Two field experiments were conducted in 2002 and 2003 to study the effect of two triazole compounds; namely paclobutrazol and uniconazole on growth, yield, storage ability of potato (Solanum tubersom L., cvs Nicola and Spunta) seed tubers and controlling of potato tuber moth (Phterimaea operculella). In addition, the anatomical study has been used to confirm the morphological data. Potato plants were sprayed twice, 60 and 70 days after planting with 500,1000 and 2000 ppm from each of paclobutrazol and uniconazole. Plant height, fresh weight of haulm and number of branches/plant were depressed proportionately to the concentration applied. Using the previous compounds significantly increased chlorophyll content in leaves, especially in Spunta cv at 2000 ppm of uniconazole. A significant increase in number and fresh weight of tubers/plant (three weeks after the second application), dry matter in tubers at harvest and total yield/feddan occurred following the application of either uniconazole or paclobutrazol at 1000 and 2000 ppm. Spraying potato plants with 2000 ppm of paclobutrazol significantly improved storage ability of harvested tubers especially with Nicola cv
Generally, paclobutrazol was more superior than uniconazole in decreasing percentage of decayed tubers due to infestation with potato tuber moth as well as percentage of sprouted tubers after four months from harvesting under the room conditions.
The anatomical study indicated that spraying potato plants with 2000 ppm of paclobutrazol or uniconazole caused considerable thickness of airial stem diameter due to the increase in thickness of the epidermis, cortex, vascular cylinder and number of cortical layers. Also, this treatment stimulated the thickness of lamina and midrib comparing with the control, which was attributed to the increase in the thickness of mesophyll and the size of middle bundle. In addition, the previous treatment increased thickness of the tuber cork, which led to an increase in the tolerance of the tubers against potato tuber moth infestation.