Effect of growth retardants on intermittent irrigation during water deficit stress period in Mrig (Monsoon flowering) crop of Nagpur mandarin (Citrus reticulata Blanco)

Abstract

A field investigation was carried out at the experimental orchard of Nagpur mandarin (Citrus reticulata Blanco) at CCRI, Nagpur in block no. 44 during 2015. Breaking the seasonality of Nagpur mandarin for commercial production would not only substitute the import of fresh fruits, but also provide the incentive prices to the Nagpur mandarin growers. Withholding water, root exposure and root pruning are the common practices adopted to regulate flowering. In the recent years, chlormequat chloride and paclobutrazol, growth retardants have been used with considerable success to induce early flowering for off-season production in several fruit crops. Citrus trees are exposed to water deficit stress by withholding water for about 30-45 days before expected flowering. Many times this stress is untimely broken due to climate change related untimely rains resulting in to sparse or no flowering due loss of flowering stimulus due to untimely rains. Therefore, to assess the effectiveness of two plant growth regulators chlormequat chloride and paclobutrazol these studies were conducted. Flood irrigation was given during the stress period in second week of May and following treatments were applied to reimpose the stress broken by intermittent irrigation. Six years old trees of Nagpur mandarin were used as experimental plants. The trees were uniform in age and size and trained to single stem. The trees were grown under drip irrigation following common cultural practices during the study period. The experiment was laid out in randomized block design with seven treatments replicated four times. Four trees were used for each replication. The treatments were imposed four months before flowering (June). The treatments tried were chlormequat chloride 2000, 3000 and 4000 ppm as foliar spray, paclobutrazol 6 g, 9 g and 12 g as soil application along with control.  Observations on soil moisture content (%) at weekly interval, leaf water potential (Ψ_L) at weekly interval, orchard microclimate: temperature, humidity and rainfall, were recorded. Paclobutrazol 12g showed the peak water stress in terms of leaf water potential (Ψ_L) which ranged from (-3.00 MPa to -3.17 MPa) till mid June and there was no flowering in June-July due to the high temperature (41.28°C), low rainfall (6 mm) and low humidity (40.71 %) during this period. The conditioning of microclimate in the orchard with sprinklers and irrigation can help in exploiting the flowering potential attained through growth retardant treatments.