Anybody else working toward perennial corn?

[Carter Phillips]

I am planning to start up the long process toward a decently productive perennial corn next year and am getting started by planning out the crosses I'll be making. The three species I am working with are Zea mays (obviously) Z. diploperennis and Tripsacum dactyloides (Eastern gamagrass). For anybody unfamiliar, Z. diploperennis is a perennial teosinte with the same number of chromosomes as field corn making it very compatible for crossing. This makes it an attractive source of genes that contribute to perenniality in corn. The problem is that this species is not winter hardy, and the bulk of the world's corn is grown in areas with hard frosts. Enter T. dactyloides.  T. dactyloides is a cousin of corn which can be crossed with corn in certain circumstances. It is perennial and rhizomatous and is able to survive winters as far north as Connecticut (probably further north in coming years given climate change). The problem is that it differs from corn in chromosome number and in ploidy (tetraploid rather than diploid). Interestingly there was once great controversy over whether or not corn was in part descended from tripsacum.

I'm planning on giving this project my full attention and am planning on going down multiple breeding routes simultaneously to maximize the likelihood of success. Therefore I am going to cross mays with dactyloides, mays with diploperennis, and diploperennis with dactyloides, and after a couple of generations of selfing each group to allow the genomes to stabilize, I can backcross with either parent or attempt riskier crosses between groups. I'd love to hear from anybody else working toward this holy grail of perennial crops.

[Mica Winnower]

You're the first I've heard of anyone even mentioning other Zea species.
If you're able to get fertile offspring in later generations, it'll definitely be a good source of new genetic material and novel traits.

[Joseph Lofthouse]

At one time, I was working towards perennial corn, and grew the mentioned species, and others. The wild zea species showed day-length sensitivity and therefore didn't make seeds in my climate. I could overwinter the zea diploperennis rhizomes by burying them 18" deep in the garden. Eventually, I sent them to someone in a warmer climate.

I grew [mays X diploperennis] but didn't find rhizomes.

Tetraploid versions of zea mays exist...

 

[AndrewB]

I grew both species and the hybrid Joseph mentioned above. Couldn't get them to over winter here. I would need a greenhouse to try again. Maybe someday I will. Diploperennis obviously would be easier to cross with.

I could never get dactyloides to germinate

[Carter Phillips]

Tetraploid versions of zea mays exist...

I wouldn't mind crossing tetraploid mays with Z. perennis but I prefer having access to the broader diversity of diploid corn. Maybe I'll go that route in the future if I get more greenhouse space.

I could never get dactyloides to germinate

With gamagrass I've found that putting seeds in the refrigerator for a few weeks and then soaking in 1/4 hydrogen peroxide for a half hour aids tremendously in germination. I think there's a team in either Oklahoma or Missouri trying to develop a gamagrass cultivar that will germinate reliably within 7 days though I think their focus is on diploid gamagrass.

[Carter Phillips]

This year I have made some progress in the perennial corn project. There were three prongs to my strategy: Planting Zea diploperennis, planting Zea diploperennis/Zea mays (corn) hybrids, and planting Tripsacum dactyloides (Eastern gamagrass). I will detail my methods so that they can be scrutinized and replicated.

ZEA DIPLOPERENNIS: Efforts started in March. I germinated Zea diploperennis seeds, which I acquired through GRIN, by refrigerating them in moist paper towels for two weeks. I then planted the seeds, 30 in all, in 9 two-gallon pots. The pots were kept in a grow tent until April and were then transplanted into the garden. About half of the plants died for unknown reasons while in the grow tent; they suddenly withered while their pot-mates thrived. Once in the garden all Z. dip plants thrived. They produced many stems and leaves. Stems bent over and produced roots where they contacted the ground. In mid-June, I began placing trash cans on plants at 7 PM and took them off at 7 AM. After a couple weeks I changed the interval to 5 PM-7 AM. Within four weeks the plants were flowering. I pollinated some of the female flowers with pollen from 'Japonica' popcorn, a variety that grows very well in my garden and produces leaves with pink variegation. I'm hoping that these flowers were successfully pollinated and will produce hybrid seed, but time will tell. In any case the other flowers should produce pure Z. dip seed which I can use in the future or can distribute to anybody who wants some.

ZEA HYBRIDS: I acquired the Z. dip/Z. mays hybrid seed from GRIN (accessions Ames 13503 and Ames 13502). I planted in April and unfortunately my region had a terrible drought for two months afterward. I watered the plants regularly to mitigate the effects of the drought. There was significant pest pressure as well. Cutworms cut many plants off at the base, delaying their productivity if they recovered. In mid-July, an unknown pest began attacking the more mature plants. The plants would bend over about three quarters of the way up and at the point where the stalk bent, parts of it would turn brown. The culprit may be a stalk borer. Two nearby non-hybrid plants I pulled up had holes that looked like borer entry points at their bases. Out of 185 seeds planted roughly 100 plants are still living; the high rate of attrition can be explained by the unusually poor weather and high pest pressure. I picked four small cobs green so that I would get something out of it in case the rest of the crop fell to predation. One cob has the teosinte form, with two opposing rows of seeds, while the others have the classic maize cob layout. Time will tell what else I will be able to harvest.

