Use of culture-derived Fusarium oxysporum f. sp. cubense, race 1 filtrates for rapid and non-destructive in vitro differentiation between resistant and susceptible clones of field-grown banana

Banana and plantain are among the most important food crops in developing countries but production is threatened by increasing virulent forms of Fusarium oxysporum f. sp. cubense. Chemical control is not economically effective and,therefore, breeding programs are necessary. Traditional field studies of new genotype resistance to this disease are time-consuming and destructive. Therefore,we developed a rapid and non-destructive procedure to differentiate field-grown banana resistant from susceptible clones. This procedure implicates application of culture filtrates of Fusarium oxysporum f. sp. cubense race 1 onto banana leaves. The relationship between duration of the fungal in vitro incubation, and the fungal culture fresh mass, the culture filtrate absorbency, and the Gross Michel (susceptible cultivar)leaf lesion area (after application of the culture filtrate) were similar and at 24day-incubation the highest values of the recorded indicators were observed. A comparison between Gross Michel and FHIA-01(resistant) was also performed. The most relevant differences between cultivars were observed at 48 hours after application of the culture filtrate, and in the middle-aged leaves. The position of the culture filtrate application in the leaf limb (distal, middle, proximal) was not determinant. A wider comparison among banana cultivars confirmed previous results informed by other researchers using different systems to study this plant-fungus interaction. Such a confirmation validates the effectiveness of the procedure described here to select rapid and non-destructively banana resistance to this disease at field level. This revised version was published online in August 2006 with corrections to the Cover Date.     

The greening of the “barrios”: Urban agriculture for food security in Cuba

Urban agriculture in Cuba has rapidly become a significant source of fresh produce for the urban and suburban populations. A large number of urban gardens in Havana and other major cities have emerged as a grassroots movement in response to the crisis brought about by the loss of trade, with the collapse of the socialist bloc in 1989. These gardens are helping to stabilize the supply of fresh produce to Cuba's urban centers. During 1996, Havana's urban farms provided the city's urban population with 8,500 tons of agricultural produce, 4 million dozens of flowers, 7.5 million eggs, and 3,650 tons of meat. This system of urban agriculture, composed of about 8,000 gardens nationwide has been developed and managed along agroecological principles, which eliminate the use of synthetic chemical pesticides and fertilizers, emphasizing diversification, recycling, and the use of local resources. This article explores the systems utilized by Cuba's urban farmers, and the impact that this movement has had on Cuban food security.     

Identification of discriminant factors after treatment of resistant and susceptible banana leaves with Fusarium oxysporum f. sp. cubense culture filtrates

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 ‘Gross Michel’ (susceptible) and cv. ‘FHIA‐01’ (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 freephenolic contents and increased protein levels in both cultivars. In ‘FHIA‐01’, 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).