Potentiation of soybean resistance against Phakopsora pachyrhizi infection using phosphite combined with free amino acids

Abstract

Considering the importance of Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, in the decrease in soybean yield, this study investigated the potential of using phosphite combined with l‐α‐free amino acids (referred to as induced resistance [IR] stimulus hereafter) to boost defence responses of soybean plants against P. pachyrhizi infection. Plants were sprayed with water (control), acibenzolar‐S‐methyl (ASM) or IR stimulus and noninoculated or inoculated with P. pachyrhizi. Urediniospore germination was not affected by the IR stimulus in vitro. Reduced ASR severity, lower malondialdehyde concentration and less colonization of leaf tissues by P. pachyrhizi (lower TEF‐1α expression from 1 to 15 days after inoculation [dai]) occurred for IR stimulus‐sprayed plants. The pattern of gene expression for IR stimulus‐sprayed and infected plants was strikingly similar but sometimes more remarkable than that in ASM‐sprayed and infected plants. Higher production of phenolics and lignin along with stronger up‐regulation of PAL1.3 (5 and 10 dai), PAL2.2 (3 dai), PAL3.1 (1, 3 and 5 dai), ICS1 (5 dai), CHIA1 (1, 5 and 10 dai), CHI1B1 (5 dai), PR‐1A (5 and 10 dai), NR1‐2 (5 and 10 dai) and INR‐2 (5 and 10 dai) for IR stimulus‐sprayed plants increased their resistance against ASR. In addition, IR stimulus‐sprayed and infected plants showed less impairment of the photosynthetic apparatus and maintained high concentrations of chlorophyll a + b and carotenoids. These findings highlight the potential of using this IR stimulus for developing a well‐tuned and effective defensive strategy in soybean plants against P. pachyrhizi infection.

Azelaic and hexanoic acids‐inducing resistance in soybean against Phakopsora pachyrhizi infection

“…Two experiments were conducted, and data presented are from the pooled experiments. Many resistance inducers can increase soybean resistance against diseases caused by a plethora of pathogens through SAR or ISR (Paula et al, 2021;Picanço et al, 2022). In infected tissues of plants exhibiting SAR, SA can originate from either phenylpropanoid or isochorismate pathways in which PAL and ICS, respectively, play a pivotal role (Vlot et al, 2021).…”

“…Among 40 proteins differentially expressed in the leaves of soybean plants from a susceptible cultivar infected by P. pachyrhizi, PR10 stood out and PR10 transcripts were significantly raised at 10 hai and at 6 and 8 dai (Park, 2010). Many antimicrobial peptides are involved in defence of plants against pathogen infection and MMP2 expression in soybean leaves seems to be of pivotal importance for resistance against some pathogens (Liu et al, 2001;Picanço et al, 2022). Up-regulation of URE enhances urea conversion to ammonium resulting in an elevated pool of compounds containing nitrogen of great value in host defence reactions, as reported for the soybean-P. pachyrhizi pathosystem (Einhardt et al, 2020).…”

“…Soybean plants (cultivar TMG 135, susceptible to rust; Einhardt et al, 2020) were grown in a greenhouse (24 ± 2°C, relative humidity 75% ± 5%, and natural photosynthetically active radiation [PAR] of 955 ± 20 μmol photons/m 2 /s measured at midday). The conditions for plant growth (e.g., substrate and fertilization) were the same as reported by Picanço et al (2022).…”

“…The leaflets of second and third leaves of each plant per replication of each treatment (four replications, 16 plants and 96 leaflets per experiment) were used to evaluate the rust severity at 5, 10, 15 and 20 dai, and data were used to calculate the area under disease progress curve (AUDPC) according to Picanço et al (2022). All leaflets from plants from each replication per treatment were collected at 20 dai, scanned (600 dpi resolution), and the images were processed using the software QUANT to obtain the rust severity values (Picanço et al, 2022).…”

“…Each sample had the amount of RNA measured in a Qubit fluorometer using a Qubit RNA HS assay kit (Invitrogen). Single-stranded cDNAs were synthesized and the quantitative PCR was performed according to Picanço et al (2022). Specific primer sequences for the expression analysis of genes encoding phenylalanine ammonia-lyase (PAL1.1, PAL1.3, PAL2.1 and PAL3.1), pathogenesis-related protein 1 (PR1-A), pathogenesisrelated protein 10 (PR10), metalloproteinase (MMP2), urease (URE), isochorismate synthase (ICS1 and ICS2), chalcone isomerase (CHIB1), 1-aminocyclopropane-1-carboxylic acid oxidase (ACO), 1-aminocyclo propane-1-carboxylic acid synthase (ACS), ethylene receptor 1 (ETR1), salicylic acid methyltransferase (SABATH2), 12-oxophytodienoic acid reductase 3 (OPR3), jasmonic acid-amino synthetase (JAR1) and NAC transcriptional factor (NAC19) were designed using the soybean assembly version Wm82.a2.v1 (https://phyto zome-next.jgi.doe.gov/ info/Gmax_Wm82_a2_v1; Table 1).…”