Tomato Powdery Mildew Research Articles

Development of diagnostic PCR markers closely linked to the tomato powdery mildew resistance gene Ol-1 on chromosome 6 of tomato

Lycopersicon hirsutum G1.1560 is a wild accession of tomato that shows resistance to Oidium lycopersicum, a frequently occurring tomato powdery mildew. This resistance is largely controlled by an incompletely dominant gene Ol-1 near the Aps-1 locus in the vicinity of the resistance genes Mi and Cf-2/Cf-5. Using a new F2 population (n=150) segregating for resistance, we mapped the Ol-1 gene more accurately to a location between the RFLP markers TG153 and TG164. Furthermore, in saturating the Ol-1 region with more molecular markers using bulked segregant analysis, we were able to identify five RAPDs associated with the resistance. These RAPDs were then sequenced and converted into SCAR markers: SCAB01 and SCAF10 were L. hirsutum-specific; SCAE16, SCAG11 and SCAK16 were L. esculentum-specific. By linkage analysis a dense integrated map comprising RFLP and SCAR markers near Ol-1 was obtained. This will facilitate a map-based cloning approach for Ol-1 and marker-assisted selection for powdery mildew resistance in tomato breeding.

Variation in Response of Wild Lycopersicon and Solanum spp. against Tomato Powdery Mildew (Oidium lycopersici)

A set of 154 accessions of nine wild Lycopersicon spp. and five accessions of three closely related Solanum spp. were tested for resistance to tomato powdery mildew (Oidium lycopersici). Screening revealed valuable sources of resistance, mainly among L. hirsutum, L. pennellii, L. cheesmanii, L. chilense, L. peruvianum and L. parviflorum. L. esculentum (all ssp.) and L. pimpinellifolium expressed high susceptibility to O. lycopersici inoculation. Results of variance and cluster analysis of responses to O. lycopersici coincide with recent taxonomic classification and genetic relationships within genus Lycopersicon.

Case study of host-pathogen interaction: tomato (Lycopersicon spp.)–tomato powdery mildew (Oidium lycopersici) – a review

The present paper tries to demonstrate progress and gap of knowledge in plant pathology through the tomato - tomato powdery mildew host-pathogen interaction as a model. Tomato powdery mildew (Oidium lycopersici) has caused serious damages on glasshouse tomato (Lycopersicon esculentum) crops during the last approximately 15 years. Although the absence of tcleomorph stage did not allow exact taxonomic classification of the pathogen, comparative morphological studies using light and scanning electron microscopy revealed that Oidium lycopersici might be included to the Erysiphe sect. Erysiphe (close to Erysiphe aqui­ legiae var. ranunculi). Effective resistance sources to 0. lycopersici were found mainly in wi ld Lycopersicon hirsutum and L. penne/lii (confirmed by testing with four different 0. lycopersici isolates). Available information on the pathogenic variability of 0. lycopersici is given; host range experiments revealed considerable differences in abi lity of different 0. lycopersici isolates to infect cucumber and tobacco. postulating existence of different pathotypcs lformae specialist of pathogen. Similarly, some Lycopersicon spp. genotypes showed remarkable differential reactions with pathogen isolates, indicating existence of different pathogen races. Information regarding recently detected mechanisms and basis of resistance in Lycopersicon spp. are also men­ tioned. However, more research based on classical, biochemical and molecular approaches is also needed.

Host range of Oidium lycopersici occurring in the Netherlands.

Nine accessions of three cucurbit species, ten of eight legume species, three of lettuce (Lactuca sativa) and 34 of 14 Solanaceae species were inoculated with a Dutch isolate of the tomato powdery mildew fungus (Oidium lycopersici) to determine its host range. Macroscopically, no fungal growth was visible on sweet pepper (Capsicum annuum), lettuce, petunia (Petunia spp.) and most legume species (Lupinus albus, L. luteus, L. mutabilis, Phaseolus vulgaris, Vicia faba, Vigna radiata, V. unguiculata). Trace infection was occasionally observed on melon (Cucumis melo), cucumber (Cucumis sativus), courgette (Cucurbita pepo), pea (Pisum sativum) and Solanum dulcamara. Eggplant (Solanum melongena), the cultivated potato (Solanum tuberosum) and three wild potato species (Solanum albicans, S. acaule and S. mochiquense) were more heavily infected in comparison with melon, cucumber, courgette, pea and S. dulcamara, but the fungus could not be maintained on these hosts. All seven tobacco (Nicotiana tabacum) accessions were as susceptible to O. lycopersici as tomato (Lycopersicon esculentum cv Moneymaker), suggesting that tobacco is an alternative host. This host range of the tomato powdery mildew differs from that reported in some other countries, which also varied among each other, suggesting that the causal agent of tomato powdery mildew in the Netherlands differ from that in those countries. Histological observations on 36 accessions showed that the defense to O. lycopersici was associated with a posthaustorial hypersensitive response.

