Unraveling the Mechanisms of Zinc Efficiency in Crop Plants: From Lab to Field Applications

Global food security and sustainability in the time of pandemics (COVID-19) and a growing world population are important challenges that will require optimized crop productivity under the anticipated effects of climate change [...]

Identification and Analysis of Zinc Efficiency-Associated Loci in Maize

Zinc (Zn) deficiency, a globally predominant micronutrient disorder in crops and humans, reduces crop yields and adversely impacts human health. Despite numerous studies on the physiological mechanisms underlying Zn deficiency tolerance, its genetic basis of molecular mechanism is still poorly understood. Thus, the Zn efficiency of 20 maize inbred lines was evaluated, and a quantitative trait locus (QTL) analysis was performed in the recombination inbred line population derived from the most Zn-efficient (Ye478) and Zn-inefficient inbred line (Wu312) to identify the candidate genes associated with Zn deficiency tolerance. On this basis, we analyzed the expression of ZmZIP1-ZmZIP8. Thirteen QTLs for the traits associated with Zn deficiency tolerance were detected, explaining 7.6–63.5% of the phenotypic variation. The genes responsible for Zn uptake and transport across membranes (ZmZIP3, ZmHMA3, ZmHMA4) were identified, which probably form a sophisticated network to regulate the uptake, translocation, and redistribution of Zn. Additionally, we identified the genes involved in the indole-3-acetic acid (IAA) biosynthesis (ZmIGPS) and auxin-dependent gene regulation (ZmIAA). Notably, a high upregulation of ZmZIP3 was found in the Zn-deficient root of Ye478, but not in that of Wu312. Additionally, ZmZIP4, ZmZIP5, and ZmZIP7 were up-regulated in the Zn-deficient roots of Ye478 and Wu312. Our findings provide a new insight into the genetic basis of Zn deficiency tolerance.

Maize Genotypes With Different Zinc Efficiency in Response to Low Zinc Stress and Heterogeneous Zinc Supply

All over the world, a common problem in the soil is the low content of available zinc (Zn), which is unevenly distributed and difficult to move. However, information on the foraging strategies of roots in response to heterogeneous Zn supply is still very limited. Few studies have analyzed the adaptability of maize inbred lines with different Zn efficiencies to different low Zn stress time lengths in maize. This study analyzed the effects of different time lengths of low Zn stress on various related traits in different inbred lines. In addition, morphological plasticity of roots and the response of Zn-related important gene iron-regulated transporter-like proteins (ZIPs) were studied via simulating the heterogeneity of Zn nutrition in the soil. In this report, when Zn deficiency stress duration was extended (from 14 to 21 days), under Zn-deficient supply (0.5 μM), Zn efficiency (ZE) based on shoot dry weight of Wu312 displayed no significant difference, and ZE for Ye478 was increased by 92.9%. Under longer-term Zn deficiency, shoot, and root dry weights of Ye478 were 6.5 and 2.1-fold higher than those of Wu312, respectively. Uneven Zn supply strongly inhibited the development of some root traits in the -Zn region. Difference in shoot dry weights between Wu312 and Ye478 was larger in T1 (1.97 times) than in T2 (1.53 times). Under heterogeneous condition of Zn supply, both the –Zn region and the +Zn region upregulated the expressions of ZmZIP3, ZmZIP4, ZmZIP5, ZmZIP7, and ZmZIP8 in the roots of two inbred lines. These results indicate that extended time length of low-Zn stress will enlarge the difference of multiple physiological traits, especially biomass, between Zn-sensitive and Zn-tolerant inbred lines. There were significant genotypic differences of root morphology in response to heterogeneous Zn supply. Compared with split-supply with +Zn/+Zn, the difference of above-ground biomass between Zn-sensitive and Zn-tolerant inbred lines under split-supply with –Zn/+Zn was higher. Under the condition of heterogeneous Zn supply, several ZmZIP genes may play important roles in tolerance to low Zn stress, which can provide a basis for further functional characterization.

Classification of Pigeonpea (Cajanus cajan (L.) Millsp.) Genotypes for Zinc Efficiency

Pigeonpea (Cajanus cajan (L.) Millsp.) is grown globally for its protein-rich seed. However, low availability of soil zinc (Zn) adversely affects the seed yield of pigeonpea. The present study was therefore conducted to assess the Zn efficiency of pigeonpea genotypes based on seed yield and seed Zn uptake efficiency. Field experiments were conducted at the Indian Council of Agricultural Research–Indian Institute of Soil Science, Bhopal, India with twenty different pigeonpea genotypes and two levels of Zn application under a split-plot design. The two levels of Zn were low (without application of Zn fertilizer) and high (with application of 20 kg Zn ha−1 (as ZnSO4∙7H2O) as basal soil application, in conjunction with three foliar sprays of 0.50% (w/v) ZnSO4∙7H2O aqueous solution) (with 0.25% lime as neutralizing agent) at flowering, pod formation, and pod filling stages). Application of Zn improved plant height, branches plant−1, pods plant−1, seeds pod−1, and 100 seed weight of pigeonpea genotypes differently. The mean seed yield, seed Zn concentration, and seed Zn uptake of the genotypes increased from 1.71 to 2.12 t ha−1, 32.4 to 43.0 mg kg−1, and 54.9 to 90.6 g ha−1, respectively, with application of Zn. The seed yield efficiency index (SYEI) and Zn uptake efficiency index (ZUEI) of pigeonpea genotypes varied from 67.0 to 92.5 and from 47.0 to 69.9, respectively. Based on SYEI and ZUEI, the genotypes were classified as efficient and responsive (Virsa Arhar-1, GT-1, GT-101, SKNP 05-05, BDN-2, AAUT 2007-04, BSMR 853, T 15-15, DT 23, Pusa 9), efficient and non-responsive (ICPL 87119, PKV Trombay), inefficient and responsive (AKT 8811, Hisar Paras), and inefficient and non-responsive (AAUT 2007-10, JKM 7, Hisar Manak, C 11, Hisar HO2-60, GAUT 93-17). The efficient and responsive genotypes are the most useful as they yield well under low soil Zn conditions and also respond to Zn fertilizer application. The inefficient and responsive genotypes could be utilized for plant breeding programs by plant breeders for identification and utilization of responsive traits.

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.