تغییرات شاخص‌های رشدی توده بومی زیره‌سبز (Cuminum cyminum L.) و رقم هندی در پاسخ به شوری و تعداد آب آبیاری

Introduction
Water shortage in Iran has always been a limiting factor for crop cultivation. Drought stress at different growth stages, especially flowering and grain filling stages decreases the yield of the plants. Drought stress may limit yield of medicinal and aromatic plants by reducing the harvest index (HI). This can occur even in the absence of a strong reduction in total medicinal and aromatic plants dry matter accumulation, if a brief period of stress coincides with the critical developmental stage around flowering stage. Water stress is the most influential factor affecting crop yield particularly in irrigated agriculture in arid and semi-arid regions. It is necessary to get maximum yield in agriculture by using the least available water in order to get maximum profit per unit area because existing agricultural land and irrigation water are rapidly diminishing due to rapid industrialization and urban development. In general, 15% of the Iran lands are saline and sodic (Parsa, 2000) and it dues to the use of widespread of water resources and the soil salinity of the farms. Unfortunately this factor (soil salinity) gradually becomes more serious, in fact even in none-saline water irrigation with salt accumulation in the soil in long period of time it may increase and the result will be the limitation of the products (Sharma, 1996). The analyzing of the growth and product is a method for discovering the factors which are effecting on the plants. The purpose of the analyzing of the plants growth is the reaction of the plants to the environmental factors (Sangwan et al., 1994). Cumin (Cuminum cyminum) is one of the most important economic and medicinal plants that can growth in arid and semi-arid conditions. Cumin is mostly grown in China, Uzbekistan, Tajikistan, Iran, Turkey, Morocco, Egypt, Syria, Mexico, Chile and India. In the ancient Egyptian civilization cumin was used as spice and as preservative in mummification. The purpose of this study was the effect of drought and salinity in different phenological stages on some of the growth characteristics of cumin cultivars.
Material and method
The experiment was split plot in a randomized complete block design with three replications, in Ferdowsi University of Mashhad, Iran during growing season of 2008-2009. Factors were including irrigation times (I1: one times irrigation, I2: two times irrigation I3: three times irrigation and I4: four times irrigation (control) and with two levels of salinity stress (irrigation with normal water and saline water five dS.m-1) and two cumin cultivars (Sarayan, Indian cultivar RZ 19). To determine the physiological properties of cumin every 14 days five plants from the bottom half of each plot was randomly picked and transferred to the laboratory and some specifications such as green area, plant dry weight and the number of side branches was measured. For Data analysis software Mstat-C was used. The growth parameters were calculated and graphs were drawn by Excel software.
Results and discussion
Dry weight variations were significant by increasing irrigation. The highest amount of dry weight for treatment with three times irrigation (260 g.m-2) and the lowest amount for one time irrigation (193.5 g.m-2) were recorded. Salinity too causes decline dry weight in such treatments that dry weight with the use of normal water was 252 g.m-2 and with saline water was 199.6 gr/m-2. In the various experiments conducted on cumin, it was found that the process of creating green area in this plant is slow, especially in the early period. According to various sources, maximum green area index for cumin not exceed the greater of 1.5 and for a large part of growing season is less than one. One time irrigation treatment showed the lowest green area index. The highest CGR was in three times irrigation with 7.92 g.m-2.day-1 and the lowest CGR was in one time irrigation with 4.87 gr.m-2.day. Leaf area index duration increased with more irrigation. Green area index duration was 15.63 m2 leaf. m-2 land in three times irrigation and By reducing irrigation frequency has been significantly reduced.
Conclusion
In this experiment, all of the growth indices were affected by drought and salinity. The lowest specifications were in one and four irrigation times with saline water. Also between Sarayan and Indian cultivar, Sarayan was better than Indian cultivar under salinity condition.