How does simulated frost treatment affect peach [Prunus persica (L.)] flowers of different cultivars from worldwide breeding programmes?

• Blooming time, fruit type and breeding programme influence the response to low temperature among cultivars.
• The greater the frost damage the greater was the proportion of flowers showing symptoms in hardier tissues.
• Tolerance response to low temperature showed important variability among peach cultivars.
• FT10, FT50 and FT90 values differ among peach cultivars.

The proportion of frost damaged flowers (FD) and frost symptoms (S1, S2, S3 and S4) was evaluated on 56 peach cultivars from several breeding programmes during 2010 and 2011 seasons in order to understand the tolerance of peach cultivars to low temperature and the susceptibility of their pistils to frost damage. The cultivars were tested at full bloom (‘F’) under simulated frost treatment. Fifteen of these cultivars were also selected in 2012 to calculate frost temperatures (FT10, FT50 and FT90) and their relationship to pistil dry matter. Mid blooming cultivars showed lower tolerances to low temperature than late and early blooming cultivars. Their pistils were also more susceptible to low temperature, showing a higher proportion of more severe symptoms. Blooming time did not affect the degree of pistil susceptibility. Fruit type or peach subspecies (peach, nectarine and flat peach) showed similar susceptibilities to low temperatures; this was not, however, the case for pistils. Significant differences in FD were found for nectarine breeding programmes, but not for peach breeding programmes. The PSB nectarine breeding programme included most of the hardiest cultivars. The susceptibility of pistils to frost damage varied according to breeding programme. Great variability and significant differences were observed between cultivars with regard to FD and frost symptoms. The three frost temperatures considered in this study (FT10, FT50 and FT90) corroborated this variability, mainly because significant differences between cultivars were found within each frost temperature. Nevertheless, no significant relationship was found between them and pistil dry matter. These results provide growers with important information to help them when selecting cultivars for new orchards.