Molecular and Morpho-Agronomical Characterization of Root Architecture at Seedling and Reproductive Stages for Drought Tolerance in Wheat

<div><p>Water availability is a major limiting factor for wheat (<i>Triticum aestivum</i> L.) production in rain-fed agricultural systems worldwide. Root architecture is important for water and nutrition acquisition for all crops, including wheat. A set of 158 diverse wheat genotypes of Australian (72) and Indian (86) origin were studied for morpho-agronomical traits in field under irrigated and drought stress conditions during 2010–11 and 2011-12.Out of these 31 Indian wheat genotypes comprising 28 hexaploid (<i>Triticum aestivum</i> L.) and 3 tetraploid (<i>T</i>. <i>durum</i>) were characterized for root traits at reproductive stage in polyvinyl chloride (PVC) pipes. Roots of drought tolerant genotypes grew upto137cm (C306) as compared to sensitive one of 63cm with a mean value of 94.8cm. Root architecture traits of four drought tolerant (C306, HW2004, HD2888 and NI5439) and drought sensitive (HD2877, HD2012, HD2851 and MACS2496) genotypes were also observed at 6 and 9 days old seedling stage. The genotypes did not show any significant variation for root traits except for longer coleoptiles and shoot and higher absorptive surface area in drought tolerant genotypes. The visible evaluation of root images using WinRhizo Tron root scanner of drought tolerant genotype HW2004 indicated compact root system with longer depth while drought sensitive genotype HD2877 exhibited higher horizontal root spread and less depth at reproductive stage. Thirty SSR markers were used to study genetic variation which ranged from 0.12 to 0.77 with an average value of 0.57. The genotypes were categorized into three subgroups as highly tolerant, sensitive, moderately sensitive and tolerant as intermediate group based on UPGMA cluster, STRUCTURE and principal coordinate analyses. The genotypic clustering was positively correlated to grouping based on root and morpho-agronomical traits. The genetic variability identified in current study demonstrated these traits can be used to improve drought tolerance and association mapping.</p></div

Correlation between genetic similarity index and average taxonomic distance for root length per plant.

<p>The genotype pair and average taxonomic distance are represented by symbol (0).</p

Digital images taken from field under drought stress conditions at vegetative and reproductive stages.

<p>Differences in the root distribution and root length production Drought tolerant wheat genotype HW2004 and drought sensitive genotype HD2877 at vegetative (A) and reproductive stage (B).</p

Root traits of 31 wheat genotypes studied under drought stress condition at reproductive stage.

<p>Wheat genotypes at seedling (A)and Maturity (B) stage grown in PVC pipes to examine root growth and development; (C) Representative picture showing variation in maximum root length of ten wheat genotypes grown in PVC pipes under drought stress conditions.</p

Genetic diversity in 7 homoeologous groups of the 31 wheat genotypes as revealed by 30 SSR markers.

<p>Genetic diversity in 7 homoeologous groups of the 31 wheat genotypes as revealed by 30 SSR markers.</p

Root traits studied at seedling stage.

<p>(A) Root distribution pattern analyzed in drought tolerant and susceptible genotypes grown under well-watered conditions in petri dishes at the interval of 6 and 9 days. (B) Relationships between root traits measured at 6 and 9 days old seedling estimated from two Clusters (I and IV) of wheat genotypes a. Total root length, Longest root, Coleoptile length and Shoot length. Total Projected area, Total Surface area and Total root volume. The solid lines indicate the best fit regression line and 95% confidence length intervals, respectively.</p

Weekly average of weather conditions during the wheat growth period in 2010–11 and 2011–12.

<p>Rainfall for the given period is represented by vertical bars.* indicates average of 8 days in the period from 28^th February to 6^th March in the year 2011–12.</p

Correlation between genetic similarity index and average taxonomic distance for root length per plant.

<p>The genotype pair and average taxonomic distance are represented by symbol (0).</p

Categorization of 31 wheat genotypes revealed by 30 SSR markers.

<p>(A) UPGMA tree constructed using Jaccard’s similarity coefficient; (B) Three subgroups formed from STRUCTURE analysis, Model based population structure plot for each variety with K = 3. Color codes are as follows: Population I red, Population II green, population III blue; (C) Principal coordinates analysis The genotypes are grouped as DT = drought tolerant genotypes, Intermediate Responsive = moderate tolerant and sensitive genotypes and DS = drought sensitive genotypes.</p

Genetic diversity at the genome level of the 31 wheat genotypes revealed by 30 SSR markers.

<p>Genetic diversity at the genome level of the 31 wheat genotypes revealed by 30 SSR markers.</p