Autoradiography of Developing Syncytia in Cotton Roots Infected with Meloidogyne incognita.

Cotton (Gossypium hirsutum) seedlings, uniformly infected with Meloidogyne incognita, were exposed for periods of 1-15 days to a nutrient solution containing tritium-labelled thymidine. Syncytium formation began with the amalgamation of cells near the nematode head, and was followed by synchronized mitoses of the nuclei which had been incorporated into a single cell. Syncytial nuclei synthesized DNA in roots harvested 3, 6, 9, 12, and 15 days after inoculation.

Free Amino Acids in Roots of Infected Cotton Seedlings Resistant and Susceptible to Meloidogyne incognita.

Quantities of free amino acids in segments of cotton roots resistant and susceptible to Meloidogyne incognita were compared. Following infection, the root-knot susceptible cultivar, M8, had greater percentage increases of certain individual free amino acids than the resistant cultivar, Clevewilt, but the sum total of free amino acids was greatest in the resistant cultivar. More free amino acids were present in infected than in noninfected plants of both cultivars.

Post-Infection Development and Histopathology of Meloidogyne incognita in Resistant Cotton.

The numbers of Meloidogyne incognita larvae which migrated from cotton roots declined over a 16-day period, but the difference in numbers migrating from resistant and susceptible cultivars was not significant. Larvae penetrated susceptible roots, matured, and reproduced within 14 days following inoculation, whereas nematode development in the resistant roots was greatly retarded. Three types of histological responses were observed in infected, resistant roots, and these correlated with the degree of nematode development.

Resistance of Cotton to the Root-Knot Nematode, Meloidogyne incognita.

Cotton plants resistant to Meloidogyne incognita had roots characterized by fewer and smaller galls, and females that produced fewer egg masses containing fewer eggs than did susceptible plants. Many galls on resistant roots contained no nematodes at the time of examination. Penetration of the resistant cultivar was equal to that of the susceptible cultivar and independent of the number of nematodes in the inoculum.