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The role of genetic solutions for overcoming subsoil constraints to lentil

Roger Armstrong, James Nuttall , Michael Materne and Kristy Hobson

Department of Primary Industries, PB 260, Horsham, Victoria 3401. Email


Physicochemical factors including salinity, sodicity and high boron (B) in the subsoil can significantly limit the water use and yields of dryland grain crops throughout much of Australia’s grains belt. There are currently few viable amelioration options to overcome these subsoil constraints (SSCs), thus creating significant interest in developing ‘genetic solutions’. Most grain breeding programs targeting southern Australia currently include tolerance for at least one subsoil constraint in their selection programs. We conducted a controlled environment trial using intact soil cores which maintain soil chemical and physical properties collected from both a soil profile containing a range of SSCs typical of the Mallee region and a ‘benign’ profile with few SSCs. The growth and water use of closely related lines of lentil that were classified as either ‘tolerant’ or ‘intolerant’ to specific SSCs were assessed. The possession of genetic ‘tolerance’ to both high soil B and salinity was associated with improved grain yield of lentil (by 247%) on a soil with significant SSCs compared to only 24% on a soil with relatively low levels of SSCs. These yield differences corresponded to a trend for the ‘tolerant’ CIPAL415 to extract more water than the intolerant Nugget at all depths on the soil with significant SSCs whereas there was no difference in extraction on the benign soil. We discuss the possible explanations for this result and suggest approaches that may assist the effectiveness of current programs aiming to develop germplasm that are better adapted to soils with SSCs.

Key Words

Lentil, salinity, boron, water use, adaptation


The yield of dryland grain crops growing throughout large areas of Australia are often limited by a number of physicochemical constraints in the subsoil (SSCs) including high boron (B), salinity and sodicity (Nuttall et al. 2003; Dang et al. 2006; Adcock et al. 2007). Attempts to develop viable management options to improve productivity of soils with SSCs have met with minimal success to date. Physical amelioration using deep ripping appears to have only limited application, especially where there are dense sodic clay subsoils (Gill et al. 2008). In low-medium rainfall zones, reduced yield potentials limit the likelihood of yield improvements being sufficiently large enough to offset the initial high implementation costs of subsoil amelioration. The use of breeding to develop better adapted crops with improved physiological tolerance to these SSCs offers a strategy for managing crop production on these soils. Significant genetic variation for tolerance to specific subsoil constraints such as B and salinity exist in lentil (Maher et al. 2003; Hobson et al. 2006). The translation of this genetic potential to better varieties is dependent on whether procedures used for phenotyping in controlled environment studies accurately reflects traits that improve performance in the field. We report results from two experiments to assess the relative effectiveness of ‘genetic tolerance’ to SSC in improving plant growth and water use.


Intact cores (60 cm deep x 15 cm diameter containing approximately 16 kg of soil and sealed at the bottom), which maintain the physiochemical integrity of the soil profile were collected from the southern Mallee region of Victoria. Physiochemical properties at one site (Site 1) indicated the soil was relatively benign whereas the second site (Site 2) had severe SSCs with high sodicity and salinity in the subsoil (Table 1).

A comparison was made between two lines of lentil (Lens culinaris) that expressed either moderate tolerance to high soil NaCl (CIPAL 415) or tolerance to both NaCl and high B (02-335*03HS005) in soil culture with the intolerant parental line Nugget (Hobson et al. 2007). The trial was a completely randomised design with 4 replicates per treatment. The trial was conducted in a naturally lighted evaporatively cooled polyhouse. A basal application of P, Zn, Cu and N was applied to ensure nutrients were non-limiting. After emergence cores were maintained at approximately 85% of field capacity by applying Reverse Osmosis water to compensate for losses by evapo-transpiration as assessed by changes in weight (every 7 to 14 days). Watering ceased across all treatments at mid podding. Dry matter samples were collected at grain maturity and dried for 48 hours at 70oC prior to weighing. Tissue elemental (B, Na, Ca) concentration was assessed on ground (< 0.5 mm sieve) tissue following oven drying by digesting in acid and analysis using Inductively Coupled Plasma Atomic Emission Spectrometry (ICP). Soil water content at grain maturity was assessed by inserting a thin walled tube (42 mm cutting tip) in each intact core, segmenting the soil into 10 cm and determining gravimetric moisture content following drying at 105oC.

Table 1: Selected soil physicochemical properties at (A) Site 1 (‘benign) and (B) Site 2 (severe SSCs)

Soil depth

pH (1:5 water)



Hot CaCl2 extr. B


(A) Site 1























(B) Site 2























Plant growth

Both maturity dry matter (data not presented) and grain yield of lentil (Fig. 1) was strongly influenced by both soil type and genetic background. Overall growth (25% for maturity dry matter and 64% for grain yield) was significantly better (P <0.001) by all lentil lines examined on the benign soil with relatively few SSCs (Site 1) compared to the soil with severe SSCs. Nugget, which was classified as ‘intolerant’ to both high B and salinity produced less yield (Fig. 1) and dry matter compared to the other two lines on both soil types. CIPAL415 (moderate NaCl tolerant) produced significantly higher grain yield than 02-355L*03HS005 (NaCl and B tolerant) on the relatively benign soil but this pattern was reversed on the soil with severe SSCs. The yield advantage of the two SSC tolerant lines compared to Nugget resulted primarily from a higher harvest index across both soil types with 02-355L*03HS005 having significantly smaller (P < 0.001) seed size than the two other lines (data not presented).

There was no clear relationship between tolerance (based on controlled environment experiments) and B uptake, with grain B concentration being lowest in the B and salinity tolerant line 02-355L*03HS005 and highest in CIPAL415 with Nugget intermediate (Table 2). Grain B concentration was unaffected by soil type but total B uptake (grain + straw) was significantly greater in the benign soil than the soil with severe SSCs. Neither the tissue Na concentration nor total Na uptake was affected by soil type or genotype (Table 2).

