April Showers Bring May Flowers: But How About Pods?

Author: David Harry, Ph.D.

When we think about what it takes to domesticate and commercialize a new crop like pongamia, the number of unanswered questions we face can sometimes feel daunting. Answers to the most basic of questions, such as when does flowering occur, and when are seeds ready for harvest, need to carefully evaluated. Why? Even well-established crops need to be ground-truthed when grown in novel conditions, so you can imagine that with new crops, for which a robust baseline is almost always lacking, it can be pretty challenging to predict what will happen when. So it is for pongamia.

Figure 1.  Pongamia’s reproductive cycle:  from flowers to developing pods, mature seeds, and finally, to young seedlings.  Because these observations were made in the tropics, developmental timelines are likely condensed relative to subtropical environments.  (From Srimathi et al. 2013).

Figure 1. Pongamia’s reproductive cycle: from flowers to developing pods, mature seeds, and finally, to young seedlings. Because these observations were made in the tropics, developmental timelines are likely condensed relative to subtropical environments. (From Srimathi et al. 2013).

Last October, I reported that we were monitoring the development of flowers and immature pods on some 2-year-old trees in Texas. Now keep in mind that this is pretty basic stuff, and yet it’s important information that provides us with a stronger basis to help pongamia growers understand how their fruit crops (i.e. pods and seeds) are likely to mature.

So you might imagine how thrilled I was to run across a new publication describing flowering and fruit development on pongamia trees in India (Srimathi et al. African Journal of Plant Science, November 2013, pp. 513-520). What I particularly appreciated was a diagram illustrating the various stages of floral and fruit development, and their corresponding time intervals (Fig. 1). Young pods become visible within a week or so after flowers mature (see green structures on red background). They enlarge rapidly within a few weeks, first lengthwise to resemble the pod of a snow pea, then later growing in width (see green pods on blue background). And while the overall size of the pods then stays about the same, seeds within the pods continue to expand and mature for some time afterward (Fig. 2 ). In this case, the Stage III seeds (Fig. 2) roughly correspond to the 12-week pods (Fig. 1). In other words, most seed growth and maturation occurs well after the pods have largely completed their expansion. Eventually, pods turn brown as the seeds mature and dry, before falling onto the ground—or in our case, are shaken from trees and collected, as described in a previous Agriculture 2.0 blog post.

Figure 2.  Developmental stages of pongamia seeds, from weeks after pollination (Stage I) until full maturity (Stage VIII).  Most expansion of immature seeds takes place after pods reach their full size, at about Stage III.

Figure 2. Developmental stages of pongamia seeds, from weeks after pollination (Stage I) until full maturity (Stage VIII). Most expansion of immature seeds takes place after pods reach their full size, at about Stage III. (courtesy of Prof Peter Gresshoff, Unv. of Queensland)

So how do we take such information and put it into practice? For example, the observations in Fig. 1 suggest only 26 weeks are needed for pods to mature. So if Florida growers observe flowering in June, might they expect to harvest pods about 26 weeks later, perhaps sometime in December? Sorry, that’s unlikely—we need to “adjust” the timing for seasonal variation associated with different locations. Observations in Fig. 1 are from Coimbatore, in southern India (about 11° N latitude). This is considerably further south (more tropical), than our US plantings. Other researchers near Hisar, in northern India (about 29 N° latitude), observed that pod maturation required 44-49 weeks (Dhillon et al. Indian Forester, 2009). From our own observations in sub-tropical Florida and Australia, we expect pod maturation in mainland US will require 40+ weeks (perhaps more quickly in Hawaii). So in other words, while we are able to glean valuable insights from results in different locations, it still requires some skill to anticipate and predict likely outcomes. And in the end, both on-the-ground observations and experience will be needed to validate such predictions in the years ahead.

David Harry is R&D Director for TerViva

 

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