The Australian System for Ranking Variety Resistance to Fusarium Wilt

Australian cotton growers requested a quantitative system to rank commercial varieties for their resistance to Fusarium wilt. The use of vague terms such as 'some', 'fair' or 'good' resistance was not considered to be satisfactory. A ranking system was developed that compares the resistance of a variety to the resistance of a standard variety based on plant survival in field experiments that are conducted according to an established protocol. The standard variety is given a F.rank of '100'. Varieties that are more susceptible than the standard have an F.rank < 100 with an F.rank of '0' indicating completely susceptible. Varieties that are more resistant than the standard have an F.rank > 100 with an F.rank of '200' indicating complete immunity. The number of field experiments where the resistance of the variety has been compared to that of the standard is included in brackets after the average F.rank.

When resistance ranking was instigated in Australia all commercial varieties were more susceptible than the standard. Over the last 10 years the situation has been completely reversed with almost all current varieties more resistant than the  standard. The most resistant cotton variety grown in Australia is Sicot F1-B which has an average F.rank of 154(19). The cotton variety that is most widely grown in Australia is Sicot 71BRF which has an F.rank of 118(8).