Four semi-quantitative screening methods were developed for plant breeding purposes to identify iron (Fe) and zinc (Zn)-dense genotypes in germplasm, elite lines and early generation progeny. Methods include colour image analysis for Fe and Zn in wheat and rice grains, and spectrophotometric analysis of Fe and Zn in ground flour of rice, wheat, potato, sweet potato and cassava. Staining with 71 mM Perl's Prussian blue solution (PPB) and subsequent image analysis with Adobe Photoshop® to determine pixel numbers in the stained regions lead to the quantification of Fe. Due to differences in grain size between the genotypes evaluated, correlations between inductively coupled plasma-optical emission spectrophotometry (ICP-OES) Fe and PPB derived Fe were improved by standardizing according to grain weight. The ratio of total blue pixel number (TPN)/total grain weight (TGW) of 21 rice lines correlated (r=0.84, p<0.001) with the Fe concentration derived by ICP-OES. Similarly, a colorimetric method was developed for Zn analysis using 1.56 mM Dithizone (DTZ) solution and subsequent quantification by image analysis with Adobe Photoshop®. As with the Fe analysis, the ratio of TPN/TGW of 70 wheat lines correlated better with ICP-OES Zn analysis (r=0.82, p<0.001) and successfully separated low and high Zn grain germplasm. Ground polished rice and wheat flour were spectrophotometrically analysed after simple extraction in 0.5 M HCl solution using a modified 2,2&#8242;-dipyridyl method for Fe, and a modified Zincon® method for Zn. These two methods show good correlations with ICP analyses (r=0.93 and 0.92 for Fe and Zn, respectively) and thus can be used for semi-quantitative screening to discriminate between genotypes that are either high or low in Fe or Zn. The more precise ICP-OES and AAS methods could then be used to quantify actual amounts of Fe and Zn in those genotypes identified as Fe- and Zn-dense from the initial screening.

English

Carelia Juarez

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