Genetic control of polymorphism for kernel-to-fruit ratio in the oil palm (Elaeis guineensis Jacq.)

A study to clarify the genetic control of polymorphism in kernel-to-fruit ratio in the oil palm Elaeis guineensis Jacq. was carried out on the basis of the following crosses from the NIFOR oil palm breeding programme-45 tenera (T) x tenera; 24 tenera (T) selfings; 33 dura (D) x tenera; and 29 tenera (T) x dura (D). The mean kernel-to-fruit ratio (K/F) for the dura and tenera fruit forms and the tenera:dura (T:D) ratio of K/F were determined for each of the segregating progenies. Estimates of correlation coefficient (r) and narrow-sense heritability (h2) derived from parent-offspring regression analysis for the T:D ratio of K/F were obtained for each type of cross. Dura and tenera fruit forms showed distinct differences in their mean K/F, thus confirming that the oil palm exhibits polymorphisms in its kernel size, with the dura progeny having a higher mean K/F than the tenera in all the segregating crosses. The coefficient of correlation between the K/F of the tenera parent and the tenera:dura ratio of K/F of selfed offspring was highly significant (r=0.52** ). The comparison between the female tenera parent T:D ratio of K/F and that of the TxT offspring was highly significant (r=0.44**) with a high narrow-sense heritability estimate (h2=67). A similar comparison with the male tenera parent was not significant (r=0.18NS) and had a low heritability estimate (h2=25). In DxT and TxD crosses the estimates of the correlation coefficient of the tenera parent to T:D ratio of K/F and the offspring values were not significant (r=0.17NS and 0.20NS respectively). This indicated that tenera parents carry a certain kernel inhibiting factor (or factors) that reduces the kernel size of the tenera offspring relative to their dura sibs. This factor(s) was transmitted to the tenera offspring especially when tenera was the female parent. The kernel inhibiting factor(s) is proposed to be closely linked with the recessive allele of the gene controlling shell thickness. The implication of this for the kernel size and fertility of pisifera palms is discussed