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Resistance of Sugarcane (Saccharum Officinarium L.) Varieties of Root-knot Nematodes, Meloidogyne Incognita and M. Javanica
Dissertation Abstract:
Fifty-two sugarcane varieties were screened for resistance to two species of root-knot nematodes, namely; Meloidogyne incognita and M. javanica. Resistance rating were based on the averages of computed indices of the four assessment parameters -- root galling, number of nematodes recovered per gram roots, number of egg masses per gram roots, and number of eggs per egg mass.
Twenty-six, 10, 8, and 8 variables were found resistant, moderately resistant, moderately susceptible, and susceptible to M. incognita, respectively. Java Lahaina and Japonesa were the most resistant, whereas CP 33-224 and Hind Special were the most susceptible.
On the other hand, 20, 14, 6, and 12 varieties were found resistant, moderately resistant, moderately susceptible, and susceptible to M. javanica, respectively. Phil 65-63 was the most resistant whereas Fiji 59, the most susceptible.
The sugarcane varieties Phil 65-63, POJ 2876, POJ 3150, CP 70-1527, Q 33, CR 440, CO 975, TUC 67-10, B 60-321, Ragnar, Java Lahaina, Ogles Selection, Japonesa, and Neptune were resistant to both nematode species. Eight varieties, namely; CP 33-224, SW 3, Hind Special, Vomo, Tritan, Walluca, Fiji 57, and Fiji 59 were susceptible to both nematode species.
Highly significant positive linear correlations were found between resistance ratings and each and among the assessment parameters used. Results showed that any of the parameters could be used to determine resistance of sugarcane varieties to the root-knot nematodes M. incognita and M. javanica. However, it was better to use all the parameters to have a more conclusive evaluation of resistance.
Pre- and post-infectional resistance mechanisms occurred in sugarcane varieties resistant to the nematode species. Histopathological observations showed that giant cell formations in susceptible sugarcane roots were more numerous than those in resistant. Some necrotic cells surrounding the area in which nematode fed were found in resistant roots.
The possible involvement of toxic chemicals in resistance was confirmed by the reduced number of eggs hatched and high larval mortality when exposed to root exudates and extracts of resistant varieties as compared to those that were susceptible. Total phenolic compounds were higher in the resistant varieties, Java Lahaina and CP 53-18, than those in the susceptible, CP 33-224 and SW 3. There was significant negative correlation between the amount of phenolic compounds and number of galls.
Separation of the phenolic compounds by thin layer chromatography showed that CP 33-224, CR 440, CP 53-18, and Java Lahaina contained catechin. CP 53-18 and CR 440 also contained phenol. Based on the number of compounds, as determined by the number of spots, resistant sugarcane varieties contained relatively more phenolic compounds than the susceptible ones.
