Southern Root-knot Nematode (Meloidogyne incognita (Kofoid and White) Chitwood) and Fungal Susceptibility of Turmeric (Curcuma longa L.) Accessions
Type of DegreeMaster's Thesis
Entomology and Plant Pathology
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Turmeric (Curcuma longa L.), a spice crop native to southeast Asia, is undergoing evaluation as a niche crop for Alabama and other southeastern U.S. production areas. Thirteen accessions of Curcuma spp. (including eight accessions of C. longa, common turmeric) are cultivated as a part of the Auburn University Medicinal Plant Collection on the campus of Auburn University. Rhizomes harvested from the turmeric plots during the 2015-2016 production season showed symptoms of rhizome rot, and mature plants exhibited stunting, chlorosis, and root galling, characteristic of Meloidogyne incognita (Kofoid and White) Chitwood infestation. Fungi were isolated from diseased rhizomes and post-harvest soil samples were taken to identify plant-parasitic nematodes present. Fungal genera isolated included Fusarium (60.9%), Rhizoctonia (21.9%), Trichoderma (9.7%), Macrophomina (2.5%), Diplodia (2.5%), and Nigrospora (2.5%). Fungal sequences were amplified by PCR, and forty-one isolate identities were confirmed. Koch’s postulates were completed for Rhizoctonia solani on C. longa. Meloidogyne incognita was identified throughout the turmeric plots and documented as the first case of M. incognita on C. longa in the United States. Greenhouse trials were conducted to assess the growth of three C. longa accessions with and without the presence of M. incognita. At 60 days after inoculation, M. incognita-inoculated turmeric accessions CL2 and CL7 exhibited significantly reduced average plant height, shoot fresh weight, and root fresh weight with the measurements being 31%, 50%, and 26% of those of the control, respectively. Final nematode population density on CL2, CL3, and CL7 ranged from 19-319, 1-2527, and 41-4703 eggs per gram of root, respectively. Reproductive factor (RF), defined as the final nematode population density divided by the initial inoculum density, was calculated to be 0.6, 4.1, and 2.1 for CL2, CL3, and CL7, respectively. Consequently, turmeric accessions CL3 and CL7 were susceptible to the nematode, as their RF values were greater than 1. Greenhouse and microplot trials were conducted in the summer and fall of 2016 to further assess the susceptibility of C. longa accessions to M. incognita. Curcuma longa 2, C. longa 4, and C. longa 7 exhibited improved growth over other accessions. All accessions tested were good hosts of M. incognita with reproductive factors of 3.9-10.4. Fields trials were conducted to evaluate potential nematicides for M. incognita management. All nematicide treatments had a M. incognita population density of 34-477 eggs per gram of root, and C. longa biomass was similar to the untreated control. Because all turmeric selections grown on the campus of Auburn University are susceptible to M. incognita and nematicides are not a labeled for control, M. incognita may prove a major pest in Alabama turmeric production. More research will be required to establish best management practices, potentially including more chemical and biological nematicides, soil amendments, and expanded variety selection.