Date of Award

1984

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

Root-knot nematode populations endemic to Louisiana soils were identified to species and race. Meloidogyne incognita (Kofoid and White) Chitwood, (MI) accounted for 97 percent of the populations identified. Of the M. incognita species 55 percent were Race 1, 38 percent Race 3, and 7 percent Race 4. Meloidogyne javanica represented 3 percent of the populations studied. Populations were compared to the M. incognita used in the LSU sweet potato breeding program (MIS) for their virulence on the susceptible 'Centennial' and resistant 'Jasper', 'Jewel', and L4-73. The populations varied in virulence to the sweet potato cultivars with some populations being more virulent than the MIS population. Several populations appeared capable of overcoming resistance exhibited by the sweet potato cultivars. The life cycle of MIS was studied on 'Centennial', 'Jasper', 'Jewel', and W-51. Varietal resistance did not inhibit the initial rate of juvenile penetration, but did reduce the number of juveniles that reached maturity. Resistance reduced the number of juveniles that reached maturity; however, the rate of nematode development was more rapid in the resistant 'Jewel' than the other cultivars. The effect of MIS on the growth of 'Centennial' and 'Jasper' was studied in field plots artifically infested with initial population densities (Pi) ranging from 0-10,000 MIS eggs per 500 cc of soil. Population dynamics were similar on both cultivars; however, higher mid season counts were recorded from 'Centennial' than from 'Jasper'. The highest Pi levels did not produce the highest mid season counts. Initial Pi levels had similar effects on the growth of 'Centennial' and 'Jasper' sweet potatoes. Pi levels were negatively correlated with marketable roots produced and root weight, but positively correlated with total cracked roots, percent cracked roots, and cracking severity ratings. 'Jasper' was able to tolerate significantly higher Pi levels with better yields and root quality than 'Centennial'. The incidence of cracking of the fleshy root was apparent on both cultivars at low Pi levels.

Pages

119

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