Evaluation of peach cultivars' leaf apparatus resistance to water deficit according to photosynthetic system condition

One of the rating methods of selection material for fruit-bearing crops is to determine how well photosynthetic system works on changing intensity of fluorescence. Photosynthetic activity was defined allowing for induction of chlorophyll fluorescence (Kautsky’s effect). This method is widespread to define a resistance level of leaf apparatus to water deficit. Crimea is in the zone with a lack of moistening and irrigation water in the summer period. A moistening deficit has an unfavourable influence on photosynthesis efficiency and as a result it reduces plant productivity. In this way breeding for drought-resistant cultivars based on the genotypes of foreign selection is extremely important for peach development as a culture. Four peach cultivars, of American origin, were chosen for research: ‘Red Haven’ (control), ‘Dakota’, ‘Jungerman’ and ‘Early Crawford’. Samples were taken in July and August, periods which differ significantly in the water regime. Our results showed that under stress conditions (July) peach cultivars most affected by drought, were ‘Dakota’, ‘Jungerman’, ‘Early Crawford’, presenting reduction of quantum efficiency of primary photosynthetic reactions (F_v/F₀) up to 49.1%. This factor causes non-productive spending of energy and transition of some chlorophyll to non-active state. According to the parameter (F_v/F_m) ‘Early Crawford’ and ‘Jungerman’ have the most considerable response to dehydration. ‘Red Haven’, control cultivar, was distinguished with its parameter of 3.0%. During more favourable period according to moist level (August) ‘Red Haven’, ‘Dakota’ and ‘Early Crawford’ kept the most stable photosynthetic activity. Quantum efficiency (F_v/F₀) of these cultivars went down to a small degree (13.6-23.5%). Therefore, parameters of photoinduced curve of chlorophyll fluorescence make it possible to get objective evaluation of introduced peach cultivars according to drought-resistance in summer period and reveal differences in mechanisms of water deficit response.