Seed size and Fe fertilization effects on seedling growth of wheat genotypes grown in Fe deficient calcareous soil

Greenhouse experiment was carried out to investigate the effect of seed size and Fe fertilization on the early growth of wheat genotypes grown in Fe deficient clay soil which characterized by high pH and high level of calcium carbonate. Seedling of 15 wheat genotypes were grown under factorial combinations of four levels of Fe treatment and two seed size groups to evaluate the effects of seed size and Fe application on the early growth and Fe efficiency of wheat genotypes. Leaf area, chlorophyll, plant height and the shoot and root dry matter production were decreased in seedling grown from small seed size which had the low seed quality (lower seed Fe content). High Fe seed resulted better root and shoot dry matter production and root depth than high soil applied Fe. The results also demonstrated that seed Fe content can improve vegetative growth of wheat genotypes grow in Fe – deficient soil more effectively than application of Fe fertilizer to soil. A considerable variation within wheat genotypes for the ability of plant to grow and yield well when the availability of Fe is low was found.. This significant genetic variation in Fe efficiency indicated that selection for improved micronutrient efficiency is possible and will allow more efficient genotype of wheat to be developed.


Introduction
Micronutrient deficiencies such as iron (Fe) is critical issues in the developing countries (Iraq is one of them), and result in severe impairments of human health and developments (1,2).In plants Fe deficiency often occurs in calcareous soil where chemical availability of Fe to plant root are extremely low.
Correction of Fe deficiency are not always easy through the use of Fe fertilizers because of their extremely poor solubility Therefore, remediation of Fe deficiency in calcareous soils by fertilizers only is a costly and time consuming management.Cereal species and varieties differ greatly in their response to Fe deficiency (3,4,5,6,7).Differences in tolerance to micro-nutrients deficiency correlated well with the amounts of phytosiderophores released from roots under Fe deficiency (3) into the rhizosphere to mobilize the micronutrient and by activating a high affinity uptake system which selectively transport the micronutrientphytosiderophores complex through the plasma membrane (4,5).Therefore we think that screening for iron-efficient varieties for micronutrients deficient soil with a combination of mineral fertilizers is an important practical approach for the correction or avoidance of Fe deficiency in cereals.In addition to that using larger seed size with higher Fe content is very important for early seedling growth and might be overcome problems temporary of insufficient micronutrient content of alkaline calcareous soil.A more vigorous crop is established by seeds with a high density of nutrient, including micronutrients (8,9) leading to higher yield.
To our knowledge, until now little data are available about seed size and seed micronutrient content roles on seedling growth of wheat plant under Fe deficient condition.In addition to that there is no study in Iraq concerning the evaluation and screening wheat varieties for Fe-efficient and in efficient (the term efficiency is used to characterize the ability of a variety to grow without or with less visual Fe deficiency symptoms and yield well under Fe deficient condition).Therefore, the objectives of this research were: 1.To study the physicochemical characteristics and micronutrients status of soil before planting .2. To investigate the effect of seed size on the early growth of wheat genotypes grown on the calcareous-alkaline soil of north part of Iraq. 3. To study the effect of Fe fertilization on growth of wheat under greenhouse conditions.

Soil collection and analysis
Soil was collected from the surface 15 cm. of the field experiment station soil at the College of Agriculture of Dohok University, Northern Iraq.The soil was airdried, passed through a 4-mm sieve and was analyzed for pH, CaCO 3 , Organic matter, and soil texture using standard procedures (10).Plant available concentration of Fe in soil was determined also according to the method stated by (11), by extraction with DTPA (diethylene triamine penta acetic acid) using a soil: solution ratio of 1:2 and shaking time of two hours.Micronutrient extracted was determined by atomic absorption spectrophotometer.Seed of each of 15 wheat genotypes which brought from Syria -ICARDA was sieved and separated to two seed size groups [ retained on 4.0 mm mesh ( group I), passed through a 4.0 mm mesh and retained on 2.8 mm mesh ( group II)].

Sowing and Watering
PVC pots (length=10.5cm, width= 12 cm ) were filled with 500g air -dry soil and fertilized with 0,0, 0.2, 0.4, 0,8 mg Fe /Kg air-dried soil applied as FeSO 4 7H 2 O. Eight seeds from each group size were sown in each pot and distilled water was added in amounts sufficient to bring soil water content to 75% of soil field capacity.Soil moisture content were kept at 75% of field capacity during the period of the experiment .Time of watering plants was determined by weighing the pots daily and adding water to obtain the original wet weight (75% of field capacity).After germination plants were thinned to 4 plants per pot, and after 45 days from sowing plants were harvested.

Plant harvest
At harvest time the soil was washed off root under running tap water.Both roots and shoots were separated gently and immediately weighted to obtain fresh weights of roots and shoots of plants in each pot.Plant samples were placed in paper bags and dried at 70 • C for 48 hours.The dry weights of both roots and shoots were then obtained.

Stastical analysis
A factorial experiment with three factors (15 genotypes X4 Fe fertilization rates X 2 seed sizes) and 3 replicates were used.The data were analyzed by analysis of variance and significance of differences between means was evaluated by the adjusted least significant difference test (Adj.LSD) .

