Abstract

Mutation by ionizing radiations such as gamma-rays is being employed as one of the mutation breeding approaches to obtain the desirable mutant cultivars and genotypes in plants. Almond cultivars 'A200' and 'Sahand' are self-incompatible following pollination and fertilization problems. Therefore, obtaining their late-flowering and self-fertile mutants with good biological traits, by means of mutation, will be very bounteous for breeders and producers. This study was conducted to evaluate the effects of different exposition times to gamma-radiation on some biological traits of two late-blooming cultivars ‘A200’ and ‘Sahand’. Current shoots of 'A200' and 'Sahand' were exposed to 36 µC gamma-radiation for 0, 5, 10, 30 and 150 min from the Cobalt 60. The factorial experiment was carried out on 4-year old irradiated trees based on completely-randomized design (CRD) and some biological traits such as: resistance to diseases agents, partial fungus and pests (aphid, mite, etc.), blooming date, leaf bud break date, bearing type, leaf area (LA) and flower density were investigated in all irradiated plants. Results showed that long exposition times have significant positive effects on resistance to disease agents such as: "polystigma occharaceum", mite, LA and flower density, but did not have significant effect on bearing type, resistance to aphids, blooming and leaf bud break dates in spring. Effects of cultivars were significant on resistance to pests (aphid, mite and other main destructive pests) and diseases agents and bearing type, while no significance was seen on blooming, leaf bud break dates, LA and flower density. Interaction effect between cultivars and exposition time was significant on resistance to diseases, mite and flowering date, but was not significant on LA, flower density, resistance to aphid and leaf bud break date. However, the maximum resistance to diseases agents, aphid and mite was observed in plants irradiated 150 min in both cultivars.

Key words:  Almond, breeding, mutants, gamma-irradiation, biological traits.