Development of Molecular Markers Linked To QTL/Genes Controlling ZN Efficiency

Zinc (Zn) deficiency is a widespread problem in reducing the yield and quality of crop plants worldwide. It is important to utilize molecular markers linked to Zn efficiency to develop high Zn efficient cultivars in pepper (Capsicum annuum L.). We constructed a genetic map using an F2 populations derived from C. annuum L. (Alata 21A) X C. frutescens L. (PI 281420) cross. The QTLs for Zn efficiency were mapped using F2:3 population. A genetic map with 929,6 cM in length and 12 linkage groups were obtained using 62 markers (31 SRAP, 19 SSR and 11 RAPD). The 41 linked QTLs related with nine (9) Zn efficiency characters were mapped on linkage groups. Results suggest that selecting plants for tolerance to Zn deficiency are expected to be rather responsive among segregating populations for breeding and developing Zn efficient genotypes in pepper. The molecular markers are expected to aid selection and expedite breeding peppers resistant to Zn deficiency in soils low for available Zn contents.

Zinc (Zn): The Last Nutrient in the Alphabet and Shedding Light on Zn Efficiency for the Future of Crop Production under Suboptimal Zn

At a global scale, about three billion people have inadequate zinc (Zn) and iron (Fe) nutrition and 500,000 children lose their lives due to this. In recent years, the interest in adopting healthy diets drew increased attention to mineral nutrients, including Zn. Zn is an essential micronutrient for plant growth and development that is involved in several processes, like acting as a cofactor for hundreds of enzymes, chlorophyll biosynthesis, gene expression, signal transduction, and plant defense systems. Many agricultural soils are unable to supply the Zn needs of crop plants, making Zn deficiency a widespread nutritional disorder, particularly in calcareous (pH > 7) soils worldwide. Plant Zn efficiency involves Zn uptake, transport, and utilization; plants with high Zn efficiency display high yield and significant growth under low Zn supply and offer a promising and sustainable solution for the production of many crops, such as rice, beans, wheat, soybeans, and maize. The goal of this review is to report the current knowledge on key Zn efficiency traits including root system uptake, Zn transporters, and shoot Zn utilization. These mechanisms will be valuable for increasing the Zn efficiency of crops and food Zn contents to meet global needs for food production and nutrition in the 21st century. Furthermore, future research will address the target genes underlying Zn efficiency and the optimization of Zn efficiency phenotyping for the development of Zn-efficient crop varieties for more sustainable crop production under suboptimal Zn regimes, as well food security of the future.

Response of rice genotypes under different zinc fertilization strategy

Soil zinc (Zn) deficiency limits crop growth and yield besides its low concentration in grain and straw. Growing of Zn efficient cultivars with high crop yield at low Zn supply would represent a sustainable approach to crop production. Therefore, to evaluate Zn efficiency of rice genotypes, twenty eight different rice genotypes were evaluated under various treatments like three levels of Zn viz. low (without Zn), medium (10 kg Zn ha-1 soil) and high (20 kg Zn ha-1 soil + three foliar sprays of 0.5% Zn). Zinc efficiency index of all genotypes ranged from 65.5 to 102.6 % and Zn uptake efficiency ranged from 53.8 to 107 % with a mean value of 87.1 and 76.5 %. Cultivar GR-101 was having the highest Zn efficiency index as well as Zn efficiency compared to other genotype. Based on grain yield and Zn efficiency, the genotypes Ashoka-20, Narmad, GR-12, GR-3, GR-1 and GR-2 were classified as efficient and responsive, genotypes GR- 11, SLR -51214. GAUR-10 and GR-13 as efficient and non responsive, whereas, genotypes GR-101, GR-104, GR-102 and Lalkad as inefficient and responsive. The Gurjari, AAUDR-1, K-Kamod, GR-9, GR-5, P-2003 SK-20 and GR-7 genotype were classified as inefficient and non responsive. The efficient and responsive genotypes are most desirable as they would produce higher yield under low Zn concentration in soil and responded well under external application of Zn sources.

