Induction of Somaclonal Variation in Strawberry and Evaluation of Variants to Different Biotic and Abiotic Stresses

Abstract

The cultivated strawberry (Fragaria × ananassa Duch.), a member of the Rosaceae is the most important soft fruit worldwide. Commercial cultivation of strawberry in Bangladesh has been initiated since 2008. However, its productivity seriously hampered due to different diseases, due to crown rot and verticillium wilt, which is proven difficult to control through fungicides. On the other hand, hot and dry weather and soil pH are the major abiotic factors affect strawberry cultivation in Bangladesh. In this context, induction of somaclonal variation can be used to create new genetic variability for improvement of the strawberry. The present study was conducted to standardize a suitable protocol of in vitro plant regeneration potentiality of seven strawberry varieties viz. AOG, JP-2, JP-3, Camarosa, Sweet Charly, Giant Mountain and Festival. Young leaves, mature leaves and nodes of seven strawberry varieties were used as explants. To collect leaf segments and node, surface sterilization and initial culture establishment of runner tips and nodal segments of field grown strawberry plants were adopted. The nodes and leaf segments were collected from the in vitro runner tip derived shoots and cultured in MS medium supplemented with different concentrations of 2,4-D or NAA alone or in combination with BA and the cultures were incubated in dark for four weeks for callus induction. The highest degree of percentage of callus was observed in some formulations such as 2.0 mg/l 2,4-D, 2.0 mg/l NAA and 0.5 mg/l NAA +1.5 mg/l BA. Calli depeloped from all types of explants were subcultured onto MS medium supplemented with different concentration and combination of BA + NAA for shoot regeneration. The medium with 1.5 mg/l BA + 0.5 mg/l NAA showed the best respons to indirect shoot regeneration. From the above description it is clear that NAA, BA combination was found to be the most suitable for callus induction and regeneration. Mature leaves were favorable for callus induction and shoot regeneration more than young leaves and nodes in all case. Successful shoot formation became evident when small green fresh leaves began to emerge. These leaves when developed in their actual shape were transferred into fresh medium containing the same hormonal combination or best one among them for further proliferation and development. Sub culture was carried out regularly at an interval of 3-4 weeks. After shoot proliferation, the mini regenerated shoots were separated aseptically and cultured in MS medium and ½ MS medium containing different concentrations of NAA, IBA alone and MS and ½ MS medium without growth regulators (MS0). Cent percent cultured shoots induced to develop roots when cultured in MS0 rooting medium. Among the seven strawberry varieties AOG was found to be the most responsive genotype in terms of different parameters such as ability to primary culture establishment, percentage to callus induction, shoot regeneration and rooting response. After sufficient root formation, the in vitro regenerated plantlets were acclimatized gradually. Then successfully acclimatized plantlets were transplanted in to field. A total of 30- 50 somaclones from each of the tested varieties were established and maintained in the field and were considered as Ro plants. Four somaclones from AOG and two somaclones from other six strawberry varieties viz. JP-2, JP-3, Camarosa, Sweet Charly, Giant Mountain and Festival were selected from Ro plants. The seven strawberry varieties were also grown in the field to compare with the somaclones. Eight morpgological and eight fruit yield and yield contributing characters were analyzed to find out better strawberry varieties for Bangladesh environment condition. In the analysis of variance the main item genotype was highly significant for all characters. In the analysis of components of variation it was found that phenotypic variation was greater than genotypic variation. In the second part of this research was field evaluation of the seven strawberry varieties and their somaclones under biotic and abiotic stress condition. Verticillium wilt, phytophthora crown rot, leaf scotch, leaf spot, leaf blight and botrytis fruit rot diseases were found in the strawberry field but disease incidences (%) of verticillium wilt and phytophthora crown rot were high. There were no plants found resistance to fungal diseases but somaclones showed better performance than the donor plants. Majority of plants were found heat sensitive in donor plants but somaclone AOG SC 3 showed better performance than other somaclones and donor parents in terms of summer overcoming capacity. These somaclones can be acceptable commercially if the good characters exhibited are transmitted through generations or could be used in future breeding programmed for the improvement of strawberry varieties in Bangladesh.