Elimination of viruses through thermotherapy and meristem culture in apple cultivar ‘Oregon Spur-II’

In the present study, an attempt was made to eliminate apple chlorotic leaf spot virus, apple mosaic virus, apple stem grooving virus and apple stem pitting virus from apple cultivar ‘Oregon Spur-II’. Thermotherapy was carried out at 37–40 °C for 4 weeks followed by culturing of meristems of different sizes. During establishment of explants, highest survival percentage (62.35%) and proliferation (30.68%) was recorded during summer season. However, size of meristems and position of buds from where meristems were excised also influenced their survival. The meristems of size 0.6–0.7 mm were found to be the most appropriate for maximum establishment. Meristems excised from buds positioned on distil portions of actively growing shoots showed better results. MS medium supplemented with BA (1.0 mg/l), IBA (0.05 mg/l) and GA3 (0.1 mg/l) resulted in 56.62% establishment of explants, while maximum number of meristems proliferated with low BA (0.5 mg/l), IBA (0.08 mg/l) and same GA3 concentration. Two to fourfold multiplication was observed. Virus indexing of shoots raised from different sizes of meristems was carried out and found that 0.3–0.6 mm size was able to eliminate ACLSV, ApMV, ASGV and ASPV. However, some of 0.5–0.6 mm sized shoots were found infected with ACLSV. Larger meristems could not completely eliminate the viruses under study.