To solve this problem, we need to identify the characteristic feature of in vitro clonal propagation in plants. Let's analyze each option:$\newline \bullet$Option 1: PCR and RAPD - PCR (Polymerase Chain Reaction) and RAPD (Random Amplified Polymorphic DNA) are molecular techniques used for DNA analysis and genetic fingerprinting, not directly related to clonal propagation.$\newline \bullet$Option 2: Northern blotting - Northern blotting is a technique used to study gene expression by detection of RNA (or isolated mRNA) in a sample. It is not related to clonal propagation.$\newline \bullet$Option 3: Electrophoresis and HPLC - Electrophoresis is used for separating DNA, RNA, or proteins, and HPLC (High-Performance Liquid Chromatography) is used for separating, identifying, and quantifying components in a mixture. Neither is directly related to clonal propagation.$\newline \bullet$Option 4: Micropropagation - Micropropagation is a method of in vitro clonal propagation where plants are cloned using tissue culture techniques. It is characterized by the production of large numbers of identical plants from a single explant.$\newline$Therefore, the correct option is Option 4: Micropropagation, as it directly relates to in vitro clonal propagation in plants.