Author: David Harry, Ph.D.
My last blog posting discussed how and why flowering and yield are closely related in many agricultural crops, including pongamia (posted August 12, 2013). That’s just one of the reasons why we’re so pleased to see flowering on trees planted only two years ago in Texas.
Another important reason is that we can now monitor flower and fruit development on trees “in our own backyard,” rather than from a distance. Of course we’ve observed reproductive structures on trees in Florida and Hawaii, as well as in various parts of Australia and India, but our backyard trees in Texas provide an opportunity to gather frequent observations on individual trees and marked clusters of flowers and fruits. Very convenient! Given the direct connection between reproductive development and yield, it behooves us to thoroughly understand pongamia’s fruit and seed development.
Our previous understanding of reproductive development in pongamia has been drawn from reading scientific publications, visiting colleagues, and from our own observations while visiting pongamia trees in far-flung locations. Consequently, we can draw a few generalizations:
- Pongamia trees will often lose their leaves as days becomes longer in late winter and spring. Senescing leaves typically lose their deep green color before they drop, and trees appear to enter a quiescent state for a time
- Flowers typically emerge on elongating shoots after such a quiescent period
- Individual flowers, or florets, are clustered together on a stalk, which collectively is called an inflorescence
- Although an inflorescence may include 10-70 florets (or more), many flowers fail to set fruit (Fig. 2 left)
- Fruits typically occur in clusters of 3-5 pods. (Numbers of pods per cluster varies substantially among trees)
- Pods grow rapidly in length and width, reaching their near-mature size in a matter of weeks (Fig. 3 below)
- Seeds within pods (usually only one per pod) expand over a period of many months
- Pods grow thicker as the enclosed seed grows. Nearly mature pods that are thin or flat are unlikely to contain viable seeds
- Developing seeds remain soft and light green until shortly before they mature, when the seed loses moisture and the seed coat turns reddish brown
- Seed oil content increases throughout seed development, and reaches a plateau before the seeds are completely mature
- Putting all these observations together, the practical application is that optimizing oil yields and harvesting efficiency may mean adjusting harvesting times to match individual varieties and local conditions. Furthermore, the optimal timing of harvesting for oil may well differ from that of optimal harvesting for other traits (e.g. seed germination).
These are all important considerations as we continue to learn by observing trees in Texas (and soon elsewhere). And while the Texas trees have yet to complete a full flower-to-fruit cycle, we can cautiously begin to “ground truth” our observations relative to what we already know. (Disclaimer—while observations of flower and fruit development on young trees can be used as early indicators, reliable patterns will emerge only after observing older trees as well.) And generally speaking, I can say “so far, so good.” That said, one of nature’s most reliable messages is to be prepared for exceptions, and I’m sure we’ll see our fair share of those in the months and years ahead. Stay tuned—we’ll share them as they come to our attention.
David Harry is Director of R+D at Terviva