Occurrence of Major Viruses in Wheat in Khuzestan Province

Dwarfing, yellowing and yellow mosaic are the most common symptoms observed in cereal fields. Various pathogens such as viruses are involved in development of these symptoms. Over 30 different plant viruses are known to infect wheat. Among them, Wheat dwarf virus (WDV), Barley yellow dwarf virus (BYDV) and Wheat streak mosaic virus (WSMV) are important viral diseases around the world. Little comprehensive information on the distribution of these viruses is available in Khuzestan Province, Iran. This study aimed to determine the occurrence of WDV, BYDV-MAV and WSMV in the major wheat-producing regions in Khuzestan province.

 A survey of wheat fields showing yellowing, dwarfing and mosaic symptoms was conducted during 2020-21 crop season. The six counties in Khuzestan province were covered in the survey include Elhai, Mollasani, Shadegan, Ramhormoz, Shush, and Andimeshk. Plant leaves exhibiting viral disease symptoms were placed separately in plastic bags and quickly transported to the laboratory. Five hundred seventy (570) wheat samples were collected. These samples were tested by Enzyme-linked immune sorbent assay (ELISA) using specific antibodies of WSMV (from Shiraz Virology Research Center), BYDV-MAV (Bioreba, Switzerland) and WDV (DSMZ, Germany).

 The results showed that three tested viruses were present in Khuzestan province. Among the tested viruses, WDV was the most commonly detected (30% of the 570 wheat samples), followed by BYDV-MAV (29%) and WSMV (5%). WDV was found in all counties except Ramhormoz (Table 1). In Elhai county, 28 of the 53 tested samples were infected with WDV, which was the highest infection ratio (52.8%). Symptoms caused by BYDV-MAV are severe dwarfism and yellowing (Figure 1), and it is impossible to distinguish between WDV and BYDV-MAV viruses. The virus was the most widespread and was found in all counties (Table 1). The infection ratio in the six counties were 35% in Elhai, 27% in Mollasani, 10% in Ramhormoz, 25% in Shush, 11% in Andimeshk and 28% in Shadegan. In Ramhormoz, BYDV-MAV existed only in 8 out of 78 tested samples. Selected plants may be shortened due to lack of physiological factors or maybe infected by other strains of the virus. It is recommended that the occurrence of other virus species, including the dominant BYDV-PAV species, be investigated. The mixed infection with WDV+BYDV-MAV was detected in 9% of tested plants. However, the severity of the plant infection was similar to that of plants infected with any of the viruses. WDV was introduced as the predominant virus in wheat fields infected with yellowing and dwarfism in Khuzestan in 2020-2021. Of course, this does not mean that most of the symptoms dwarfing and yellowing in wheat are related to this virus. Studies in Germany also show that grain infection ratio with WDV and BYDV has been different between different years, so that in 1998-1998 WDV was predominant, while in 2005-2001 BYDV was predominant. WSMV is less common than other viruses. It was not found in Shadegan, Ramhormoz, and Mollasani counties. The highest incidence of the virus was observed in Andimeshk county. 13 of the 111 tested samples were infected with the virus (Table 1). Considering that in recent years corn cultivation has been developed as summer crops in Andimeshk and Dezful counties, the corn plant probably provides suitable conditions for strengthening the source of virus and its vector. As a result, crop damage caused by the virus will increase in these farms. In Khuzestan, wheat is cultivated in December, when the temperature is colder than other seasons, and the conditions for mite activity are not completely favorable, and as a result, the incidence of WSMV is lower. It is possible that cultivated wheat cultivars are resistant to mites. Since a positive correlation has been reported between mite resistance and virus resistance, this may play a role in reducing the incidence of the virus.

In this study, the distribution of major wheat viruses in six counties of the province was first investigated. The results showed that wheat dwarf virus and barley yellow dwarf viruses infect high percentages of wheat fields. Considering the important of Khuzestan province in the country’s self-sufficiency in wheat production, the available information about these viruses will cause extensive research in the field of virus damage assessment and additional molecular studies to be on the agenda.