Modeling the pollen tube growth for 'Gala' and 'Fuji' apples (Hector A. Camargo Alvarez)

ISHS Secretariat
Hector A. Camargo Alvarez

Flower fertilization and fruit set success in apples depend on the behavior of the pollen tube growth, namely, the pollen tube length after pollination and the time taken to reach the base of the style. Predicting these characteristics will assist in controlling the crop load, by permitting the fertilization of the desired number of flowers and discarding the rest by the use of chemicals which inhibit pollen tube growth prior to fertilization. The main factors affecting pollen tube growth rates are temperature and the resistance of the style tissue. In this way, the objective of this study was to develop a model for the prediction of pollen tube growth based on temperature and the percentage of style penetration.
For this purpose, flowers of two apple cultivars ('Fuji' and 'Gala') were emasculated, hand pollinated and placed in growth chambers at one of eight constant temperatures (4.5, 7, 11.5, 14.5, 21.5, 22.6, 28 and 30°C). The flowers were sampled at five different times (hours) after pollination (HAP), and the pollen tube length was measured. Curves were adjusted for pollen tube length as a function of the HAP for each temperature, and the hourly growth rate was calculated as the derivative of the adjusted curves. Then, a response surface model was fixed for the growth rate in function of temperature and percentage style penetration (calculated from HAP taking the style length as 100%). Pollen tube length was simulated with Euler's integration, accumulating the growing rates every time step of one hour after a starting point.
Pollen tube under temperatures below 7°C did not reach the stylar base, causing a sigmoidal growth. On the other hand, the tissue softened as the pollen tube penetrated the style at warmer temperatures, producing an exponential growth. Pollen tube length and time of fertilization was simulated using the hourly weather data from 20 stations in Washington State and a fixed starting point during April for the last six years. In conclusion, the prediction of the pollen tube length and the duration to flower fertilization can be used as a decision support tool for growers to provide guidance on the timing for chemical bloom thinning application.

Hector A. Camargo Alvarez won an ISHS student award for the best poster at HortiModel2016: V International Symposium on Models for Plant Growth, Environment Control and Farming Management in Protected Cultivation in France in September 2016.

Contact
Hector A. Camargo Alvarez, Biological Systems Engineering Department, Washington State University, Prosser, WA, USA, e-mail: h.camargoalvarez@wsu.edu

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Modeling pollen tube growth for 'Gala' and 'Fuji' apples
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