Sexual reproduction increases the possibility that Phytophthora capsici will develop resistance to dimethomorph in China

Abstract

A total of 1511 isolates of Phytophthora capsici were collected from farms with no history of exposure to the carboxylic acid amide (CAA) fungicides in 32 provinces in China during 2006 to 2013. All 1511 isolates were assayed for mating type and 403 were assayed for sensitivity to dimethomorph (DMM) and metalaxyl. The DMM EC 50 values ranged from 0Á126 to 0Á339 lg mL À1 . Both A1 and A2 mating types were detected on the same farms in four provinces and with a 1:1 ratio. Most isolates were sensitive to metalaxyl but a few exhibited intermediate resistance or resistance to metalaxyl. The segregation of DMM resistance and sensitivity among 337 progeny obtained from hybridization or self-crossing in vitro indicated that the resistance of P. capsici to DMM is controlled by two dominant genes. Eighteen progeny that were derived from hybridization differed in DMM sensitivity and in fitness. Some progeny were as fit as parental isolates. Given the distribution of mating types and therefore the potential for sexual reproduction, the control of resistance by two dominant genes, and the fitness of hybrid progeny, the risk of P. capsici populations developing DMM resistance in China is substantial.

Challenges and Strategies for Breeding Resistance in Capsicum annuum to the Multifarious Pathogen, Phytophthora capsici

“…Given the global emergence of insensitivity to phenylamide fungicides in P. capsici , alternative fungicides have been evaluated ( Cui et al, 2009 ; Sun et al, 2010 ; Bi et al, 2014 ). Some of these compounds include azoxystrobin, cyazofamid, cymoxanil, dimethomorph, fluazinam, fosetyl-A1, oligochitosn, oxathiapiprolin, and zoxmide ( Matheron and Porchas, 2000 ; Ivors et al, 2006 ; Keinath, 2007 ; Xu et al, 2007a , b ; Ji and Csinos, 2015 ).…”

“…Some of these compounds include azoxystrobin, cyazofamid, cymoxanil, dimethomorph, fluazinam, fosetyl-A1, oligochitosn, oxathiapiprolin, and zoxmide ( Matheron and Porchas, 2000 ; Ivors et al, 2006 ; Keinath, 2007 ; Xu et al, 2007a , b ; Ji and Csinos, 2015 ). However, soon after their first use to manage the disease, insensitivity is often observed ( Kousik and Keinath, 2008 ; Cui et al, 2009 ; Sun et al, 2010 ; Bi et al, 2014 ; Miao et al, 2016 ).…”

“…The unusually rapid and high preponderance of fungicide insensitivity in P . capsici is likely due to the pathogen’s ability to sexually reproduce resulting in high rates of genetic recombination in addition to the production of oospores that can persist in the soil for many years ( Lamour and Hausbeck, 2000 , 2001b ; Bi et al, 2014 ). Additionally, this is further evidence that resistant cultivars are the best management strategy for P .…”

“…Additionally, once mefenoxam insensitivity has been introduced into a population it is persistent and the frequency of insensitive individuals does not decrease after selection pressure is removed ( Bower and Coffey, 1985 ; Lamour and Hausbeck, 2001b ). Sensitivity to dimethomorph was found to be controlled by two dominant genes ( Bi et al, 2014 ) and oxathiapiprlin by a single gene ( Miao et al, 2016 ).…”

Insights into the adaptive response of the plant-pathogenic oomycete Phytophthora capsici to the fungicide flumorph

“…The sexual reproduction of P. capsici 15 plays an important role in its disease cycle initiating infection in host plants 5 16 , while the resulting genetic recombination can contribute to the development of isolates that exhibit complete insensitivity to certain fungicides 17 . P. capsici is a heterothallic pathogen that produces two mating types, A1 and A2, and it has been shown that the co-occurrence of both mating types in regions of the United States, South Africa, and the northern provinces of China, can facilitate frequent outcrossing and increase the risk of resistance developing 18 19 20 21 . Previous studies have shown that flumorph resistance in P. capsici is controlled by two dominant genes, which implies that once resistance has developed it could rapidly spread through a population via both sexual and asexual reproduction 22 .…”