Rolled Towel Assay for seedling root growth evaluation: An effective protocol of delineating juvenile root differences in rice (Oryza sativa L.)

Roots define plant productivity under stress and can be effectively harnessed to improve moisture stress resilience in crop plants. However, root traits are being largely ignored in crop improvement programmes, mainly because of the difficulties associated with root recovery and evaluating these traits in situ. Among various in vitro methods used, the Rolled Towel Assay (RTA) has been used in several crops like wheat, maize, beans and soybean to assay the juvenile root traits. In the present study, we standardized the rice RTA to allow for maximum germination rates, synchronize seedling growth and minimize fungal contamination. The root towel method provides ample opportunity to screen large germplasm sets for response to hormones, nutrient treatments and stress conditions. We used a diverse panel of 264 temperate rice germplasm and found significant variability in tap root length among the genotypes. The seedlings’ tap root length had a mean value of 8.03 cm with a range of 2.80 to 14.57 cm and a CV of 12.44 percent. Genotype GS-33 had the largest seedling root length of 14.57 cm followed by GS-214 (14.2 cm) and GS-62 (13.70 cm). The lowest value (2.80 cm) of root length was recorded in the genotype GS-610. The experimental material used did not suffer from any fungal infection issues and is highly reproducible as has been reported in other cereal crops like wheat and maize. The method is simple, cheap and has high throughput, and can be used in stress breeding programs for the initial screening of genotypes in the diverse germplasm panels.