Impact of moisture management regimes on root characteristics in maize inbred lines at seedling stage

Drought stress affects maize growth badly and ultimately the stability in yield. The present study wasused to understand the variability in maize linesby evaluating the performance of seedling root traits viz., germination %, number of seminal and crown roots, primary root length, fresh and dry root weight under three moisture management regimes. Wide range of variability existed in the population as indicated by analysis of variance, components of variability implying considerable scope for improvement through phenotypic selection. High broad sense heritability associated with high genetic advance revealed that the traits were genetically determined with an ample scope for the improvement of these traits by breeding and selection process. Mean performance of few inbred lines showed superiority in root traits over population mean and they were considered elite lines with inbuilt drought tolerance viz., CM-129, KDM-361A, KDM-372, KDM-1051, KDM-331, KDM-402, KDM-717, KDM-463, KDM-912A, KDM-343A, KDM-932A, KDM-961, KDM-1156,KDM-918A and KDM-1236.These elite lines exhibited maximum % increase for all the traits in stress regime as compared to well watered regime. As maize is cultivated asrainfedcrop and there is lack of hybrids showing resilience to moisture stress. So these elite lines would be exploited as parents in future breeding programmes for developing single cross hybrids with drought resilience to boost maize production and yield stability. Keywords: irrigation, seedling, drought, dry weight, shoot, root Introduction Maize is third among the major cereal crops used for human consumption in developing countries, while in the developed world it is mainly employed for animal feeding purpose and industrial use. Interms of agriculture crops, drought stress is a condition wherein the available soil moisture gets reduced to such a point at which the plant growth gets affected to a greater extent (Osmanzai et al., 1987) . In maize, drought stress lossesvary with different growth stages, affecting dry mass and grain production, inhibiting growth, initiations of reproductive meristem, leaf area and extension (Bilgin et al., 2008) . Selecting drought tolerant genotypes/ cultivars is difficult to achieve in fluctuating edapho-climatic conditions. The induction of turgor pressure below maximum potential pressure is water stress and its magnitude is determined by the duration and extend of water deprivation. (Osmond et al., 1987; Fitter and Hay, 1987) [14, . Moisture deficiency losses get resolved either by giving supplemental irrigation in rainfed areas to cope under stress conditions or by breeding drought tolerant cultivars/genotypes for achieving higher and stable yields under water stress conditions. Under water-deficit stress, improvements in grain yield are attributed towards selecting parental inbred lines with an enhanced performance along with their hybrid progenies (Moreno et al., 2005) . Also, drought resilient maize lines reflect their tolerance at the early crop establishment phase (Bilgin et al., 2008) . Significant number of studies on evaluation for drought tolerance at the seedling stage have revealed variation among superior cultivars (Liu et al., 2004; Saif-ul-malook et al., 2014) [10, . The root architecture of every crop is crucial for its water and nutrient uptake as well as plant stand establishment. In three-week old plant seedling roots are made up of root hairs, seminal, primary andlateral roots (Zhu et al., 2006) . From primary roots, lateral roots branch outwardsand contribute towards water and nutrient uptake, determiningthe root architecture of the plant and help increase the surface area of the root system (Lynch, 1995) . Substantial amount of variations both in genotype and phenotypeof root architecture has been reported hence, providing opportunities for selecting superior lines despite quantitative mode of inheritance and difficult measurement strategies for root traits. Studying adult root trait system using shovelomics is time consuming and laborious and destroys root system as roots need to be dug out of the ground hence, limiting the number of evaluations in one season (Trachsel et al., 2010) whereas seedling phenotyping is less laborious, gets completed in less ~ 1418 ~ Journal of Pharmacognosy and Phytochemistry time, and experiments are carried out more than once during the same year enabling quicker and effective results as compared to shovelomics (Pace
