Growing vegetables
M. Jabbari; R. Darvishzadeh
Abstract
Introduction
Pepper is a rich source of essential vitamins and minerals. Like tomatoes, pepper plays an important role in preventing heart diseases due to its high amount of antioxidants. Fruit yield is a complex trait that is not only controlled by several genes, but also greatly influenced by the ...
Read More
Introduction
Pepper is a rich source of essential vitamins and minerals. Like tomatoes, pepper plays an important role in preventing heart diseases due to its high amount of antioxidants. Fruit yield is a complex trait that is not only controlled by several genes, but also greatly influenced by the environment. On the other hand, fruit yield is affected by a large number of other traits and their interaction. Therefore, it is very important for plant breeders to know the relationships between these traits and their interaction effects. The path coefficient analysis is a method that clarifies the relationships between traits and their direct and indirect effects on fruit yield. In this method, the correlation coefficient between two attributes is divided into components that measure direct and indirect effects. Considering the limited studies regarding the evaluation of relationships between fruit yield and other traits affecting fruit yield in pepper, this research was conducted with the aim of identifying these important relationships and evaluating their direct and indirect effects in Iranian pepper populations.
Materials and Methods
In order to carry out this research, the seeds of 30 Iranian pepper accessions were collected directly from the farmers. The experiment was conducted in the form of pot cultivation in the research greenhouse of the Faculty of Agriculture of Urmia University in a completely randomized design with five replications during 2015-2016. After the flowering stage, the desired traits were estimated. Variance analysis was estimated, after examining the basic hypotheses of variance analysis by SAS9.4, as well as the genotypic and phenotypic correlation between traits based on the restricted maximum likelihood (REML) procedure in the SAS9.4 software. Step-by-step regression analysis was used to determine the traits with the most variation justified the fruit yield. The Durbin-Watson test was performed to investigate the independence of experimental errors. Analysis of path coefficients was performed based on the results of stepwise regression and genotypic correlation of traits in the R V.4.0.5.
Results and Discussion
In order to understand the relationships between traits and use them in breeding programs, the phenotypic correlation was estimated. In this study based on the results of phenotypic correlation, leaf width and leaf length (0.651), single fruit weight and fruit circumference (0.784), fruit circumference and fruit diameter (0.625) and pulp weight and fruit diameter (0.610), showed positive and significant correlation. The purpose of estimating genotypic correlation coefficient is to determine relationships in conditions which in environmental factors are not involved. In the investigation of genotypic correlation, a positive, strong and significant relationship between fruit yield and pulp weight (0.907), fruit circumference (0.891), fruit diameter (0.697), single fruit weight (0.646) and around the plant (0.381) were observed. Given that most of these traits are factors contributing to fruit yield, the presence of such positive and significant genotypic correlation coefficients is reasonable. It can be inferred that pepper accessions with higher fruit characteristics, encompassing factors such as plant density and branching, are likely to exhibit higher fruit yields as well. It's important to note that correlation coefficients are mathematical tools used to measure the linear relationship between two variables. Their significance lies in their mathematical interpretation, and as such, they alone do not provide sufficient proof of a cause-and-effect relationship. Utilizing the results of stepwise regression, less impactful traits or those with minimal effects were eliminated from the model. As a result, seven key traits were identified as the most influential factors affecting fruit yield: pulp weight, plant density, fruit diameter, fruit count, plant height, total seed weight, and branch count.The first characteristic was pulp weight, which was included in the model and explained 78.8% of the fruit yield changes between genotypes. The second characteristic (around the plant) along with pulp weight explained 80.9% of the fruit yield variations. Fruit diameter, together with the previous two characteristics, explained 81.5% of fruit yield variations. In total, the traits included in the model for fruit yield justified 84.6% of the total changes in fruit yield in 30 pepper accessions. In order to better understanding and more accurately interpret of the results, as well as to know the direct and indirect effects and the effect of the traits that were entered into the model through stepwise regression, the path coefficient analysis method was used in this research. Fruit diameter (0.709) and pulp weight (0.289) respectively showed the most positive and direct effect on fruit yield. Fruit pulp weight through fruit diameter had the most positive indirect effect (0.595) on fruit yield. Around the plant showed an indirect positive effect on fruit yield through pulp weight (0.157), fruit diameter (0.392) and number of branches (0.080).
