Effect of covered smut disease on phenological, physiological and agronomic traits of barley cultivars

Covered smut disease caused by the biotrophic fungus, Ustilago hordei (Pers.) Lagerh., is one of the significant limiting factors in barley cultivation. This disease is present in all barley cultivation regions, and if seeds of sensitive cultivars are planted without the use of fungicides, it can become a serious problem. Moreover, this disease adversely affects grain quality by contamination of healthy seeds with teliospores. The contamination level in the farms of Karaj and Zabol in 1990-1992 ranged from zero to 90%. Considering the importance of organic agriculture and the public demand for production systems with reduced chemicals inputs, planting improved seeds with genetic resistance is the most effective and economical approach to control this disease. This research was conducted to assess the sensitivity of barley cultivars to the covered smut disease and to evaluate the effect of this disease on the phenological, physiological, and agronomic characteristics of barley cultivars.

 In this study, 148 spring barley varieties from common commercial varieties from European countries along with Oxin and Zehak cultivars from Iran were investigated. This experiment was conducted in field conditions using an alpha lattice design with two replications under two environmental conditions, disinfection of seeds with fungicide and disease stress by inoculation of the covered smut pathogen, in the Zehak Agricultural Research Station, Sistan and Blouchestan province, Iran, in 2021-22 growing season. To induce the stress of covered smut disease, the seeds of the studied cultivars were artificially contaminated. The measured traits in this experiment included phenological, morphological, physiological, and agronomic traits, as well as spike infection percentage after maturity. To perform statistical analyses, the normal distribution of the collected data was firstly tested using the Shapiro-Wilk test, and then combined analysis of variance was conducted. Comparison of means, simple correlation coefficients between traits, principal component analysis, and heritability of the studied traits were conducted.

The results showed that the accurence rate of covered smut disease among the studied cultivars under disease inoculation conditions varied from 0% to 26.48% with the average of 3.51%. The genotype × environment interaction for all studied traits including days to tillering, tiller number per plant, plant height, flag leaf length and width, flag leaf sheath length, peduncle length, spike length, number of nodes, internode distance, 1000-grain weight, grain yield, biological yield, harvest index, water-soluble carbohydrate concentration, and disease infection percentage, was significant at 1% probability level, except for phenological traits including days to germination, days to tillering, days to heading, as well as canopy temperature. The heritability rate of resistance to covered smut disease was 97.89%. Also, a negative and significant correlation was observed between the percentage of disease infection with plant height, flag leaf sheath length, peduncle length, spike length at the 1% probability level, and with biological yield at the 5% probability level.

The results of this research showed that there was a significant genetic diversity among the evaluated cultivars and the studied cultivars exhibited diverse reactions to different environmental conditions. Due to the significant impact of covered smut disease or loose smut disease on spike-related traits during the maturity stage, therefore it is challenging to differentiate resistant cultivars from susceptible ones in other stages and traits, and the selection of resistant cultivars requires waiting until the end of the cropping season.