In vitro Evaluation of Somaclonal Variation of Two Potato Cultivars Santana and Spunta for Resistance against Bacterial Blackleg Pectobacterium atrosepticum

Recently, tissue culture based in vitro selection have been studied as cost-effective feasible tool for developing stress-tolerant plants. Somaclonal variation created in an experiment conducted with two potatoes (Solanum tuberosum L.) cultivars Santana and Spunta to create somaclonal variation by repetitious subcultures on MS medium for the purpose of evaluating this somaclonal variation for biotic stress resistance, the two cultivars were inoculated in vitro with four concentrates 1 × 102, 1 × 104, 1 × 106 and 1 × 108 cfu/ml Pectobacterium atrosepticum. Both cultivars showed significant reduction of disease severity index (DSI) at highest inoculum level 1 × 108 cfu/ml between pre and post subculture. Santana cv. DSI was 51.17% and 61.5% improved significantly to 25.17% and 44.17% for calcium treated and non-treated respectively, while in Spunta cv. DSI was 54.00% and 62.33% improved significantly to 32.67% and 46.17% for calcium treated and non-treated respectively. The highest DSI recorded in pre-subculture non-treated with Ca were 33.23% and 35.16% for Santana and Spunta cvs. respectively while the lowest DSI recorded in post subculture treated with Ca were 11.97% and 15.20% for Santana and Spunta cvs. respectively. In vivo inoculation of in vitro survived plantlets with the same inoculum levels showed better performance of Santana cv. over Spunta cv. at 1 × 104 ,1 × 106 cfu/ml with (20.33%, 33.33% ) and (34.00%, 42.67% ) respectively. Calcium nitrate improved plants tolerance by reducing DSI significantly from 66.33% to 35.00% at 1 × 108 cfu/ml for non-treated and treated respectively.