Selection for multiple traits in upland rice progenies using the Z Index

Rice research institutions have been dedicated to solve problems related to increasing grain yield and enhance the performance of rice lines for important agronomic qualitative traits.However, breeding for multiple traits is difficult since traits frequently show a not always positive phenotypic correlation between each other. Among all alternatives to deal with multiple traits, index selection is expected to be the most efficient and the easier choice in many crops.Therefore, the aim of this study was to select upland rice progenies for important agronomic traitssimultaneously using the Z index approach. Genotypes from the Upland Rice Breeding Program from the Federal University of Lavras, MG, Brazilwere evaluated for plant height, number of days to flowering, neck blast resistance, leaf blast resistance, grain discoloration resistance, brown spot resistance, and leaf scald resistance using a simple square lattice 14x14 design comprising of 192 progenies F2:4 and four commercial upland rice cultivars.The Z index was obtained per plot from the sum of the standardized values of the six traits, except plant height, and the genotypes means ofZwere compared according to the Scott-Knott approach. The phenotypic selection was performedfirst for plant height, and then considering the Z index. Of the 196 progenies, 96 were selected for plant height, and of these, 60 were selected for the Z index, corresponding of a selection intensity of 30%. The progenies that stood out considering the traits separatelyalso showed the best index, indicating that the Z index was efficient in selecting upland rice genotypes for multiple traits simultaneously.