Selekcija linija kukuruza sa poboljšanim kvalitetom proteina i adaptiranih na umereno klimatsko područje upotrebom molekularnih markera

Abstract

Hranljiva vrednost kukuruza je niska zbog niskog sadržaja dve esencijalne aminokiseline - lizina i triptofana. Poboljšanje hranljive vrednosti kukuruza predstavlja jedan od glavnih ciljeva savremenih programa oplemenjivanja zbog sve značajnijih klimatskih promena i rasta ljudske populacije, odnosno sve veće potrebe za hranom. Najveći uspeh postignut je 60-ih godina prošlog veka otkrićem opaque2 (o2) mutanta sa superiornim hranljivim svojstvima. Međutim, plejotropni efekti o2 mutacije čine endosperm zrna kukuruza mekim, a samo zrno osetljivim na pucanje, trulež i štetočine. Istraživači Međunarodnog centra za poboljšanje pšenice i kukuruza u Meksiku (eng. International Maize and Wheat Improvement Center - CIMMYT) su metodama konvencionalnog oplemenjivanja stvorili kukuruz visokog kvaliteta proteina (eng. Quality Protein Maize – QPM), koji istovremeno ima visoku hranljivu vrednost proteina endosperma i dobre agronomske performanse. Iako je QPM razvijen klasičnim metodama selekcije, poslednjih godina se sve više primenjuje selekcija upotrebom molekularnih markera (eng. Marker Assisted Selection - MAS) sa ciljem poboljšanja elitnih linija za kvalitet proteina. Unutar sekvence o2 gena identifikovana su tri različita SSR markera – phi057, phi112 i umc1066, koji se koriste za utvrđivanje polimorfizma inbred linija i kao selekcioni markeri za o2 gen (eng. foreground selection). Molekularni markeri se koriste i radi utvrđivanja procenta genoma rekurentnog roditelja u potomstvima povratnih ukrštanja (eng. background selection). Primena foreground i background selekcije smanjuje broj generacija potrebnih za stvaranje željenog genotipa klasičnim metodama selekcije koje se zasnivaju na fenotipskom odabiru biljaka. Osnovni cilj ovog rada bio je dobijanje linija kukuruza poboljšanog kvaliteta proteina adaptiranih na umereno klimatsko područje, korišćenjem specifičnih molekularnih markera za opaque2 gen, kao i da se održe dobre agronomske osobine i kombinaciona sposobnost poboljšanih linija...

Maize nutritional quality is poor due to the low levels of two essential aminoacids - lysine and tryptophan. Because of the climatic changes and increased food demands due to the human population growth, improvement of the maize nutritional quality is one of the main goals of many breeding programs. A major breakthrough has been the isolation of the opaque2 (o2) mutant with superior nutritional properties in the 1960s. However, pleiotropic effect of the o2 mutation makes the maize endosperm soft and susceptible to cracking, ear rots, and storage pests. Using conventional breeding methodologies, interdisciplinary research team in the International Maize and Wheat Improvement Center (CIMMYT), Mexico, created the new, agronomically acceptable and nutritionally improved opaque2 types by the name of Quality Protein Maize (QPM). Although QPM was created through conventional breeding, marker assisted selection (MAS) is becoming increasingly used approach for improvement of protein quality in maize. Three simple sequence repeats (phi057, phi112 and umc1066), located as internal repetitive sequences within the o2 gene, are being utilized as foreground selection markers for the o2 gene. Molecular markers are also effectively employed for identification of the genotypes with the highest proportion of recurrent parent genome (background selection). Both foreground and background selection decrease the number of the generations required to create desirable genotype through conventional breeding based on the fenotypic selection. The main objective of this research was to create high quality protein maize lines adapted to temperate regions using opaque2 specific molecular markers, while maintaining their good agronomic performances and combining abilities. Two elite inbred lines - ZPL 3 and ZPL 5 were selected as the recurrent parents, to be the recipients of the o2 allele and to improve the tryptophan content. CML 144, a QPM tropical inbred line, was selected as the donor line of o2. Identification and confirmation of the QPM selection results involved biochemical analysis (determination of protein content, tryptophan content and quality index - tryptophan to protein ratio) and evaluation of the agronomicaly important traits in the field trials...