Identification, Pathogenicity, and Genetic Diversity of Fusarium spp. Associated with Maize Sheath Rot in Heilongjiang Province, China

Abstract

Maize sheath rot is a prevalent maize disease in China. From 2020 to 2021, symptomatic samples were collected from the main maize-growing regions of Heilongjiang province. To clarify the population and genetic diversity, as well as the virulence of pathogens responsible for maize sheath rot, a total of 132 Fusarium isolates were obtained and used for follow-up studies. Ten Fusarium species were identified based on morphological characteristics, and phylogenetic analysis was conducted using the TEF-1α gene sequences, including F. verticillioides (50.00%), F. subglutinans (18.94%), the Fusarium incarnatum-equiseti species complex (14.39%), F. temperatum (5.30%), F. acuminatum (3.03%), F. solani (2.27%), F. sporotrichioides (2.27%), F. tricinctum (1.52%), F. asiaticum (1.52%), and F. proliferatum (0.76%). All 10 Fusarium species could produce oval-to-annular lesions on maize sheath, and the lesions were grayish yellow to dark brown in the center and surrounded by a dark gray-to-dark brown halo. Of these, F. tricinctum and F. proliferatum showed significantly higher virulence than the other Fusarium species. In addition, haplotype analysis based on the concatenated sequences of the ITS and TEF-1a genes showed that 99 Fusarium isolates which belonged to the Fusarium fujikuroi species complex-consisting of F. verticillioides isolates, F. subglutinans isolates, F. temperatum isolates, and F. proliferatum isolates-could be grouped into 10 haplotypes, including 5 shared haplotypes (Haps 1, 2, 4, 5, and 6) and 5 private haplotypes (Haps 3, 7, 8, 9, and 10). Furthermore, the F. verticillioides clade in the haplotype network was radial with the center of Hap 2, suggesting that population expansion occurred. This research showed that Fusarium species associated with maize sheath rot in Heilongjiang province are more diverse than previously reported, and this is the first time that F. subglutinans, F. temperatum, F. solani, F. sporotrichioides, F. tricinctum, and F. acuminatum have been confirmed as the causal agents of maize sheath rot in Heilongjiang province.

Keywords: Fusarium spp.; genetic diversity; haplotype analysis; maize; pathogenicity test.

Figure 1

Isolation frequency of Fusarium isolates collected from 7 locations of Heilongjiang Province in 2020 and 2021, respectively.

Figure 2

Colony appearance of representative isolates of 10 Fusarium species. (A–J) Colonies of the representative isolates of F. verticillioides, F. subglutinans, Fusarium incarnatum-equiseti species complex, F. temperatum, F. acuminatum, F. solani, F. sporotrichioides, F. tricinctum, F. asiaticum, and F. proliferatum, respectively.

Figure 3

Conidia morphology of representative isolates of 10 Fusarium species. (A–J) Macroconidia or microconidia of representative isolates of F. verticillioides, F. subglutinans, Fusarium incarnatum-equiseti species complex, F. temperatum, F. acuminatum, F. solani, F. sporotrichioides, F. tricinctum, F. asiaticum, and F. proliferatum, respectively.

Figure 4

Phylogenetic tree obtained from maximum likelihood analysis based on the TEF-1α gene sequences.

Figure 5

Inoculation of maize leaf sheaths with different Fusarium species (var. Zhengdan 958). (A) Maize sheath rot symptoms observed in the field; (B–K) typical symptoms on maize sheaths caused by F. verticillioides, F. subglutinans, Fusarium incarnatum-equiseti species complex, F. temperatum, F. acuminatum, F. solani, F. sporotrichioides, F. tricinctum, F. asiaticum, and F. proliferatum, respectively; (L) CK. Bar = 5 mm.

Figure 6

Haplotype distribution and TCS analyses based on the concatenated sequences of ITS and TEF-1α genes of 99 FFSC isolates obtained from different locations of Heilongjiang province, China. Each haplotype is represented by a circle, the size of which is proportional to the haplotype frequency.