High throughput screening of rooting depth in rice using buried herbicide

Abstract

Root research requires high throughput phenotyping methods that provide meaningful information on root depth if the full potential of the genomic revolution is to be translated into strategies that maximise the capture of water deep in soils by crops. A very simple, low cost method of assessing root depth of seedlings using a layer of herbicide (TRIK or diuron) buried 25 or 30 cm deep in soil‐filled boxes of varying size is described that is suitable for screening hundreds or thousands of rice accessions in controlled environment conditions. Variation in cultivar sensitivity to the herbicide when injected into pots was detected but considered small in relation to the variation detected when the herbicide was buried. Using 32 rice cultivars previously characterised for root traits in rhizotron and hydroponic systems, 80% of variation in herbicide score at 35 days was explained by cultivar and herbicide score correlated strongly with rooting depth traits. Using 139 genotypes of the Bala × Azucena mapping population, heritability for herbicide symptoms reached 55% and quantitative trait loci were detected which match those previously reported in this population. In repeated experiments using different soils, the method did not always perform to its maximum potential (in terms of speed of symptom development or discrimination between cultivars). This was not due to degradation or reduced bio‐availability of the herbicide in the soil but is believed to be due to the soil water content and water release characteristics as it relates to plant water use. Therefore, when using this technique, thorough preliminary experiments to determine the best water application regime for the particular combination of soil and environmental conditions are required. The method should be applicable to seedling stage screening of rice and other crops.

The roots of future rice harvests

“…In this case the plant starts to die when its root system reaches the herbicide layer. This reflects the rapidity with which the root develops in depth which is a combination of root gravity perception (or root angle) and growth rate (Al-Shugeairy et al [ 2014 ]). Another system, called shovelomics uses the partial digging up of the root system under field conditions, through a rapid (8 minutes per plant) phenotyping of some parameters such as root biomass in top soil and the total number of crown roots (Trachsel et al [ 2011 ]).…”

High-throughput phenotyping (HTP) identifies seedling root traits linked to variation in seed yield and nutrient capture in field-grown oilseed rape (Brassica napusL.)

“…More involved methods of observing root traits include soil-coring/washing/breaking ( Gregory and Eastham, 1996 ; Ostonen et al ., 2007 ; Watt et al ., 2013 ; Wasson et al ., 2014 ) and the use of interfaces such as ‘windows’, trenches and minirhizotrons ( Jose et al ., 2001 ; Dupuy et al ., 2010 ; Maeght et al ., 2013 ; Vansteenkiste et al ., 2014 ). In situ proxy measurements for studying root traits include: (1) using buried herbicides to monitor root depth ( Maeght et al ., 2013 ; Al-Shugeairy et al ., 2014 ); (2) electromagnetic induction to estimate root biomass from water depletion ( Srayeddin and Doussan, 2009 ; Shanahan et al ., 2015 ); (3) measuring root capacitance ( Dietrich et al ., 2012 , 2013 ); and (4) quantifying plant root DNA concentrations ( Huang et al ., 2013 ). Ex situ methods for studying the roots of soil-grown plants include X-ray microcomputed tomography (µCT; Tracy et al ., 2010 ; Mooney et al ., 2012 ) and magnetic resonance imaging (MRI; Rogers and Bottomley, 1987 ; Metzner et al ., 2015 ), which may have potential for field-grown crops in the future.…”

Assessing the genetic diversity of rice originating from Bangladesh, Assam and West Bengal

“…The genetic diversity of the aus and boro ecotypes is large and includes a number of cultivars known for their adaptation to different environments. Cultivar FR 13A, for example, is the flood tolerant donor of the submergence tolerance gene Sub1 (Xu et al, 2006); Kasalath is the efficient phosphorus uptake donor of the phosphorus starvation tolerance gene Pstol1 (Gamuyao et al, 2012); Dular is a rice cultivar that has increased drought resistance, associated with greater root length and root density (Henry et al, 2011); Rayada also has a large root length and high root density (Henry et al, 2011); Black Gora is a rice cultivar with high seedling vigour (Redoña and Mackill, 1996) and deep roots (Shrestha et al, 2014; Al-Shugeairy et al, 2014) and; N 22 is a heat tolerant rice cultivar (Jagadish et al, 2008). …”