Jonathan Manito Niones

Field evaluation on functional roles of root plastic responses on dry matter production and grain yield of rice under cycles of transient soil moisture stresses using chromosome segment substitution lines

BackgroundFluctuating soil moisture resulting from the transient occurrences of waterlogging and drought are frequently reoccurring in the rice field, which adversely affects plant growth and yield. We previously established the significant contribution of plastic development and associated physiological responses of root to shoot dry matter production under soil moisture fluctuation stresses.AimTo evaluated the functional roles of root plastic development on yield under field condition of continuous cycle of transient soil moisture stresses.MethodsPreviously selected CSSL47 and the recurrent parent Nipponbare were exposed to two soil moisture conditions; cycles of alternating waterlogging and drought condition (CAW-D) and continuous waterlogging (CWL; control).ResultsUnder continuous waterlogging (CWL) conditions, the two genotypes showed no significant differences in most of the traits examined. In contrast, under continuous cycle of alternate waterlogging and drought (CAW-D) conditions, CSSL47 showed greater shoot dry matter production than Nipponbare, which was attributed to its higher stomatal conductance and photosynthetic rate, which then led to higher grain yield. The root system development of CSSL47 expressed as total root length was greater compared with Nipponbare. Before heading stage, plasticity was expressed as enhanced aerenchyma formation based on root porosity, which was associated with the promotion of lateral root production, elongation and branching and the eventual increase in total root length. Moreover, after heading, compared with Nipponbare, CSSL47 continued to produce more nodal roots from newly produced tillers, thus maintaining leaf photosynthesis and eventually resulting in heavier panicles.ConclusionsWe provide evidences that root plasticity, which better expressed in CSSL47 than Nipponbare, under continuous cycle of transient soil moisture stresses contributed to increase in grain yield in fields. Genetic variation in plastic responses of roots could have substantial impact on yield in areas experiencing these kind of soil moisture stresses.

Roles of Root Aerenchyma Development and Its Associated QTL in Dry Matter Production under Transient Moisture Stress in Rice

Abstract Enhanced aerenchyma development in rice under transient drought-to-waterlogged (TD-W) stress promotes root system development by promoting lateral root production. This study analyzed the quantitative trait loci (QTLs) associated with the plasticity in aerenchyma development under TD-W stress. A mapping population of 60 F2 genotypes of chromosome segment substituted lines (CSSL) derived from CSSL47 and Nipponbare crosses were grown in rootboxes and evaluated for shoot and root growth, and aerenchyma development (expressed as root porosity). The TD-W stress was imposed starting with water saturated soil condition at sowing and then to progressive drought from 0 to 21 days after sowing (DAS) prior to exposure to sudden waterlogging for another 17 days (21 to 38 DAS). We performed simple and composite interval mapping to identify QTLs for aerenchyma development. QTL associated with aerenchyma development was mapped on the short-arm of chromosome 12 and designated as qAER-12. The effect of qAER-12 on the plasticity in aerenchyma development under TD-W was significantly associated with the increase in lateral root elongation and branching. This resulted in greater root system development as expressed in total root length and consequently contributed to higher dry matter production. This qAER-12 is probably the first reported QTL associated with aerenchyma development in rice under TD-W and is a useful trait for the improvement of the adaptive capability under fluctuating soil moisture conditions.

QTL associated with lateral root plasticity in response to soil moisture fluctuation stress in rice

BackgroundLateral root (LR) plasticity is a key trait that plays a significant role in plant adaptation to fluctuating soil moisture stressed environments. We previously had demonstrated that promoted LR production (LR plasticity) contributed to the maintenance in shoot dry matter production and grain yield under soil moisture fluctuation (SMF) stress.AimTo identify quantitative trait loci (QTLs) associated with LR plasticity under SMF condition and their contributions to shoot dry matter production.MethodsF2 lines derived from Nipponbare x chromosome segment substituted line number 47 (Nipponbare/Kasalath) backcrosses were used to analyze ten substituted chromosome regions with ‘Kasalath’ allele that are associated with root plasticity under SMF stress.ResultsWe mapped two closely linked QTLs on chromosome 12 region namely qTLRN-12 at seedling stage and qLLRN-12 at vegetative stage. Under SMF conditions, qTLRN-12 found at the flanking markers between TG154 and RM247 is responsible for the plasticity in total LR number while qLLRN-12 detected at the flanking markers between RM6296 and TG156 is associated with plasticity in L-type LR production. Kasalath genome contributed the corresponding alleles for increasing the mentioned root traits that resulted in a significant increase in shoot dry matter production under SMF stress.ConclusionWe identified two QTLs associated with LR plasticity on chromosome 12 which significantly contributed to the greater root system development and maintenance of total dry matter production under SMF stress.

Plasticity in nodal root elongation through the hardpan triggered by rewatering during soil moisture fluctuation stress in rice

Rainfed lowland (RFL) rice fields have hardpans and experience soil moisture fluctuations (SMF) stress, which influence root system development. Here, we clarify the expression and timing of the plasticity in nodal root elongation through the hardpan under SMF and its contribution to shoot growth using a shallow-rooting IR64 and its deep-rooting introgression line, YTH304. Under SMF, soil moisture content had negative relationship with soil penetration resistance, regardless of hardpan bulk densities. YTH304 had greater root system below the hardpan than IR64 in hardpan with 1.50 but not in 1.70 g cm−3 bulk density (BD). YTH304 had greater plasticity in nodal root elongation through the hardpan than IR64 under SMF, which was clearly expressed during rewatering. YTH304 also had greater soil water uptake below the hardpan during drought and greater shoot growth than IR64. The results imply that deep root system development during SMF was due to the plasticity in nodal root elongation through the hardpan expressed during rewatering rather than during drought periods. This is against the long standing belief that active root elongation through the hardpan happens during drought. This also implies a need to revisit current root screening methods to identify rice lines with good hardpan penetration ability.

Root plasticity under fluctuating soil moisture stress exhibited by backcross inbred line of a rice variety, Nipponbare carrying introgressed segments from KDML105 and detection of the associated QTLs

Abstract In rainfed lowland rice ecosystem, rice plants are often exposed to alternating recurrences of waterlogging and drought due to erratic rainfall. Such soil moisture fluctuation (SMF) which is completely different from simple or progressive drought could be stressful for plant growth, thereby causing reduction in yield. Root plasticity is one of the key traits that play important roles for plant adaptation under such conditions. This study aimed to evaluate root plasticity expression and its functional roles in dry matter production and yield under SMF using Nipponbare, KDML 105 and three backcross inbred lines (BILs) and to identify QTL(s) associated with root traits in response to SMF at two growth stages using Nipponbare/KDML105 F2 plants. A BIL, G3-3 showed higher shoot dry matter production and yield than Nipponbare due to its greater ability to maintain stomatal conductance concomitant with greater root system development caused by promoted production of nodal and lateral roots under SMF. QTLs were identified for total nodal root length, total lateral root length, total root length, number of nodal roots, and branching index under SMF at vegetative and reproductive stages. The QTLs detected at vegetative and reproductive stages were different. We discuss here that relationship between root system of G3-3 and the detected QTLs. Therefore, G3-3 and the identified QTLs could be useful genetic materials in breeding program for improving the adaptation of rice plants in target rainfed lowland areas.