Effects of some Synthetic Auxins on Yield and Marketability of Four Plum Cultivars

Size of fruit in Japanese plum has an important role in marketability and fruit quality. In Golestan province, one of the most important areas of plum production in Iran, due to high temperatures in summer that led to unfavorable conditions in fruit ripening stage, final fruit size are reduced in commercial scale. In this respect, the large financial loss is imposed to plum growers. Today, synthetic auxins are widely applied in the commercial gardens of the world in order to increasing fruit size and improving fruit growth . Auxins can promotes cell division, cell enlargement in fruit growth stages and it also acts as sink for nutrients absorption. In this study, the effects of the foliar application of two synthetic auxins were investigated on fruit qualitative and quantitative of Japanese plums in Golestan province climatic conditions.
Material and

A split-plot factorial experiment based on randomized complete block design with four replications was conducted in a commercial orchard from Run Agri Company in Golestan province, Iran for two years (2015 and 2016). The main factor was considered four plum cultivars including ‘Ghatreh Tala’, ‘Shablon Zodras’, ‘Shablon Mianras’ and ‘Shablon Dirras’ which were spraying by two synthetic auxins: NAA (0, 300 and 400 mg/l) and 2, 4-D (0, 10 and 30 mg/l) along and in combination. Fruit length, diameter, length to diameter ratio and fruit weight, yield, yield efficiency and percentage of first and second fruit grade production characteristics were evaluated. Data analysis was performed by SAS 9.1 software and the comparison of mean values was done by Duncan's multiple range tests at 0.05 of probability level.

The results showed that foliar application of auxin significantly increased fruit size and weight. The results showed that the response of plum cultivars to synthetic auxins was different. Fruit length and width of ‘Shablon Dirras’ cultivar were increased with the 2,4-D application at 10 and 30 mg/l , but in the ‘Shablon Mianras’ cultivar, the combination of 2,4-D with NAA improved fruit size. NAA at its highest concentration (400 mg/l) plus 2, 4-D at its highest concentration (30 mg/l) produced the largest fruits and the highest yield in ‘Shablon Mianras’ cultivar. Stern et al. (16) also obtained similar results from NAA and 2, 4-D treatments in plum, which is confirmed our results. The yield (kg/tree) and yield efficiency in plum cultivars increased significantly by synthetic auxin treatments. The average of yield (kg/tree) by 2, 4-D and NAA foliar application increased 30, 60, 28 and 34 percent in ‘Shablon Zodras’, ‘Shablon Mianras’, ‘Shablon Dirras’ and ‘GhatrehTala’ cultivars, respectively. The highest yield efficiency was obtained in ‘Shablon Mianras’ cultivar (0.38 kg/cm2) in 30 mg/L of 2, 4-D plus 400mg/L of NAA, which showed a 120 % increasing in comparison to control trees. Denis (7) reported increases the quantitative characteristics of stone fruits such as fruit size and weight by using synthetic auxin spray. The effect of auxin on increase cell proliferation and cell size are main reason for increasing the length and weight of the fruits (7). The results showed that 2, 4-D and NAA auxins were able to increase the percentage of first grade fruit relative in all plum cultivars in comparison to the control trees, but the concentrations and composition of plant growth regulators that increased the percentage of first grad fruits were not completely same to best treatments on fruit size, weight or yield. It referred to the first-grade fruits selection criteria. In selecting of best marketable fruits, in addition to the size of the fruit, others feature such as fruit appearance, color, physical damage and the absence of symptoms of diseases are also taken into grading. Temperature, water, nutritional and genetic conditions can affect the effect of plant growth regulator treatments (13).

Plum cultivars showed different reactions to synthetic auxin treatments. The largest fruit, highest yield and yield efficiency obtained in 2,4-D (30 mg/l ) with NAA (400 mg/l) in ‘Shablon Mianras’, ‘Shablon Dirras’ and ‘Ghatreh Tala’ cultivars and 2,4-D at 30 mg/l with NAA at 300 mg/l concentration in ‘Shablon Dirras’ and ‘Ghatreh Tala’ Cultivars. The highest degree of first grad-fruit was observed at 10 mg/l 2,4-D in ‘Shablon Zodras’ and ‘Dirrras’ cultivars and 300 mg/l of NAA in ‘Shabolon Mianras’ and ‘Ghatreh Tala’ cultivars.