ANNOUNCEMENTS
7.1 Micropropagation of Malus:
In the present study, efficient micropropagation protocol for all four rootstocks namely, M 7, MM 111, Merton 793 and MM 106 was established for production of clonally uniform plants employing enhanced axillary proliferation. The results have been summarized in Table 7.1 comparing the four selected rootstocks. The cultures were initiated from nodal explants, although browning remained a major obstacle. The successful serial surface sterilization protocol involved the use of 70% ethanol for 30s and 0.1% mercuric chloride for 2-8 minutes. The explants were then inoculated individually on MS medium supplemented with BA (4.4 or 8.8 /M) IBA (0.245 /M), GA3 (1.445 /M) antioxidants ascorbic acid or citric acid (200 mgl-1), 3% sucrose and 0.8% agar in glass test tubes. Shoot multiplication and rooting was optimized. Hardening of all the rooted plantlets of Malus rootstocks was successfully done and healthy plant growth was obtained. To this date more than 20, 000 plants of each rootstock variety have been produced.
7.2 Mycorrhizae studies on the micropropagated rootstocks:
Arbuscular mycorrhiza (AM) was inoculated during hardening to further enhancement of the growth of the micropropagated plantlets of all the apple rootstocks. However, none of the rootstocks showed any positive response when inoculated with Glomus intraradices alone. Therefore, further studies were carried out with M7. Significant growth enhancement was observed with combination of soil: FYM (4:1) and NPK (0.2%) and AMF. Through this treatment 100 % plants obtained grafting thickness in less than a year’s time in contrast to control where only 8% plants obtained graftable thickness.
7.3 Clonal fidelity analysis of the five micropropagated Malus rootstocks:
The sustainability of the micropropagation process depends, however, upon the production of true-to-type plants and maintenance of the genetic integrity of the micropropagules. Extensive reports on the occurrence of tissue culture induced variation, warrants the need to verify the clonal fidelity of regenerated plants and assess the reliability of the micropropagation protocol. Therefore, ISSR marker assay was employed for the molecular characterization and establishment of the clonal uniformity of tissue culture raised plants of M 7, MM 111 and Merton 793 subcultured upto a duration of more than two years and of MM 106 which was subcultured for more than 4 years. Although plantlets of M 7, MM 111 and Merton 793 were found identical, a polymorphic pattern (6.02% polymorphism) was obtained with MM 106.
7.4 Field transplantation of micropropagated plants of MM 106, MM 111, and M 7:
The season of transplantation was found to play a major role in the survival of plants. Maximum survival of 90% was observed during March when transplanted through direct method. I.e. transplantation of plants directly to the fields without any secondary hardening in the greenhouse/glasshouse at the respective sites.IN overall, M 7 performed better in all the locations followed by MM 106 and MM 111.
7.5 Graft compatibility studies of micropropagated rootstocks with potential scions:
All the rootstocks were found compatible with the scion varieties studied. However, 100% survival was observed with seedling rootstocks. Fanny Delicious and Red Delicious were found to have maximum growth when grafted on any of the rootstock. However, in MM 111 maximum growth was observed with Ambri. The difference in growth may also be attributed to the use of different combinations of spur varieties of scion and different rootstocks
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