A quarter of the world’s Potato (Solanum tuberosum L.) is produced from China, making it the largest producer of such an important crop globally . Recently, potato has been listed as the fourth largest staple crop in China, after rice, wheat, and maize. Potato Verticillium Wilt caused by Verticillium spp. has progressively become a serious problem in the major potato-producing regions in China (Chen et al. 2013; Liu et al. 1992; Wang et al. 2014; Zhang 2004). It may cause up to 50% yield losses (Dung et al. 2012). Verticillium dahliae, one of the important species within the Verticillium genus, not only causes extensive yield losses in potato (Johnson and Cummings 2015; Johnson and Dung 2010) but also threatens many other dicotyledonous plants, such as cotton, lettuce, tomato, strawberry, pepper, and sunflower (Inderbitzin and Subbarao 2014; Klosterman et al. 2009).
Sunflower (Helianthus annuus L.) is one of the top oilseed crops grown for their edible oil. Sunflower seeds contain over 40% edible oil and 23% proteins and are good sources of fiber, vitamin E, copper, zinc, and B complex vitamins. Sunflower wilt caused by V. dahliae is a devastating disease threatening sunflower production worldwide (Addrah et al. 2019). V. dahliae is a soil-borne and seed-borne phytopathogenic fungus that causes wilt via the vascular system in many plant species (Pegg et al., 2002). It can form resting structures called microsclerotia that can survive in the soil for more than 20 years, thus making the control of the disease rather difficult. Methyl bromide fumigation was once used as an efficient way to control wilt caused by V. dahliae, but it has been banned due to its harmful environmental effect, which has made the control of Verticillium wilt on different hosts challenging (Chen et al. 2013). Conventional control of V. dahliae through cultural practices such as crop rotation has proven limited due to the existence of cross-pathogenic isolates capable of infecting and surviving in several different plant species, including weeds (Bhat and Subbarao 1999; Qin et al. 2006). There are some exceptions, however, such as the use of broccoli as a rotation crop, which has proven to be effective in reducing soilborne propagules and disease incidence in several cropping systems (Hao et al. 2003; Njoroge et al. 2009).
Verticillium dahliae is a heterothallic fungus. In heterothallic fungi, sex compatibility is determined by a number of genes, one of which is the idiomorph of the MAT locus. The MAT1-1 idiomorph contains a gene that encodes an α-domain, while MAT1-2 contains a gene that encodes the high-mobility group (HMG) DNA-binding domain for mating proteins. In V. dahliae, only one idiomorph can be found in any one isolate, as it stands now (Usami et al. 2009, 2012). The presence of both mating types could potentially lead to sexual reproduction, thus producing new sources of inoculum in the form of ascospores in the life cycle of V. dahliae. However, V. dahliae has been confirmed to reproduce only asexually on different hosts thus far.
In terms of race types, two different types, race 1 and race 2, have been confirmed among different isolates of V. dahliae (Short et al. 2014). Potato Verticillium wilt outbreaks on different Solanaceae cultivars on most farms have been caused by V. dahliae race 1 (Gayoso et al. 2007). During the 1950s, Ve genes were introduced into tomato, which provided farmers with new varieties that were resistant to race 1 strains (Louws et al 2010). In lettuce and cotton, both race 1 and race 2 have been identified; race 1 of V. dahliae was identified in potato isolates in Lebanon (Baroudy et al.), while potato isolates in China have been largely identified as race 2. In our laboratory, over the years, we identified all the V. dahliae strains isolated from sunflower as race 2 only. In some cases, two different race types of V. dahliae were identified on different hosts, except for sunflower (Vallade et al. 2006; Hu et al. 2015; Baroudy et al. 2019; Zhang et al. 2017)
In this research, we isolated and identified V. dahliae from diseased potato and sunflower plants via Koch’s postulate and determined their race and mating types via PCR with specific primers. The correlation between mating type and pathogenicity was also determined in this study.