Macrophomina phaseolina is a typical soilborne fungal pathogen causing crown and root rot in strawberry (Fragaria × ananassa Duch.) worldwide. M. phaseolina has become a major problem for strawberry growers parallel to the phase-out of methyl-bromide since 2004 and is considered the most destructive soilborne pathogen of strawberry since then. Global warming is characterized by extreme weather conditions, in the Mediterranean area, as reflected by long, hot, dry summers without rain and relatively short, cold rainy winters. This together with regulatory restrictions on toxic fumigants creates favorable conditions for M. phaseolina to thrive. Screening for resistant germplasm is currently the most effective and sustainable approach for managing the disease. In order to screen for susceptible/tolerant strawberry cultivars, various inoculation techniques were assessed on five strawberry cultivars. Artificial inoculation of growth medium with naturally infected plant material and the use of the ‘toothpick’ method resulted in no significant differences. However, the use of artificially produced sclerotia in a soil mix at concentrations of 2.5 × 103 sclerotia/g soil exhibited differential cultivar mortality rates. High variation was found among 32 tested strawberry varieties (Israeli and US) grown under outdoor conditions in a screenhouse. Cultivars ‘Pelican’ (US), ‘Orly’, ‘Tamir’ and ‘Rotmy’ were considered tolerant compared to cultivars ‘Florida 90’ (US) and ‘Peles’ that were the most susceptible. The overall results indicate that the choice of certain Israeli and US cultivars may provide future germplasm for resistance breeding against M. phaseolina.

Many animal and plant viruses depend on arthropods for their transmission. Virus-vector interactions are highly specific, and only one vector or one of a group of vectors from the same family is able to transmit a given virus. Poleroviruses (Luteoviridae) are phloem-restricted RNA plant viruses that are exclusively transmitted by aphids. Multiple aphid-transmitted polerovirus species commonly infect pepper, causing vein yellowing, leaf rolling, and fruit discoloration. Despite low aphid populations, a recent outbreak with such severe symptoms in many bell pepper farms in Israel led to reinvestigation of the disease and its insect vector. Here we report that this outbreak was caused by a new whitefly (Bemisia tabaci)-transmitted polerovirus, which we named Pepper whitefly-borne vein yellows virus (PeWBVYV). PeWBVYV is highly (>95%) homologous to Pepper vein yellows virus (PeVYV) from Israel and Greece on its 5' end half, while it is homologous to African eggplant yellows virus (AeYV) on its 3' half. Koch's postulates were proven by constructing a PeWBVYV infectious clone causing the pepper disease, which was in turn transmitted to test pepper plants by B. tabaci but not by aphids. PeWBVYV represents the first report of a whitefly-transmitted polerovirus. IMPORTANCE The high specificity of virus-vector interactions limits the possibility of a given virus changing vectors. Our report describes a new virus from a family of viruses strictly transmitted by aphids which is now transmitted by whiteflies (Bemisia tabaci) and not by aphids. This report presents the first description of polerovirus transmission by whiteflies. Whiteflies are highly resistant to insecticides and disperse over long distances, carrying virus inoculum. Thus, the report of such unusual polerovirus transmission by a supervector has extensive implications for the epidemiology of the virus disease, with ramifications concerning the international trade of agricultural commodities.

Since 2007, the tobamovirus Cucumber green mottle mosaic virus (CGMMV) has become widespread in Israel, causing severe damage to trellised cucumber and melon in greenhouses and watermelon grown in open fields. To reduce disease damage below the economic threshold, this study focused on four objectives: (a) monitoring the patterns of virus distribution within commercial cucumber greenhouses; (b) studying the potential transmission of CGMMV by agrotechnical activities; (c) virus localization in plant tissues; and (d) searching for techniques that might be adapted for mitigating the disease in trellised cucurbit growth. The results of our surveys demonstrated the role of contaminated seeds and soil as primary inoculum sources, and secondary spread caused by agrotechnical activities. The patterns of secondary disease spread were demonstrated in a series of inoculation experiments involving contaminated knives, shears or hands on wet and dry plants, conducted under research-greenhouse conditions. In parallel experiments using CGMMV-specific antibody and secondary antibody conjugated to Alexa fluor 488, the viral coat protein was visualized in several plant tissues: phloem, xylem, trichomes and grasping tendrils. In addition, commercial-greenhouse experiments were aimed at reducing the number of inoculum sources by identifying and removing infected plants from the plots (early monitoring) prior to agrotechnical activities and/or by adding intermediate medium (IM), such as virus-free compost, to the planting pits at the planting stage. It is suggested that the use of IM combined with early monitoring, awareness of worker mobility (from contaminated structures to young planting areas) and proper sanitation (e.g. disinfection of agrotechnical tools) may reduce the yield losses caused by CGMMV below the economic threshold.

