Instability of ramulosis reaction of cotton cultivars with respect to crotection and registration procedures
Renata Silva-Mann; José Roberto Bernandino Filho; Eliseu Norberto Mann; Maria das Graças Guimarães Carvalho Vieira; José da Cruz Machado; Michelle da Fonseca Santos and Alessandra de Jesus Boari
Abstract: The reaction to ramulosis is a descriptor in the protection and registration of cotton cultivars. This descriptor is however not as homogeneous, distinguishable and stable as desired, since it depends on the isolates and the edaphoclimatic conditions. To evaluate the stability of this descriptor for cotton cultivars the Specific combining ability (SCA), general combining 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 gossypii var. cephalosporioides, causal agents of ramulosis. The symptoms were evaluated 10 and 40 days after inoculation. The significance of the variables SCA, GCA and GA indicated variability of horizontal resistance and isolate aggressiveness. This performance suggests specific responses of the cultivars to the contact with different pathogen isolates and consequently, instability of this descriptor.