Study of root length system of Afghan wheat landraces in response to drought condition

 

Aziz Ahmad Osmani2, Sayed Hasibullah Ahmadi1,2, Emdadul Haque1, Alagu Manickavelu1, Hiroyuiki Tsuji1 and Tomohiro Ban1

 

1: Kihara Institute for Biological Research, Yokohama City University, Japan

2: Ministry of Agriculture, Forestry, Irrigation and Livestock, Afghanistan

 

Corresponding author: Emdadul Haque

E-mail: haque@yokohama-cu.ac.jp

 

 

Abstract

To enhance the selection of high yielding genotypes to make better use of ground water for rain-fed cultivation in any breeding program, a greater understanding of root length system is necessary. We developed an efficient managed drought condition by controlling ground water to simulate rain-fed regions of Afghanistan. We used soil filled 2 m PVC pipes where moisture were controlled until 1m by keeping 30 cm water at the bottom. The top 20 cm of pipe was maintained as irrigated field condition by placing 2% water holding gel on top. Thus, approximately 80 cm of middle layer of the pipes were created as dry zone. This screening system was used to understand the root system in Afghan wheat landraces (AWLR) collected by Dr. Kihara et al. through Kyoto University Scientific Expedition (KUSE) to the Karakoram and Hindukush in 1955. 360 AWLR were grown on 2 m PVC pipes and root length systems were measured after flowering. AWLR showed wide range of genetic diversity in terms of root growing capacity pass the dry zone and catch moisture from the deep-stored water. 29% of AWLR showed long root type (~180 cm), 55% as medium (100-150 cm) and 16% as short root type (~100 cm). Root length density along the primary root system revealed that each of the category has greater and distinct root density compared to modern wheat; some are highly dense at the top, some at mid and some at bottom, implying their potential roles for drought tolerance.

Keywords: Drought, Root length, Root density, Wheat landraces

 

Introduction

Water limitation reduce crop yield in rain-fed cultivation worldwide (Manschadi et al. 2006) where maximizing soil moisture capture for transpiration is the main target yield improvement under drought stress. Under soil water deficit, crop water extraction depends on root distribution and depth (Dardanelli et al. 2004). Deeper roots can extract more water from depth thus avoiding water deficits at critical growth stages resulting in higher harvest indices and reduced water loss by deep drainage (Ludlow and Muchow 1990).

 

Afghanistan is an agricultural country where more than 75% of the people are engaged in agriculture sector. The main food and crop for Afghan people is wheat which is basically cultivating in rain-fed and irrigated lands but most cultivation area for this crop is rain-fed area which accounts for 60% of total production (Afghanistan Statistical Yearbook 2010-11). The country is located in the dry part of the world with an annual precipitation between 300-400 mm, even this amount is some year decreasing in the rain-fed area (FAO 1972; Beekma and Fiddes 2011). Thus, the production of the wheat in the rain-fed regions depends mostly to the deep-stored water and occasional rains in the summer. Deep-stored water is more predictable than variable in-season rainfall and this moisture is converted into grain with twice the efficiently of in-season rainfall since it is taken up later in crop growth during the grain-filling period when the roots already reach deeper layers (Wasson et al. 2012). Therefore, long root wheat cultivars will be good for this type of area. On the other hand, for the irrigated land, shallow root system would be beneficial. Thus, it is very necessary to isolate such types of root system from the primary wheat gene pool of a country. Landrace is a local variety with a high capacity to tolerate biotic and abiotic stress, resulting in high yield stability and an intermediate yield level under a low input agricultural system in the marginal area. Afghan wheat landraces (AWLR) were hypothesized to be such kind of root systems fittest to rain-fed regions. SATREPS-Afghan project has been working in AWLR collected by Dr. Kihara et al. in KUSE 1955 (Yamashita et al. 1965) to improve the wheat system in various aspects (Manickavelu et al. 2013).

