Hybrid micropropagation of selected tomato (Solanum lycopersicum L.) Varieties using shoot tip culture

Abstract

Tomato (Solanum lycopersicum L.) is one of the most important vegetable crops in the world. Its production is low because of many production constraints like biotic and abiotic stresses. The use of hybrid varieties is a great option to increase its production. The hybrid seeds of tomato are being produced by hand emasculation and hand pollination to get F1 seeds, which is the major method used in tomato breeding. However this method is slow, time consuming, labor intensive and need more space. Using F2 seed also leads to lack of uniformity as a result of segregation. Therefore mass propagation using tissue culture could help to solve these problems. The objective of this study was to optimize an optimum micropropagation protocol for Valouro, Uwezo and Shelter hybrid tomato varieties using shoot tip culture. Three successive experiments: shoot initiation; shoot multiplication and root inductions were conducted at Jimma Agricultural Research Center plant tissue culture laboratory. Different concentrations of BAP (0.0, 0.25, 0.5, 0.75, 1.0 and 1.25 mg/l) and (0.0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3 mg/l) were used for shoot initiation and shoot multiplication, respectively. While different concentrations of IBA (0.0, 0.25, 0.5, 0.75, 1.0, 1.25 and 1.5 mg/l) were used for root induction. The three separate experiments were laid out as factorial arranged in completely randomized design. The result of shoot initiation showed that the interaction of BAP*Varieties highly significantly (P<0.01) influenced days to shoot initiation. The early days for shoot initiation took 5, 6.4 and 5.2 days for Valouro, Uwezo, and Shelter varieties, respectively on hormone free MS medium. Highest percentage of shoot initiation (92%) was also recorded from hormone free MS medium for all the three varieties. The lowest percentage of shoot initiation was recorded from higher concentration of BAP (1.25 mg/l). Hormone free MS medium was optimum for days of shoot initiation and percentage of shoot initiation. In multiplication experiment, all parameters: number of shoots per explant, average shoot length and number of leaves per shoot, showed highly significant difference (P<0.01). The maximum numbers of shoots (5, 4.3 and 4) were recorded from MS medium augmented with 2mg/l BAP for Valouro and Uwezo varieties and 1.5mg/l for Shelter variety. While the lowest shoot numbers was obtained from hormone free MS medium. The highest shoot length (5.8, 5.3 and 5 cm) was obtained from 0.5 mg/l BAP, whereas the lowest shoot length (2.69, 2.81 and 3.04 cm) was recorded from 3 mg/l BAP. The maximum number of leaves/shoot was recorded on MS medium supplemented with 1.5 mg/l BAP for Valouro (4 leaves), Uwezo (3.6 leaves) and Shelter (3.4 leaves) varieties. In rooting experiment the interaction effect of IBA*Variety showed highly significant difference for days to rooting, number of roots and root length (P<0.01). Rooting percentage also showed a significant (P<0.05) difference. Early root induction (5 days for Valouro and Shelter and 7.67 days for Uwezo) was recorded on hormone free media. Maximum number of roots (15.36, 13.06 and 18.26), highest root length (5.92cm, 5.5cm and 6.55cm) were observed at 0.5 mg/l IBA for Valouro, Uwezo and Shelter varieties. Maximum percentage of rooting (100%) was recorded from IBA concentration ranging from 0.0-0.5 mg/l but the minimum was observed from higher level of IBA. Well rooted shoots were transferred to green-house and the survival percentage were 81.13%, 73.58% and 69.8% for Valouro, Uwezo and Shelter varieties, respectively. In conclusion, hormone free MS medium is found to be optimum for shoot initiation in all the three varieties. For shoot multiplication 2.0 mg/l BAP was optimum for Valouro and Uwezo varieties and 1.5 mg/l BAP for Shelter variety. In rooting experiment, half strength MS medium augmented with 0.5 mg/l IBA was optimum for number of roots and root length while for days to rooting and percentage of rooting half strength MS medium without IBA was optimum in all the three varieties. Since this study focused only on the effect of BAP hormone alone for shoot multiplication, further research is suggested to be done on multiplication performance by using other combination of hormones and by taking other explant sources.