Light and Electron Microscopy Studies on the Infection of a Wild-type and Metalaxyl-resistant Isolate of Phytophthora sojae in Soybean Hypocotyls

Abstract

Resistance of soybean cultivars, depending on single dominant genes to Phytophthora sojae, may easily be overcome by emerging new virulent races. Light microscopy (LM) and electron microscopy (EM) were used to study the infection process of the wild-type isolate Ps411 and metalaxyl-resistant mutant Ps411-M of P. sojae in hypocotyls of soybean seedlings grown from untreated and metalaxyl-treated seeds. The isolate Ps411-M of P. sojae exhibited a high degree of resistance to metalaxyl compared to Ps411. The pathogenic fitness of Ps411-M in hypocotyls of soybean seedlings was lower compared to Ps411. LM observations showed distinct differences in the infection process of both isolates in hypocotyls of treated soybean seedlings. EM studies revealed differences in the prepenetration stage between Ps411 and Ps411-M on hypocotyls grown from seeds treated with 0.02% metalaxyl until the whole seed surface coated. The number of infection sites was markedly reduced and few hyphae continued to spread. Numerous ultrastructural alterations in hyphae were observed in treated hypocotyls infected with Ps411, including pronounced thickening of hyphal cell walls and encasement of haustorium-like bodies; electron-dense material was deposited in host cell walls in contact with hyphal cells. Neither the prepenetration process nor penetration or spread of hyphae in the hypocotyls of the resistant isolate was affected in treated compared to non-treated tissue. While in treated hypocotyls infected with the wild-type isolate, host defence reactions were induced, no such reactions were detected in treated hypocotyls infected with the resistant isolate. Hypocotyls from metalaxyl-treated seeds infected with the wild-type isolate resembled an incompatible interaction, whereas during infection with the metalaxyl-resistant mutant, the compatible interaction was not changed.

Variation in the Resistance of Japanese Soybean Cultivars to Phytophthora Root and Stem Rot during the Early Plant Growth Stages and the Effects of a Fungicide Seed Treatment

“…This is because soybean plants grown in fields converted from rice paddies are at high risk of being infected by P. sojae . Although seed treatments with pesticides are important for protecting young soybean plants from P. sojae and enhancing stand establishment, the pesticides are costly and repeated applications of the same pesticide may decrease the sensitivity of P. sojae to the active ingredient (i.e., pesticide resistance) ( Han et al, 2011 ; Hunger et al, 1982 ). Planting cultivars exhibiting complete and/or incomplete disease resistance may be a more economically viable option for combating Phytophthora root and stem rot of soybean.…”

Proteomics Reveals the Mechanism Underlying the Inhibition of Phytophthora sojae by Propyl Gallate

“…This phenomenon is particularly prominent in the prevention and control of Phytophthora root and stem rot. It has been reported that Phytophthora sojae has developed resistance to fungicides such as metalaxyl, fluorophenylalanine, and benzil. , As an important economic crop, research on the biological control of major diseases of soybean has attracted the attention of researchers; previous studies have revealed that plant extracts, such as plant essential oils, acids, and polyphenols, are often used for the control of diseases caused by Phytophthora . − The essential oil of Beilschmiedia miersii can inhibit Phytophthora cinnamomi, and its half inhibition concentration (IC 50 ) is 200 μg/mL. Inhibition by essential oils may be associated with their antioxidant activity .…”

Biocontrol and Action Mechanism of Bacillus amyloliquefaciens and Bacillus subtilis in Soybean Phytophthora Blight

“…At present, the prevention and control of P. sojae is mainly achieved by rationally planting soybean-resistant varieties, spraying effective fungicides, and improving field management measures [2]. However, with the improper application of fungicides, P. sojae begins to develop resistance to fungicides, such as metalaxyl, fluorophenylalanine, mefenoxam, zoxamide, phenylamide, and oxathiapiprolin [3,4,5,6,7], and some of the researchers have begun to study their resistance mechanisms. The results showed that the resistance of Phytophthora to metalaxyl and mefenoxam was related to RNA polymerase I or its subunit RPA190 [8], and the β-tubulin and oxysterol binding protein from P. sojae is related to the resistance of Zoxamide and oxathiapiprolin [4,7].…”