 

As part of the project, the study was conducted to understand AWLR root systems for soil dryness and classify them into long, medium and short. We have established a simulated wheat cultivation condition for rain-fed region of Afghanistan using 2 m soil-filled PVC pipes by controlling soil moisture until 1 m and maintaining top 20 cm of the pipes as field condition. When grown under this condition, it was hypothesized that those genotypes that have long root system will pass the dried zone to catch the wet layer at 1 m of the pipes.

 

Materials and Methods

Approximately 360 AWLR collected by Dr. Hitoshi Kihara from 17 different provinces of Afghanistan in KUSE 1955 (Yamashita et al. 1965) and 15 modern checks that released in Afghanistan by CIMMYT were screened under this study. Seeds were sown in the plastic trays and then three healthy seedlings were transferred at 3-cm depth in each of soil-filled PVC pipes (Soils: Kobayashi Sangyo Co. LTD., Japan). The PVC pipes were placed in the big plastic pools having 35 cm water for understanding the movement of the moisture in the pipes. The top 5 cm layer of each pipes were modified with 2% water-holding gel (San Tech, Kochi, Japan) so that it can keep the surface moisture for longer period (Fig. 1). The upper 20 cm soil of the pipes was saturated as field conditions with measured volume of irrigation (100 mL) until two months after transplanting. Then the irrigation was stopped upto heading stages and by the completion of flowering, water was drained out from bottom. Sensors were fixed in each 40 cm inside the pipe and recorded soil moisture throughout the experiment.

 

The diversity in root growing capacity towards dry zone inside 2 m pipe were investigated and based on root growth characteristics, the landraces were grouped into three major categories of root systems: long, medium and short. Root length density in each of the 20 cm depth along the primary root systems were calculated and normalized to construct the graph.

 

Results and Discussion

In Afghanistan, the distribution of rainfall (300-400 mm annual) in rain-fed area is greatly different, especially in March and April (FAO 1972) which is the time of heading and grain filling stage. Also due to the particular soil type and structure (mostly sandy and calcareous), the underground water during the mid-spring and beginning of summer time reduce too much and moisture table goes down. The first goal of this research is to establish of methodology to simulate the above condition which is very important for drought study. Here the scientific methodology was established and confirmed the system with our AWLR. The merit of this method is simulating quite similar system of natural water movement in the soil gradient where the drought is mostly happening in Afghanistan. Our data showed that the water level was kept stopping movement at 1 m depth position inside the PVC pipes from the bottom until April when the flowering is completed (Fig. 1, Fig. 2 left) and after draining out the water from the pool, the moisture level was downing in the soil in each of the 20 cm soil depth (Fig. 2 right). Therefore, the condition will be able to differentiate genotype that has long root from the genotypes with mid and short root systems. So far there is very few large-scale screening methodology like us where we can easily screen the root traits under the drought conditions at the later stages of drought.

 

The screening of AWLR under this system resulted into grouping of landraces with different root length system categories. While modern wheat showed around 50 cm root length, surprisingly some landraces had around 3 m length of root which might showing the potential of AWLR as well as the system that established in this study can able to find such ideotypes. Overall, the AWLR were shown wide range of genetic diversity in terms of growing capacity to pass the dry zone and catch the deep-stored water. It is varied ranging 30-230 cm (Fig. 3). Based on the data, AWLR were categorized 29% as long root system, 55% as medium root type and 16% as short root type (Fig. 3). This variation can make very good source for breeding programs. Beside the root length, AWLR has shown great variations in root length density in the upper, medium and deeper soil layers compared to modern cultivars; for example some landraces has greater top density, some has middle and some of them shown bottom density along the primary root systems (Fig. 4, Fig. 5, Fig. 6). Reynold et al. (2007) postulated that landraces generally show better water uptake characteristics than the modern check at soil depths below 60 cm, but not between 30-60 cm. The yield advantage was found due to greater partitioning of root mass at deepest layer and increased ability to extract water, not an overall increase in dry root mass (Reynold et al. 2007). Currently authors are studying the drought tolerance potential of this traits at various soil depths under optimum moisture (control) and dry soil condition (used in this study) both in PVC pipes as well as in real field condition in Afghanistan.

 

References

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