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

The number of sclerotia of Sclerotinia sclerotiorum gradually declined over the years following outbreaks of lettuce drop in four naturally infested fields. The rates of population decline did not differ significantly among the four fields tested. In two fields located in a semiarid region, 5.5 and 2% of the initial amounts of sclerotia were still viable after 7 yr. Sclerotia removed from soil samples were classified by weight into four groups: 14-40, 7-14, 3-7, and 1-3 mg per sclerotium. The frequency distribution of the four sclerotial weight groups changed over the years, as small sclerotia became increasingly predominant over large ones. This trend was significant according to a generalized logit model. The number of apothecia produced per sclerotium showed a significant nonlinear increase with increasing sclerotial weight. The percentage of apothecia-producing sclerotia decreased significantly with increasing depth of burial in the soil. In addition, apothecial production was delayed with depth. Of the apothecia produced by sclerotia in lettuce fields 80 days after planting, 94% were located in the top 5 cm of the soil. The highest relative frequency of carpogenically germinated sclerotia (24.6%) was found at a depth of 2 cm.

In seven fields free of local viable sclerotia, the part played bySclerotinia sclerotiorum ascospores transported from outside these fields in the incidence of lettuce drop was determined on plants not sprayed against the fungus. Ascospores were continuously deposited on the crop during the growth period and were found in low numbers in five of the fields (average of 0.4-3.5 per plate) and in high numbers in the two other fields (average values of 22 and 62 ascospores per plate) at each exposure in the two fields, respectively. Lettuce drop was 0-0.2% in the fields with the lower inoculum and 1.5 and 2.5% in those with the higher inoculum. Thus, even though plants were not sprayed, transported inoculum caused negligible yield losses.

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

Effets compares de 3 modes d'application du metam-sodium en champ sur la viabilite des microsclerotes de verticillium dahliae, a une profondeur de 40 cm dans le sol, sur l'incidence sur la maladie, et sur le rendement en tubercules de pommes de terre

Garlic bulbs heavily infected withDitylenchus dipsaci were chemically treated to control the nematode. Treatment with ethoprop resulted in greatest reduction of nematodes early in the season; oxamyl provided good control; methomyl was ineffective. Treating the soil with aldicarb or phenamiphos was also effective. Later in the season, nematode populations increased with all treatments and crop damage was severe. In a soil heavily infested with this pathogen, nematode populations in the untreated plots were initially low but had increased rapidly 100 days after planting, resulting in total loss of plants by the end of the season. Excellent control was obtained by treating the soil with methyl bromide (MB) or solar heating with transparent polyethylene sheets prior to planting, although MB treatment caused severe stunting of the plants. Treatment with ethylene dibromide (EDB) controlled the pathogen initially, but later in the season the population level increased. The yields (kg/m2) were: untreated, 0; solar heating, 2.325; EDB, 0.813; and MB, 1.152.