The present investigation was carried out to evaluate the six generations of the
two crosses of G. barbadense L. (CB 58 × G80) and (CB 58 × G90) to estimate the type of
gene action, heterosis, inbreeding depression, heritability estimates and genetic advance
under selection. Scaling test indicated that the additive – dominant gene effects were not
adequate in controlling these characters. Therefore, the interaction of genes must be
taken into account. The additive gene effects (a) were significant for all of the studied
traits in both crosses, except NB/P and L% in cross I, and L%, SI and FL in cross II.
Moreover, dominance gene effects (h) were significant for all traits in cross I (CB 58 ×
G80), except for Mic and PL. Meanwhile the traits L% and Fiber properties were
significant in cross II (CB 58 × G90). The interaction of additive × Additive (i) type of
epistasis was significant for all studied traits, except for L%, Mic and FL in cross I and
BW, SI, LI and PI in cross II. The interaction additive × dominance (j) gene effects were
highly significant for BW, SCY/P, LY/P, Mic, PI, FL and UR in cross I. While in crosses
II, the traits BW, PI, FL and UR recorded highly significant additive × dominance
epistatic gene effects (j). Dominance × dominance (l) types of epistasis gene effects were
highly significant for all traits except for L% only in crosses I. The traits NB/P, SCY/P,
LY/P, Mic, PI and UR recorded significant or highly significant epistasis gene effects (j)
in cross II. Heterosis relative to better parent was highly significant and positive for PI,
FL and UR in both crosses, while Mic value recorded positive and negative significant
effects in cross I and cross II, respectively. On the other hand heterosis relative to midparent
was highly significant for PI, FL and UR in both crosses, while SCY/P and LY/P
recorded highly significant and significant heterotypic effects relative to mid-parent in
cross I and cross II, respectively. Inbreeding depression for both crosses was
insignificant for all traits. High values of broad-sense heritability (over 50%) were
detected for BW, L%, PI, FL and UR in cross I and BW, LI, Mic and PI in cross II.
Moderate broad-sense heritability estimates were found for LI and Mic in cross I and SI
and UR in cross II. Low broad sense heritability values (˂ 30%) were obtained for NB/P,
SCY/P, LY and SI, and NB/P, SCY/P, LY, L% and FL in cross I and cross II,
respectively. High narrow-sense heritability estimates (˃ 50%) were obtained only for UR
in cross I and Mic and UR in cross II. Moderate heritability estimates were observed for
BW, L%, LI, PI and FL in cross I. Low heritability in narrow sense values were obtained
for NB/P, SCY/P, LY, SI and Mic in cross I and all traits under study except Mic and UR
in cross II. The expected genetic advance values from selecting the desired 5% of F2
population indicated that the improvement by selection could be effective for SCY/P and
L% in cross I and BW, PL, FL and UR in cross II. |
