بررسی تاثیر تراکم بوته بر برخی خصوصیات بیوشیمیایی و اسانس گیاه دارویی زوفایی ((thymbra spicata

جهت بررسی تغییرات برخی از خصوصیات فیزیولوژیکی و فیتوشیمیایی برگ و سرشاخه دو اکوتیپ از گیاه دارویی زوفایی (thymbra spicata) در پاسخ به تغییر تراکم بوته، آزمایشی به‌صورت فاکتوریل بر پایه بلوک‌های کامل تصادفی در سه تکرار و در سال زراعی 1396-1395 در مزرعه تحقیقاتی دانشکده کشاورزی دانشگاه ایلام انجام شد. تیمارهای آزمایش شامل سه تراکم کشت (فاصله روی ردیف 20، 30 و 45 سانتی‌متر) و دو اکوتیپ بومی گیاه زوفایی از ارتفاعات زاگرس ایلام (ملکشاهی و سومار) بودند. بر اساس نتایج حاصل از این آزمایش میزان ترکیبات آنتی‌اکسیدانتی، رنگیزه‌های فتوسنتزی ( a، b و کل)، کارتنوئید، آنتوسیانین، و درصد اسانس به‌صورت معنی‌دار؛ تحت تاثیر اکوتیپ و تراکم کاشت قرار گرفتند. به‌طوری‌که بیشترین میزان فنل و فلاونوئید کل به‌ترتیب (91.64 میلی‌گرم اسید گالیک در گرم وزن خشک) و (5.20 میلی‌گرم کوئرستین در گرم وزن خشک برگ) در فاصله روی ردیف 20 و 30 سانتی‌متر مشاهده شد و با کاهش تراکم بوته میزان فنل و فلاونوئید کل به‌ترتیب 7.2 و 12 درصد کاهش یافتند. فاصله روی ردیف 30 سانتی‌متر، موجب افزایش میزان کلروفیل a وb  به میزان 14 تا 16 درصد و کارتنوئید به میزان 10 درصد گردید. بیشترین میزان آنتوسیانین (2.5 میکروگرم بر گرم وزن تر) در فاصله روی ردیف 20 سانتی‌متر مشاهده شد که با کاهش تراکم 10 درصد کاهش نشان داد. بیشترین درصد و عملکرد اسانس در فاصله روی ردیف 20 سانتی‌متر (91.38 کیلوگرم در هکتار) و اکوتیپ ملکشاهی (87.5 کیلوگرم در هکتار) مشاهده شد که با افزایش فاصله روی ردیف، درصد و عملکرد اسانس به‌ترتیب 6 و 13 درصد کاهش یافت. اکوتیپ ملکشاهی در مقایسه با اکوتیپ سومار از محتوای بیشتری از رنگیزه‌های فتوسنتزی، فنل و فلاونوئید کل، کارتنوئید، آنتوسیانین و درصد و عملکرد اسانس برخوردار بود.

Investigating the Effect of Plant Density on Biochemical Characteristics and Essential Oil in Wild Thyme (Thymbra spicata L.)

AbstractIntroductionAmong all major genera and species in the mint family, different types of organic compounds or metabolites such as phenolic compounds, flavonoids, anthocyanins, ascorbates, and carotenoids with antioxidant, antimicrobial, and antiinflammatory effects are produced by means of metabolic processes. Research studies in this field have established that planting distance can have a significant effect on essential oil yield as well as the quantity and quality of secondary metabolites in medicinal plants. The main purpose of spacing between plants is also to provide a suitable mix of environmental factors (i.e. water, climate, light, and soil) to achieve optimum quality performance. Materials and MethodsThe present study was conducted using a factorial experiment based on randomized complete block design (RCBD) with three replications at Ilam University Research Farm, Iran, during 20162017. Planting density treatments at three levels (i.e., 20, 14, and 10 plants per m2) were determined based on changes in plant spacing on rows (i.e., three distances of 20, 30, and 45 cm). Two ecotypes were accordingly included: Malekshahi and Sumar. The characteristics measured were photosynthetic pigments (chlorophyll a/b, total chlorophyll, and carotenoid), total phenol and flavonoid content, anthocyanin, as well as essential oil content and yield. Results and DiscussionThe results of this experiment revealed that the amount of antioxidant compound, photosynthetic pigments (i.e., chlorophyll a/b, total chlorophyll, and carotenoid), anthocyanin, and essential oil yield had been significantly affected by ecotype and plant density. Therefore, the highest amounts of total phenol (91.64 mg GAE/g DW) and flavonoid (5.20 mg QUE/ g DW) were observed at 20 and 30 cm row spacing. Total phenol and flavonoid also decreased by 7.2% and 12% as plant density was reduced. Moreover, row spacing of 30 cm increased the amount of chlorophyll a/b by 14 to 16% and carotenoid by 10%. The highest amount of anthocyanin (2.5 μg/g FW) was noticed at 20 cm row spacing. In the same vein, the highest yield of the essential oil was spotted at 20 cm row spacing (91.38 kg/ha) and for Malekshahi ecotype (87.5 kg/ha). Compared with the Sumar ecotype, the Malikshahi had higher content of photosynthetic pigments, total phenol and flavonoid, carotenoid, anthocyanin, as well as essential oil yield content and yield. Growth, quantity, and quality of medicinal plants are controlled by genetic processes as well as environmental and agronomic factors such as plant density. As plant density is enhanced to an optimum level, competition increases for absorption of water, nutrients, and quantity and quality of light received by leaves due to branching density and moderated penetration into canopy. As a result, the rate of cell division and leaf area development reduces and the content of photosynthetic pigments is diminished following the destruction of chloroplast structure and inhibition of biosynthesis of new chlorophylls. On the other hand, secondary metabolites such as phenolic compounds, flavonoids, and anthocyanin develope in the plant in response to environmental conditions in order to protect it against environmental stresses through suppressing oxygen free radicals. In line with the results of the related literature, it was observed that the content of photosynthetic pigments had diminished after increasing the density to 20 plants per m2, but the content of carotenoid, anthocyanin, total phenol and flavonoid, as well as the essential oil yield had improved in the wild thyme (Thymbra spicata L.). ConclusionThe results revealed that the leaves of the plant have good amounts of essential oils, phenolic compounds, and flavonoids. Since the highest percentage and yield of essential oil, phenol, flavonoids, and anthocyanins were observed in the treatment of density of 20 plants per square meter and Malikshahi ecotype, this level of density and Malikshahi ecotype is introduced for production and review in breeding programs.