This Is AuburnElectronic Theses and Dissertations

Biological Control Studies on the Reniform nematode (Rotylenchulus reniformis) on Cotton in Alabama.




Castillo, Juan D.

Type of Degree



Entomology and Plant Pathology


Cotton production in the Southeastern United States is limited by the reniform nematode (Rotylenchulus reniformis) causing an estimated loss of $98,000.000 per year. Currently, management is based on crop rotation and use of nematicides because there are no resistant cotton cultivars to R. reniformis. Therefore, biological control of R. reniformis is an option that needs to be explored. The objective of this work was to isolate, identify, and evaluate fungi as biological control agent associated with R. reniformis in cotton plants. Soil samples were collected in cotton fields naturally infested with R. reniformis and from cotton stock plants cultured in the greenhouse. Nematodes were extracted from the soil by gravity screening and centrifugation-flotation method. Nematode samples were observed under the stereoscope and vermiforms colonized with mycelia and discolored eggs were tacitly collected, placed in a syracuse dish, and rinsed with sterile water. These nematodes were cultured on 1.5% water agar supplemented with antibiotics, and incubated at 27°C. Fungal growth from the nematodes was transferred to Potato Dextrose Agar (PDASA) plates supplemented with streptomycin sulfate to establish pure cultures. Identification of the nematophagous fungi was based on morphological characters and the ITS regions and 5.8S rDNA amplified by PCR using the primers ITS1 and ITS4. A total of 16 fungi were identified from R. reniformis with four of the fungal isolates previously reported as nematophagous fungi: three isolates of Drechslerella dactyloides and one isolate each of Drechslerella brochopaga, Paecilomyces lilacinus, and Fusarium oxysporum. In vitro pathogenicity tests for Drechslerella dactyloides and Dr. brochopaga were conducted and iii revealed the start of conidial germination after 14 hours. Ring formation began after 16 hours, and its completed between 36 and 42 hours. Nematodes were attracted to the ring after 60 hours, and 12 hours later the nematodes were trapped. The pathogenicity of these fungi was tested in the greenhouse in a factorial arrangement of a RCBD with two soil types (autoclaved and natural) and three fungal carriers (wheat, oat, and corn meal) replicated 6 times. Cotton plants ST5599 BGRR were cultivated in 500 cm³ pots and 1% (v/v) of fungal inoculum was added per pot with 3000 R. reniformis nematodes at planting. After 60 days plants were harvested, and plant height, shoot, and root mass, number of R. reniformis in soil, and eggs in root were recorded. In autoclaved soil, Dr. dactyloides, Dr. brochopaga, and P. lilacinus reduced (P< 0.05) the number of vermiform R. reniformis nematodes in soil. Paecilomyces lilacinus and F. oxysporum reduced (P< 0.05) the number of juveniles and eggs in the roots. In natural soil, A. dactyloides and F. oxysporum reduced R. reniformis numbers in soil, but none of the fungal isolates affected R. reniformis numbers of eggs in roots. The fungal isolates did not exhibited phytoxicity and did not reduce plant shoot or root mass or reduce plant height. Interestingly, oat when used as a fungal carrier, increased plant root mass. All six fungal strains of Dr. dactyloides, Dr. brochopaga, P. lilacinus, and F.oxysporum reduced R. reniformis numbers in autoclaved soil. The reduction in numbers of nematodes was consistently observed in autoclaved soil