Evaluation of the tolerance of ten different sainfoin populations to powdery mildew ‎disease in the climatic conditions of Karaj, Iran

 Powdery mildew of sainfoin (Onobrychis viciaefolia Scop) is one of the most important diseases of this crop, which primarily spreads in the last cuts and causes loss. If this disease spreads widely on plants, it will cause the loss of leaves and, as a result, reduce the crop's forage yield. On the other hand, because there is little research in this field in the country, it was necessary to conduct research to identify the superior populations that are tolerant to the disease and have desirable agronomic traits, which was the goal of this study.

For investigating the reaction of different populations of sainfoin (Onobrychis viciaefolia) to powdery mildew, an experiment was conducted using a randomized complete block design in three replications in Karaj, Iran, with ten treatments including two improved populations and eight ecotypes of cultivated sainfoin collected from its habitat and identified from different regions of the country. Evaluation of powdery mildew disease was done in natural conditions in the last cut of plants in the summer of 2021. Disease evaluation of treatments in the field was done by recording traits such as disease incidence and severity. Also, a greenhouse experiment was conducted on the same populations using a completely randomized design with four replications of the treatments, and at least five plants were considered for each ecotype in each replication. The inoculum was prepared by creating a spore suspension with a concentration of 106 spores per ml and sprayed on sainfoin seedlings of different ecotypes at the four to five-week stage that had eight to ten leaves in a greenhouse with a temperature of 23 to 29°C and relative humidity of about 75%. The reaction of ecotypes to the disease was evaluated two weeks after inoculation, and the infection percentage of each population was recorded. The evaluation in the greenhouse and the scoring scale similar to the field evaluation was conducted following a scoring scale of one to four based on the treatments' disease severity percentage. Also, the dry matter (DM) yield of populations for four cuts was calculated. 

Based on the variance analysis data of the field trial in Karaj over two years, it was concluded that there was a significant difference for both disease severity and disease incidence at α=1% level. Also, there was a significant difference in disease severity and incidence at α=1% level among all populations in greenhouse trials. The results related to the disease incidence of the populations in both years showed that in the field trials among all the populations in the first and second years of the research, population number 2 had the minor disease incidence in the field, with values of 33 and 30 percentages, respectively. In the greenhouse test, the same population with values of 47 and 60 percent, respectively, had the lowest DI rate among the populations. Also, the results related to the disease severity (DS) of the populations in two years showed that population number 2 was known to be the most tolerant to the disease, with values of 18 and 10 percent in the first and second years, respectively, and other populations were considered as susceptible to the disease. In greenhouse trials, population number 2 was recognized as the most tolerant population, with 23% and 22% disease severity in the first and second years, respectively, and other populations showed a semi-susceptible to susceptible reaction to the disease.

In total, by comparing the average data in field and greenhouse tests over two years, it was concluded that population number 2, with an average disease severity of 14% and an average dry matter yield of 14.68 tons per hectare, was known as a disease-tolerant population coupled with desirable dry matter yield. Although this population was not completely resistant to powdery mildew, it was introduced as a semi-resistant variety (MR) to the disease, as its disease severity was less than 25% in all experiments.