Conclusion
In the present study, the trait of fruit diameter had a positive, strong and significant genotypic correlation (0.697) with fruit yield, and it also showed a positive direct effect (0.709) on fruit yield, these two coefficients can be considered equal, Approximately. Therefore, direct selection based on fruit diameter proves to be a valuable strategy for enhancing fruit yield. The magnitude of residual effects serves as an indicator of the model's accuracy in path analysis. When this value is substantial, it may be advisable to incorporate additional causal variables into the model. In the current study, the residual effects value (0.213) affirms the model's optimal accuracy.This research highlights the effectiveness of employing stepwise multivariate regression and path coefficient analysis to gain a deeper understanding of the fundamental relationships between traits. It underscores that relying solely on correlation relationships is insufficient for comprehensively justifying the associations between these traits.
Ghahraman Bagheri; Bahman Zahedi; Reza Darvishzadeh; Ahmad Hajiali
Abstract
Introduction: Pepper is one of the most important vegetables in the world that belongs to the family of Solanaceae. It is used as a food flavoring, coloring agent and a pharmaceutical ingredient in different innovative ways. Capsicum annuum is one of the five cultivated species in the genus and the ...
Read More
Introduction: Pepper is one of the most important vegetables in the world that belongs to the family of Solanaceae. It is used as a food flavoring, coloring agent and a pharmaceutical ingredient in different innovative ways. Capsicum annuum is one of the five cultivated species in the genus and the others are C. baccatum L., C. chinense, C. frutescens and C. pubescens. While C. pubescens and C. baccatum are morphologically quite distinct, C. annuum, C. chinense and C. frutescens show evidence of parallel evolution for a variety of plant and fruit morphological characteristics as a result of similar regimens of human selection. The near continuous overlapping in morphological traits among these three species led various authors to recognize them as a complicated species. Within complex, taxa are differentiated from one another based primarily on differences in corolla color, the presence or absence of a calyx constriction and the occurrence of multiple pedicels/node.
Materials and Methods: This research was conducted to evaluate genetic diversity in pepper genotypes. Morphological traits of 42 genotypes were investigated in rectangular lattice 6×7 with three replications in two separate experiments at West Azerbaijan research institute. Analysis of variance was conducted by using SAS, SPSS and MINITAB softwares. 14 traits including length and width of fruits, thickness of fruit wall, width of plant canopy, length of shoots, length of corolla, fruits fresh and dry weight, SPAD, photosynthesis, yield, vitamin C, TSS and pH were assessed according to the International Board for Plant Genetic Resources (IBPGR) descriptor. Solid contents (TSS) were assessed by using refractometer, pH by using pH meter, and fruits fresh and dry weight by using a digital scale. For measuring vitamin C content, 3-10 g of the fruit tissue (pericarp and pulp) was homogenized and 100 mL of distilled water were added. Then 10 mL of sulfuric acid 20%, 1 mL of 0.01 N potassium iodide, 1 mL of 1% starch were added to the solution and then for titrating, 0.01 N potassium iodide was used.
Results and Discussion: Analysis of variance showed significant differences (at 1% level) among pepper genotypes, in terms of width of fruits, fruit wall thickness, yield, plant height, shoots diameter, length of shoots, and dry weight of fruit, TSS and vitamin C. But there were no significant difference between pH, SPAD and photosynthesis. The highest heritability was observed in length and width of fruits, fruit wall thickness, fruit pedicel length, yield, dry and fresh weight of fruits, and the lowest heritability obtained in SPAD and pH. Phenotypic variation coefficient was higher than genotypic variation coefficient for all traits, indicating the significant effects of environmental conditions. The maximum phenotypic correlation obtained between fruit fresh and dry weight (r=0.95) and also observed between fruit fresh weight and fruit wall thickness. Cluster analysis with Ward method classified studied landraces into six different groups. The highest distance was observed between groups four and five. This result showed that the maximum expected heterosis could achieve from crosses between genotypes from groups four and five.
Conclusions: High genetic variation was observed among pepper genotypes that could be helpful for morphological traits studies and to improve superior genotypes in next breeding programs.
