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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Publications at this Location » Publication #393719
Research Project: Disease Management and Improved Detection Systems for Control of Pathogens of Vegetables and Strawberries

Location: Crop Improvement and Protection Research

Title: The emergence of Fusarium oxysporum f. sp. apii race 4 and Fusarium oxysporum f. sp. coriandrii highlight major obstacles facing agricultural production in coastal California in a warming climate: A case study

Author
item EPSTEIN, LYNN - University Of California
item KAUR, SUKHWINDER - University Of California
item Henry, Peter

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2022
Publication Date: 6/13/2022
Citation: Epstein, L.E., Kaur, S., Henry, P.M. 2022. The emergence of Fusarium oxysporum f. sp. apii race 4 and Fusarium oxysporum f. sp. coriandrii highlight major obstacles facing agricultural production in coastal California in a warming climate: A case study. Frontiers in Plant Science. 13. Article 921516. https://doi.org/10.3389/fpls.2022.921516.
DOI: https://doi.org/10.3389/fpls.2022.921516

Interpretive Summary: This article reviews the history of Fusarium wilts of celery and cilantro in California and the insights gained by almost a decade of research on these diseases. Fusarium wilts of celery and cilantro are caused by fungal pathogens called Fusarium oxysporum f. sp. apii (Foa)and F. oxysporum f. sp. coriandrii (Foci), respectively. Further subdivision based on differential host resistance has split F. oxysporum f. sp. apii into “races” 1 through 4. Although Fusarium oxysporum f. sp. apii race 4 emerged recently in 2013, it has already become the most destructive celery pathogen in coastal California. An unusual aspect of these pathogens is how closely related they are based on comparison of their genomes. Furthermore, the hyphae or tissue of Foa race 3, race 4, and Foci can fuse, which means they can exchange genetic materal with each other. This mechanism could lead to new, virulent genotypes of these pathogens in the future. These Fusarium wilt diseases are much more severe at higher temperatures. Climate change, resulting from human-produced greenhouse gases, is predicted to raise temperatures in their coastal California growing region. Therefore, methods for disease control are urgently needed for these pathogens to protect crop production in a warmer environment.

Technical Abstract: Currently in California, Fusarium oxysporum f. sp. apii (Foa) race 4 in celery and F. oxysporum f. sp, coriandrii (Foci) in coriander have the characteristics of emerging infectious plant diseases: the pathogens are spreading, yield losses can be severe, and there are no economical solutions for their control. Foa race 4 and the Foci are an example in which two distinct organisms are in different forma speciales, but are in the same somatic compatibility group, and form conidial anastomosis tubes (CAT) with each other as readily as they form CATs with themselves. Coriander is a host of both Foci and Foa race 4. In contrast, Foa race 4 and Foa race 2, which can be isolated from the same celery, do not form CATs, and as members of different clades in the Fusarium oxysporum species complex (FOSC), may be biologically blocked in the nuclear entry that is required for acquisition of a novel accessory chromosome. Foa race 2 and any Foa race 3 can be controlled with resistant cultivars, but cultivars that control race 4 are not available yet. A phylogenomic analysis indicated that Foa races 3 and 4 and the two Foci are closely related in their conserved genomes. Differences in host range between the Foci and either Foa races 3 or 4 might be due to differences in one or possibly two accessory chromosomes; consequently, a previous horizontal chromosome transfer may account for divergence of the two forma speciales. How Foa race 4 evolved its hyper-virulence remains unknown. Although the accessory chromosomes of Foa races 3 and 4 are highly similar, there is no evidence that Foa race 4 evolved directly from race 3, and it seems likely that races 3 and 4 have a common ancestor. The accessory chromosomes in Foa race 2 are highly divergent from those in Foa races 3, 4 and the Foci. Based on comparisons of in vivo vs. in vitro expression, Foa race 4 expresses 23 putative effectors in planta including two homologs of the conserved FOSC effector Secreted in Xylem1 (SIX1); both SIX1 homologs are on a host-specific accessory chromosome.