Frosts are not rare in the peach production region of Southern Brazil, during the months of July, August and, in some years, even in September. This period coincides with peach blooming and initial fruit development. Aiming to test possible difference among peach genotypes regarding tolerance to low temperatures, two completely randomized experiments were set up in 2009 and 2010. Two factors were tested (genotype and flower bud development stage) using three replications and 20 flower buds per plot. The genotypes included cultivars Chimarrita, Coral and BR-1 and the selection Cascata 730. In the 2010 trial, cv. Charme was added. The phenological stages tested were silver bud, pink, balloon and opened flower. Detached twigs from the genotypes to be studied were submitted during 16 hours to temperatures between -2,2 and - 5,5 ºC. Twigs with fruits before and after pit hardening stage were tested in another experiment. Differences among genotypes were small and seemed to be more dependent on preconditioning of the bud. However, the selection Cascata 730 seemed to be more sensitive to these temperatures. The flower buds were generally less sensitive to negative temperatures (around -3 ºC) on the pink and balloon stages. Soft endocarp fruits were sensitive to cold damage regardless the genotype. Temperatures around -2 ºC do not cause damage on fruits when the endocarp is already hard.
frost tolerance; phenologic stages; genotypes
