Heritability and heterosis of agronomical characteristics, yield and yield

Introduction

Sweet corn (Zea mays L.Saccharata) is one of the most popular vegetable in countries like United States of America and Canada. It is characterized by translucent, horny appearance of kernel when matures and wrinkled when it dries. The research reports indicate that the sweet corn has arisen as a mutant from field corn in the 19th century. Sweet corn is consumed in immature stage of the cob. Sweet corn derives from a mutation in genes that affect starch synthesis in the seed endosperm of dental corn which results in higher level of water soluble sugars and decrease starch (Dinges et al., 2001).

The efficiency of maize breeding programs would be significantly enhanced if superior crosses could be predicted before field evaluation based on screening of parental inbred lines. Even though remarkable advances in maize breeding have been achieved, field trials involve significant resources and are time consuming. However, field tests still have aunique role in modern hybrid breeding programs. Determining performances of inbred lines as potential hybrid parents in field experiments and diallel crosses are still widely used in sweet corn breeding programs (Kashiani et al, 2010., Assuncao et al, 2010).

Inbreeding the lines is the most frequent breeding technique in maize. Six to eight inbreeding results in sufficient homozygosity at heterozygote individuals. During this period, selection is performed base on important agronomical characteristics. The general and specific combining ability of lines is investigated too. The field test of hybrid's crossing continue for three to four generations (Hallauer, 1993., Hallauer and Miranda, 1988).

Sweet corn breeders have not relied on heterotic patterns in the development of commercial hybrids. Establishment and improvement of new heterotic patterns in sweet corn could be helpful for improving agronomic performance and adaptation of sweet corn in new regions of production. Furthermore, sweet corn breeders should theoretically be concerned with the risk of exhausting heterosis if the same inbred are recombined repeatedly without introduction of new heterotic combinations( Revilla et al., 2000).

Role of genetic regulation of yield component in order to enhance kernel yield has studied by several researchers (Hallauer and Eberhart,1966., Stuber et al., 1966).

Researchers reported that kernel yield, ear diameter, kernel number, ear number, days to anthesis and days to maturity affect by gene epistasis (Mihailov and Chernov, 2006).

(Melchinger et al., 1990) reported that corn kernel yield is highly controlled by additive × additive epistasis.

Sugar content and kernel nutritional content controlled by non-additive genes (Zhaoyuanzeng et al, 2002., Jyothi kumara et al, 2008). Other researchers reported that sugar and carbohydrate content affects by over dominant and specific combining ability (Asbishkhanduri et al, 2010., Zhaoyuanzeng et al, 2002., bordello et al, 2005).

Researchers investigated the effect of heterosis on yield and yield components of sweet corn genotypes via diallel analysis. They reported that genetic diversities results in significant difference between genotypes in respect of all studied traits except for ear industrial index and brix index. Measured characteristics enhanced in heterosis hybrids. Anthesis, plant height, ear height and kernel weight was controlled by dominant genes (Assuncao et al., 2010).

Significant heterosis reported for ear length, ear diameter, kernel weight and kernel number per row for maize (Devi and Sarma, 2005).

(Rokadia and Kaushik, 2005) found significant heterosis for leaves number per plant and grain yield at maize several crosses (L5×T1, L7×T1, L10×T1).

Introducing the proper sweet and super sweet corn single cross hybrids is the subject of this study. This study was performed in order to screening and introducing the best parental inbred lines and hybrids of sweet and super sweet corn in Iran.