Study of genetic diversity in different wheat species with various genomes based on morphological characteristics and zinc use efficiency under two zinc-deficient growing conditions

Screening of cash crops to tolerate and grow under low levels of micronutrients is important issue in the plant breeding programs. Thus, the study screened the tolerance of 50 wheat genotypes to zinc (Zn) deficiency in the calcareous soil. The Zn treatment was carried out with application of 5 mg kg^-1 (+Zn) and without (-Zn) to the collected soils with initial Zn extractable of 0.5 mg Zn kg^-1 soil. The results revealed that the supplementary application significantly increased shoot dry matter, shoot Zn concentration and shoot Zn content compared to the without Zn application (control), but Zn utilization decreased under Zn application. There was considerable genetic variation in Zn efficiency (55 - 118 %), shoot Zn concentration (11.8 - 27.0 and 14.3 - 39.6 mg kg^-1 DM under deficient and sufficient Zn, respectively), shoot Zn content (0.56 - 2.02 and 0.90 - 2.83 µg plant^-1, under deficient and sufficient Zn, respectively) and Zn utilization efficiency (39 - 87.2 and 31.2 - 71.5 mg DM µg^-1 Zn under deficient and sufficient Zn, respectively) within wheat genotypes. Cluster analysis based on Zn efficiency, and shoot dry matter at deficient and adequate Zn conditions classified the genotypes into four clusters. Over the two conditions, the most Zn-efficient and Zn-unefficient genotypes were ‘Ankara-98’ and ‘Altintoprak-98’ and ‘Pg"S’ and ‘Zarin’, respectively. Most durum genotypes had a greater Zn efficiency than modern bread wheat genotypes, therefore these genotypes could be effectively used to breed the new cultivars with high Zn efficiency for calcareous soils.

A soil-based method to screen for zinc efficiency in seedlings and its ability to predict yield responses to zinc deficiency in mature plants

Nutrient efficiency measures the ability of a plant to grow and produce grain when the availability of a nutrient is low. Seedling tests for nutrient efficiency will be most useful if the results correlate well with grain yield responses. In two experiments, a diverse range of barley genotypes was screened for zinc (Zn) efficiency at the seedling stage and the relationship between vegetative and grain measures of Zn efficiency was examined. In Expt 1, 54 barley and 4 wheat genotypes were grown at 2 levels of Zn (0.02 and 0.8 mg/kg soil) for 21 days. Zinc efficiency ranged from 18% to 52%. The visual symptoms of Zn deficiency varied considerably between genotypes and was significantly correlated with Zn efficiency. Root:shoot ratio was increased by Zn deficiency and varied between genotypes, but these differences were not related to Zn efficiency. Zinc concentration and especially Zn content at 0.02 mg Zn/kg were significantly related to Zn efficiency. In Expt 2, 15 genotypes, selected on the basis of their response in Expt 1, were grown to maturity at either 0.1 mg Zn/kg or 2.4 mg Zn/kg. Zn efficiency, based on relative grain yield, ranged from 5% to 54%. High efficiency was associated with a large number of grains per plant and high kernel weight. Rankings of Zn efficiency in the experiment were significantly correlated with the rankings for visual scores in Expt 1. The 2 experiments suggested that deficiency symptoms at the seedling stage can identify efficient genotypes and could be useful for routine screening for Zn efficiency. Independent data from multisite comparisons over 8 years were used to examine the long-term performance of efficient and inefficient genotypes in the field. Hierarchical cluster was used to define efficient and inefficient groupings within the 56 genotypes examined in Expt 1, based on their responses to Zn. The Zn-efficient genotypes tended to yield more than the Zn-inefficient genotypes. The data provide prima facae evidence that high Zn efficiency may contribute to improved adaptation of barley in South Australia.