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.
Highlights
In rainfed lowland rice ecosystems, it is believed that the main constraint to production is water deficit mainly due to either erratic rainfall (Ding et al, 2011; Gomez et al, 2006; Serraj et al, 2011; Wade et al, 1999) or limited access of water in deep soil layer where water is available because of the presence of hardpan (Bengough et al, 2011; Clark et al, 2008; Samson et al, 2002)
Shoot dry matter production For the three years, G3-3 consistently showed no significant differences in shoot dry weight (SDW) with Nipponbare from early vegetative to maturity under continuous waterlogging (CWL) (Figure 1(a), (c), (e))
The QTLs identified at the vegetative stage for lateral root length (LRL) and total root length (TRL) on Chr 7and nodal root length (NRL) on Chr 10 as well as QTLs detected at reproductive stage for TRL on Chr 10 and nodal root number (NRN) on Chr 12 may have contributed to the root plasticity in G3-3 since they were not found in the substituted segments of KDML 105 in G3-10 and G3-12
Summary
In rainfed lowland rice ecosystems, it is believed that the main constraint to production is water deficit mainly due to either erratic rainfall (Ding et al, 2011; Gomez et al, 2006; Serraj et al, 2011; Wade et al, 1999) or limited access of water in deep soil layer where water is available because of the presence of hardpan (Bengough et al, 2011; Clark et al, 2008; Samson et al, 2002). The current technology still often suffer from yield penalty as compared with continuously flooded conditions while it has greatly improved water use efficiency (Patel et al, 2010; Peng et al, 2006; Tao et al, 2006; Zhao et al, 2009, 2010, 2011) The cause of such yield reduction has not yet been identified a number of studies have been conducted and found out PLANT PRODUCTION SCIENCE 107 that possible causes for such yield reduction include high soil pH resulting in reduction of nitrogen uptake, decline of soil organic matter which affects soil physical properties such as high bulk density, low porosity and poor structure (Bouman et al, 2007; Carrijo et al, 2017; Tuong & Bouman, 2003). In this aspect, Suralta et al (2008, 2010) suggested that the AWD and aerobic culture may inherently involve SMF, which could be stressful for rice plants and cause yield reduction
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