OTLs affecting oviposition rate mapped to chromosome 1 (Tv-i) and 12 (Tv-2). F3 lines homozygous for either the L. esculentum allele or the L. hirsutum f. glabratum allele at one or both loci confirmed the effects of Tv-i and Tv-2. The F2 population was also evaluated for segregation of type IV and type VI glandular trichome densities. Two QTLs affecting trichome type IV density (TriIV-i and TriIV-2) and one affecting type VI trichome density (TriJ/I-i) mapped to chromosomes 5, 9 and 1, respectively. These results do not support the hypothesis that the density of type IV trichomes is involved in whitefly resistance.

No abstract

Since the late 1980s powdery mildew, designated Oidium lycopersicum, frequently invaded the tomato crop in Western Europe . All commercial cultivars are susceptible . To screen for resistance in wild species a reliable and efficient disease test was developed . Young plants with two to three true leaves are inoculated at high relative humidity by spraying with a freshly prepared suspension of 2 x 10 4 conidia, ml-' . Symptoms are periodically evaluated according to a scale based on the percentage of leaf area with mycelium .One hundred and twenty seven accessions, representing eight wild Lycopersicon species, were screened for resistance to O. lycopersicum . A large variation in resistance was found between species . L. hirsutum was the most resistant species ; L. pennellii was moderately resistant ; species of the subgeneric group of L . esculentum and of the 'peruvianum-complex' were all susceptible . L. parviflorum was classified separately due to a large variation between accessions. Except for this species, a low variation was found between accessions within species . High levels of resistance were observed in four accessions of L. hirsutum, in one of L . parviflorum and in one of L . peruvianum . This resistance is characterized by a very low disease incidence and a strongly restricted mycelium growth and lack of sporulation.

The inheritance of resistance to powdery mildew (Oidium lycopersicum) in Lycopersicon hirsutum was investigated by disease tests in segregating populations obtained by hybridising tomato (L. esculentum) cv Moneymaker with the wild relative L. hirsutum G1.1560. One incompletely dominant gene Ol-1 was found to largely control resistance to the disease. To map Ol-1, DNA pools from seven resistant and ten susceptible F2 plants were analyzed for random amplified polymorphic DNA (RAPD). With 32 primers tested, one RAPD, primed with the sequence 5'-GACGTGGTGA-3', was observed between the susceptible and the resistant bulks, which cosegregated with resistance in the F2 population of L. esculentum × L. hirsutum G1.1560. This RAPD was mapped on chromosome 6 by using an F2 (L. esculentum × L. pennellii) already mapped for 49 RFLPs. RFLP analysis of the F2 from L. esculentum cv Moneymaker × L. hirsutum G1.1560 demonstrated that Ol-1 maps near the Aps-1 region on chromosome 6, in the vicinity of the resistance genes to Meloidogyne spp. (Mi) and to Cladosporium fulvum (Cf-2/Cf-5).

Eighty-five accessions of Lycopersicon esculentum and related species were tested for resistance to the glasshouse whitefly, Trialeurodes vaporariorum WESTW. High levels of resistance were found in L. hirsutum, L. hirsutumglabratum and Solanumpennellii. In other species, too, some resistance was observed. A breeding program is in progress.