ISHS Acta Horticulturae 386: XVI International Symposium on Fruit Tree Virus diseases
IN VITRO THERMOTHERAPY OF ROSACEOUS FRUIT TREES |
| Authors: | S. Spiegel, A. Stein, Y. Tam |
| Abstract:
Several cultivated woody species (e.g., Prunus, Vaccinium, and Vitis) are very sensitive to prolonged exposures to elevated temperatures. As a result, survival rates of heat-treated plant material is low. Therapy procedures applied to in vitro grown plant material allows controlled modification of various components of the nutrient media and other environmental factors which affect survival and regeneration of virus-free shoot tips. High temperature regimes were successfuly applied to eliminate prunus necrotic ringspot virus (PNRSV) from in vitro grown shoot cultures of sweet cherry (Snir and Stein, 1985), peach (Stein et al., 1991) and recently almond (unpublished). Alternating heat treatment regimes (38°C 16 hrs; 28°C 8 hrs dark for 18–20 days) applied to PNRSV-infected Hermosa and Summerset peach shoots grown on a nutrient medium following Almehdi and Parfitt (1986)(AP) supplemented with 6-benzylamino purine (BA) allowed regeneration of virus-free plants from relatively large (about 10 mm) shoot-tips. The concentration of BA in the medium was a major factor in survival of treated shoot cultures. At 0.2 mg/l, BA supported elongation of existing shoots whereas at higher concentration (up to 6 mg/l) shoots mostly proliferated. Survival of the shoots through the heat treatment exceeded 90% in a AP medium containing 0.2 mg/l BA and dropped markedly with the increase in BA concentration (Stein et al., 1991). In a study summarized and presented in Table 1, measurements were made of the elongation of shoot tips during the heat treatment in comparison to controls grown at 25°C. A 2.5–3 fold increase in the length of shoot tips was measured in both cultivars during the heat treatment as compared to controls. It has not yet been determined whether the enhanced growth of tips resulted from accelerated cell division or cell elongation. PNRSV level, as determined by ELISA, was very low in the tip segment grown during the heat treatment and allowed easy regeneration of virus free shoots of both cultivars. A difference in sensitivity to heat which affected survival rates of the two cultivars was noted, 48% of Summerset shoots and 88% of Hermosa shoots survived the heat treatment. The hormone composition of nutrient media plays an important role in the efficiency of thermotherapy of rosaceous cultivars. A proliferation medium was used for thermotherapy of sweet cherry (Snir and Stein, 1985; Deogratias et al., 1989), apple (Gabova, 1988) and raspberry (Janeckova, 1988), an elongation medium for peach (Stein et al., 1991 and data presented in this paper) and a medium with zero hormones for pear (Postman and Hadidi, this volume). Selecting the best medium with optimum hormone concentrations for a given plant material requires an empirical approach if no information is available regarding hormone and other media requirements for successful thermotherapy. | |
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