As soon as the new rice transplants settle into the mud, they begin "tillering" - that is growing new stems just like the clump grass it is. Each of these stems eventually will produce a seed head, so the bigger the clump, the more stems or tillers, the more rice. At the first tillering, the paddies get fertilized. We use high nitrogen, organic, chicken litter pellets cast directly into the paddy water where they dissolve and quickly become available to the plants.
The weather has been perfect for growing rice - very warm and very wet. The plants are getting taller and tillering rapidly.
This is the Khudwani rice, a variety from China. It's doing very well. But we notice something odd about the second main variety we are growing, Hayayuki, a variety from northern Japan. Some of the Hayayuki plants are "bolting" or going to seed early.
These plants will never bulk up and their rice production will be minimal. A few days later we find many plants are bolting. What's going on here?
Let's ask The Expert! We explained our problem to Dr. Susan McCouch (Cornell University, Rice Research Lab) and the relevant circumstances... We'd had a long, cold, spring followed by hot and dry weather through May into mid-June. Thinking of the ever-longer fall to come, and that larger seedlings would be easier to plant, we delayed transplanting our seedlings by two weeks to mid-June, which coincided with the onset of almost daily rain.
Dr. McCouch's response was most informative and has given us much to think about as we try to adjust our growing of many edible and ornamental plants to our shifting seasons:
"As for the Hayayuki issue with bolting, I can wager a guess as to why it is, but its only a conjecture. Hayayuki is a ‘Hokkaido variety’ bred for northern latitudes, and it (like many other temperate japonica varieties) has been selected genetically to have weak photosensitivity. This allows it to flower under relatively long days (i.e. before the solstice in September) and mature before frost. Rice evolved in the tropics as a “short day plant” and most tropical rice varieties have very strong photosensitivity so they will not flower until they experience short days, timed to have their seeds mature when the rains usually come to aid in survival.
"Some of the varieties from Japan are known to have photosensitivity alleles that are so weak that flowering may be triggered under either very short or very long days. It seems the plants can’t really tell the difference, so when other environmental stimuli play havoc with the flowering time pathway due to erratic or unseasonal temperature and/or rainfall patterns, flowering occurs and the plant moves from its juvenile to its reproductive stage, sometimes with only a single tiller. I’ve seen the same thing happen in the greenhouse in the middle of December when a very young plant will suddenly bolt if our heating or watering regime is disrupted for some reason.
"So I think genetics explains why Hayayuki has bolted and Khudwani is doing just fine. In my experience, if a plant has bolted, it cannot reverse course and go back to its juvenile (tillering) phase (without some kind of fancy hormone treatment!), so unfortunately, you probably won’t be able to rescue those plants. I do think the fact that they experienced a long cold spring followed by hot, dry weather in May and late transplanting probably explains the behavior. These varieties tend to survive cold weather during the seedling stage without a problem (I’ve seen seedlings in the field in Japan with snow on them in the spring) but their developmental pathways are easily confused by rapid shifts in temperature and possibly by the disruption of late transplanting (if the plants are bigger than usual, transplanting causes more of a shock to the system). I hope you get good seed set on the Khudwani plants to make up for Hayayuki’s performance this year."
Wow. OK. Thanks, Dr. McCouch, for your thoughtful response. So, the Hayayuki (the sparse right side paddy, below) is mostly a loss this year. That was our largest planting and was to be the subject of another experiment testing a portion of it for drought tolerance. But, more on our various trials in the next blog. For now, we'll just monitor and compare the progress of the two rice varieties over the season. The contrast will be interesting given what we now know more about what stress can do!!!