Figure 1: Grain yield of different lentil genotypes with either NaCl (CIPAL415) or B and NaCl tolerance (02-335*03HS005) compared to the parent Nugget when grown on soil with either relatively few (Site 1) or severe (Site 2) SSCs. Vertical bar is the l.s.d. (5%).

Water use

All lentil lines had extracted more soil water at maturity on the benign soil (Site 1) than the soil with severe SSCs (Site 2) (Figure 2). There was a trend however for the NaCl moderately tolerant CIPAL415 to extract more water than the intolerant Nugget at Site 2, especially at intermediate depths whereas there was no difference between the two genotypes on the benign soil.

Table 2: Concentration of Boron (B) in grain, total B uptake by plant (grain + straw), sodium (Na) concentration of straw and total plant uptake of Na, of different Lentil genotypes when grown on a soil with relatively few SSCs (Site 1) or severe SSC (Site 2). n.s. = not significant (P > 0.05)



Grain B

Total B uptake

Straw Na

Total Straw Na (g/core)


Site 1






Site 1






Site 1






Site 2






Site 2






Site 2





l.s.d. (5%)


Genotype 0.91
Soil n.s.

Genotype 0.052
Soil 0.041

Genotype n.s.
Soil n.s.

Genotype n.s.
Soil n.s.

Figure 2: Ability of a lentil genotype possessing tolerance to high soil NaCl (CIPAL415) compared to the parent (Nugget) to extract soil water at grain maturity on a soil with either relatively few (Site 1) or severe subsoil constraints (Site 2).


This study demonstrated that the inclusion of tolerance to both high B and salinity improved the growth and yield of lentil. Significant genetic variation exists for both tolerance to high B and NaCl in lentil (Maher et al. 2003; Hobson et al. 2007) and this variation provided the foundation for breeders to incorporate these traits into widely grown parent used in this study. The potential advantage of these new genotypes in terms of grain yield were tested on soils that were either relatively benign (although there was evidence of some SSCs) or had severe SSCs. The latter soil is representative of large sections of the cropping zone of southern Australia (Nuttall et al. 2003). Ideally, the best assessment of the relative agronomic value of a particular trait such as tolerance to high B would be through the use of isogenic lines (Ludlow and Muchow 1990). Although such lines are not currently available, comparisons were limited to crosses and the original parent to minimise the potential for other unintended traits also being expressed.

The higher yield of the tolerant lentil lines was not associated with either tissue B or Na concentration or uptake. Holloway and Alston (1992) have previously noted that neither Na nor B concentration is a useful indicator of tolerance to salinity or B toxicity, respectively, in wheat due to the influence of water uptake. However there was a better association with greater water use in lower sections of the soil profile, which can be critical during dry spells during grain filling.

Subsoils in southern Australia contain multiple physicochemical constraints that are potentially limiting to water use and plant growth and often the occurrence of these constraints is strongly correlated (Nuttall et al. 2003). In contrast, most current screening procedures focus on a single factor eg. high B or NaCl. However the successful adaptation of crops to these soils will likely require tolerance to all these constraints as possessing tolerance to a single constraint will result in only minimal gain in yield as the ‘Law of the Minimum’ will then come into play. Significantly the lentil genotype 02-335*03HS005, which exhibited both tolerance to high B and NaCl, performed better than CIPAL415 which contained only tolerance to moderate levels of NaCl. In order to maximise adaptation it is recommended that a pyramiding approach (Yeo and Flowers 1986), whereby physiological traits conferring tolerance to several different SSCs are simultaneously selected for, be adopted by breeding programs targeting soils in southern Australia. Breeding programs could also focus on the constraint of greatest limitation if it is known for a species. However this is problematic in the case of B and NaCl as although their occurrence in the neutral-alkaline soils of South-eastern Australia is correlated, the relative levels can vary spatially and quantifying which factor is of greater significance is difficult without studies such as outlined in this paper.

Our study also demonstrated that lentil growth was affected by even relative low levels of SSCs. The yield advantage of 02-355L*03HS005 over Nugget in the relatively benign Site 1 soil was evidence of this as the yield potential of Nugget is greater than that of the cross in similar climate zones but where there are no SSCs. The level of SSCs in the Site 1 soil are relatively low compared to that found throughout large sections of the Victorian Wimmera and Mallee (Nuttall et al. 2003), indicating that SSCs are a very significant potential abiotic limitation to achieving higher lentil yields in these regions.

Even when new germplasm possesses a particular trait that can putatively enhance adaptation to a particular environment, quantifying this advantage in the field can be difficult due to high background variability as well as the confounding effect of other factors such as seasonal conditions, especially soil moisture availability. This is especially so on the neutral-alkaline soils that constitute a major proportion of the grain belt of Victoria and South Australia due to the inherent high spatial variability in important soil properties, especially SSCs (Nuttall et al. 2003). We aimed to minimise this background variability through the use of intact cores that were collected over a relative small area but that maintained the physicochemical integrity of different soil profiles. Importantly the use of intact cores permitted a simultaneous comparison of the performance of a range of genotypes under a uniform climate. The intact cores proved to be a relatively cost effective experimental strategy for studying the interaction between germplasm and soil conditions (especially when drought conditions resulted in widespread failure of field trials). It is acknowledged however that field trials under commercial conditions are the ultimate level of validation.


This experimentation was funded by the Department of Primary Industries (Victoria) and the Grains Research and Development Corporation (Project DAV00049).We wish to thank the Smith and Barber families (Birchip) for access to their properties to collect the intact cores.


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