Concerning pretreatment of pollen I found interesting literature. Handicap is in vitro culture but with this method one would have much more possibilities as can be read here - just two articles as for example:
https://www.intechopen.com/books/pollination-in-plants/pollen-germination-in-vitroPollen Germination in vitroBy Jayaprakash P
Submitted: November 20th 2017Reviewed: February 13th 2018Published: June 6th 2018
DOI: 10.5772/intechopen.75360
Abstract
Pollen germination in vitro is a reliable method to test the pollen viability. It also addresses many basic questions in sexual reproduction and particularly useful in wide hybridization. Many pollen germination medium ranging from simple sugars to complex one having vitamins, growth regulators, etc. in addition to various minerals have been standardized to germinate pollen artificially. The different media, successful pollen germination methods, procedures from pollen germination studies with wheat, rye, brinjal, pigeonpea and its wild relatives are discussed.
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1677-04202002000100009Pollen treatment in high osmotic potential: a simple tool for in vitro preservation and manipulation of viability in gametophytic populations By: Leandro Lopes Loguercio
Departamento de Ciências Biológicas - DCB, Universidade Estadual de Santa Cruz, Rod. Ilhéus-Itabuna, Km 16, Ilhéus, BA, 45650-000, Brasil; E-mail: leandro@uesc.br
Brazilian Journal of Plant Physiology
On-line version ISSN 1677-9452
Braz. J. Plant Physiol. vol.14 no.1 Londrina Jan./April 2002
http://dx.doi.org/10.1590/S1677-04202002000100009 Abstract
A method for in vitro preservation and manipulation of pollen viability based on simple changes in osmotic potential (sucrose concentrations) in culture media was developed using tobacco pollen as the experimental model. High osmotic potentials were capable of reversibly inhibiting pollen germination, preserving its viability at room temperature for long periods, as assessed by subsequent incubation in germination medium. When pollen was pre-germinated for different periods and subsequently incubated in 80 % sucrose medium (inhibiting medium) there was a progressive decrease in its viability, which was a trend best described by a quadratic regression line. Nevertheless, very small variations in pollen-tube lengths and viable pollen grains more resistant to the pre-germination step were detected by this procedure. Consequences and potential applications of these findings were discussed for use in analyses of variability, selection in gametophytic populations and pollen storage.