزمون بیماری­زایی در شرایط گلخانه، F. oxysporum تهاجمی­ترین و A. alternata ضعیف­ترین گونه از نظر بیماری­زایی بودند. گزارش قبلی از وقوع F. acuminatum و F. solani بر روی بنه زعفران از جهان و ایران وجود نداشت و به نظر میرسد که این اولین گزارش از بیماریزایی گونه­ی F. acuminatum روی بنه­ ی زعفران در دنیا باشد.

English. SIntroduction: Saffron (Crocus sativus L.) a perennial herbaceous is one of the most important crops. It is a valuable ketchup and its demand for consumption has been increased due to many medicinal and pharmacological applications. Saffron is a male sterile and can be propagated only by its corm and produces daughter corms. Cultivation of saffron is challenged by biotic stresses and corm rot as a biotic stress, is one of the most destructive diseases subterranean organs. Because of the insufficient information about corm rot etiology, investigation and identification of harmful agents is essential. Different pathogens such as fungi affect growth of corm and identification of these fungi is critical in cultivation of saffron. Occurrence of saffron corm rot has been reported from many countries and various microorganisms such as Fusarium, Rhizoctonia, Sclerotinia, Penicillium, Aspergillus, Bacillus and Burkhulderia have been isolated from rotted corm of saffron. The present study was conducted to identify fungi associated with corm of saffron in Khorramabad. Materials and Methods: Infected corms of saffron were randomly collected from different regions of Khorramabad in Lorestan province (10 regions). The infected tissues were surface-sterilized with sodium hypochlorite (5%) for 1 min, and washed three times by sterile distilled water, dried on sterile filter paper and directly placed on the surface of potato dextrose agar medium. The PDA plates were incubated for 7 days at 25±2°C and then were purified using single spore method. Morpho-cultural characteristics of fungi were studied on carnation leaf agar and potato carrot agar media. Microscopic measurement and images of reproductive structures were carried out under a Nikon microscope. Pathogenicity test was conducted to evaluate the ability of isolates to colonize saffron corms. Conidial suspension was prepared from cultured isolates on potato dextrose broth medium and adjusted at a concentration of 1×106 conidia/ml. To inoculation, saffron corms were submerged in the conidial suspension, then planted in an aseptic soil and maintained for 4 weeks under controlled conditions in a greenhouse with 23 ± 2°C and 70% relative humidity. The disease incidence and severity was inspected daily and finally Koch’s postulates were tested.Results and Discussion: Totally, 58 isolates were collected and four species including of Alternaria alternata, Fusarium solani, F. acuminatum and F. oxysporum were isolated and identified on the basis of morphological characteristics. The A. alternate (25 isolates) and F. acuminatum (4 isolates) were the most and the least frequent respectively. According to the pathogenic test under the controlled conditions, F. oxysporum was the most aggressive and A. alternate was weakly pathogenic. There was not previous report of incidence of F. acuminatum and F. solani on saffron corm from the world and Iran respectively. The results of this research are in agreement with previous studies that showed corm rot is a major challenge in saffron cultivation. Corm rot is a complex disease and frequency, diversity and distribution of pathogens may be different due to cultivar type, agricultural practices, and climatological parameters. However, Fusarium spp. are the main agent of corm rot and F. oxysporum is the most predominant in saffron growing areas of the world. Moreover, Fusarium spp. have been reported as serious pathogen of subterranean organs of many crops such as potato, rice, wheat, and barley. Conclusion: The results of this study showed that corm rot is a serious constraint in saffron production. Although A. alternata was the most frequent species in rotted corms, Fusarium spp. especially F. oxysporum were more aggressive and virulent on saffron. In addition, isolating saprophytic fungi such as Aspergillus, Penicillium and Rhizopus in our research showed that saffron corm is potentially exposed to infectious by varous fungi. Etiology of saffron corm rot is essential and results of this study can be helpful in management of saffron cultivation.