Grain zinc and yield responses of two rice varieties to zinc biofortification and water management

Zinc (Zn) biofortification can improve grain yield and nutritional quality in rice, but its effectiveness is subject to agronomic practices and other factors. In a previous study, the application of Zn to soil enhanced grain Zn in lowland rice in well-drained and waterlogged soil, whereas grain Zn in upland rice increased only in well-drained soil. This new study explores the hypothesis that the application of foliar Zn can enhance grain Zn in upland and lowland rice grown under waterlogged and well-drained conditions. Two rice varieties, CNT1 (wetland rice) and KH CMU (upland rice) were grown in containers in waterlogged or well-drained soil with three Zn treatments (no Zn, soil Zn and foliar Zn). For the soil Zn treatment, 50 kg ZnSO4 ha−1 was applied to the soil before transplanting. For the foliar treatment, 0.5% ZnSO4 (equivalent to 900 L ha−1) was applied at booting and repeated at flowering and milky growth stages. Grain yield in CNT1 was 15.9% higher in the waterlogged than in the well-drained plants, but the water regime had no effect on grain yield in KH CMU. Grain Zn concentration in CNT1 increased from 19.5% to 32.6% above the no Zn control when plants were applied with soil or foliar Zn. In KH CMU, there was an interaction between the water regime and Zn treatment. Application of foliar Zn increased grain Zn by 44.6% in well-drained and 14.7% in waterlogged soil. The results indicate strong interaction effects between variety, water regime and Zn fertilizer application on Zn biofortification in rice. Thus, the selection of rice varieties and growing conditions should be considered in order for producers to achieve desirable outcomes from high grain Zn concentrations

Boron requirement for reproductive development in wheat

The effect of boron (B) deficiency on reproductive development was examined in a wheat line SW41 at 4 B levels in a field experiment. The soil B levels (designated BO, B1, B2, B3) ranged from 0.1 to 0.2 mg hot water soluble B kg-1. No effect on vegetative growth was detected at any of the B levels, but the number of grains per ear increased with B, from 7 in BO to 21 in B3; and Grain Set Index (GSI) also increased from 22 to 60%. At ear emergence, B content (mg B kg-1 DW) of the ear ranged from 2.2 to 3.1, and of the flag leaf from 4.1 to 4.7, but these bore slight to no relationship to the number of grains per ear or GSI. Higher B concentrations were found in the carpel, and higher still in the anthers. More significantly, grain set was closely correlated with B in the carpel (R2 = 0.86) and anthers (R2 = 0.77). The significant correlation between GSI and carpel and anther B was confirmed with a larger set of data. With 7 mg B kg-1 DW in the anthers and 5 mg B kg-1 DW in the carpel, the number of grains per ear was doubled when cross pollination with B deficiency tolerant Fang 60 growing near by was allowed. In ears with 9 mg B kg-1 in the anthers and 8 mg B kg-1 in the carpel the effect of cross pollination was smaller, but still significant. The critical deficiency concentration (CDC) of B for the anthers was determined at 10 mg B kg-1 and for the carpel at 8 mg B kg-1. Histological examination of SW41 anthers revealed that microsporogenesis in B-deficient plants proceeded normally up to at least the uninucleate, vacuolate stage. However, pollen maturation was severely affected resulting in shrivelled pollen grains. The programmed development of the tapetum and endothecial layers appeared normal in anthers where partial or complete sterility occurred. It is concluded that reproductive development in wheat requires more B than vegetative growth. The B requirement of the male reproductive organ, the anthers, was also greater than that of the carpel. Since the B requirement in the carpel for successful fertilization and grain set probably also reflects B requirement for pollen germination, it is suggested that B requirement for female gamete development may be lower than the apparent requirement of the carpel

