There is a lack of information about the level of resistance of cotton genotypes to a wider range of Ramularia areola isolates occurring across the cotton growing areas of Brazil. For this purpose, firstly it is necessary to know the existence or not of genotypic and phenotypic variability among the R. areola isolates from different geographical origins. The objective of the present investigation was to verify the existence of phenotypic variability among 23 R. areola isolates collected from six cotton growing states of Brazil. Two resistant genotypes, FMT 02102996 and CNPA BA 2003-2059, and the susceptible genotype FMT 701 were individually inoculated with 23 R. areola isolates under glasshouse conditions and the severity of infection was evaluated 30 days after inoculation. Genotypes CNPA BA 2003-2059 and FMT 02102996 were susceptible to three isolates and resistant to the rest of the isolates. Genotype FMT 701 was susceptible to all the isolates except the isolates 22.3 and 42.7. Results indicate the existence of variability among R. areola isolates and that the three genotypes are useful in distinguishing phenotypic variability within isolates of this pathogen.

Spore production of Ramularia areola has always been a difficult task. Brazilian isolates of R. areola produce spores of variable size and shape. The typical spores are 3 septate, rarely 4 and 5 septate, together with abundant single celled oblong to round bodies-a phenomenon not reported earlier for R. areola. Budding of spores is a continuous process as observed in our isolates. By repeated culturing the pathogen either ceases to produce typical spores or loses its pathogenic character. To solve this problem, a technique was developed to produce large quantity of typical spores under laboratory conditions. Sporulating cultures produced on Petri plates containing V8 juice-agar were kept on the laboratory bench till they became dry and then stored at 5˚C for reisolation and/or for production of fresh inoculum. In such dried cultures spores remain viable for a period of over 12 months, and hence isolates of R. areola originated from different geographic regions can be maintained in sporulating form. Results of the present investigation would aid cotton breeders and pathologists in screening germplasm resistant to Ramularia and in other genetical studies under glasshouse conditions.