**4. Conventional strategies to enhance oil production in biofuel crops**

To achieve commercial biodiesel production from nonedible oil plants, development of new varieties/hybrids of oil plants with high oil contents, tolerance to biotic and abiotic stresses, and no toxic proteins are a critical step. During the last decade, different breeding strategies have been used to improve these traits in crop plants of interest. The main activities pursued in plant breeding include developing variation, selection, evaluation for target traits, multiplication, and finally, release and distribution of new varieties [28]. Commonly, creation of genetic variation is performed through domestication, germplasm collection, introduction, intra- and inter-species hybridization, mutation, polyploidy, somaclonal variation, germaclonal variation, and genetic engineering [29, 30]. During the last decades, using conventional breeding strategies, different edible and nonedible oil plants have been improved to enhance oil quality, oil yield, and tolerance to biotic and abiotic stresses [31, 32]. In spite of such successful experiences, these methods face some disadvantages, such as being laborious and time-consuming, low accuracy in achieving desired traits, impossibility of inter-species hybridizations and wild crosses. The long methodologies and less precision created gap between identification of lines with potential to be the source of biofuels and the application for production of biodiesel.
