Homozygosity and segregation ratio in F4 generation of tomato for fruit morphology

Abstract

Diversity in tomato shape is one of the most prominent traits which distinguish one variety of tomato from other. Our research aims to find the segregation ratio for fruit morphology in F4 lines and to determine the level of homozygosity within the lines. Plants with desirable traits were selected from F3 generation in 2017 and were sown as F4 generation in next season i.e 2018. Data were recorded for each plant in each line for fruit and blossom end shape and were analyzed through chi square test. Chi square test showed that more than 50% lines deviated from the expected ratio for fruit shape and showed significant difference between expected and observed ratios. Most of the obovoid-square fruit shaped F3 parents did not segregate further and produced all the obovoid-square shaped fruit plants in F4 generation. Obovoid fruit shaped F3 parents segregated into different fruit shapes in different ratios and did not show any homozygosity in F4 generation. Obovoid-pear fruit shaped F3 parents segregated into the Obvoid and pear shapes. Obovoid-cylindrical fruit shaped F3 parents did not produce any cylindrical fruit in F4 generation and segregated into square and obovoid shaped fruit plants. However, for blossom end shape, nearly all the lines segregated in F4 generation into flat blossom end and pointed blossom end shapes in the expected ratio i.e 3:1, respectively. Some lines did not segregate further for blossom end shape showing that those lines have attained homozygosity in F4 generation for the trait.