Identification of fungal pathogens and analysis of genetic diversity of Fusarium tricinctum causing root rots of alfalfa in northeast China

Authors: LI, Y - Northeast Agricultural University, China; ZHANG, X - Northeast Agricultural University, China; ZHANG, R - Northeast Agricultural University, China; JIANG, W - Northeast Agricultural University, China; Harris-Shultz, Karen; JI, P - University Of Georgia; ZHAO, T - Northeast Agricultural University, China

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2020
Publication Date: N/A
Citation: N/A

Interpretive Summary: Alfalfa root rot is one of the most destructive diseases of alfalfa causing a yield loss of 20-40% worldwide. This disease, which shortens the life of the alfalfa grassland, is caused by many soil-borne pathogens that differ based on geographic location. Little is known about the alfalfa root rot pathogens in northeast China. In this study, pathogens that cause alfalfa root rot were identified from Heilongjiang province and the pathogenicity and the sensitivity to carbendazim (a fungicide commonly used to treat the disease) of each isolate was assessed. 480 fungal isolates were identified by morphological characteristics and molecular analysis as Fusarium tricinctum (112 isolates, 23.3%), F. acuminatum (92 isolates, 19.2%), F. oxysporum (67 isolates, 14%), F. solani (59 isolates, 12.3%), F. equiseti (45 isolates, 9.4%), Phoma medicaginis (36 isolates, 7.5%), Alternaria alternata (29 isolates, 6.0%), Plectosphaerella cucumerina (21 isolates, 4.4%), and Chaetomium globosum (19 isolates, 3.9%). No isolate was sensitive to 1 and 10 µg/ml of carbendazim. Genetic diversity of the most predominant fungi F. tricinctum was examined using AFLP markers. The isolates were divided into eight groups based on geography. This study identified the causative agents of alfalfa root rot of alfalfa in Heilongjiang province and identified that the most used fungicide is ineffective in this area for control of the disease.

Technical Abstract: Alfalfa root rot, caused by various plant pathogenic fungi, is a devastating disease of alfalfa worldwide. Population structure and genetic diversity of fungal pathogens causing alfalfa root rot in northeast China are not well understood. In this study, 480 fungal isolates were collected from six major alfalfa growing regions in Heilongjiang province, China, which were identified as Fusarium tricinctum, F. oxysporum, F. acuminatum, F. solani, F. equiseti, Phoma medicaginis, Plectosphaerella cucumerina, Alternaria alternata, and Chaetomium globosum. F. tricinctum was the predominant species among the isolates, and P. medicaginis and C. globosum were not reported previously causing alfalfa root rot in northeast China. A total of 73 F. tricinctum isolates were identified and the majority of isolates were moderately or highly aggressive on alfalfa. No isolate of F. tricinctum was sensitive to carbendazim (1 and10 µg/ml), indicating this commonly used fungicide for alfalfa root rot is not suitable for management of the disease in this area. The F. tricinctum isolates were analyzed using AFLP markers and were divided into eight genetic groups with 28 pairs of primers. AMOVA analysis indicated that there was significant correlation between genetic groups of the F. tricinctum isolates and their geographical locations or aggressiveness. Pairwise comparison and Structure analysis also indicated that geographical locations and aggressiveness of the isolates had a significant effect on the population differentiation of the isolates. This study provides insight into the fine-scale genetic diversity and reproductive biology of the alfalfa root rot pathogen F. tricinctum, which facilitates development of effective strategies for managing this destructive disease in alfalfa production.