Frost Tolerance of Eight Olive Cultivars

By D. Barranco, N. Ruiz, M. G. Campo. 2005

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This study aims to determine the relationship between laboratory frost-resis- tance data for the leaves of eight olive cultivars and observed field resistance in the same genotypes undergoing natural frost damage. The lethal freezing temperature (LT 50 ) for each cultivar was established by measuring the electrical conductivity (EC) of the medium into which solutes from damaged leaf tissue were leaked. The value obtained was then correlated with percentage frost shoot for the same eight cultivars damaged by natural frosts in a field test. A negative correlation was observed between the percentage frost shoot and leaf LT 50 for all the cultivars under study. The most frost-hardy cultivars ('Cornicabra', 'Arbequina', and 'Picual') were those presenting the lowest percentage frost shoot and lowest LT 50 . Conversely, the most frost-susceptible cultivar ('Empeltre') displayed 100% frost shoot, together with one of the highest LT 50 values (-9.5 °C). Accord- ing to these results, lethal freezing temperature (LT 50 ) calculated from leaf ion leakage at a range of freezing temperatures, seem to be a valid parameter for evaluating frost tolerance in olive cultivars. The olive is an evergreen plant grown mainly in the Mediterranean basin. Olive growth and productivity are limited by low temperatures in winter and frost damage in spring and fall. Although the olive is moderately resistant to subzero temperatures, below a certain re- sistance threshold freezing temperatures can damage the plant; damage to aerial parts of the plant at below -7 °C can reduce productivity (Palliotti and Bongi, 1996), while at -12 °C damage may be serious enough to threaten the life of the tree (Larcher, 1970). Frost conditions occur quite frequently in Italy and Spain, but also in some southern zones of Europe and America (Denney et al., 1993). The most char- acteristic symptoms of frost damage include tip burn of shoots tips and nearby leaf tips, leaf chlorosis, defoliation, bark split on branches and also damages to buds and fruits. Cultivation techniques such as irrigation, re- duction in nitrogen fertilizer rates, late pruning and bare-soil maintenance systems, have been widely used in commercial orchards to limit frost damage. However, the most effective way to combat damage, apart from simply avoiding frost-prone areas, is to use cold-hardy plant- ing material. Selection of the least susceptible varieties is the most effective indirect method of avoiding frost damage. A number of surveys and field trials follow- ing natural frosts have provided frost-tolerance data for several olive varieties (Antognozzi and Catalano, 1985; Barranco, 2004; Barranco et

Subfields: Organic Chemistry, Plant Science

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