Disease incidence, severity and changes in morphological characteristics of some high value hybrid genotypes of oil palm (Elaeis guineensis Jacq.) seedlings as influenced by fusarium oxysporum f. sp. Elaeidis

Fusarium oxysporum f. sp. elaeidis (F.o.e) which is a causative agent of vascular wilt disease is the main threat to oil palm (Elaeis guineensis) cultivation in Africa. Its effects are more widely known on adult palms at production stage than on palm trees at the pre-nursery stage. The aim of his study was to evaluate the effects of F.o.e on the morphological parameters and the disease incidence and severity on seedlings during four months of pre-nursery stage. Ten high value hybrid genotypes of germinated seeds, including three tolerant to F.o.e were used. Seedlings were inoculated at four weeks of age with F.o.e. The morphological parameters (height and stem diameter of the seedlings, leaf length and width, leaf area) were recorded every two weeks and the disease incidence and severity on seedlings were determined. All the observed parameters were negatively influenced by F.o.e. Seedling height showed the highest difference (5.34%) and two genotypes (T1N and T3F) out of the ten assessed recorded no influence of F.o.e. As these results are not correlated with the internal symptoms of vascular wilt, it is not evident to deduce tolerance of the progeny solely based on F.o.e effects on the growth traits. There was a positive and significant correlation (r = 0.67, P<0.05) between the index of Fusarium (IF) and the disease severity, between the IF and disease incidence (r = 0.85, P< 0.01). However, the correlation between the IF and seedling morphology was negative and not significant (r = - 0.17, P> 0.05). The morphological parameters of T3N and T5N genotypes initially known to be susceptible to Fusarium wilt were the most affected (19.05% and 13.33% respectively) of the inoculated seedlings compared to control seedlings. T1N initially known to be susceptible here manifested signs of tolerance confirming the observations made on internal symptoms. Moreover, T3F, T2F and T1F progenies recorded an IF<100 and have also been morphologically more efficient thus confirming their Fusarium tolerance status. These results may serve as a pre-diagnostic index of Fusarium wilt in oil palm.Keywords: Elaeis guineensis, Fusarium oxysporum f. sp. elaeidis, growth parameters, hybrid genotypes, pre-nursery.