Random mutagenesis in vegetatively propagated crops: opportunities, challenges and genome editing prospects

In order to meet the growing human food and nutrition demand a perpetual process of crop improvement is idealized. It has seen changing trends and varying concepts throughout human history; from simple selection to complex gene-editing. Among these techniques, random mutagenesis has been shown to be a promising technology to achieve desirable genetic gain with less time and minimal efforts. Over the decade, several hundred varieties have been released through random mutagenesis, but the production is falling behind the demand. Several food crops like banana, potato, cassava, sweet potato, apple, citrus, and others are vegetatively propagated. Since such crops are not propagated through seed, genetic improvement through classical breeding is impractical for them. Besides, in the case of polyploids, accomplishment of allelic homozygosity requires a considerable land area, extensive fieldwork with huge manpower, and hefty funding for an extended period of time. Apart from induction, mapping of induced genes to facilitate the knowledge of biological processes has been performed only in a few selected facultative vegetative crops like banana and cassava which can form a segregating population. During the last few decades, there has been a shift in the techniques used for crop improvement. With the introduction of the robust technologies like meganucleases, zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and clustered regularly interspaced short palindromic repeats (CRISPR) more and more crops are being subjected to gene editing. However, more work needs to be done in case of vegetatively propagated crops.

Development of an efficient in vitro mutagenesis protocol for genetic improvement of saffron (Crocus sativus L.)

Saffron (Crocus sativus L) is a triploid (2n = 3x = 24), sterile geophyte which can only be propagated by means of underground vegetative corms. Since corm multiplication does not induce genome variations, therefore, the entire saffron population is expected to have a similar genetic makeup. Keeping in view the economic importance of the plant and the factors responsible for its low yield, the present investigation has been undertaken to establish an in vitro ethyl methanesulfonate (EMS) mutagenesis protocol followed by characterization of the induced variability in the advanced generations. The present report is limited to standardization of in vitro mutagenesis protocol only. Among the mutagenic treatments tested, concentrations ranging from 0.1 to 0.5% EMS showed a varied survival of explants. Based on various growth parameters, the LD₅₀ was calculated to be 0.3% EMS for 3 h. Among the two types of explants analyzed, the corm explant gave better results for in vitro survival and the growth parameters than callus explant. An average of 57.33 and 92.00 daughter cormlets in all EMS treatments as compared to 47.67 and 57.67 daughter cormlets in control, obtained from callus and corm explants respectively, were transferred to the field. The maximum, average daughter cormlet weight was obtained in control (3.01 g, corm explant) followed by 0.1% EMS (2.8 g, corm explant). In general, the growth parameters showed decreasing trend with an increase in EMS concentration in both the explants. The present study has been a significant achievement in the sense that the first mutagenesis protocol for C. sativus has been standardized.