TUEBINGEN, GERMANY
Eberhard-Karls-University

Morphological characterization of heterotic traits in early root development of maize

— Höcker, N; Hochholdinger, F

Heterosis describes the phenomenon that crosses between two genetically different inbred lines often result in more vigorous F1-plants. Heterosis in maize is manifested already during early plant development. This study analyzed morphological traits of the young primary root of the flint inbred lines UH002 and UH005 and the dent inbred lines UH250 and UH301 and the reciprocal hybrids generated from these four inbred lines. All inbred lines and hybrids used in these experiments were developed in the breeding program of the University of Hohenheim (Germany).

First, primary root length of hybrids and their parental inbred lines were compared in a time course between 3 and 7 days after germination (see Fig. 1 for the combination of UH005 with UH301). As early as 5 days after germination the primary roots of all hybrids analyzed in this study were significantly longer than the midparent value of the primary root length of their corresponding parental inbred lines. Moreover, analyses of the size of cortical cells in the primary root of hybrids and their parental inbred lines with a confocal laser scanning microscope revealed that cortical cells in hybrids are significantly longer than the midparent value of their parental inbred lines 5 days after germination (data not shown). However, primary root width of hybrid plants was not different between inbred lines and hybrids (data not shown). Finally, hybrids displayed an increased lateral root density per cm differentiated primary root compared to the midparent value of the parental inbred lines (see Fig. 2 for the combination of UH005 and UH301) while lateral root length was not different between inbred lines and hybrids at the same developmental stage (data not shown).

 

Figure 1: Determination of primary root length of reciprocal hybrids and their parental inbred lines in a time course between 3 to 7 days after germination. As early as 5 days after germination both reciprocal hybrids showed significantly longer primary roots compared to the midparent value of their parental inbred lines UH005 and UH301. For each column the length of at least 100 primary roots was determined. Asterisks indicate values different from the midparent value (t-test P=0.05).

Figure 2: Determination of lateral root density in reciprocal hybrids and their parental inbred lines 5 days after germination. Reciprocal hybrids displayed significantly more lateral root initial sites per cm differentiated primary root than the midparent value of their parental inbred lines UH005 and UH301. For each column initial sites of at least 35 roots were determined. Asterisks indicate values different from the midparent value (t-test P=0.05).


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