Further observations on variation of lettuce mosaic virus in relation to lettuce (Lactuca sativa), and a discussion of resistance terminology

Abstract

Two potyvirus isolates from endive, originating from southern France (Ls252) and from the Netherlands (Ls265), that were highly and poorly pathogenic on lettuce, respectively, were compared with a common isolate (Lsl) of lettuce mosaic virus (LMV) and with two highly deviant Greek isolates from Helminthia (Picris) echioides (Gr4) and endive (Gr5), earlier recognized as LMV. The isolates could not be distinguished by particle morphology and serology, and were all identified as LMV. Leaf curling, plant stunting and necrosis were more characteristic of the virus than mosaic. The isolates studied varied considerably on differential host species and a range of lettuce cultivars including pathotype differentials of Pink et al. [1992b]. Lsl and Ls265 reacted largely as pathotype II, including the 'common strain' of the virus, but Ls265 was least pathogenic on lettuce. Ls252 fitted pathotype IV and was very similar to LMV-E (the 'Spanish strain'). The Greek isolates were very similar to each other in causing very severe symptoms on some non-lettuce hosts and a number of lettuce cultivars. In lettuce varietal reaction Gr4 resembled pathotype I, but Gr5 severely affected 'Salinas 88', resistant to pathotypes I, II and III, and i t appears to be a novel pathotype. Genetic interaction between lettuce and LMV is not following a simple yes-or-no pattern, and it is not a mere matter of resistance versus susceptibility. Adoptior~ of a more realistic resistance terminology is proposed. None of the lettuce cultivars tested was resistant to the most pathogenic isolate Ls252, but resistance to it was found in 2 out of 12 wild Lactuca species tested (Lactuca perennis and L. tatarica) while the symptomless plants of L. perennis clearly reacted in ELISA.

Mutational Analysis of Plant Cap-Binding Protein eIF4E Reveals Key Amino Acids Involved in Biochemical Functions and Potyvirus Infection

“…The result of the interaction, resistance or tolerance, depends on the virus isolate and genetic background (52,60), but mo1 1 is generally associated with resistance and mo1 2 with tolerance (9,20). In order to identify which eIF4E amino acids are important for the virus cycle, we set up an experimental system by which the role of eIF4E in the virus cycle can be dissociated from its physiological function in cellular mRNA translation.…”

Lettuce ring necrosis, caused by a chytrid-borne agent distinct from lettuce big-vein ‘virus’

“…Internal rib necrosis and rusty brown discoloration causing extensive losses in California in 'Climax' crisphead lettuce is symptomatologically also different and was found to be caused by lettuce mosaic virus (Coakley et al, 1973). Such necrosis is far from rare in lettuce with lettuce mosaic virus (Bos et al, 1994).…”

Quantitative control of Lettuce mosaic virus fitness and host defence inhibition by P1-HCPro

“…LMV-E, isolated from lettuce plants in Spain (5), has the ability to infect Salinas 88, but causes only mild symptoms in this cultivar, 15 dpi. These differences were only observed in lettuce cultivars carrying mo1 2 , such as Salinas 88 and Vanguard 75. In the cultivar Floribibb (mo1 1 ) both isolates induce similar symptoms at 8-10 dpi.…”

“…Three LMV resistance genes have been described in lettuce, two alleles (mo1 1 and mo1 2 ) of the recessive gene mo1, which encodes the cap-binding protein eIF4E (10), and the dominant gene Mo2 (2,11,12). Two main sub-groups of LMV isolates cause epidemics in the field, LMV-Common and LMV-Most (7).…”

“…Two main sub-groups of LMV isolates cause epidemics in the field, LMV-Common and LMV-Most (7). LMV-Most isolates (for mo1-breaking seed transmitted) overcome the resistance afforded by the mo1 1 , mo1 2 and Mo2 genes and are seed-borne in cultivars carrying these genes. LMV-Common isolates are seed-borne but do not overcome the resistance associated with mo1¹ and mo1² (7).…”