APPLICATION OF CHEMICAL PRODUCTS ON OVERCOMING THE ENDODORMANCY IN PEAR TREES IN REGIONS OF LOW COLD UNITIES

Abstract

The pear is the third temperate fruit specie more consumed in Brazil. However, the expansion of this species requires the development of modern cultural techniques to allow proper cultivation. The objective of the present study was to evaluate the effect of different chemical products to overcome endodormancy of cultivar ‘Santa Maria’ pear (Pyrus communis L.) in Southern Brazil. The experiment was conducted at the Frutirol orchards in the city of Vacaria, Rio Grande do Sul State (28°29’27.12” S, 50°56’09.78” W). The following formulates were used: Dormex (Hydrogen Cyanamide H2CN2) at 0.7% + mineral oil 3%; Dormex 0.3% + mineral oil 3%; potassium nitrate 10% + mineral oil 3%. Control trees were sprayed only with water. The experimental design was completely randomized, with ten replicates, the experimental unit was a single tree with two selected branches. The number of buds was counted on the day of application and 60 days after to determine bud break rate. The number of fruits was counted the 09/01/2008. The obtained results showed that the use of the two dormancy breaking agents is necessary to standardize the bud break and the harvest in cultivar ‘Santa Maria’ pear. Dormex at 0.7% + mineral oil 3% allowed the best result for bud break and fruit number. INTRODUCTION The pear is a temperate fruit specie characterized by leaf fall at the end of the vegetative cycle and subsequent by the entrance into endodormancy. This physiological inactivity allows survival in low temperatures, providing natural conditions to initiate a new vegetative cycle in spring (Leite, 2005). In mild winter climatic regions, bud break is insufficient and characterized by heterogeneous flowering (Leite, 2005). Moreover when chilling requirement is not satisfied, other anomalies might occur, such as, lack of vegetative growing, small leaves, low fruit set, small and misshapen fruits (Petri and Leite, 2004). To satisfy chilling requirement in mild winter conditions, such as Southern Brazil, the use of chemicals to overcome endodormancy is necessary. The most widely products used such as mineral oil, calcium cyanamide (CaCN2), potassium nitrate (KNO3) and hydrogen cyanamide (H2CN2) can standardize and induce early bud break and flowering in certain circumstances, as found in peach, pear, grape and apple (Arellano, 1991; Mann et al., 1994). Since no research activity on dormancy breaking agents is available in Southern Brasil, a specific study was carried out on cultivar Santa Maria pear to evaluate the effects of some formulates on bud-break and fertility with the aim to increase its productivity and profitability. MATERIALS AND METHODS The experiment was carried out from August 2007 to January 2008, in the company Agricultural Frutirol in Vacaria City RS, Brazil (50°56’02” S and 28°30’14” W, altitude of 955 m) on an orchard of the ‘Santa Maria’ pear (Pyrus communis L.), four year old, spaced at 0.7×3.0 m between trees and rows. The experimental design was Proc. XI IS on Plant Bioregulators in Fruit Production Ed.: G. Costa Acta Hort. 884, ISHS 2010 246 completely randomized, with 10 replicates, where different chemicals were tested to induce bud-break. The products used were Dormex 0.7% (Hydrogen Cyanamide H2CN2) + mineral oil 3%; Dormex 0.3% + mineral oil 3%; potassium nitrate 10% + mineral oil 3%, while the control was treated only with water. Application time was September 5 2007, when trees were at swollen flower bud stage. The considered experimental unit was a tree, where two one year branches were selected for data collection. On these branches, the total number of lateral buds present was counted at application time and 60 days after and the result was expressed as percentage of bud break. The number of fruits per tree was counted on January 9 2008. Data Percentage data were transformed to arcsine of the square root of % / 100 and data were statistically analyzed (variance and Tukey s test (5% probability)). RESULTS AND DISCUSSION As far as budbreak in concerned, all the formulates induced higher bud-break value than control. The best results were obtained using Dormex 0.7% + mineral oil 3% (Fig. 1). Hydrogen Cyanamide partially allow to overcome endodormancy and standardize bud break, showing its efficacy also on ‘Santa Maria’ pear cultivar, as previously found on kiwifruit (Walton and Fowke, 1993). The higher bud break lead to higher production of fruits per plant; again Dormex® 0.7% + mineral oil 3% showed better results than control while Dormex at a lower concentration (0.3% + mineral oil 3%) lead to a higher number of fruits (Fig. 1). These chemicals also increased fruitset, as similarly found by Schuck and Petri (1995) in kiwifruits , Citadin et al. (2006) in peach and Mizobutsi et al. (2003) in persimmon. As a result of the dormancy breaking agents application the yield/tree resulted higher than control and the profitability was also higher especially in the Dormex 0.7% and potassium nitrate sprayed trees as compared to control (Fig. 2). More in details the application of Dormex 0.7% + mineral oil 3%, guarantees besides higher yield also higher profitability for the grower. According to the average price paid, in Brazil, for the pear (€ 1.55), the Dormex 0.7% increased up to 43% the profitability (Fig. 2). In addition, on the basis of Francisconi et al. (1992) result, the number of flower clusters might increase the return bloom leading to higher flower bud formation in the year following the application. CONCLUSIONS 1. The treatment Dormex 0.7% + mineral oil 3% and potassium nitrate 10%, were the most effective on the pear cultivar ‘Santa Maria’; 2. The percentage of bud break, the number of fruits and the productivity of pears of cultivar ‘Santa Maria’ is negatively affected when chilling requirement are not satisfied. Literature Cited Arellano, L.S. 1991. Uso de cianamida hidrogenada em plantas de folhas caducas no Chile. Workshop-Dormex, Vitoria, Brazil, p.15. Citadin, I., Bassani, M.H., Danner, M.A., Mazaro, S.M. and Gouvea, A. 2006. Uso de cianamida hidrogenada e oleo mineral na floracao, brotacao e producao do pessegueiro ‘Chiripa’. Rev. Bras. Frutic. 28:125-130. Francisconi, A.H.D., Barradas, C.I.N., Marodin, G.A.B. and Seibert, E. 1992. Efeito de oleo mineral, cianamida hidrogenada e thidiazuron na quebra de dormencia e producao da pereira (P. communis L.) cv. Packham’s Triumph. Rev. Bras. Frutic. 14:161-166. Leite, G.B. 2005. Evolucao da Dormencia e a Heterogeneidade na Brotacao. Encontro Nacional Sobre Fruticultura De Clima Temperado, Fraiburgo, Brazil, p.269-275. Mann, S., Singh, H., Sandu, A.S. and Grewal, G.P.S. 1994. Effect of cyanamide on bud burst, flowering and fruit maturity of Baggugosha pear. Acta Hort. 367:214-223.