In vitro Selection of Strains of Phytophthora cactorum Resistant to Metalaxyl

Abstract

Isolates of Phytophthora cactorum resistant to the systemic fungicide metalaxyl were obtained by exposing them to sequentially increased concentrations of metalaxyl. A linear relationship was observed between the concentrations of metalaxyl and percentage inhibition of mycelial growth of P. cactorum. The stability of metalaxyl‐resistant isolates 150R and 250R was confirmed after six serial transfers on corn meal agar without fungicide. The in vitro metalaxyl‐resistant isolate (Ph10) was less aggressive on apple rootstocks compared with the Ph07 isolated from metalaxyl‐treated trees and the Ph03 isolated from untreated trees. Metalaxyl‐resistant and sensitive isolates remained sensitive to the chemically unrelated fungicide fosetyl‐Al at high concentration (600 μg/ml), to mancozeb, and to a mixture of metalaxyl + mancozeb. Significant differences in resistance to metalaxyl existed among P. cactorum field isolates.

Mixed-Mating Model of Reproduction Revealed in European Phytophthora cactorum by ddRADseq and Effector Gene Sequence Data

“…Another possible important consequence of revealed gene flow between groups is the spreading of resistance to chemical compounds across P. cactorum populations. The development of such resistance has been repeatedly evidenced in this pathogen [ 95 , 96 , 97 ], and its heritability has also been confirmed [ 34 , 98 ]. Therefore, the issue of the outbreeding of P. cactorum plays an important role in the spread of this pathogen to new host species and environments; outbreeding is equally important in chemical plant protection as well.…”

Effect of herbicides, plastic mulch, and hand-weeding on development of phytophthora crown and root rot of apple trees

“…Methods recommended for control of phytophthora crown and root rot (PCRR) include using tolerant rootstocks, inarching partially girdled mature trees with resistant seedlings, improving soil drainage, eliminating weeds around the base of trees, reducing nitrogen fertilizer applications, and using chemical treatment with metalaxyl for non-bearing trees or with fosetyl-Al for bearing and non-bearing apple trees. An earlier report (Utkhede & Gupta 1988) indicated the possibility of metalaxyl-resistant isolates of P. cactorum developing under orchard conditions. Several apple rootstocks, breeding lines, and germplasm collections have been screened for resistance to crown and root rot (Borecki et al 1978, Mclntosh & Mellor 1954, Utkhede 1986b, Utkhede & Quamme 1988, but complete immunity to the disease has not been discovered and rootstock susceptibility varies from one region to another (Mclntosh 1975).…”

ThePhytophthoradiseases of stone fruit trees in Greece

“…Metalaxyl has a specific suppressive effect on ribosomal RNA (rRNA) resulting in inhibition of fungal growth. In vivo mode of action of metalaxyl seems more complicated than that observed in vitro, and may involve induction of a hypersensitive reaction accompanied by accumulation of phytoalexin (Stossel et al, 1981;Utkhede and Gupta, 1988).…”