 et al., 2014). Therefore, the present study was an attempt in such direction, carried over two years on a homozygous group of hundred maize inbred lines maintained at different stages of selfing in response to different irrigation regimes. This evaluation was carried out to determine the survival of seedlings under drought stress, to differentiate between lines and to identify lines with inbuilt mechanism for drought tolerance which would be reflected by early crop establishment stages and statistical procedures. Material & Methods A set of diverse hundred homozygous maize inbred lines were evaluated at seedling stage under three moisture management regimes. In first treatment, plantswere irrigated at regular intervals of three weeks, second one irrigated at an interval of two weeks; and the third oneirrigated only once. Irrigation at sowing was given uniformly to all the three treatments. Each inbred line was sown in pots (plate-1), replicated twice in factorial randomized block design. The pots composed of soil mixture of clay with sand in 3:7ratio. Observations was recorded on data generated on traits viz., germination %, the number of seminal and crown roots, primary root length (cm), fresh and dry root weight (g). Observations were recorded after 50% of the mortality was seen within the replications. Twenty-four days after sowing, seedlings from each of the pots were uprooted carefully to record the observations, washed free of sand and clay, and divided at the cotyledonary node to their respective root and shoot portions. The collected data was subjected to analysis of variance, components of variability and heritability for all the traits in each of the moisture management treatments for testing variation among the lines as per the procedure suggested by Verma et al. (1987) [13] through windostat version 9.1. statistical package. Results Individual effects of different moisture management regimes (stress, intermediate stress and well watered regimes) over years revealed highly significant mean sum of squares due to lines over different moisture management regimes for all the traits under study indicating importance of water for these traits at critical stages of plant development (Table-1,2). Year effects also exhibited highly significant mean sum of squares revealing differential response of individual effects of moisture management regimes over years. Line  year interaction exhibited significant mean sum of squares for all the traits. Irrigation within year within replication exhibited significant mean sum of squares for all the traits. Perusal of Table-3 revealed that among seedling traits highest GCV was recorded for fresh root weight (48.52) followed by dry root weight (47.95), primary root length (42.11), number of seminal roots (37.44), number of crown roots (35.98) and germination per cent (17.57). Highest genetic gain under stress conditions was recorded for fresh root weight (97.30) followed by dry root weight (97.30), primary root length (86.44), number of seminal roots (70.22), number of crown roots (63.82) and germination per cent (35.02). Water played an important role in plant development at seedling stage for seedling traits recorded under laboratory conditions (Table-4). On an average application of water improved seedling root traits viz; germination per cent (11.85%), number of seminal roots (69.00%), number of crown roots (43.93%), fresh root weight (43.54%) and dry root weight (42.43%) with decreased primary root length by 0.74%. Well watered situation recorded highest per cent increase for number of seminal roots (83.63%) followed by number of crown roots (58.70%), fresh root weight (49%), dry root weight (47.82%) associated with negative effect on primary root length (0.43%). Table 1: Analysis of variance for germination (%) and primary root length (cm) over irrigations (pooled over years) in inbred lines of maize (Zea mays L.) Mean Sum of Squares Germination % Primary root length Number of seminal roots SV d.f S IS WW S IS WW S IS WW Rep 1 33.77* 0.09 2.28 20.57** 20.52** 20.06** 0.07 0.03 0.01 Years 1 200.20** 323.02** 96.88** 13.53** 11.37** 10.42** 62.01** 121.55** 92.64** Lines 99 483.44** 340.00** 185.95** 65.89** 49.20** 38.36** 2.06** 1.81** 2.14** Line x Year 99 13.46** 13.72** 11.55** 0.28** 0.16** 0.15** 0.22** 0.19** 0.07** Repx year 1 3.09 17.56 0.01 0.02 0.01 0.01 0.01 0.01 0.01 IWYWR 3 79.02** 113.56** 33.05** 11.37** 10.63** 10.16** 20.69** 40.52** 30.88** Error (POY) 297 8.2 7.62 7.85 0.11 0.06 0.06 0.1 0.08 0.04 IWYWR=Irrigation within years with replication, POY=pooled over years, S= Stress; IS= Intermediate stress; WW= Well watered *,** Significant at 5 and 1% level, respectively, Table 2: Analysis of variance for fresh root weight (g) and dry root weight (g) over irrigations (pooled over years) in inbred lines of maize (Zea mays L.) Mean Sum of Squares Number of crown roots Fresh root weight (g) Dry root weight (g) SV d.f S IS WW S IS WW S IS WW Repl 1 0.14 0.01 0.02 4.16** 5.59** 4.90** 3.07** 3.55** 3.46** Years 1 43.23** 91.20** 84.64** 26.13** 2.99** 4.50** 4.71** 0.48** 0.70** Lines 99 1.54** 1.51** 1.57** 19.33** 24.17** 24.69** 3.18** 3.88** 3.98** Line x Year 99 0.28** 0.19** 0.19** 0.44** 0.15** 0.08** 0.06** 0.02** 0.01** Repl x year 1 0.01 0.06 0.01 0.01 0.07 0.01 0 0.02 0.01 IWYWR 3 14.46** 30.42** 28.22** 10.10** 2.89** 3.13** 2.59** 1.35** 1.39** Error (POY) 297 0.12 0.08 0.09 0.16 0.1 0.03 0.02 0.01 0.01