Fitness and cross-resistance of Alternaria alternata field isolates with specific or multiple resistance to single site inhibitors and mancozeb

Abstract

42 field isolates of Alternaria alternata collected from infected tomato fruit of processing plants located in the region of Pelloponisos, South Greece, were characterized in terms of sensitivity to mancozeb, tebuconazole, fludioxonil, iprodione and cyprodinil. Fungitoxicity tests in vitro revealed that 63 % of the isolates tested were sensitive to all the above fungicides whereas the remainder of the isolates exhibited reduced sensitivity to one or more of these fungicides. The observed resistance phenotypes were confirmed by in vivo experiments on artificially inoculated tomato fruit. EC 50 in vitro values ranged from 2.34 to >100 μg/ml for mancozeb, 0.16 to >10 μg/ml for iprodione, 0.43 to 20 μg/ml for tebuconazole, 0.007 to >5 μg/ml for cyprodinil and from 0.002 to >10 μg/ml for fludioxonil. Sensitivity distributions of A. alternata isolates to mancozeb, iprodione, cyprodinil and fludioxonil was bimodal indicating a probable initiation of a discrete shift of the population towards reduced sensitivity to these fungicides. Correlation analysis of respective EC 50 values showed positive cross-resistance relationships between fludioxonil and iprodione while positive correlation was observed between mancozeb and cyprodinil, mancozeb and tebuconazole, and cyprodinil and tebuconazole. Interestingly, a number of A. alternata isolates were specifically resistant to the multi-site inhibitor mancozeb, a fact reported for the first time. Isolates resistant to mancozeb were more aggressive while those with reduced sensitivity to both fludioxonil and iprodione produced significantly less conidia than sensitive ones. A considerable portion of the sample exhibited reduced sensitivity and no apparent fitness penalties, a fact that should be considered in future planning and implementation of anti-resistance strategies.

Phenylpyrroles: 30 Years, Two Molecules and (Nearly) No Resistance

“…In most cases fludioxonil resistance due to mutations in the HHK gene seems to induce a strong fitness penalty; e.g ., extremely reduced sporulation, osmosensitivity, loss of pathogenicity, etc. (Ziogas et al, 2005; Viaud et al, 2006; Ajouz et al, 2011; Malandrakis et al, 2015), definitely counter-selecting fludioxonil resistance. In the case of A. brassicicola , the absence of evident developmental defects in some fludioxonil resistant field isolates (Iacomi-Vasilescu et al, 2004), might be due to compensatory mutations in a given genetic background.…”

“…Field strains cross-resistant to phenylpyrroles and dicarboximides have been isolated from A. brassicicola, A. longipes , and A. alternata populations (Dry et al, 2004; Iacomi-Vasilescu et al, 2004; Avenot et al, 2005; Luo et al, 2012; Avenot and Michailides, 2015; Malandrakis et al, 2015). No significant developmental defects could be detected in the A. brassicicola resistant mutants and only moderate osmosensitivity (Avenot et al, 2005; Iacomi-Vasilescu et al, 2008).…”

“…No significant developmental defects could be detected in the A. brassicicola resistant mutants and only moderate osmosensitivity (Avenot et al, 2005; Iacomi-Vasilescu et al, 2008). However, phenylpyrrole resistance seems limited in Alternaria field populations (Avenot and Michailides, 2015; Malandrakis et al, 2015) indicating a potential fitness penalty not detected under controlled laboratory conditions.…”

Actividad antifúngica in vitro del aceite esencial de ajo (Allium sativum L.) contra Alternaria tenuissima

“…The most widely used against Alternaria are azoxystrobin, difenoconazole, mancozeb, tebuconazole, and others (Malandrakis et al, 2015;Savitha and Ajithkumar, 2016). However, these fungicides have adverse effects on the environment and human health.…”

“…Considering that about 374,000 plant species have been described, there is a wide window of (Malandrakis et al, 2015;Savitha y Ajithkumar, 2016). Sin embargo, estos fungicidas causan efectos adversos al ambiente y a la salud humana.…”