Boron deficiency in maize

Boron (B) deficiency depresses wheat, barley and triticale yield through male sterility. On the basis of field responses to B fertilization, maize (Zea mays L.) is affected by B deficiency in five continents. In a series of sand culture trials with maize subject to B0 (nil added B) and B20 (20 mu M added B) treatments, we described how B deficiency depressed maize grain yield while showing an imperceptible effect on vegetative dry weight. With manual application of pollen to the silk of each plant, B0 plants produced 0.4 grain ear(-1) compared with 410 grains ear(-1) in B20 plants. Symptoms of B deficiency was observed only in B0 plants, which exhibited symptoms of narrow white to transparent lengthwise streaks on leaves, multiple but small and abnormal ears with very short silk, small tassels with some branches emerging dead, and small, shrivelled anthers devoid of pollen. Tassels, silk and pollen of B0 plants contained only 3-4 mg B kg(-1) DW compared with twice or more B in these reproductive tissues in B20 plants. A cross-fertilization experiment showed that, although the tassels and pollen were more affected, the silk was more sensitive to B deficiency. Pollen from B20 plants applied to B0 silk produced almost no grains, while pollen from B0 on B20 silk increased the number of grains to 37% of the 452 grains plant(-1) produced from B20 pollen on B20 silk. Therefore, the silk of the first ear may be targeted for precise diagnosis of B status at maize reproduction, for timely correction by foliar B application, and even for B-efficient genotype selection

Genotypic variation in response to low boron in eucalypt clones

Eucalypts are increasingly important in the tropics for meeting growing demand for timber, wood chips, paper pulp and biofuel. Many new plantations are planted on low boron (B) soils, with adverse effects on plant growth and productivity. Two experiments in sand culture with different levels of added B, from 0 to 10 μM B, examined the effect of B deficiency on growth, wood yield and morphology of fibres of three commercially available eucalypt clones: K7 (Eucalyptus camaldulensis × E. deglupta), K51 (E. brassiana × E. grandis) and K57 (E. camaldulensis). In plant height, dry weight and wood production, K7 was more tolerant of B deficiency, but K57 and K51 were more responsive to increasing B. At the level of B that depressed growth by up to 54% and wood yield by up to 65%, no significant effect of B deficiency was observed on fibre morphology. However, as the wood:shoot ratio in K51 and K57 increased with increasing B, there is a possibility that B has a direct effect on wood production in some genotypes, in addition to an indirect effect via better growth. These results indicate that attention to B nutrition in eucalypt plantations would be beneficial to plant growth and productivity before effects of B on individual wood fibres becomes detectable. Selection for B-efficient genotypes could be useful for plantations on low B soils, and the full potential of sites where B is not limiting could be better realised with B-responsive genotypes

Variation in responses to boron in rice

Background and aims: Boron (B) deficiency depresses grain set and grain yield of wheat and maize while having little effect on their vegetative growth. This paper describes effects of B deficiency in rice and how these vary with planting season and variety. Methods: Three rice varieties (KDML105, CNT1, SPR1) were grown in sand culture without (B0) and with 10 μM (B10) B added to the nutrient solution, in the cool season of 2007/08 and 2008/09 and the hot season of 2011 in Chiang Mai, Thailand (18°47′N, 98°59′E). Boron responses were measured in growth and yield parameters, pollen viability and B concentration of the flag leaf and anthers at anthesis. Results: Grain weight was strongly depressed by B deficiency ranging from 28 % in SPR1 to 79 % in CNT1, and the yield was much lower in the cool season than in the hot season plantings. The variation in grain weight was closely associated with grain set and number of spikelets but not with shoot dry weight or tillering. Grain set was closely related to pollen viability, and both were increased with increasing anther B concentration at >20 mg B kg-1. In addition to its adverse effect on grain set, B deficiency also depressed grain filling and weight of individual grains in rice. Conclusions: Boron deficiency depressed rice grain yield through adverse effects on reproductive growth, panicle and spikelet formation and grain filling, in addition to grain set as in wheat and maize

Responses of grain yield and nutrient content to combined zinc and nitrogen fertilizer in upland and wetland rice varieties grown in waterlogged and well-drained condition

