This study examined variation in seed zinc (Zn) in a local upland rice germplasm that may affect adaptation in a system of slash-and-burn. Individual seed Zn in farmers' seed lots of local upland rice varieties from a slash-and-burn system was evaluated by staining with dithizone (DTZ). Concentration of Zn in the farmers' seed lots and their single-seed descent genotypes grown at Chiang Mai University was determined by chemical analysis. The DTZ staining of individual seeds in most of the farmers' seed lots covered the intensity of standards that ranged from 19 mg Zn/kg (RD21) to 31 (Nam Roo) mg Zn/kg. Zinc content by chemical analysis was closely correlated with the weighted-average staining for each seed lot. Almost all of the single-seed descent genotypes had higher seed Zn than RD21; two-thirds were higher than Nam Roo. The variation within seed lots detected by DTZ staining was confirmed by seed Zn in the single-seed descent genotypes. Evolutionary adaptation to soil with limited Zn, exacerbated by alkalinity of the ash from slash-and-burn, is made possible by variation in seed Zn among individuals growing together in the same field, and benefits the eaters with Zn-enriched seed.
The impact of foliar applied zinc fertilizer on zinc and phytate accumulation in dorsal and ventral grain sections of four Thai rice varieties with different grain zinc
This study evaluated grain anthocyanin, zinc (Zn) and iron (Fe) concentrations, and grain yield of eleven purple rice varieties (PP1-PP11) grown under wetland (W+) and aerobic conditions (W0) in 2 years. There was a significant variation in the concentrations of anthocyanin, Zn and Fe, by water regime and year among the varieties with a wide range of anthocyanin (1-117 mg 100 g −1) and narrower ranges of Zn (19-41 mg kg −1) and Fe (6-19 mg kg −1) concentrations. The nutritional quality in aerobic grown rice was lower than wetland grown among the varieties with higher levels of anthocyanin (>40 mg 100 g −1), Zn (>30 mg kg −1) and Fe (>15 mg kg −1), with smaller effects of water among varieties in the lower quality ranges. The lowering of anthocyanin in aerobic grown rice was observed in the two varieties of the upland ecotype that were highest in anthocyanin concentration, as well as some wetland varieties. The grain yield (1.4-6.7 Mg ha −1) was associated negatively with grain Zn concentration (r = −0.50, P ≤ 0.001), but not with grain Fe (r = −0.14, NS 0.05) or anthocyanin (r = −0.27, NS 0.05). The anthocyanin concentration in the purple rice increased with Zn concentration (r = 0.57, P ≤ 0.001). Wetland condition was shown to be more favorable than aerobic culture for intense pigmentation in the production of purple rice, as well as higher Zn and Fe concentrations.
Cereal Chem. 91(2):124-129This study examined the distribution of zinc in dorsal and ventral grain sections of rice varieties with low (RD21), moderate (CNT1 and KDML105), and high (KPK and NR) zinc concentrations. Samples of unhusked rice grain were partitioned longitudinally and analyzed for zinc. The concentration of zinc was higher in the dorsal grain section than the ventral section, but to a different extent in different varieties. In unpolished rice, the zinc concentration in the dorsal section exceeded that in the ventral section by 14% in CNT1 to 63% in RD21. The higher zinc concentration in the dorsal section of unpolished rice might be explained by storage in the multiple cell layered aleurone and thicker pericarp. The higher concentration of dorsal zinc, however, was maintained after polishing, irrespective of the removal of grain surface by polishing that varied with variety and polishing time from 11 to 207 μm in depth. Zinc concentration of polished rice, ranging from 14 to 28 mg of zinc/kg, was strongly predicted by the zinc in unpolished rice (P < 0.01). This uneven distribution of zinc in the dorsal and ventral sections of rice grain suggests a specific pattern by which zinc is laid down. Whether the region of endosperm and aleurone proximal to the dorsal vascular bundle may have a greater concentration of zinc transporters and zinc storage structures than in more distal areas is yet to be investigated. Understanding this distribution may aid efforts in zinc biofortification and evaluation of rice varieties for other nutritive characteristics. 2 Corresponding authors.
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