Crown and root rot of strawberry, caused by Macrophomina phaseolina, have become predominant soilborne diseases of strawberry in Israel over the past 5 years. In total, 151 isolates of the pathogen were isolated from infected strawberry plants of commercially grown cultivars in Israel onto a modified agar medium for the genus Macrophomina. Sclerotia viability declined more rapidly in soil maintained at 25°C or at soil temperatures fluctuating from 18 to 32°C under greenhouse conditions, compared with sclerotia viability in soil kept at 30°C. After 30 to 40 weeks of exposure in soil, inocula maintained at 25 or 30°C or at fluctuating temperatures in a greenhouse declined to negligible levels. A significant increase in plant mortality was observed in infested soils maintained at 30 versus 25°C, whereas water stress at 25 or 30°C did not affect plant mortality in M. phaseolina-infested soils. This demonstrated the importance of elevated soil temperature, not moisture stress, on plant mortality caused by M. phaseolina. Host specificity was not evident when strawberry plants were inoculated with each of seven Israeli isolates of M. phaseolina obtained from six other plant species, suggesting the importance of keeping strawberry crops out of rotation with other host crops of the pathogen. The soil fumigants methyl bromide (applied at 500 kg/ha) and metam sodium (730 liter/ha) caused 90 and 95% pathogen mortality in field experiments, respectively, indicating that fumigation may be an effective method of managing this pathogen in infested soils. The increase in prevalence of crown and root rot caused by M. phaseolina in strawberry crops in Israel may be related to the phase-out of methyl bromide.

