The root-knot nematode, Meloidogyne incognita (Kofoid and White) Chitwood, is a significant pest of cotton on lighter soils. The objective of the greenhouse research was to determine the effect that two sources of resistance have on the development of M. incognita. Some possible effects of resistance are reduced penetration by juveniles, failure to undergo molts, or development of juveniles into males.

Three inch plastic pots were filled with methyl bromide-fumigated soil and inoculated with 10,000 M. incognita (race 3) eggs. One week after inoculation, M8 (susceptible), T78 (moderately resistant), and Aub634 (highly resistant seed were planted. Starting at six days after emergence, two plants of each strain were harvested at six day intervals. The nematode developmental stages were stained within the root with acid fuchsin.

M. incognita development was different on each cotton strain. At 6 days after emergence 97 juveniles had penetrated the roots of M8 and they developed normally into females (84 at 36 days). More juveniles penetrated the roots of T78 roots, more developed into males and fewer females (23) were observed at 36 days. The most juveniles (437) were observed in Aub 634 roots and the number did not decline until after 18 days. Very few of the juveniles in Aub634 molted and only on female was observed at 36 days.

The resistance of Aub634 or T78 to M. incognita does not appear to be due to reduced infection by juveniles. Juveniles enter Aub634 roots but most do not molt to latter stages. This failure to molt may indicate an inability of M. incognita to induce a parasitic relationship in Aub634. The resistance of T78 may be a different mechanism or a lower level of the resistance found in Aub634.