Prof. Varda Kagan Zur: Research Interests
I. Study of desert truffles: Most desert truffles are the fruiting bodies of mycorrhitic fungal species belonging to the genus Terfezia. Though considered inferior to European forest truffles, they are prized for their flavour and nutritional value by desert dwellers. To this day they are collected from the wild. We are studying several truffle species of this genus, both with a view to cultivation and as a model of truffle symbiosis. Israeli truffles: Israeli Negev truffles are collected by Beduins during March and April and sold for prices ranging from 15 to 50 shekels per kg
II. Potential of development as agricultural crops. This study was supported by the Israeli Marketing Board, followed by the Israel Endowment Fund and then the Jewish Agency and Ministry of Industry & Trade between the years 1985-1990. We succeeded in isolating truffle mycelia and mycorrhizing a host root system with the truffle (Roth-Bejerano, Livne & Kagan-Zur, 1990). We now needed to be able to track the mycorrhizal fungus in the roots of out-planted seedlings. To do so, we proceeded to develop an appropriate molecular tool (see below). However, the project was discontinued when economic calculations predicted that desert truffle cultivation on perennial plants was not worthwhile for Israeli farmers.
III. Molecular studies. Development of genetic markers specific to truffles and studying the possibility of identifying these markers in mycorrhizas were the initial aims of this study. The study was supported by a Seed Money grant, and later in part by an EU grant.
RAPD markers were found to be a bit less reliable than rRNA gene markers. We identified two size variants of the ITS region of the rRNA genes and three RFLP patterns. Sequencing of the three RFLP variants showed a 4% difference between the two equal-sized fragments and the larger one (Holdengraeber et al., 2001). Such a difference is ordinarily taken to indicate a separate species, and this point is still under study. The ITS distinct profiles also enabled us to prove that lobed truffles may be formed through fusion of separately initiated fruit bodies (Holdengraeber et al., 2001), thus predicting no limit on no. of close by fruit-body initiations. A double-profiled mycelium was isolated and was found to harbour two ITS forms within a common cytoplasm (Aviram, Roth-Bejerano & Kagan-Zur, submitted). It seems as though the two forms may be carried in two different nuclei suggesting a long tem dikaryon in ascomycetes (Roth-Bejarano, Li & Kagan-Zur, submitted)
IV. Physiological studies: In conformity with their high pH and calcium preference, we found that the level of symbiosis formation by Israeli desert truffles rises when iron content in the medium is low (Kagan-Zur et al. 1994). External Ca2+ stimulated mycelial growth of this truffle in both liquid media and solidified substrates. The response to Ca2+ was very faint in well-aerated culture but pronounced in mycelia immersed in the medium, indicating a role for Ca2+ in overcoming hypoxia (Roth-Bejerano, Mendlinger & Kagan-Zur, Submitted).
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Kalahari Terfezia: These low pH, low calcium favoring truffles appear in May-June. They are collected by Bushmen and sold locally or exported to Europe. The research was supported by an AID-CDR grant, followed by an EU grant.
I. Identifying a host plant. No host of Kalahari Terfezias was known. As traditional methods of defining a host were unsuccessful (Taylor et al., 1995), we tried a molecular approach. A molecular method we developed for tracing truffle mycorrhizas on host roots enabled us to identify a local Kalahari variety of watermelon as a bona fide symbiont (Kagan-Zur et al. 1999).
II. Potential cultivation: Watermelon is a tempting candidate as a host for co-cultivation of truffles. We were lately (2002) granted an AID-CDR grant to pursue the subject.
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Moroccan terfezias. Although mycorrhitic fungi – truffles included – are not very exclusive in their choice of plant partner, they exhibit some preferences. T. boudieri enters into symbiosis with both perennial and annual Helianthemum species. Annual couples may prove to be more amenable to modern agricultural practices than perennial couples, and studies aimed at assessing this possibility were supported by an AID-MERC grant. Unfortunately collaboration with Morocco proved to be problematic. We are about to start research on our own, as annual truffles have been lately defined among Israeli truffles.
V. Introduction of Tuber melanosporum, the black Périgord truffle into Israel. European forest truffles are a culinary delicacy used as a spice. They command very high prices in specialty markets. The initial research was supported by the Moriah Fund, then taken over by the Jewish agency, followed by the Stern Fund; the research is now supported by the Market Oriented Program, Chief Scientist of the Ministry of Agriculture.
a. Support of oak-truffle plantations, initiated by Pinkas & Shabi from the Volcani Institute. The plantation maintained the T. melanosporum mycorrhiza fairly well (Kagan-Zur et al., Plant & Soil, 2001). First truffle was collected January 2000 (Kagan-Zur et al. Mycol. Veget. Mediter, 2000)
b. Cistus-truffle research: We are seeking to develop a more intensive system of agricultural cultivation based on an indigenous host plant. T. melanosporum mycorrhizes the local wild shrub Cistus incanus. We successfully effected symbiosis between the black Périgord truffle and cistus. Mycorrhization was obtained using either spores, or detached mycorrhized roots, or donor plants. We have developed potentially useful growth media combinations, (Ventura et al. Submitted) have proved that soil cooling in summer can help maintain a strong presence of Tuber mycorrhizas (Roth-Bejerno, Sela & Kagan-Zur, Mycol. Veget. Mediter. In Press) and have elaborated methods for efficient proliferation of chosen plants (Mills et al. Agr Med 2002), as well as molecular methods for identifying T. melanosporum as the symbiotic partner in roots. We have developed a method for assessing proliferation of Tuber mycelium in growth media and a procedure for rapid production of reliable inoculating material through maintenance of T. melanosporum mycelia in symbiosis with detached Agrobacterium rhizogenes-transformed cistus roots (Wenkart et al., Plant Cell Rep. 2001). This dual culture system is currently used for basic studies on the initial stages of Tuber melanosporum mycorrhiza.
