By Gal Sapir
When planning to perform precision mechanical pollination in orchards, there are several important aspects of precision to consider. One such aspect is the precise amount or dosage of pollen dispersed. As the production process of pollen is expensive, excess dispersion can harm the economics of the treatment. Additionally, the physical distribution methods used in orchards must be considered as they can vary from crop to crop. It is crucial that the maximum amount of pollen possible reaches its intended destination – the flower stigma. Finally, accuracy during pollination is also of utmost importance, which we will discuss further in this article.
When comparing mechanical and natural pollination in pistachio in terms of timing, the first advantage of mechanical pollination is avoiding the need for the overlap of flowering between the male and female trees. In mechanical pollination, the production of pollen from male trees is carried out separately, just when the pollen release is at its peak. From this, it follows that in mechanical pollination it is possible to match each female cultivar with the male cultivar that is suitable for fertilization, free from the constraints of overlapping blossoms and focus only on nature, viability, and the genetic or physiological suitability of the specific pollen for fertilizing the specific female cultivar. For these reasons, the timing of the mechanical pollination that we will review here will deal solely with the female bloom.
The timing of flowering in pistachios consists of several levels, starting with the development of a single flower in the inflorescence, the development of the inflorescence itself, which includes a certain number of receptive flowers at a given time, the development of different inflorescences at the flowering branch, which often depends on the location of the branch and its exposure to the sun, the overall development of inflorescences at the complete tree, and finally the development of inflorescences in the total of the trees in a given block or orchard.
When one wants to monitor the state of flowering in a certain area, first of all, there is a need for a careful understanding and definition of the various phenologies during flowering and their effect on the flower’s ability to receive pollen grains and set fruit. From other research points of view (with the exception of pollination) there is no need for too much detail in the different stages of the inflorescence progress during bloom (1) which led to some lack of knowledge (Figure 1).
Fig. 1 Developmental stages of male and female inflorescences, and fruits of pistachio. (a) Male stage 1, beginning red, (b) Male stage 2, beginning open, (c) Male stage 3, full open, (d) Male stage 4, pollen, (e) Female stage 1, total brown, (f) Female stage 2, beginning green, (g) Female stage 3, extended green, (h) Female stage 4, opening, (i) Fruit set, (j) Rapid pericarp growth, (k) Fruit maturation, (l) Fruit ripening. (Photos: a–d by A. Sheikhi; e–l by L. Ferguson)
From our perspective, the current situation motivated us to create a more accurate and specific definition that meets our requirements for the growth stages of the female inflorescence (shown in Figure 2) and the duration of each phenology (illustrated in Figure 3).
Fig. 2 Developmental stages of female inflorescences during the bloom period with relation to capability of pollination. (0) dormant bud, (1) emerging inflorescence, (2) first stigmas appear, (3) fully open inflorescence, (4) end of flowering small amount of stigmas are receptive. (5) start of fruit set.
Fig. 3 Duration of inflorescence progress in days, phenologies as stated in Fig, 2.
Once we have learned how to define the growth of the flowers on the inflorescence, the next step involves observing entire trees at the blocks/orchards to assess the development of flowering at the agricultural level. Figure 4 provides an example of one method for monitoring the progress of flowering and its percentage in the orchard population. When analyzing this data, we search for timing where the majority of flowering in the treated region is at the target phenology to ensure optimal pollination.
Fig. 4 percentage of inflorescence progress during bloom in a block level, phenologies as stated in Fig, 2.
It is important to carefully consider and examine the impact of pollination on inflorescences at different stages of growth. According to research conducted on the ‘Kerman’ cultivar, early pollination during bloom proved to be advantageous (2). The study revealed that there are 2-3 critical days for pollination within the 8–10 days flowering period, particularly at the beginning of the bloom. It is essential to conduct further research on various cultivars of plants in light of the changing climate, which can significantly affect both dormancy and therefore inflorescence viability (cold temp in winter) and the progress and duration of the flowering process (in spring).
Currently, EDEDTE is conducting various tests to enhance the precision of pollination operations, including determining the optimal date for pollination.
REF
(1) Sheikhi, A., Arab, M.M., Brown, P.J., Ferguson, L., Akbari, M. (2019). Pistachio (Pistacia spp.) Breeding. In: Al-Khayri, J., Jain, S., Johnson, D. (eds) Advances in Plant Breeding Strategies: Nut and Beverage Crops. Springer, Cham. https://doi.org/10.1007/978-3-030-23112-5_10.
(2) effect of time of pollination on nut production in ‘Kerman’ pistachio (1982). https://calpistachioresearch.org/wp-content/uploads/2018/03/01906.pdf
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