This study explored the response in grain yield and quality of upland and wetland rice varieties to a combination of zinc (Zn) and nitrogen (N) fertilizers under two water management regimes. A factorial arrangement based on a randomized complete block design composed of three factors was carried out with three independent replications. Upland and wetland rice varieties were grown with three fertilizer treatments; the optimum N rate (86 kg N ha−1) without Zn application, the optimum N rate with Zn (50 kg ZnSO4 ha−1), and the high N rate (172 kg N ha−1) with Zn under waterlogged and well-drained conditions. Grain yield was 27% lower in the well-drained than in the waterlogged condition in wetland rice, while there was no effect in upland rice. Application of optimum N with Zn application produced the highest grain yield in upland rice, while yield was the highest in wetland rice in high N with Zn application. Upland rice grown in the well-drained condition with the optimum and high N with Zn treatments enhanced Zn concentration by 45% and 29% higher than the treatment without Zn, respectively, while it had no difference among three treatments in the waterlogged condition. Wetland rice variety grown under the well-drained condition in optimum and high N rate with Zn treatments were equally effective in improving grain Zn concentration at the average of 88% compared to the control. While rice grown under the waterlogged condition in the high N with Zn treatment had improved 92% the concentration. The optimum N rate with Zn application increased grain yield in upland rice, while the higher N input is required for wetland rice. Grain Zn concentrations of upland and wetland rice varieties were enhanced by applying Zn fertilizer; however, the increased level was depended on N application rate in the individual water condition

Foliar zinc application improved grain zinc accumulation and bioavailable zinc in unpolished and polished rice

This study examined the effect of foliar zinc (Zn) application on grain yield, Zn and phytate concentrations and its impact on the phytate:Zn molar ratio, an indicator for Zn bioavailability in human digestive tracts, in unpolished and polished rice between two rice cultivars across two cropping years. The modern improved rice cultivar CNT1 and the traditional improved cultivar KDK were foliar applied with five rates of ZnSO4 in two cropping years. In 2016, 0.3% ZnSO4 increased the Zn concentration of unpolished rice in KDK by 21% over the nil Zn, while the effect was not found in CNT1. In polished rice, 0.2–0.4% ZnSO4 increased the Zn concentration by 11.2–20.0% in CNT1 and by 8.3–24.1% in KDK, and decreased the phytate concentration by 5.2–16.9% in KDK but not in CNT1. In 2017, 0.4% ZnSO4 increased the Zn concentration by 18.2–26.2% and 32.4–42.6% in unpolished and polished rice, respectively, in both cultivars. Application of 0.4% ZnSO4 decreased the phytate:Zn molar ratio in polished rice from 29.7 to 18.3 and from 26.4 to 17.9 in CNT1 and KDK, respectively in 2016, and from 15.7 to 12.6 in KDK in 2017. Foliar Zn application decreased the phytate:Zn molar ratio in unpolished rice from 27.9 to 22.7 and from 21.9 to 17.2 in CNT1 and KDK, respectively in 2017, but had no effect in 2016. Thus, foliar Zn application can improve grain Zn concentration and decrease the phytate:Zn molar ratio in both unpolished and polished rice but the response can vary with cropping year and cultivar

Boron requirement for vegetative growth of Sacha inchi (Plukentia volubilis L.)

Sachi inchi is a useful traditional plant in South America that has recently gained notoriety as a nutritional food crop and hence is being cultivated outside its native range. In Thailand, the crop is being grown on soils where boron (B) may be limiting to growth. To determine the response of early vegetative growth of sacha inchi to B supply, to identify B deficiency symptoms, and to define leaf B concentrations for optimum growth. The two experiments were conducted in sand-culture pot arranged in a randomized complete block design with three independent replications. Plants were grown in the preliminary experiment consisted of complete nutrient solution and complete nutrient solution without B. The main experiment was continued by growing plants in the five series of B rate (0, 2.5, 5.0, 7.5 and 10.0 µM B). Plant growth parameters were recorded and B concentration in different plant parts were analyzed. B deficiency strongly inhibited root and shoot development causing stunting and organ malformation. In a sand-culture experiment, maximum growth was obtained with 7.5 µM B and 10 µM B reduced growth. Leaf B concentration of 27–29 mg kg−1 was associated with 90% of maximum vegetative yield. Symptoms of B deficiency and the foliar B concentrations are useful for extension workers and producers looking to improve the productivity of sacha inchi on nutrient poor soils