Evaluation of Genetic Stability of some Agronomic Traits in Potato Hybrids and Cultivars under Different Climate Conditions

Potato (Solanum tuberosum L.) is an important food and cash crop ranking fourth after maize, wheat and rice annual production in the world. It is a high biological value crop that gives an exceptionally high yield with more nutritious content per unit area per unit time than any other major crops. Thus, it can play a remarkable role in human diet as a supplement to other food crops such as wheat and rice. The main objective of the breeding program is to increase yield production. One of the major factors contributing to potato yield reduction is limited number of cultivars with wide range of adaptability and stability in tuber yield. Thus, evaluating genotypes across various environments for their stability of performance and range of adaptation is crucial and is an important component of the research activity of the national as well as regional research program. 20 potato hybrids along with five commercial cultivars (Savalan, Agria, Caesar, Luta and Satina) were evaluated in randomized complete block design with three replications at Agricultural and Natural Resources Research Station of Ardebil, Khorasan razavi, Karaj, Isfahan and Hamedan in 2016.  In this investigation each of the hybrids and control cultivars were planted in 2 rows of six meters. Row spacing of 75 cm and plant spacing of 25 cm was considered. There were 25 tubers in each row. Pest control was performed using 250 ml of Ha-1 Confidor. During growing period and after harvest the traits such as: plant height, day of tuberization, main stem number per plant, tuber number and weight per plant, total tuber yield and percentage of tuber dry matter were measured. Combined analysis of variances was done and comparison of means was done by LSD at five percent probability level. The linear correlation between traits was also calculated. In order to understand the inter-relationships of attributes and determine the variables with the highest correlation, factor analysis with Varimax rotation of factors was used. Grouping of the hybrids was performed based on the first three factors. In order to study the genetic diversity and heritability of traits, some genetic parameters of the traits in potato cultivars and hybrids were calculated. All analyses were carried out using the SAS9 and SPSS16 softwares. Combined analysis of variance for traits showed significant differences among potato hybrids for all traits. The hybrids and environment interaction was significant for plant height, day of tuberization, tuber number and weight per plant, total tuber yield and tuber dry matter percent. Hybrids with number of 5, 9, 17 and 19 had the highest total tuber yield and the hybrid 20 and Satina cultivar had the lowest total tuber yield. The hybrids number 1, 3 and 20 had the highest amount of dry matter percentage compared to other hybrids suggesting that these hybrids are suitable for chips production. In factor analysis, three independent factors totally explained 75.744 percent of the variations. According to the results of factor analysis the following factors were nomenclature: the first factor as yield, the second factor as tuberization and third factor as plant. The weight per plant and tuber number per plant had the highest heritability, genetic gain, genotypic and phenotypic coefficient of variation. These traits can be improved through selection in breeding programs. In general, the results of the mean comparison and grouping of hybrids based on the first three factors showed that hybrids 5, 17 and 19 were better than the other hybrids. Hybrids 1, 3 and 20 with the highest percentage of dry matter are recommended for processing as chips. The weight per plant and the number of tubers per plant had the highest genetic gain and heritability rates, and these two traits could be improved through selection in breeding programs.