Resistance of <i>Zymoseptoria tritici</i> to azoxystrobin and epoxiconazole in the lower North Island of New Zealand

Abstract

In response to a suspected fungicide resistance problem in the spring of 2013 23 isolates of Zymoseptoria tritici (also known as Mycosphaerella graminicola) were collected from wheat fields showing symptoms of speckled leaf blotch around the lower North Island EC50 values for the collected isolates and three sensitive isolates against rates of azoxystrobin epoxiconazole and isopyrazam were determined by growth in microplates as measured by light absorbance Furthermore greenhouse inoculations on fungicidesprayed plants were conducted with selected isolates Resistance to azoxystrobin appears widespread as does reduced sensitivity to epoxiconazole Most growers supplying the samples were using epoxiconazole as their standard cereal fungicide but at lower than label rates A combination of conducive weather low fungicide rates resistance to azoxystrobin and reduced sensitivity to epoxiconazole is likely to have contributed to the disease epidemic

Detection and Characterization of QoI-Resistant Phytophthora capsici Causing Pepper Phytophthora Blight in China

“…This chemical inhibits mycelial growth, spore germination, and conidial production, and its protection, treatment, and systemic activity have been characterized (Burnett et al 2010;Matheron and Porchas 2000). Nonetheless, some pathogens have reportedly developed resistance to azoxystrobin, including Colletotrichum siamense, Pyricularia oryzae, Zymoseptoria tritici, and Cercospora beticola (Hu et al 2015;Oliveira et al 2015;Stewart et al 2014;Vaghefi et al 2016). Although azoxystrobin is a very effective fungicide for the control of Phytophthora capsici, in vitro sensitivity studies based on encysted zoospores and mycelia have indicated that P. capsici in China (Qian et al 2006) and the United States (Matheron and Porchas 2000) is not highly sensitive to azoxystrobin.…”

The effect of fungicide dose rate and mixtures on <i>Zymoseptoria tritici</i> in two cultivars of autumn sown wheat

“…Reduced sensitivity of STB to triazole fungicides has meant higher rates of fungicide are required to obtain the same level of control prior to the detection of resistance mutations (FAR 2014). This was found by Stewart et al (2014), where reduced sensitivity to epoxiconazole was widespread in the lower North Island of New Zealand, and Cools & Fraaije (2008), who found a decline in the efficacy of some azoles against STB in the United Kingdom. This supports Martin et al (2005), where resistance to triazole fungicides develops as a gradual decrease in sensitivity over time, which can be aided by repeated use of atrisk fungicides at reduced rates; as commonly practiced by growers (van Toor et al 2013).…”

“…The recommendation was for both products to be used preventatively, when disease levels were low, but disease pressure was high (Martin et al 2005). Stewart et al (2014) found widespread resistance to the strobilurin azoxystrobin and reduced sensitivity to the triazole epoxiconazole but no evidence of reduced sensitivity to the SDHI isopyrazam. Both Stewart et al (2014) and van Toor et al (2013) found that growers were routinely applying fungicides at lower than recommended rates.…”

“…Stewart et al (2014) found widespread resistance to the strobilurin azoxystrobin and reduced sensitivity to the triazole epoxiconazole but no evidence of reduced sensitivity to the SDHI isopyrazam. Both Stewart et al (2014) and van Toor et al (2013) found that growers were routinely applying fungicides at lower than recommended rates. Resistance could be delayed by limiting the number of applications of the at-risk fungicide group, mixing or alternating the at-risk fungicide with another fungicide from a different cross-resistance group (Martin et al 2005).…”

“…With Zymoseptoria tritici resistance to strobilurin (quinone outside inhibitor, QoI) fungicides and reduced sensitivity to triazole demethylation inhibitor (DMI) fungicides (Fraaije et al 2007;Stewart et al 2014), it has become increasingly important to look to the succinate dehydrogenase inhibitors (SDHI) General pathology fungicides (FAR 2014) as the basis of new mixtures since they have a different mode of action. While the potential for the development of resistance to SDHI fungicides appears to be low (Stewart et al 2014), SDHIs are at a moderate-high risk of resistance development (FAR 2014) because of incremental build up that may lead to cross-resistance (Sierotzki & Scalliet 2013). Martin et al (2005) gave fungicide recommendations aimed at reducing the development of resistance of no more than three applications of triazoles at full label rates and two applications of strobilurins in a season.…”