GAMAGRASS: I refrigerated 'Pete' gamagrass seeds for six weeks and planted a plot with it in April. Out of 100 seeds perhaps a dozen plants came up. The soil of the plot was very poor and native warm-season grasses are notoriously difficult to establish so I was unsurprised by the poor results. I will plant more seeds in the same plot next year and maybe scarify the seeds with peroxide or soak them in water to improve emergence. Gamagrass doesn't usually produce seed until its second year so I wasn't expecting them to be ready to cross with Z. dip until next year anyway.

[Joseph Lofthouse]

Delightful project. Thanks for doing this so carefully.

[Carter Phillips]

Attached is a picture of the four cobs, with one displaying the classical teosinte form and the other three displaying a maizelike cob form.

My immediate plan for the future is to hybridize Z. dip and gamagrass. According to Mary Eubanks, a researcher who has been most successful in introgressing gamagrass genes into maize, Z. dip and gamagrass are relatively easy to interbreed despite their genetic differences due to quirks in their chromosome structure (read "A Cross between Two Maize Relatives: Tripsacum dactyloides and Zea diploperennis" for more details). Hybridizing these two is important because Z. dip can act as a "bridge species", meaning that it is easier to pass genes from gamagrass to Z. dip and then to maize than it is to pass genes directly from gamagrass to maize. The two species differ in chromosome count and as a result their hybrid offspring often have unstable genomes. I will self and mass cross the gama/Z. dip progeny for a few generations while screening for perenniality and other useful traits, to allow the genome to stabilize. Both while the population is stabilizing, and especially once it is stable, I will cross the gama/Z. dip hybrids with maize and maize/Z. dip hybrids. The resulting progeny will be screened for perenniality and the process will begin again.

[Carter Phillips]

Delightful project. Thanks for doing this so carefully.

Thank you. I will have more results at the end of the growing season.

[Carter Phillips]

Pictured is the "tassel ear" trait observed in some Z. dip/Z. mays hybrids, and the extreme branching that some of these hybrids can develop. I found these traits to become more pronounced after the "decapitations" plants endured by cutworms and stalk borers. Until these stresses were applied, most plants had a standard maize appearance.

[Carter Phillips]

Here is what 466 seeds of a Z. mays/Z. dip hybrid look like. I planted 185 seeds and harvested 466. As I mentioned previously, extreme drought, high pest densities, and extreme rain during dry-down hurt my yields quite a bit. My seeds-harvested-to-seeds-planted ratio is 2.5, not much better than yields during the Great Famine in the 1300s. I think without pest damage I could have harvested three or four times as many seeds at a minimum.

This lackluster harvest has multiple implications for the immediate future of this project. It does prove that these plants are resilient, given how many of them managed to reproduce after multiple decapitations. Unfortunately, it has also narrowed the genetic base I have to work with in future growing seasons, as well as the maximum number of plants I will be able to work with next season. It has also denied me a good population of plants to screen for perenniality this winter. I was planning on putting surviving plants in pots and observing them indoors under grow lights to see if they will continue to live in frost-free conditions. The high mortality rate has caused me to abandon this plan. This burst of pest pressure is also forcing me to give up that particular garden plot next year. I can normally get at least two years out of a corn plot before pests significantly affect yield, but rotation is clearly needed here.

My biggest concern is the significantly narrowed genetic base of the project. These seeds are not freely available at my local garden store. I'm not sure how restrictive GRIN is or if they pay attention to your request history, but I don't think they would take kindly to me requesting the same presumably rare seed multiple years in a row. Doing the work to produce a similar product with 87% Z. dip DNA would take years more, and while I am hybridizing these species on my own in a parallel project, the value of the time saved by using existing germplasm is undeniable. I am especially wary of requesting too much from GRIN given that they are my only means of acquiring some other accessions, including a particular maize selection with significant introgression of T. dactyloides genes, Z. perennis (tetreploid perennial teosinte), and tetraploid maize.

In the next few days I will describe my efforts to hybridize Z. mays and Z. dip (very minor success), and my future plans to continue what I have started and to widen the scope of the project further.

[Tim DH]

Hi Carter,
      There is a bit of conflict between 'Perennial' and 'Rotation'!

Tim DH

[Steve1]

Hi Carter, have been working on perennial maize for about 5 yrs now. Working with diploperennis x mays. Was a PITA to get it all lined up though. In a warmer place than you though at 9A/9B. 

[reed]

I tinkered with that for a bit but in my climate the perennial teosinte would not flower so I wasn't able to cross it to my other corn. 

[Steve1]

Yeah. the daylight sensitivity makes it annoying away from the equator. The rubbish bin works for small plants, but I have several clumps of multiple plants that would be 5 ft round and about 5ft tall. The clump I have in the tunnel is the one I cross to most, as it turns cold (by our standards) when it flowers and seeds haven't formed on outside plants at this point. Once you get F1 plants that daylength sensitivity is overcome. Interestingly the F1/some of the F2 plants tend to have aerial roots that the teosinte does not have. I have seen the dripping exudate on these aerial roots in F2 plants. My hypothesis is that the N fixing endophyte that got so much press is likely endemic to teosinte as they don't get fertilizer here and grow vigorously (but as they are rhizomatous and don't make aerial roots - you don't see it), and is only visualized when integrated into mays that have aerial roots.