The Effect of Temperature on Disease Severity and Growth ofFusarium oxysporumf. sp.apiiRaces 2 and 4 in Celery

Abstract

Fusarium oxysporum f. sp. apii (Foa) race 4, which is in F. oxysporum species complex (FOSC) Clade 2, causes a new Fusarium wilt of celery. We compared Foa race 4 with race 2, which causes Fusarium yellows of celery and is in FOSC Clade 3. Optimal temperatures for celery yield are 16 to 18°C. Soil temperatures in California celery production areas can range up to 26°C, and the maximal rate of hyphal extension of Foa races 2 and 4 in culture are 25°C and 28°C, respectively. Here, we compared the effect of temperatures from 16 to 26°C on growth of Foa races 4 and 2 in two celery cultivars: Challenger, which is resistant to Foa race 2 and susceptible to race 4; and Sonora, which is susceptible to both Foa races 2 and 4. Based on linear regressions, as temperature increases, there is an increase in the log of Foa race 4 DNA concentration in celery crowns and in the reduction in plant height. Based on logistic regressions, as temperature increases, the incidence of vascular discoloration increases in celery with either Foa race 2 or 4 infection. In both cultivars, temperatures of 22°C and above resulted in a significantly (α=0.05) greater concentration of Foa race 4 than race 2 in planta. The concentration of Foa race 2 in crowns in Challenger is temperature-independent and comparatively low; consequently, Challenger is, at least partly, resistant rather than tolerant to Foa race 2.

The Emergence of Fusarium oxysporum f. sp. apii Race 4 and Fusarium oxysporum f. sp. coriandrii Highlights Major Obstacles Facing Agricultural Production in Coastal California in a Warming Climate: A Case Study

“…In severe cases, particularly with Foa race 4, the discoloration can extend into the base of the petioles. Stunting is strongly associated with vascular discoloration on more than 1/4 of the circumference of the vascular ring in the crown ( Kaur et al, 2022 ). The extent of stunting and vascular discoloration is also associated with more Foa biomass in the celery crown ( Kaur et al, 2022 ).…”

“…Stunting is strongly associated with vascular discoloration on more than 1/4 of the circumference of the vascular ring in the crown ( Kaur et al, 2022 ). The extent of stunting and vascular discoloration is also associated with more Foa biomass in the celery crown ( Kaur et al, 2022 ). Both Foa races 2 and 4 can cause some chlorosis, frequently in a lower leaf, but chlorosis ( Figure 2C ), is typically more noticeable in a field with race 2 than race 4.…”

“…A major difference between Foa race 2 and Foa race 4 is that while both Foa race 2 and Foa race 4 are temperature-sensitive, the magnitude of the high temperature response in Foa race 4 is significantly greater ( Kaur et al, 2022 ). In the celery cultivar Sonora, which is susceptible to both Foa race 2 and race 4, at 18°C, there were no significant (α = 0.05) differences between races in either stunting, i.e., the reduction in plant height, or in the concentration of the Foa in the crown, as estimated by qPCR.…”

“…Global warming in California ( Oakely et al, 2019 ) could have a large impact on the growth of multiple FOSC pathogens and consequently the production of high-quality crops in California. The FOSC typically have temperature optima from 25 to 28°C ( Kaur et al, 2022 ). There are multiple examples of diseases caused by F. oxysporum formae speciales in which disease severity in susceptible varieties increases as temperatures increase from 22 to 28°C (e.g., f. sp.…”

“…dulce ) that causes an emerging disease in California, United States. Foa race 4 apparently arose in approximately 2013 ( Epstein et al, 2017 ), is highly aggressive at temperatures above 22°C ( Kaur et al, 2022 ), has been spreading in its geographic distribution within California, and currently cannot be controlled via either host resistance or economical methods that reduce the pathogen abundance in infested soil. Although F. oxysporum f. sp.…”