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Pathogenicity and Host Range Studies of Helicotylenchus dihystera and Xiphinema insigne Associated with Sugarcane (Saccharum officinarum L.)
Thesis Abstract:
Height of sugarcane variety Phil 56226 grown in 4,500 cc of potted baked soil was reduced by 7 percent within 18 weeks and 8.4 percent within 20 weeks when inoculated with 2,000 Helicotylenchus dihystera as compared with the control. At this inoculum level, fresh shoot and root weights also reduced by 33 percent and 62.5 percent, respectively, within 20 weeks. The root were sparse, lacked secondary and tertiary rootlets, with dark colored spots or lesions at the root tips, and generally had deteriorated root systems. The primary roots were blunt. The nematode number recovered increased by 4.6 times within 20 weeks. These indicated that H. dihystera parasitic on and pathogenic to sugarcane.
H. dihystera was found to be an ecto- and a semi- endoparasite on roots of corn, tomato, and itchgrass (Rottboellia exaltata), and as an endoparasite in the root of Amaranthus spinosus.
Very good hosts of H. dihystera were A. spinosus, Centrosema pubescens, R. exaltata and Purslane (Portulaca oleracea); good hosts were wild sweet potato (Ipomoea trilaba), tomato (Lycopersicon esculentum var VC-11-1), cotton (Gosssypium hirsutum var. Deltapine 16), corn(Zea mays var. DMR 2), and wiregrass(Eluesine indica). Some of the affected plants had stunted growth, reduced and necrotic root systems, and chlorotoc leaves.
With the highest inoculum level (400 nematodes/pot). Xiphinema insigne reduced fresh root weights of sugarcane by 34 percent as compared to the control. Top growth was not affected. The roots were sparse with slight swelling, curling of the tops, and generally dark colored. A 2.5-fold increase in nematode number was recorded within 20 weeks compared with the initial population.
Tomato and itchgrass were considered good hosts of X. insigne. The inoculated plant did not exhibit tany perceptible symptoms. However, jungle rice (Echinocholoa colona), itchtgrass, and wiregrass showed a malformation of the roots, indicating that X. insigne has a potential damage the plants.