Physicochemical characteristic of soil
Various physical and chemical characteristic of soil are presented in table 1. Soil had high pH (8.06) and was calcareous, which contain more than 20% CaCO 3 .The organic matter content was 1.60%.Soil had a clay texture, where the clay fraction was higher than the sum of both sand and clay fractions.In soil sample concentration of DTPA-extractable Fe was 2.80 mg kg -1 which was less than the adequate amount of Fe in calcareous soils (4 mg kg -1 ) as stated by (12), and it was marginal with the critical level for calcareous soils (2.5 mg kg -1 ) obtained by (13).
The high pH and the high concentrations of CaCO 3 and clay in soil together with low annual precipitation can be considered to be the major factors causing Fe deficiency in plant grown in the north part of Iraq.Fe moves to plant root in soils is limited largely by diffusion in the soil solution (14,15,16), and thus absorption is highly dependent on soil water status and root growth (17).Iron nutrition of plants is often threatened in arid soils having low plant available concentration of Fe.Diffusion of micronutrients in soil is also greatly affected by soil pH.In calcareous soils, diffusion coefficient for micronutrients is lower than in acid soils (18).At neutral to basic soil pH, inorganic Fe levels available for transport to the plant roots by both mass flow and diffusion are below plant requirements (14).Fe 2+ decreases in solubility 100-fold for every unit increase in pH (19).

Seed size and wheat early growth Leaf area and chlorophyll concentration
The first characteristic reaction of plants to micronutrients deficiency is leaf area (20).The chlorophyll content is often regarded as the best measure of iron availability inside the plants.Some additional information about the extent to which the energy absorbed by photosynthetic pigment is utilized, and more precisely, about the functioning of photosynthetic pigment II, might be obtained from chlorophyll measurements.The difference in wheat genotypes comes from the difference in chlorophyll concentration (21).
After six weeks of growth with chlorophyll concentration of the fresh leaf area there was no significant effect of seed Fe content (Table 3), while after eight weeks of growth leaf area of fresh leaf tissue (third leaf blade) was significantly influenced by seed Fe content (Table 2).High -Fe seed improved the leaf area and chlorophyll concentration compared to those from low Fe seed (Tables 2, 3).The present results of importance of seed Fe content in wheat are in line with the results obtained by other researchers in wheat and other crops and with other micronutrients.Working on wheat a significant effect of seed Zn content on early seedling growth parameters was demonstrated (22).They concluded also that higher seed Zn content acted similar to a starter-fertilizer effect by improving vegetable growth.Sowing high -Zn seed significantly improved the leaf area and chlorophyll concentration of oil seed rape plants (23).
Leaf area and chlorophyll concentration of the fresh leaf were decreased in seedling grown from small seed size with low Fe content and the reduction were 8.63% and 2.05% respectively as compared to that of larger seed.These result showed that not only seed size but seed quality (higher quality expressed as a higher seed Fe content ) results in improved growth parameters (9).

Shoot and root dry matter and other seedling growth parameters:
The results (Tables 4-7) demonstrated that the larger seed size (high Fe content) improved an early growth parameter of wheat seedlings and gave higher shoot dry matter accumulation(Table 4) and root depth (Table 5) as compared to that of the smaller seed size.These results are consistent with the finding of ( 9) and ( 24) were a more vigorous crop is estimated by seeds with a high density of nutrients, including micronutrients, and also with results of(25) who stated that seed size is an important determinant of seedling vigour and early growth of cereals.
Plant height (Table 6), shoot dry matter production and root dry matter production (Table 7) were decreased significantly from seedling grown from small seed size (low micronutrient content) and the reduction percentages were 4.29%, 12.75% and 6.88% respectively.No significant reduction in root depth was found when comparing the results of small and larger seed size.The reduction in plant height, shoot dry weight and root dry weight were attributed to in sufficient of Fe supply which in turn decrease the plant metabolism and functions (16,17).Similar results were found with barley plants growing from seeds with low Fe and Zn content on Fe and Zn -deficient calcareous soil which had poor seedling growth parameters ( 26) , and they concluded that large seeds have a strong impact on early vegetative growth.

Iron and seedling growth parameters
Seedling growth parameters (root dry matter, shoot dry matter, root depth, plant height, leaf area and chlorophyll concentration) were influenced by seed size (seed Fe content) and soil Fe fertilization rate.Soil Fe application had no significant effect on all the above seedling growth parameter except on leaf area of the fresh tissue (Table 2).Similar results were found by (27) who stated that all growth and yield parameters of wheat obtained by applying different doses of Fe were statistically non significant or at par with each other.High Fe seed resulted in better root dry matter production, shoot dry matter production and root depth than high soil applied Fe, and had non significant effect on leaf area, chlorophyll concentration and plant height as compared with the heighest rate of Fe fertilization (Tables 2, 3 and 6 ).Where seed Fe was low, a high level of soil applied Fe fertilizer did not cause any significant changes in all the above seedling parameters (Tables 2-15), and still the results of the high-Fe seed with out soil applied Fe fertilizer better than it.Similar results were found with wheat plants growing from high and low Mn seed content with Mn fertilization (24).These results have demonstrated that seed Fe content can improve vegetative growth of wheat genotypes grown in Fe -deficient soil more effectively than application of Fe fertilizers to soil.Iron content (dry weight basis) in wheat grain were 28.8 -56.5 mg Kg -1 (mean=37.2mg Kg -1 ) as stated by (28).Decreases in dry matter production and plant development in low -Fe seed and low-Mn soil are attributed to insufficient Fe supply which in turn decreased photosynthesis and plant metabolism (16).

Genotypes and seedling growth parameters
Wheat genotype Doma/1 generally gave higher seedling growth and performed better than other varieties, followed by Karoniah genotype, Tilaafar/3 genotype and Haama/14 genotype (Tables 4-7).Genotypes Doma/1 and Karoniah had better responses to soil Fe fertilizer by producing more root dry matter, shoot dry matter, leaf area, chlorophyll concentration and plant height than other varieties.Similarly wheat varieties grown under Mn deficient conditions or Zn deficient conditions had different responses to Mn soil application (24) and to Zn soil application (29).