Phenotypic and molecular characterization of Green Super Rice (Oryza sativa L.) in response to drought stress

Abstract

Rice is among the major staple food and cash crops of Pakistan. Rice cultivation depends upon appropriate irrigation; however, an increasing number of extreme drought spells is currently a main challenge in rice production and breeding for unfavorable environments. The drought stress at reproductive stage is among the main restrictive factors leading to the drastic grain yield reduction in rainfed rice. The complex genetic and morpho-physiological mechanisms are associated with drought tolerance. This study investigates the drought tolerance ability of a set of 22 Green Super Rice genotypes along with four local cultivars under field drought conditions to improve the farmers' ability to cope with the drought risk in rice production. The present research relies on morpho-physiological and molecular characterization of the experimental genotypes under normal and drought stress. The study assessed the performance of 26 rice lines under 30 days drought stress at anthesis stage compared to normal growing condition. These genotypes were transplanted in the field during June 2020 according to randomized complete block design with 3 replication and two treatments (i.e., normal and drought condition). Three physiological traits including pollen fertility percentage (PFP), cell membrane stability (CMS) and normalized difference vegetative index (NDVI) were characterized at anthesis stage during the last week of drought stress. Morphology based attributes i.e., plant height (PH), tillers per plant (TPP), grain yield per plant (GY), straw yield per plant (SY), total biomass per plant (TBM), harvest index (HI), drought susceptibility index (DSI), 1000-grain weight (TGW) and grain length (GL) were measured at maturity stage. The descriptive statistics and analysis of variance demonstrated a noteworthy variation among the accessions for studied traits. Correlation and PCA analyses were performed that showed the highly significant associations among studied traits and genetic diversity among observed genotypes, respectively. Among the screened genotypes, NGSR-15 and NGSR-18 were designated as drought tolerant, while NGSR-3 and NIAB-IR-9 were identified as drought susceptible. qRT-PCR based expression analysis of novel drought genes was also performed to understand the mechanism involved in drought responses. The study concludes that investigated drought down regulated (LOC_Os05g23880 and LOC_Os05g08480) and drought upregulated genes (LOC_Os11g36190, LOC_Os12g26290, OsSADR1, OsDSM1 and OsDT11) could be further utilized in future breeding strategies of genetic improvement towards drought tolerance in rice.