Susceptibility to Root‐Knot Nematodes in Cotton Lines Resistant to the Fusarium Wilt/Root‐Knot Complex1

Abstract

The cotton (Gossypium hirsutum L.) breeding lines CABCS'‐1‐81, CAHUS‐2‐81, and LEBOCAS'‐3‐81, developed by the multiple adversity resistance (MAR) technique, have been reported to be resistant to the fusarium wilt [Fusarium oxysporum Schlecht f. sp. vasinfectum (Atk.) Synd. and Hans.]/root‐knot nematode [Meloidogyne incognita (Kofoid and White) Chit.] complex. Host wilting was the sole criterion upon which resistance to the complex was based. Resistance to the nematode, usually predicted upon the inability of the nematode to reproduce on the host, was never directly measured. Our objective, therefore, was to measure the resistance of these breeding lines to the nematode alone. When nematode inoculated plants were grown in 15 cm pots in replicated greenhouse tests, the cotton breeding lines supported levels of M. incognita egg production that did not differ from that produced on the nematode susceptible ‘TAMCOT SP37’. All lines supported greater (P = 0.01) egg production than did the root‐knot nematode resistant ‘Auburn 634’. In replicated microplot tests, seed cotton yields of the breeding lines were not different from that of the susceptible TAMCOT SP37 at several nematode inoculum levels. Similarly, reproduction of M. incognita on susceptible and putatively nematode‐resistant cotton lines did not differ in microplot tests. Thus, while the cotton lines CABCS'‐1‐81, CAHUS‐2‐81, and LEBOCAS‐3‐81 may be more resistant under field conditions to fusarium wilt than is TAMCOT SP37, our study indicates they are not more resistant to M. incognita. Therefore, the indirect selection for resistance to root‐knot neniatodes based on host wilting, even in the presence of both pathogens, was found to be an inadequate test of resistance to M. incognita.