Abstract

Bedding plants are considered to be a very important element of the landscape for their variety of colours. Petunia is one of,the most important bedding plants in urban landscape. According to recent droughts, determining the amount of irrigation and the selection of resistant varieties are necessary. In this study, the effect of drought stress was tested on some characteristics of three petunias. The two cultivars and one of the species of Petunia were Petunia hybrida “Explorer”, Petunia hybrida “Carnival” and Petunia violacea, respectively. Irrigation treatments based on ET-HS model water requirement included S, (100% irrigation), S2 (75% irrigation) and S3 (50% irrigation), The results showed that drought stress affected the morphological and physiological properties of Petunia plants. With increase in stress, the number of primary branches, flower diameter and canopy were reduced. Fifty per cent level significantly reduced the apparent factors in comparison to 75 and 100%. In severe stress, canopy of the Explorer was more affected in comparison with the two others, and showed the greatest sensitivity to drought stress. The flower's diamfeter of Violacea in S3 had the largest decrease compared to the other two varieties. The results showed that the root length increased with increase in stress levels for the availability of moisture. The highest root increase was observed in the level of S3. The drought stress affected total chlorophyll and proline content. Water stress reduced plant chlorophyll. The total chlorophyll in the three irrigation levels was significant for the Explorer and Violacea. The amount of amino acid proline increased with low irrigation levels. Only in Carnival, 50% had significant difference with two other treatments. So, the treatment of 75% ET-HS was recommended for saving in the use of water to keep up growth factors.