Diversity of the Seedborne Fungi and Pathogenicity of Fusarium Species Associated with Intercropped Soybean.

Xiaoli Chang,Wenyu Yang,Taiwen Yong,Taiguo Liu,Hongju Li,Muhammd Naeem,Chun Song,Xiaoling Wu,Wanquan Chen

doi:10.3390/pathogens9070531

Abstract

Maize/soybean relay strip intercropping has been widely practiced in Southwest China due to its high productivity and effective application of agricultural resources; however, several seedborne diseases such as seedling blight, pod and seed decay are frequently observed causing severe yield loss and low seed quality. So far, the population and pathogenicity of the seedborne fungi associated with intercropped soybean remain unexplored. In this study, seeds of 12 soybean cultivars screened for intercropping were collected from three growing regions in Sichuan Province of Southwest China, and the seedborne fungi were isolated from the surface-sterilized seeds. Based on sequence analysis of ribosomal DNA internal transcribed spacer (rDNA ITS), 148 isolates were identified into 13 fungal genera, among which Fusarium covered 55.0% as the biggest population followed by Colletotrichum. Furthermore, Fusarium isolates were classified into five distinct species comprising F. fujikuroi, F. proliferatum, F. verticillioides, F. asiaticum and F. incarnatum through sequence analysis of translation elongation factor 1 alpha (EF-1α) and DNA-directed RNA ploymerase II second largest subunit (RPB2). Among them, F. fujikuroi accounted for 51.22% (42/82) and was isolated from 91.7% (11/12) soybean varieties. Pathogenicity assay showed that five Fusarium species were able to infect the seeds of soybean cultivar “Nandou12” and caused water-soaked or rot symptoms, while F. fujikuroi and F. asiaticum had much higher aggressiveness than other species with significant reductions of seed fresh weight and germination percentage. Accordingly, this study indicates that Fusarium species are the dominant seedborne fungi in the intercropped soybean in Sichuan, China, and this provides some useful references for the effective management of seedborne fungal diseases as well as soybean resistance breeding in maize/soybean relay strip intercropping.

Highlights

Soybean (Glycine max L.) is one of the most important oil seeds and economic crops across the world
Our results demonstrate that F. asiaticum and F. fujikuroi had the highest aggressiveness on soybean seeds, and these seedborne Fusarium species had some negative effects on seed fresh weight and seed germination
This study demonstrated that soybean seeds are commonly colonized by different fungal genera, especially Fusarium spp

Summary

Introduction

Soybean (Glycine max L.) is one of the most important oil seeds and economic crops across the world. Pathogens 2020, 9, 531 tons, accounting for 31.18% of global consumption, but more than 90% consumption is still dependent on the overseas import because of limited domestic production that was averaged about 16 million metric tons in 2018–2019 (USDA, https://www.usda.gov/oce/commodity/wasde/). Several seedborne fungal diseases have been known as one major limiting factor of soybean production [1,2,3,4]. Most of these seedborne fungi are facultatively parasitic in soybean, and they can infect and colonize seeds, which often cause seedling blight, pod and seed decay; significantly affect the yield; and reduce the germination, vigor and quality of seeds [2,5,6]. Management of seedborne diseases has been conducted using a combination of fungicides, intercropping or rotation with non-host crops, early harvest and application of resistant cultivars to minimize the yield loss [11,12,13,14,15,16]

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