الفهرس 
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Abstract
This study included two groups (laboratory and field studies).
The obtained results of laboratory study are summarized as follows:
A virus- free (free from PVA, PVM, PVS, PVX, AND PLRV) Plantlets of potato CV.”Alpha”, ”diamante” and ”spunta”were obtained by tissue culture technique and further used throughout this study.
A significant improve in the micro-propagation of the tested potato cutivars ”Alpha”, ”diamante” and ”spunta” was obtained when corn starch was used instead of the gelling agent agar in the tissue culture media. Potato cv. ”spunta” gave the best growth characters in vitro, i.e. length of plantlet (9.56cm),number of nodes (8.23 nodes/ plantlet)shoot as well as root fresh (90.37 and 173mg, respectively) and dry weights (9.01 and 11.72mg of shoot and root, respectively).
Amendment corn starch medium with ascorbic acid (AA) caused significant increase in the growth characters while these characters were significantly decreased in the medium supplemented with salicylic acid (SA). Also microtuberization was affected in the same manner.
Microtubers were variously responded to streptomyces scabies the causal agent of potato common scab infection depending on potato cultivars. The microtubers of potato cv. ”spunta” showed highest susceptibility followed by ”diamante”.