Meta-Analysis of Root Yield and Sugar Yield of Sugar Beet Genotypes in Karaj Region

Food security is affected by many factors, including increased demand, high input prices, soil degradation, the need to limit greenhouse gas emissions, and increased competition for land and non-potable water. In addition, climate change is expected to have an increasing impact on performance, with statistical analysis of product performance indicating that such an event is taking place. The purpose of plant breeding programs is to develop new varieties with improved characteristics such as yield and nutritional quality. Sugar beet is a root crop specific to temperate regions mainly produced as a sucrose source for human diets. Sugar beet can be planted on any continent except Antarctica, but it performs best in temperate climates. Worldwide production of sugar beet is relatively stable. Studies on the effect of environment and year on sugar beet yield has a long history in Iran. However, it is difficult to achieve a general conclusion due to the dispersion and disparity in the results of various studies. In this study, a meta-analysis method was used to integrate and re-analyze results of independent experiments to achieve a single result.

Twenty-one experiments carried out at Motahhari Research Station in Karaj, Iran during 2002-17 were evaluated. The effect size was calculated and studies were weighted by replication. Then, the mean effect sizes were estimated followed by confidence intervals, effect size back-transforming and graphs were designed.

Among studied years, the highest mean root yield of 89.5, 89.1 and 87.8 t ha-1 were obtained in 2018, 2006 and 2012, respectively. Results integration showed that in 2006, 2011, 2014, and 2017, root yield of sugar beet increased by 19.2%, 2.2%, 2.8% and 18.6%, respectively. Different parameters can be used to describe improved agricultural productivity; one of which is the yield increase over time attributed to advances in plant breeding as well as changes in crop operations and environmental conditions (especially climate). Another parameter is the yield potential of a crop described as the performance of a cultivar grown in compatible environments without nutrient and water restrictions and under the effective control of pests, diseases, weeds, and other stresses. Meta-analysis results showed that increase in sugar yield of sugar beet genotypes was similar to the root yield, with the difference that in the years 2006, 2011, 2014 and 2017, variations in percentage was less than root yield. One of the most important results in this study was the illustration of the reduction in slope of negative relationship between root yield and sugar yield in commercial cultivars.

In this study, trials were performed under normal conditions and in a disease-free environment. According to the obtained results, use of meta-analysis method in breeding programs to estimate the effect of year on performance along with other statistical methods is recommended.