Genetic Resistance of Lactuca spp. against Fusarium oxysporum f. sp. lactucae Race 1

Abstract

Fusarium wilt of lettuce is caused by the pathogen Fusarium oxysporum f. sp. lactucae (Fol) and is a growing threat to global lettuce production. Fol was first detected in Florida in 2017 and was subsequently confirmed as race 1. Management strategies for this long-persisting soil pathogen are limited, time-consuming and expensive, and they may lack efficacy. Identifying diverse sources of genetic resistance is imperative for breeding adapted cultivars with durable resistance. The objectives of this study were to identify sources of resistance against a race 1 isolate of Fol in Florida, delineate the relationship between foliar and taproot symptoms, and investigate the inheritance of resistance and partial resistance in two F2 populations. Thirteen experiments were conducted in greenhouse and field locations to characterize the diversity of genetic resistance in the genus Lactuca. Leaf cultivars Dark Lollo Rossa and Galactic; romaine breeding lines 43007, 60182, and C1145; and iceberg breeding line 47083 consistently exhibited low foliar and taproot disease symptoms. Resistance was not identified among the wildtype Lactuca or primitive plant introductions (PI) in this study based on taproot symptoms. An additional test was conducted to study the segregation pattern of Fol resistance between one resistant and one susceptible accession (R × S) and one partial resistant and one susceptible accession (PR × S). The F2 population from ‘60182 × PI 358001-1’ fit the expected segregation ratio for a single recessive locus model, whereas the ratio for ‘Dark Lollo Rossa × PI 358001-1’ did not fit either recessive or dominant single locus models. These sources of resistance are potential candidates for developing commercial cultivars with multiple resistance loci against Fol race 1, especially for the Florida lettuce production system.

Pathogenicity of Fusarium oxysporum f. sp. lactucae in lettuce cultivars at different temperatures

“…Disease severity seems to be related to the cultivar characteristics, to isolate aggressiveness, and to inoculation conditions for the same race of inoculum virulence and density (Garibaldi et al, 2004b;Scott et al, 2010b;Gilardi et al, 2021;Cabral and Reis, 2013;Cabral et al, 2019;Murray et al, 2021). Inconsistency between disease development and the susceptibility of the cultivars for trials carried out in different periods (Oct, Nov, Dec) or temperature ranges was observed by Cabral et al (2014).…”

Comparative genomics and transcriptomics reveal differences in effector complement and expression between races ofFusarium oxysporumf.sp.lactucae

“…Moreover, there are also specific PCR assays published for both Fola1 (Pasquali et al, 2007) and Fola4 (Gilardi et al, 2017b). Although resistance to Fola1 is available within commercial cultivars (Garibaldi et al, 2004; Scott et al, 2010; Murray et al, 2021), these are not always adapted or suitable for some locations and are often also susceptible to Fola4. Moreover, the lettuce cultivars commonly used in indoor production in Europe are highly susceptible to Fola4 and hence the plant breeding industry has had to try and react quickly to identify and deploy resistant cultivars to this new race.…”