Instability of ramulosis reaction of cotton cultivars with respect to protection and registration procedures

Abstract

The reaction to ramulosis is a descriptor in the protection and registration of cotton cultivars. This descriptoris however not as homogeneous, distinguishable and stable as desired, since it depends on the isolates and the edaphoclimaticconditions. To evaluate the stability of this descriptor for cotton cultivars the Specific combining ability (SCA), generalcombining ability (GCA) and the general aggressiveness (GA) were estimated for the cultivars EPAMIG 5 - Precoce 1, IAC-22, EPAMIG 4 - Redenção, CNPA – ITA 96 and CNPA – ITA 90, which were inoculated with isolates of Colletotrichum gossypiivar. cephalosporioides, causal agents of ramulosis. The symptoms were evaluated 10 and 40 days after inoculation. Thesignificance of the variables SCA, GCA and GA indicated variability of horizontal resistance and isolate aggressiveness. Thisperformance suggests specific responses of the cultivars to the contact with different pathogen isolates and consequently,instability of this descriptor.

Keywords

• Colletotrichum gossypii var. cephalosporioides
• disease resistance
• horizontal resistance.