Evaluation effect of seed-borne fungal infection on defence responses of wheat (Triticum aestivum L.) seedlings

Wheat is the main food crop, and agricultural development aims to ensure the food security of many wheat-dependent countries. One of the critical challenges for wheat production to increase yield and quality is seed-borne fungal disease, resulting in yield losses. Seed-borne fungal pathogens and diseases can reduce the physiological potential, yield and quality of wheat seeds (Hassani et al., ۲۰۱۹). Understanding the physiological and biochemical mechanisms involved in basal resistance of wheat seedlings of natural fungal infected seeds is limited so far. This study aimed to identify seed-borne fungi isolated from some wheat seed fields in Iran. To identify seed-borne fungi, samples were taken from wheat seed fields of Khuzestan, Golestan, Fars, Mazandaran, Zanjan and Ardebil provinces according to the International Rules for Seed Testing (ISTA). For isolation of fungi, seeds were washed in tap water and surface disinfected with ۱% sodium hypochlorite and were placed on different agar media, including Potato Dextrose Agar (PDA) and Potato Carrot Agar (PCA) with alternating ۱۲ hours light and ۱۲ hours darkness at ۲۵ ± ۱ °C. The isolated fungi were identified by analyzing the morphological characteristics and confirmed by specific primers reported by other researchers. In the greenhouse experiments, the pathogenicity test of Fusarium and Alternaria isolates on wheat was investigated using the method described by Yoshida et al. (۲۰۰۷) and Mangwende et al. (۲۰۱۸), respectively. Then, we investigated the role of reactive oxygen species (ROS) such as H۲O۲, OH- and O۲- and pathogen responsive defense-related enzymes activities (superoxide dismutase (SOD), Guaiacol peroxidase (GPOX)) in basal resistance of wheat to the hemibiotrophic and necrotrophic seed-borne fungal species from wheat seeds (Khaledi et al., ۲۰۱۶). Based on morphological and molecular characters were identified that belonged to three species, which included Alternaria alternata, Fusarium graminearum and F. culmorum. According to the frequency of pathogen occurrence and its geographic distribution in Iran, species belonging to genera Alternaria and Fusarium are the most common fungi associated with wheat seeds. Among the identified species, A. alternata was the most frequent (۳۳.۳%) followed by F. graminearum (۳۰.۹%) and F. culmorum (۱۴.۲%) (Figure ۱). Among the isolates, A. alternata was the predominant species with the highest incidence and relative density of ۰.۶ and ۴۵.۲%, respectively. Results similar to our findings were obtained in India (Pathak & Zaidi, ۲۰۱۳) and Serbia (Lević et al., ۲۰۱۲). Our results showed that the increase of fungi-infected seeds affects some physical and chemical indicators compared to the non-infected plant. Our study about pathogenicity showed that ۴۰% of the isolates were non-pathogenic and other isolates were weakly pathogenic or pathogenic. Among the identified species of disease transmission rate from seed to seedling observed that A. alternata was the most frequent (۳۰.۱%) followed by F. graminearum (۱۸.۳%) and F. culmorum (۱۲.۲%) (Figure ۲). Accumulation of ROS and enzymatic antioxidants in wheat seedlings from infected seeds was higher than the non-infected plant. Results indicated ROS (Figure ۳) and enzymatic antioxidants (Figure ۴) have been involved in physiological, biochemical and defensive processes in wheat seedlings from infected seeds. The ROS and antioxidants play a role in hemibiotroph (F. graminearum), necrotrophic (F. culmorum and A. alternata), and interactions with wheat (Lightfoot et al., ۲۰۱۶; Khaledi et al., ۲۰۱۶), which is in accordance with our observations. According to our results, rapid induction and high amount of ROS and induction of antioxidant enzymes activity in wheat may play an important role in defense responses against natural fungal infection from seeds. These results provide novel information about seed-borne fungal species and the role of signal transduction pathways in basal resistance of wheat that response patterns depend on the pathogen lifestyle and pathogenicity rate of seed-borne fungal isolates. The results of this study can be used to complete the basic information for identifying seed-borne fungi of wheat and help to write the national seed health standard.

کلیدواژه ها:

Antioxidants ، Hemibiotroph ، Necrotrophic ، Seed-borne ، Seed health ، Wheat