The Endophytic Strain Trichoderma asperellum 6S-2: An Efficient Biocontrol Agent against Apple Replant Disease in China and a Potential Plant-Growth-Promoting Fungus

Abstract

A study was conducted for endophytic antagonistic fungi obtained from the roots of healthy apple trees growing in nine replanted orchards in Shandong Province, China. The fungi were assessed for their ability to inhibit Fusarium proliferatum f. sp. malus domestica MR5, a fungal strain associated with apple replant disease (ARD). An effective endophyte, designated as strain 6S-2, was isolated and identified as Trichoderma asperellum. Strain 6S-2 demonstrated protease, amylase, cellulase, and laccase activities, which are important for the parasitic and antagonistic functions of pathogenic fungi. The inhibition rate of 6S-2 against Fusarium proliferatum f. sp. malus domestica MR5 was 52.41%. Strain 6S-2 also secreted iron carriers, auxin, ammonia and was able to solubilize phosphorus. Its fermentation extract and volatile substances inhibited the growth of MR5, causing its hyphae to twist, shrink, swell, and rupture. The antifungal activity of the 6S-2 fermentation extract increased with increasing concentrations. It promoted the production and elongation of Arabidopsis thaliana lateral roots, and the strongest effects were seen at a concentration of 50 mg/mL. A GC-MS analysis of the 6S-2 fermentation extract and volatile substances showed that they comprised mainly alkanes, alcohols, and furanones, as well as the specific volatile substance 6-PP. The application of 6S-2 spore suspension to replanted apple orchard soils reduced plant oxidative damage and promoted plant growth in a pot experiment. Therefore, the endophytic strain T. asperellum 6S-2 has the potential to serve as an effective biocontrol fungus for the prevention of ARD in China, and appears to promote plant growth.

Controlled-Release Diammonium Phosphate Alleviates Apple Replant Disease: An Integrated Analysis of Soil Properties, Plant Growth, and the Soil Microbiome

“…proliferatum, and F. moniliforme were convincingly the major pathogenic fungi causing ARD in China after investigations of the main apple-producing regions. − Fusarium produces a variety of toxins that cause root necrosis and decay, resulting in short, withered, and dead plants, and the destruction of the microbial community structure. , In the present study, the copy number of these four pathogenic Fusarium fungi exhibited a downward trend over time under the different treatments (except MBF) (Figure ), which may be related to the changes in the soil temperature and moisture (Figure S5). Moreover, the copy numbers of the four pathogenic Fusarium fungi in T1 and T2 were significantly lower than those in CK, providing a strong evidence that adding N/P from an external source reduced the number of harmful microorganisms, which is consistent with the studies of Utkhede and Simth and Wang et al At a given time point, the number of Fusarium was related to the type of fertilizer.…”

Allium fistulosum L. Alleviates Apple Replant Disease by Suppressing Fusarium solani

“…The isolation procedure was based on that described in Wang et al with slight modification of the separation scheme [ 39 ]. First, the roots were washed with deionized water, soaked in 75% alcohol for 10 min, soaked in 4% sodium hypochlorite for 10 min, soaked in sterile water for 10 min, and rinsed in sterile water 4–5 times.…”

Effects of Trichoderma asperellum 6S-2 on Apple Tree Growth and Replanted Soil Microbial Environment

“…In earlier research, we isolated an apple root endophyte designated strain 6S-2 and identified it as T. asperellum. 6S-2 was shown to be an efficient biocontrol agent against ARD in China and had potential plant-growth-promoting activity [25]. The aims of the present study were therefore (i) to characterize the effects of 6S-2 fertilizer application on the growth of apple plants in greenhouse, pot, and field experiments; (ii) to analyze changes in the soil microbial community structure after 6S-2 fertilizer application (especially the abundances of Trichoderma and harmful Fusarium species); (iii) to document changes in root exudates of M. hupehensis Rehd seedlings after 6S-2 fertilizer application and the relationship between these exudates and the soil microbial community structure; and (iv) to gain insight into the mechanisms by which 6S-2 fertilizer alleviates ARD.…”