Evaluation of Cultivar Effects on Yield and Water Consumption Efficiency in Potato by Meta-Analysis Method

Abstract
Conducting various studies on potato cultivation in relation to the effects of cultivar on yield and water use efficiency has a long history and in this regard has been associated with dispersion and many differences in thier results. With the aim of investigating the effects of the cultivar on the yield and water consumption efficiency of potatoes, the research conducted in different regions of the country, in the 20-years period from the beginning of 2000 to 2019 AD or from the beginning of 1379 to the end of 1398 SH, was extracted and analyzed through the meta-analysis model. Studies on cultivar type were divided into early to mid-early and mid-late to late groups and in the early group Sante cultivar and in the late group Agria cultivar were considered as controls. The results of meta-analysis of cultivars in the studies showed that in the group of mid-late to late cultivars there was no statistically significant difference between the cultivars used and the control Agria cultivar in yield (P≥0.05). The mean yield of other mid-late to late cultivars and control Agria cultivar were very close with a slight difference (0.61 t / ha). In the early to mid-early group, although the difference between other early and control cultivars of Sante was not statistically significant in general studies, but Sante cultivar had a higher average yield (2.93 tons per hectare) compared to other cultivars in its group. In general, in all the studies, although mid-late to late cultivars had a yield increase of 2.3 tons per hectare compared to early to semi-early cultivars, but due to the long growing period and the number of times of irrigation (at least 2 up to 3 times), they have less ability in water consumption efficiency.
 Introduction
Achieving food security and preventing price fluctuations requires the introduction of suitable potato cultivars for reliable production in all seasons and for different uses (Hassan-panah and Hassan-Abadi, 2018). So far, a lot of research has been done on the effect of cultivar on the yield and water efficiency of potato crops in order to achieve maximum production with minimum water consumption in a scattered manner and with different goals. However, there are always differences of opinion regarding the amount of water consumed during the growth period of different potato cultivars, which hinders the determination to promote specific cultivat or cultivars for better adaptation in the region and to achieve the improvement of water consumption efficiency in the region. Therefore, performing a meta-analysis (meta-analysis) by combining the results of comparison tests of cultivars (with identical control cultivars) in different regions of the country provides access to a single guideline that can draw a more specific and regular model.
 Materials and Methods
In this research, firstly, researches were conducted in different regions of Iran, in a period of 20 years from the beginning of 2000 to 2019 from WOS foreign data bank and internal data bank and official websites of Iran DOC. , Fipak, Magiran.Com and SID were searched. In the following, screening was done among the searched researches. Then, the final sources were extracted which had a lot to do with the issue of cultivar and its effects on yield and water efficiency. In the investigation of the cultivar type in the conducted studies, it was found that the set of studies could be separated into two evaluation groups of early and late cultivars in potato. For this purpose, the full text of the extracted sources was fully examined and the required statistical data from each of the studies including mean, standard deviation and sample size were extracted from the control cultivar and other experimental cultivars in each independent studies. Finally, the resulting data were combined and subjected to meta-analysis using Stata/SE version 11.1, StataCrop., Lp, Station, TX software. To evaluate the homogeneity of the study results, the I² index and the Q test (Hedges et al, 1999; Higgins and Thompson, 2002) were used.
Results and Discussion
The results of the meta-analysis of cultivars in the studies showed that in the group of late cultivars, there was no statistically significant difference in yield between Agria control cultivar and other used cultivars. The yield average of other late cultivars and the control cultivar of Agria were very close with a slight difference (0.61 tons per hectare). In the early group, although the difference between the other early cultivars and the Sante control was not significant in the total of studies, the Sante cultivar had a higher average yield (2.93 tons per hectare) compared to other cultivars in its group. totally, in all studies, although the late cultivars had a yield increase of 2.3 tons per hectare compared to the early cultivars, they were less capable in terms of water consumption efficiency as compared with early ripening cultivars. Usually, in late cultivars, the length of the irrigation period and the amount of water consumption is two to three times higher than that of early cultivars. This amount is usually 10 to 15% of the water requirement of potatoes. If we consider the efficiency of water consumption in the sprinkle irrigation system of 250 liters and in the drip system of 150 liters per kilogram of potato production (Gadami Firouzabadi and Parvizi, 2017), in this case, in late cultivars, on average, 594 cubic meters per hectare more water is consumed compared to early ripening cultivar.
Conclusion
Based on the results of this meta-analysis and in order to achieve the optimal yield and water efficiency in terms of the type of potato cultivar, it is necessary to cultivate cultivars with a shorter growing period and with High functional capacity and resistant to stress and water deficiency such as Sante should be prioritized. In addition, the superiority of Sante variety among the studied early ripening cultivars was higher than the average in all studies, therefore, it can be considered in breeding programs to produce new cultivars.