Host Genotype and Hypersensitive Reaction Influence Population Levels of Xanthomonas campestris pv. vitians in Lettuce

Abstract

Dynamics of population sizes of Xanthomonas campestris pv. vitians inoculated onto or into lettuce leaves were monitored on susceptible and resistant cultivars. In general, population growth was greater for susceptible (Clemente, Salinas 88, Vista Verde) than resistant (Batavia Reine des Glaces, Iceberg, Little Gem) cultivars. When spray-inoculated or infiltrated, population levels of X. campestris pv. vitians were consistently significantly lower on Little Gem than on susceptible cultivars, while differences in the other resistant cultivars were not consistently statistically significant. Populations increased at an intermediate rate on cultivars Iceberg and Batavia Reine des Glaces. There were significant positive correlations between bacterial concentration applied and disease severity for all cultivars, but bacterial titer had a significantly greater influence on disease severity in the susceptible cultivars than in Little Gem and an intermediate influence in Iceberg and Batavia Reine des Glaces. Infiltration of X. campestris pv. vitians strains into leaves of Little Gem resulted in an incompatible reaction, whereas compatible reactions were observed in all other cultivars. It appears that the differences in the relationship between population dynamics for Little Gem and the other cultivars tested were due to the hypersensitive response in cultivar Little Gem. These findings have implications for disease management and lettuce breeding because X. campestris pv. vitians interacts differently with cultivars that differ for resistance mechanisms.

Comparative Genomic Analysis of the Lettuce Bacterial Leaf Spot Pathogen, Xanthomonas hortorum pv. vitians, to Investigate Race Specificity

“…Investigation into Xhv strain diversity has been vital to the development and application of effective strategies for the management of BLS. In 2015, Bull et al (2015) demonstrated that some, but not all, of the 120 Xhv strains evaluated resulted in a hypersensitive response (HR) to limit the spread of infection upon inoculation into Lactuca sativa cvs. Little Gem, Pavane, and La Brillante, and that these strains did not cause HR in the other lettuce cultivars that were tested.…”

Differential Symptomology, Susceptibility, and Titer Dynamics Manifested by Phytoplasma-Infected Periwinkle and Tomato Plants

“…The variations in host responses to phytoplasma infection may be attributed to differences in physiology, genetics, and defense mechanisms of these two plant species. The variation in pathogen load across different plant hosts is a well-established phenomenon [ 35 , 36 , 37 , 38 , 39 ]; for instance, the population sizes of Xanthomonas campestris pv. vitians change in lettuce with different genotypes [ 36 ].…”

“…The variation in pathogen load across different plant hosts is a well-established phenomenon [ 35 , 36 , 37 , 38 , 39 ]; for instance, the population sizes of Xanthomonas campestris pv. vitians change in lettuce with different genotypes [ 36 ]. Another example is the differing susceptibility of grapevine varieties to Plasmopara viticola , the causal agent of downy mildew, where specific grapevine cultivars support higher pathogen loads due to genetic differences in disease resistance [ 35 ].…”

The Ionomics of Lettuce Infected by Xanthomonas campestris pv. vitians

“…The lettuce cultivars used in this study were previously characterized for their resistance to BLS by Nicolas et al (2018; Table 1), according to a modified version of the method developed by Bull et al (2015). Cultivars were classified into three groups based on their susceptibility to BLS: tolerant group with Batavia Reine des Glaces (BRG), Little Gem (LIG), Estival (EST) and Hochelaga (HOC); intermediate group with Romora (ROM) and Turbo (TUR); and susceptible group with Chief (CHI), Gorilla (GOR), Paris Island Cos (PIC) and Vista Verde (VIV).…”

“…The current phytosanitary products used to control BLS have to date shown poor efficiency (Lu and Raid, 2013). Common control strategies such as prophylactic measures, specifically removal of crop debris and use of clean farm machinery, are often ineffective because occurrence of this disease is sporadic (Bull et al, 2015). Nevertheless, the most widely accepted strategy for controlling BLS of lettuce is the use of resistant cultivars (Bull and Koike, 2005).…”