Does elephant foot yam become bigger after stem has withered?

From the literature, it is seen that when the canopy of  elephant foot yam turns yellow and withers  away, the yam is ready for harvesting. But my friend, who has been cultivating elephant foot yam for the last several years says that if you dig up the yam immediately after the canopy has withered away, you will get only a small yam. He says that you should allow two more months to the tuber, when it will become bigger. I cannot understand how the yam will become bigger without the photo-synthesizing canopy. But he was insistent about it.

Thinking about it further, we see that a yam with withered canopy, if left in the ground, will sprout shoots in April to May some time before the monsoons. In Kerala, the traditional knowledge is that the yam setts of 750gm to 1 kg are planted in the month of Kumbha (Phalgun, Feb-March) on the day of the full moon (and the yam will grow to be as big as the full moon!). The sprouts will appear in Apr May. This means that the underground tuber undergoes a change independent of canopy or photo-synthesis. So it is possible that  the the yam that has stored certain material (starch and others) before the canopy withers away, could continue to process those initial material and transform them into a more voluminous and tasty (for humans) form silently under ground without any help from the canopy, leaves and photo-synthesis. This could be the plant equivalent of the rumination technology followed by the cows.  That is, create a first set of chemicals using photo-synthesis  (quickly eat the grass, mix it with saliva and process it in the first 2 chambers of the stomach), store them in a small tuber in a concentrated form, shed the canopy and then quietly work underground transforming the concentrated material to a voluminous form (regurgitate and chew the cud later at a safe place and eat it again).

Another indication of the non-essential nature of the canopy of elephant foot yam is indicated by its single stem canopy that does not form new leaves nor grows. The stem comes out of the conical sprout and opens out like an umbrella, but that is it. If the leaves are cut, or the stem is cut, new sprouts do not turn up. Does’nt it mean  that the elephant foot yam is not critically dependent on its canopy?

I searched for any findings on this “grow underground without canopy or photosynthesis” but could not locate any. I seek opinion of experts on this.

Cheers

k vinod kumar–
पृथिवी सस्यशालिनी
the earth be green

Found further evidence to support “elephant foot yam continues to grow after the foliage has withered away”.

[fao.org/docrep/x5415e/x5415e03.htm#TopOfPage], an FAO documennt says:

Root and tuber crops are still living organisms after they have been harvested and losses that occur during storage arise mainly from their physical and physiological condition. The main causes of loss were discussed in Chapter 2 which indicated these were associated with mechanical damage, physiological condition (maturity, respiration, water loss, sprouting), diseases and pests.

In chapter 2, it is said that roots and tubers are living organisms and they respire. The respiration results in conversion of starch into water, co2 and heat. The respiration rate varies with whether the root/tuber is sprouting or is in dormant phase.  There are other factors too that affect respiration.

It appears that for elephant foot yam, there is a pre-dormant phase after the withering away of the foliage. In this pre-dormant phase, the foliage compartment is absent, but the roots and the tuber continue to undergo chemical processes. It is not a dormant phase as the roots uptake nutrients, and the roots and the tuber respires. The chemical process happening is not the oxidation of starch, but the conversion of pre-starch chemicals in the tuber to starch using the nutrients absorbed through the  functioning roots. The energy for this transformation, if required, may be obtained from the soil or from the composting of vegetable material laid on the ground as manure. Agricultural practices for elephant foot yam do emphasize fertilizing the crop with dried farm yard manure, green mulches and straw. The green mulches and straw may not only be providing nutrients to the yam but also the warmth to complete its chemical processes.

k vinod kumar

पृथिवी सस्यशालिनी
the earth be green

It is quite possible that the yam will grow bigger once the canopy is shed, obviously it is storing nutrients and energy for the next generation, if you leave the corm long enough underground it will sprout a beautiful flower too.  I have a photo of one such flower taken in Kerala, in my album, I shall upload it soon.

George

If the Elephant Foot Yam (EFY) grows under ground after the foliage has withered away, then the Agricultural Practices should state clearly that the EFY should be harvested, say,  only 2 months after the withering away of the foliage. The AP should also say what should be done  to the underground EFY, whether you should water it or provide mulch and manure to the underground plant, or just leave it alone. I have seen some documents that talk about the physiological changes taking place in the EFY in the harvested form in storage. But I could not find any study of a pre-dormant stage between the withering away of the  foliage and harvesting from the ground after, say, 2 months.  I have also not seen, what happens during the withering away of the foliage. I expect that the plant will move out of the foliage, as much useful chemicals as it can before the foliage is lost.

I strongly feel that the physiology of EFY must have been studied and all the stages, pre withering, withering, pre-dormant, and dormant,  documented. Could an expert explain them in simple terms and update the Agricultural Practices for EFY please?

k vinod kumar

पृथिवी सस्यशालिनी
the earth be green