Effect of Humidity on Development of Tomato Powdery Mildew (Oidium lycopersici) in the Glasshouse

A series of experiments was carried out over four years in a glasshouse with computer control of humidity and temperature to investigate the effect of humidity on the development of tomato powdery mildew. Four relative humidities (RHs) (80%, 87%, 90% and 95%) at constant 19°C were maintained over an eight-week experimental period during the Autumn. Disease was greatest at 80% RH and was progressively less with increasing RH to a minimum level at 95% RH on both inoculated plants, introduced to act as initial infection sources, and on adjacent uninoculated plants. The results indicate that high humidities may decrease severity of this disease in the glasshouse and may help management of this disease in the future.

Characteristics and host range of tomato powdery mildew

The anamorphic state of a powdery mildew, which first appeared on tomato in the UK in 1987, currently listed as Erysiphe orontii (anamorph Oidium violae), was examined microscopically on both tomato and alternative hosts. Host range studies were also carried out. In 1993–95, species and cultivars of plants from 26 of the 30 families listed as hosts of E. orontii were inoculated with tomato powdery mildew in the glasshouse and assessed for susceptibility on a 0–3 scale based on degree of sporulation and growth. Thirteen families contained species or varieties that were susceptible and a total of 80 varieties, including many economically important Cucurbitaceae and Solanaceae, supported sporulation to some extent (susceptibility score 1–3). Necrosis was not a constant feature of plants exhibiting resistance, as it could accompany sporulation on some susceptible varieties. Microscopic measurements showed that conidial size, conidiophore length, conidiophore foot‐cell length and width, and the number of cells distal to the foot‐cell were remarkably constant between samples of powdery mildew taken from tomato each year and from the various alternative hosts. Based on the production of conidia singly, the presence of nipple‐shaped to moderately lobed appressoria, and occurrence of straight conidiophores, it is concluded that this fungus on tomato should more correctly be named Oidium lycopersicum until the sexual stage is discovered. The highly polyphagous nature of this powdery mildew would suggest that it represents a potential risk to UK agriculture and horticulture, but the failure to recover any powdery mildew from 120 samples of potato, including varieties Cara and Maris Piper, on which the tomato powdery mildew could sporulate in the glasshouse, suggests that environmental factors may play a key role in preventing establishment of this powdery mildew on alternative hosts on a commercial scale in the field.

Effect of filtration of solar light on the production of conidia by field isolates of Botrytis cinerea and on several diseases of greenhouse-grown vegetables

New custom-made polyethylene films with light Mockers in the far-red region of the spectrum were tested for their effect on sporulation of Botrytis cinerea. A pink-pigmented polyethylene sheet partially screened visible light mainly from 470–650 nm, with lowest transmissihility at 500–580 nm, and a green-pigmented sheet partially screened it mainly from of 560–800 nm, with lowest transmissihility at 600–700 nm. Both films screened ultraviolet radiation up to 380 nm. Light filtration inhibited sporulation of B. cinerea cultures on artificial medium, tomato leaves, and cucumber fruits. However, the extent of inhibition varied with fungal isolate, the quality of the light that reached the culture and the medium that supported the fungal colonies. Some isolates sporulated in darkness, so an indirect effect on the host plant has been important in reducing the disease suppression. The greenpigmented polyethylene reduced conidial load and grey mould in commercial greenhouses by 35–75%. Diseases caused by Sclerotinia sclerotiorum on cucumber, Fulvia fulva on tomato and cucumber powdery mildew also were reduced. The green film could be incorporated in disease management.

トマトうどんこ病の発病に及ぼす温度ならびに湿度の影響

トマトうどんこ病の発病に及ぼす温度ならびに湿度の影響