Author
Davis, Richard | |
Webster, Theodore | |
BRENNEMAN, T - UNIVERSITY OF GEORGIA |
Submitted to: Weed Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/24/2006 Publication Date: 11/1/2006 Citation: Davis, R.F., Webster, T.M., Brenneman, T.B. 2006. Host status of tropical spiderwort (Commelina benghalensis) for nematodes. Weed Science. 54:1137-1141. Interpretive Summary: Nematodes are the most damaging pathogens of cotton, and one of the most important pathogens of peanut. Crop rotations utilizing cotton, peanut, and corn are used to manage the southern root-knot, peanut root-knot, and reniform nematodes. However, weeds can support nematode reproduction and reduce the effectiveness of rotation as a management tool. This study documents 1) the relative host status of tropical spiderwort for the southern root-knot nematode, the peanut root-knot nematode, and the reniform nematode, and 2) the host status of tropical spiderwort for the fungal pathogens that cause southern stem rot and Cylindrocladium black rot. Both the southern root-knot nematode and the peanut root-knot nematode reproduced well on tropical spiderwort, causing significant galling of the roots and increases in nematode populations of seven to 15 fold. In the first trial with the reniform nematode, reproduction on tropical spiderwort was low but still similar to cotton. In the second trial, nematode populations increased four fold on tropical spiderwort, which was a significant increase but less than the 14-fold increase on cotton. The severity of southern stem rot symptoms on tropical spiderwort was approximately half the severity on peanut, and the fungus could be seen growing on 40% of the tropical spiderwort plant in the first trial and all of the plants in the second trial. The trials with Cylindrocladium black rot were inconclusive due to low infection rates, but the fungus appears to be weakly pathogenic to tropical spiderwort. In conclusion, it appears that tropical spiderwort is a sufficiently good host for some of the primary nematode and fungal pathogens of major crops in the southeastern US that the presence of tropical spiderwort at typical plant population densities will greatly reduce the pathogen-suppressive effects of crop rotation. Technical Abstract: Nematodes are the most damaging pathogens of cotton, and one of the most important pathogens of peanut. Crop rotations utilizing cotton, peanut, and corn are used to manage the southern root-knot (Meloidogyne incognita), peanut root-knot (M. arenaria), and reniform (Rotylenchulus reniformis) nematodes. However, weeds can support nematode reproduction and reduce the effectiveness of rotation as a management tool. This study documents 1) the relative host status of tropical spiderwort for the southern root-knot nematode, the peanut root-knot nematode, and the reniform nematode, and 2) the host status of tropical spiderwort for the fungal pathogens Sclerotium rolfsii and Cylindrocladium parasiticum. A reproductive factor (RF) was calculated for each nematode as the final population level divided by the initial population level (Pf/Pi). Galling was estimated on a 0 to 10 scale for the root-knot species. The southern root-knot nematode reproduced well on tropical spiderwort, leading to a mean gall rating of 3.1 and a mean RF of 15.5. The peanut root-knot nematode also reproduced well on tropical spiderwort, with a mean gall rating of 2.1 and a mean RF of 7.2. Due to significant trial by treatment interactions for the reniform nematode, data were not combined over trials for analysis. In the first trial with the reniform nematode, the RF was 2.4 on tropical spiderwort and 1.4 on cotton. In the second trial, the RF was 3.6 on tropical spiderwort and 13.5 on cotton. The severity of symptoms caused by Sclerotium rolfsii was estimated on a 0 to 10 scale. In the first trial, peanut had a mean disease severity rating of 4.0 and tropical spiderwort had a mean rating of 1.4, and the fungus could be seen growing on 40% of the tropical spiderwort plants. In the second trial, peanut had a mean disease severity rating of 10.0 and tropical spiderwort had a mean rating of 5.0, but the fungus could be seen growing on all of the tropical spiderwort plants. The trials with Cylindrocladium parasiticum were inconclusive due to low infection rates, but the fungus appears to be weakly pathogenic to tropical spiderwort. In conclusion, it appears that tropical spiderwort is a sufficiently good host for some of the primary nematode and fungal pathogens of major crops in the southeastern US that the presence of tropical spiderwort at typical plant population densities will greatly reduce the pathogen-suppressive effects of crop rotation. |