Influence of Air Temperature in the Emission of Nodes, Ramifications and Flowers in Hybrids of Watermelon (Citrullus lanatus)

The culture of watermelon develops mainly under conditions of high temperature, being the temperature an element that directly affects the emission of vegetative and reproductive organs. There are no reports of the accumulation of temperature required for emission of branches, nodes and flowers. Thus, this experiment aimed to evaluate the rate of emission of vegetative and reproductive organs for hybrids of watermelon in relation to air temperature, using the hybrids of Manchester and Top Gun watermelons. The experiment was conducted in Federal University of Santa Maria, campus Frederico Westphalen-RS, from September to December 2014. Evaluations were conducted at every two days and it was determined the variables: nodes emission, final number of nodes on the main stem, number of primary and secondary ramifications and number of staminate flowers and open pistillate flowers related to accumulated thermal sum for the emission of such organs, and the ratio between the number of staminate flowers to the pistillate. The hybrids of watermelon present for plastochron of 18.8 °C node day, final number of nodes of the main ramification of 43 and number of primary and secondary ramifications of eight and 20, respectively. For the emission of staminate and pistillate flowers the hybrids need an accumulation 10.5 and 46.7 °C day, respectively. The number of staminate and pistillate flowers is 52 and nine, respectively, and the ration between flowers of 6.6:1.