Protein quality analysis of F2 maize kernels

Abstract

Protein quality of standard maize kernels is poor, due to the low levels of two essential aminoacids - lysine and tryptophan. The opaque2 mutation which increases lysine and tryptophan content also confers an undesirable phenotype leading to low yields, soft and chalky kernels that renders seeds susceptible to storage pest and ear rots. Quality protein maize (QPM) is the maize with increased levels of these amino acids and good agronomic performances. At the Maize Research Institute, a program on creating QPM germplasm developed for conditions of temperate climatic zone is in progress. The aim of this study was to test quality traits of F2 kernels derived from the crosses between 24 QPM inbred lines with three standard inbred lines and two opaque2 lines. Most of the analyzed 108 genotypes had tryptophan content under the threshold of 0.075 set for QPM (83.5%). However, 50% had elevated tryptophan content in the range from 0.065 to 0.074. High tryptophan content was found in 16.5% of the analyzed genotypes, the highest being 0.088. Only one genotype had quality index over 0.80 (threshold for QPM). Biochemical analysis identified genotypes with good protein quality which will be further tested for agronomic performances in order to potentially be considered as QPM hybrids.

Proteini kukuruza su siromašni u sadržaju dve esencijalne aminokiseline - lizina i triptofana. Prirodna opaque2 mutacija udvostručava nivo ovih aminokiselina, ali istovremeno smanjuje prinos, čini endosperm kukuruza mekim i brašnjavim, a seme osetljivim na trulež klipa i štetočine skladištenog zrna. Kukuruz visokog kvaliteta proteina (Quality Protein Maize - QPM) se može definisati kao kukuruz sa visokom nutritivnom vrednošću proteina endosperma i istovremeno dobrim agronomskim performansama. U Institutu za kukuruz već nekoliko godina postoji program stvaranja genotipova kukuruza visokog kvaliteta proteina, adaptiranih na umereno klimatsko područje. Cilj ovog rada je bio da se ispita kvalitet proteina F2 zrna kukuruza dobijenog ukrštanjem 24 QPM inbred linija sa tri standardne inbred linije i dve opaque2 linije. Većina od 108 analiziranih genotipova (83,5%) je imala sadržaj triptofana ispod praga od 0,075, od čega je poboljšani nivo triptofana (0,065-0,074) imalo 50% genotipova. Visok sadržaj je imalo 16,5% analiziranih genotipova, od kojih je najviša vrednost bila 0,088. Samo jedan genotip je imao indeks kvaliteta proteina iznad praga od 0,80. Biohemijskom analizom utvrđeni su genotipovi poboljšanog kvaliteta čija će agronomska svojstva biti ispitana kako bi se utvrdilo da li se mogu smatrati potencijalnim QPM hibridima.