Determination of cold and freezing injury grade indexes for three tropical characteristic fruit trees

Abstract: 【Objective】The planting benefits of wax apples, mangos and Zizyphus mauritiana are relativelylarge and these fruit trees had developed rapidly in recent years in Fujian, Guangxi, and Guangdong prov-inces.However, these areas belong to the northern edge of the tropical fruit trees planting area and cou-pled with the blind actions of farmers, cold and freezing injuries occur annually in varying degrees.Cur-rently, there are no cold and freezing injury grade indexes of Zizyphus mauritiana and mangos and onlypreliminary studies on wax apples.In order to achieve a reasonable layout, to reduce the loss from coldand freezing injuries and to ensure the healthy and stable development of tropical fruit trees, there is an ur-gent need to establish cold and freezing injury grade indexes for wax apples and mangos and Zizyphus mauritiana by using a variety of different methods.【Methods】Based on the historical climate data and theinvestigated data of large-scale cold and freezing injuries and other experimental methods, the morpholog-ical changes of wax apples, Zizyphus mauritiana and mangos were analyzed.According to the morphologi-cal standard of cold and freezing injuries, the grade of injury samples was determined.On the basis of thecold and freezing grade (x) and the minimum temperature (Td) samples of process before 2015, the rela-tionship between X and Td was established by means of mathematical statistics and the grade indexes ofcold and freezing injuries were preliminarily determined.The grade indexes of three fruit trees were deter-mined by validation methods of artificial climate chamber experiments and geographical transplantationexperiments and actual orchard disaster samples in 2016.【Results】The relationship between the grade di-saster (X) of three fruit trees and the minimum temperature (Td) of the related processes were determinedby applying many functional equations, with the results showing that the fitting effect of an equation of onedegree, an equation of two degrees and an equation of three degrees was very good.The cold and freezinginjury grade (x=0.5, 1.5, 2.5, 3.5) was divided into the following three equations for the fruit trees:the criti-cal thresholds of no to light grade, light to moderate grade, moderate to severe grade and severe to most se-vere grade at low temperature (Td) could be concluded;the Td values from the three equations were aver-aged, for the convenience of the application and the values were required to take an integer of 0.5 ℃;ourwork in this paper determined the cold and freezing injury grades of the three tropical characteristic fruittrees with morphological indexes as follows:wax apple:Tmin>5.5 ℃, without cold and freezing injury, nor-mal growth;3.0 ℃