Identification of discriminant factors after treatment of resistant and susceptible banana leaves with Fusarium oxysporum f. sp. cubense culture filtrates B. Companioni 1 , N. Mora 1 , L. Dı ´az 1 , A. Pe ´rez 1 , M. Arzola 1 , P. Espinosa 1 , M. Herna ´ndez 1 , J. Ventura 2 , M. C. Pe ´rez 3 , R. Santos 1 and J. C. Lorenzo 1 1 Laboratory for Plant Breeding, Bioplant Centre, University of Ciego de Avila, Cuba, E-mail: bcompanioni@bioplantas.cu; 2 Cuban National Institute for Tropical Food Crop Research, Santo Domingo, Villa Clara, Cuba; 3 GEPROP, Centro de Gerencia de Programas y Proyectos Priorizados, Ciudad de La Habana, Cuba With 4 figures and 1 table Received November 11, 2003/Accepted January 30, 2004 Communicated by C. Jung Abstract Among the most important crops in developing countries are banana and plantain. However, the production is threatened by increasingly virulent forms of Fusarium wilt, and therefore, intensive breeding programmes are being carried out worldwide. As conventional field studies of banana resistance to this disease are time-consuming and destructive, an easy-to-do procedure was previously developed to differentiate field-grown resistant and susceptible banana cultivars at leaf level. Such a procedure involved the in vitro treatment of fungal culture filtrates on to field-grown adult leaves and the measurement of lesion areas 48 h later. The present report includes measurements of other indicators such as biochemical compounds. The cultivar ÔGross MichelÕ (susceptible) and cv. ÔFHIA-01Õ (resistant) leaves were treated with Fusarium oxysporum f. sp. cubense race 1 culture filtrates. Evaluations were performed 48 h after leaf treatment. Compared with culture medium-treated leaves (control treatment), fungal metabolites produced leaf lesions, decreased free-phenolic contents and increased protein levels in both cultivars. In ÔFHIA-01Õ, the culture filtrate increased contents of cell wall-linked phenolics and the pool of aldehydes (except malondialdehyde). Fungal metabolites did not cause variations in peroxidase activity, chlorophyll pigment contents or malondialdehyde level in any cultivar. The use of Fisher’s linear discriminant analysis to differentiate resistant and susceptible banana cultivars in breeding programmes is also a novel aspect of this report. Such an estimation was performed from a data matrix that included the effects of the fungal metabolites (leaf lesion area and levels of free and cell wall-linked phenolics, aldehydes, except malondialdehyde, and proteins) on banana leaves of seven cultivars (four susceptible and three resistant). Key words: Musa sp. — Fusasium oxysporum — early selection — discriminant analysis — Panama disease Banana and plantain are the fourth most important food crops in developing countries (FAO 1999) but continued production is threatened by the development of more virulent forms of Fusarium wilt (Vuylsteke et al. 1996). In the susceptible cultivars, the pathogen attacks the vascular root tissues and toxins are transported to the rest of the plant. To the contrary, resistant plants produce gels, tyloses and phenolics to trap the fungal spores (Beckman and Talboys 1981). Chemical control of this disease is economically impracticable (Rowe 1987, Stover and Simmonds 1987) and therefore, breeding programmes are needed. Procedures to differentiate resistant and susceptible cultivars are important tools to accelerate banana-breeding programmes and reduce research costs. Conventional field studies of banana resistance to Fusa- rium wilt are time-consuming and destructive (Stover and Buddenhagen 1986, Rowe and Rosales 1993, Daniells et al. 1995). Therefore, a rapid and non-destructive procedure was previously developed to differentiate field-grown resistant and susceptible banana cultivars at leaf level (Companioni et al. 2003). Such a procedure involved the use of fungus culture filtrates on adult leaves and was based on the measurement of leaf lesion area. The present report inclu- des measurements of other indicators (biochemical com- pounds) after the treatment of culture filtrate on to banana leaves. Several biochemical indicators have been described to alter during fungal disease symptom progress, such as phenolic levels (Horsfall and Cowling 1980, Beckman 1987, Gurr et al. 1992), peroxidase activity (Novak et al. 1992, Aguilar et al. 2000), lipid peroxidation intensity (Beckman and Talboys 1981, Wu and von Tiedemann 2002), and pigment variations (Favaron et al. 1994, Lauge´ et al. 2000, Kombrink and Schmelzer 2001). However, it appears that the use of biochemical compounds to detect banana resistance to Fusa- rium oxysporum f. sp. cubense (Panama disease) at leaf level has not been reported. Fisher’s linear discriminant functions to differentiate resist- ant and susceptible cultivars were estimated from a data matrix that included the effects (leaf lesion area and levels of biochemical compounds) of the fungal metabolites on banana leaves of seven cultivars (four susceptible and three resistant). Discriminant analysis is useful for situations where the building of a predictive model of group membership based on observed characteristics of each case is desirable. The procedure generates discriminant functions based on linear combinations of the predictor variables, which provide the best discrimination between the groups. The functions are generated from a sample of cases for which group member- ship is known. The functions can then be applied to new cases with measurements for the predictor variables but unknown group membership (Teshome et al. 1997, Cardi 1998, Somersalo 1998, Daoyu and Lawes 2000, Figlivolo et al. 2001, Bantte and Prasanna 2003). The use of this kind of analysis for differentiation of banana resistance or susceptibility to Panama disease at leaf level is a novel aspect of this report. Plant Breeding 124, 79—85 (2005) Ó 2005 Blackwell Verlag, Berlin ISSN 0179-9541 U. S. 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