# Evaluation of Germplasm Resistance in Several Soybean Accessions Against Soybean Fusarium Root Rot in Harbin, Heilongjiang Province, China

## TL;DR

This study evaluates soybean germplasm resistance to Fusarium root rot in China, identifying resistant lines and exploring their molecular mechanisms.

## Contribution

The study identifies 53 soybean accessions with resistance to Fusarium root rot and provides molecular insights into resistance mechanisms.

## Key findings

- Fusarium oxysporum was confirmed as the main pathogen causing root rot in the region.
- 53 soybean accessions were identified as highly resistant or resistant to the disease.
- Resistant lines showed higher expression of GmFER and GmSOD1, and lower expression of GmJAZ1 and GmTAP1 compared to susceptible lines.

## Abstract

Soybean root rot, caused by diverse soil-borne pathogens, is a major constraint on production worldwide, with yield losses ranging from 10 to 60% under epidemic conditions. Symptomatic plants were collected from three locations in Harbin, Heilongjiang Province, China, and 23 fungal isolates were recovered using standard tissue isolation procedures. Integrated morphological characterization and rDNA-ITS sequencing identified these isolates as three Fusarium species: F. oxysporum (18 isolates, 78%), F. equiseti (3 isolates, 13%), and F. brachygibbosum (2 isolates, 9%). Pathogenicity assays following Koch’s postulates confirmed F. oxysporum as the predominant and most aggressive pathogen in this region. To identify resistance resources, 200 soybean germplasm accessions adapted to Northeast China were screened using an etiolated seedling hypocotyl inoculation method with Fusarium oxysporum isolate A3 (DSI = 68.5) as the test pathogen. Disease severity indices exhibited a continuous distribution (mean = 52.84, range = 0–100), suggesting quantitative inheritance. Accessions were classified as highly resistant (13, 6.5%), resistant (40, 20%), moderately susceptible (67, 33.5%), susceptible (43, 21.5%), or highly susceptible (37, 18.5%). To explore potential molecular mechanisms underlying resistance, RT-qPCR analysis was performed on two extreme genotypes—a highly resistant line (H9477F5, DSI = 15.3) and a highly susceptible line (HN91, DSI = 88.7) at 1, 3, and 5 days post-inoculation. The resistant line maintained consistently higher expression of positive regulators GmFER and GmSOD1, with GmFER reaching 15.89-fold induction at day 3. Conversely, expression of negative regulators GmJAZ1 and GmTAP1 remained lower in the resistant line, with susceptible plants showing 5.62-fold higher GmJAZ1 expression at day 3. These findings provide characterized pathogen isolates, resistant germplasm resources (53 accessions with HR or R classifications), and preliminary molecular insights that may inform breeding strategies for improving root rot resistance in Northeast China.