S OF PRESENTATIONS AT T H E 22ND C O N G R E S S O F T H E I S R A E L I P H Y T O P A T H O L O G I C A L S O C I E T Y February 12-13, 2001 ARO, The Volcani Center, Bet Dagan, Israel Opening Lecture The Contribution of Epidemiological Research to Plant Disease Management D. Shtienberg Dept. of Plant Pathology, ARO, The Volcani Center, Bet Dagan 50250, Israel [e-mail: danish@ netvision.net.il ] Epidemiological research deals with the three components of the disease triangle: the host, the pathogen and the environment. One important goal of epidemiological research is to develop means for rational and cost-effective disease management. In some pathosystems it is possible to identify one (or a few) distinctive factors that govern(s) the occurrence of disease outbreaks. Manipulation of this factor may enable us to prevent the development of an epidemic. However, in most systems the situation is more complicated and many factors, and their interactions, govern the intensity of epidemics. In the 1970s, models based on past (measured) weather and decision rules were used for development of management tools. With the progress in computer science in the 1980s, models that simulated the development of the host and the pathogen were developed. However, simulation models were found inadequate for decision-making. Epidemiological knowledge is currently formulated as relatively simple, hence precise, decision models. These decision models are the frameworks I?y which epidemiological knowledge is transferred to the decision-maker. Nevertheless, the models would not necessarily be suitable in dissimilar environments. (L) A: PHYSIOLOGY AND RESISTANCE Endo-l,4-fl-Giucanase Activity in Isolates ofAlternaria alternata in Relation to Their Virulence in Apple Fruit M. Reuveni, 1 N. Shegalov, 1 D. Shegalov, 1 D. Eshel, 2 Ruth Ben-Arie 3 and D. Prusky 2 1Golan Research Institute, Qazrin 12900 [e-mail: mreuveni@research.haifa.ac.il]; 2Dept. of Postharvest Science, ARO, The Volcani Center, Bet Dagan 50250; and 3Fruit Storage Research Laboratory, Qiryat Shemona 10200, Israel The fungus Alternaria alternata is one of the principal causal agents of moldy core rot of different strains of "Delicious' apples. Disease symptoms generally become apparent after cold storage of the fruit, even though the apple core becomes infected in the orchard. Suitable temperature and humidity conditions in the orchard are evidently conducive to inoculation, but the mode and phenology of infection are not yet clearly understood. Artificial inoculation with fungal spores, of fruits at different stages of development, indicated that the initial blossom (10-30%) and full bloom stages were the most susceptible to infection. Of the 150 A. alternata isolates collected in three orchards in the Golan Heights and Galilee region, three strains with different levels of virulence were chosen for further study. The degree of virulence was based on the level of disease that developed on postharvestinoculated fruit. Inoculation of flowers with strains showing low and high virulence resulted in 30% L = lecture sessions; P = poster (market place) sessions. Phytoparasitica 29:3, 2001 243 and 56% disease incidence, respectively, in harvested fruit. In an attempt to clarify the mode of fungal infection of the fruit, the ability of the three strains to produce two hydrolytic enzymes, endo1,4-/3-glucanase (EG) and polygalacturonase (PG), when grown on apple cell walls, was examined. Thus it was tound that EG production of the virulent strain was twice and six times higher than that of the strains with intermediate and low levels of virulence, respectively. The level of PG production was 2.3 times higher in the highly virulent than in the least virulent strain. Activity gels following electrophoresis of protein extracts from the three strains indicated quantitative, but no qualitative, differences between the strains. A purified EG preparation caused disease symptom development on sensitive apple fruit skin, similar to symptom development following wound inoculation. Disease development in apple fruit following infection with A. ahernata may possibly be related to the ability of the fungus to produce EG and PG enzymes in the core and surrounding fruit tissue. (L) Cotton-Associated Vegetative Compatibility Groups of VerticiUium dahliae in Israel and Their Pathogenicity Nadia Korolev, 1,* J. Katan 2 and Talma Katan 1 1Dept. of Plant Pathology, ARO, The Volcani Center, Bet Dagan 50250 [*e-mail: vpptlg@agri.gov.il]; and 2Dept. of Plant Pathology and Microbiology, The Hebrew Universi~. of Jerusalem, Facul~. of Agricuhural, Food and Environmental Quali~. Sciences, Rehovot 76100, Israel A collection of 351 Verticillium dahliae isolates from cotton, recovered between 1992 and 2000 at 20 sites in Israel, was tested for vegetative compatibility using nitrate-nonutilizing (nit) mutants. Three cotton-associated vegetative compatibility groups (VCGs) were found and identified as VCG1 (34 isolates), VCG2B (218 isolates), and VCG4B (98 isolates). VCG2A was represented by one isolate only, although it was frequently recovered from non-cotton hosts. Three cotton pathotypes were defined among 40 isolates tested, using G. hirsutum cv. 'Acala SJ2' as differential. VCGI isolates induced severe leaf symptoms, stunting and defoliation, and were defined as the previously described cotton-defoliating (D) pathotype; VCG2B isolates also caused severe foliar symptoms, stunting and often death but no-to-partial defoliation, and were defined as cotton-defoliating-like (DL) pathotype; most of the VCG4B isolates induced weak-to-moderate symptoms on cotton and were similar to the previously described cotton-non-defoliating (ND) pathotype. Representatives of each VCG-associated pathotype were tested for their pathogenicity to a range of plant species. The D and DL pathotypes differ in their aggressiveness (D >DL), but the order of hosts (from highly susceptible to resistant) was the same: okra (commercial cultivar), cotton (Acala S J2), watermelon ('Crimson Sweet'), safflower (PI 251264), sunflower (2053), eggplant ('Black Beauty'), tomato ('Rehovot 13'). The ND pathotype formed another sequence differing from the DL pathotype with respect to cotton tolerance and eggplant susceptibility. Tomato was resistant to all tested cotton isolates and pathotypes. (P) Fusarium verticillioides: The Causal Agent of Corn Blight in Israel? A. Sharon, 1'* L. Oren, 1 S. Ezrati 1 and D. Cohen 2 1 Dept. of Plant Sciences, Tel-Aviv Universi~., Tel Aviv 69978 [*e-mail: amirsh @ tauex, tau. ac. il]; and 2Northern R&D, Qiryat Shemona 10200, Israel Corn rots are the most severe diseases of sweet corn in Israel. The incidence of stalk rot and the associated plant blight has increased in recent years, rendering some areas in northern Israel unsuitable for corn. Fusarium verticillioides is known as the causal agent of corn rots, but although previous findings demonstrated that the fungus can be lound in the soil, seeds and plants, it is unclear if this pathogen is indeed the primary cause of plant blight. In the current study we characterized the disease using E verticiUioides-transgenic strains that express the reporter genes green fluorescent

Crops grown in walk-in tunnels covered with UV-absorbing plastic sheets were highly protected from infestation with sweetpotato whitefly, Bemisia tabaci (Gennadius); western flower thrips, Frankliniella occidentalis (Pergande); and cotton aphid, Aphis gossypii Glover. Protection against B. tabaci was associated with a dramatic reduction in the spread of the whitefly-borne geminivirus tomato yellow leaf curl (TYLCV) and with a pronounced delay in plant infection and disease severity. Two months after transplantation, the average TYLCV disease incidence under 3 different UV-absorbing plastic sheets was 50, 30, and 20% compared with 93% under UV-nonabsorbing polyethylene sheets. In additional experiments, it was shown that the UV-absorbing sheets were also highly effective in the protection of cucumbers against F. occidentalis and A. gossypii . Filtration of full spectrum and monochromatic UV light by UV-absorbing plastic sheets reduced significantly the attraction of B. tabaci to these light sources. The association of the described phenomena with the UV vision of insects is discussed.

S OF PAPERS PRESENTED AT THE 8TH CONGRESS OF THE P H Y T O P A T H O L O G I C A L SOCIETY O F I S R A E L