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Sweet corn breeding programme have been implemented at the Maize Research Institute, Zemun Polje - Belgrade, for the last 40 years. Sweet corn is used as human food at the milk stage when the kernel is sweet, soft and succulent. It is one of the most popular vegetable crops in countries where maize consumption is traditional. Sweet corn is the mutant. The mutation at the Su lokus probably occurred at different time and in different types of maize. The su mutation affects the endosperm composition by causing it to accumulate two or more times water-soluble polysaccharides (WSP) then normal field corn has at the immature stage when it is normally consumed. Sucrose is predominant sugar in grain of standard sweet corn. Sweet corn is harvested 18-23 days after pollination. The homozygous recessive su gene has its limitations, and the major one is the very short period when kernels remain at high quality. Sometimes this period is as short as one day, which makes problems for sweet corn growers and processors. The identification of additional endosperm genes causing a higher level of sugar, leds to utilization of these genes in the development and improvement of sweet corn. Most sweet corn commercial hybrids are based on one or more recessive alleles which modify endosperm composition. These mutants are enzymic "injuries" in the path way of starch synthesis, which change endosperm carbohydrate composition and result, almost in all causes, in decreased starch level. The hybrids with the sh, sh2, bt, bt2 gene contain two to three times more sucrose than hybrids with the su gene. As a result the kernels (seeds) are of poor quality, winkled, light, angular, brittle and susceptible to injuries. Consequently, germination and emergence in the field, as well as, early growth, are harder than of standard grain quality maize. The aim of sweet corn breeders is to develop hybrids which will meet the demands of the market. Rad na oplemenjivanju kukuruza šećerca započet je sedamdesetih godina u Institutu za kukuruz "Zemun Polje". Do sada je priznato 20 ZP hibrida kukuruza šećerca različite dužine vegetacije. Svi domaći ZP hibridi kukuruza šećerca su sa sugary genom. U našoj zemlji najveći deo proizvedenog šećerca se prerađuje u obliku zamrznutog zrna. Standardni kukuruz šećerac je mutant. Mutacija su uslovljava takvu kompoziciju endosperma gde se akumulira dva puta i više u vodi rastvorljivih polisaharida (WSP) nego kod običnog kukuruza u fazi nezrelog zrna kada se ono konzumira. Ukus šećerca određuje slatkoća koja zavisi od udela šećera i skroba u endospermu. Ove osobine menjaju važnost zavisno od načina korišćenja hibrida. Glavni resursi u selekciji šećerca su elitni hibridi i elitne inbridovane linije, koji se preporučuju i odabiraju za poboljšanje osobina, kao i sintetičke populacije uže i šire genetičke osnove. Mnogi selekcionari šećerca se uzdržavaju od korišćenja germplazme koje nisu šećerac u svojim selekcionim programima zbog teškoća da se sačuva niz faktora kvaliteta i specifičnost sirovog proizvoda što je karakteristič no za šećerac. Naravno, germplazma koja nije u tipu šećerca se koristi za poboljšanje šećerca od samih početaka selekcionih programa. Ovaj tip germplazme se koristi kao izvor za povećanje relativne otpornosti prema bolestima i štetočinama u zavisnosti od aktuelnosti određenog svojstva za šećerac. |
