Effects of Plant Growth Regulators, Sevin and Maize Extract on Chemical Thinning, Fruit Quality and Return bloom of Apple (Malus domestica, borkh cv. Golden Delicious)

‘Golden delicious’ is one of the commercial cultivars of apple in Iran. Isfahan Province especially Semirom has remarkable hectares under cultivation of this cultivar. One of the cultural problems of this cultivar is alternate bearing, that is common in ‘Golden Delicious’ apple resulting in poor flower bud development and low crops in following year. To regulate bearing, 6-benzyladenine (BA) (100 and 150 mg l-1), kinetin (100 and 150 mg l-1), naphthaleneacetic acid (NAA) (15 and 30 mg l-1), sevin (600 and 1200 mg l-1) and extract of corn seeds were applied, 20 days after full bloom. The experiment was arranged in completely randomized block design with four replications in two successive years (2008, 2009). The results showed that NAA at 15 and 30 mg l-1 induced fruit abscission 59.55% and 71.53%, respectively. Sevin at 600 and 1200 mg l-1 induced fruit abscission 48.80% and 73.83%, respectively. Sevin at 600 mg l-1 had no significant effect on fruit drop compared with control. BA at 150 mg l-1 increased fruit drop up to 53.05% compared with control. Corn seed extract had no significant effect on fruit drop. NAA at 15 and 30 mg l-1 significantly increased return bloom in the following year and the average of fruit weight was increased up to 142 and 145 g, respectively. Therefore NAA at 15 and 30 mg l-1 and BA at 150 mg l-1 can be used for fruit thinning of Golden Delicious apple.