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Tuesday - July 17, 2012

From: Portal, AZ
Region: Southwest
Topic: Propagation, Grasses or Grass-like
Title: Can two species of Muhlenbergia be cross-pollinated from Portal AZ
Answered by: Barbara Medford

QUESTION:

Will Muhlenbergia lindheimeri (Big Muhly) cross-pollinate with Muhlenbergia porteri (Bush Muhly)? I am attempting to restore the grasslands on my private property to a pre-1900 state. Bush Muhly was a dominant grass at that time but it is extremely difficult to obtain the seed in quantities that I can afford. There is still some native Bush Muhly present, but it is mostly found in conjunction with individual Tarbush and Mormon Tea plants. My elevation is 4,200 ft. and the annual rainfall is about 12" per year (10-15" range). I am also reseeding with Sideoats and Blue Grama.

ANSWER:

According to this USDA Plant Profile Map, Muhlenbergia porteri (Bush muhly) does grow natively in Cochise County AZ, about as center of the state as you can get. However, according to this USDA Plant Profile Map, Muhlenbergia lindheimeri (Lindheimer's muhly) does not grow in Arizona, at all. How did you determine that Muhlenbergia lindheimeri would help repopulate your property to a pre-1900's state?

From Oregon State University, please read this article on Grass Growth and Regrowth for  Improved Management.

 Of particular interest in this article:

"Self Pollination and Cross Pollination Mechanics

Among grass species, sexual reproduction may occur with few restraints, however, the processes are often constrained by mechanisms which govern whether or not cross-breeding is possible. Some of these constraints are listed below.

  1. The species may be self incompatible.
  2. The grass may be dioecious, where the florets on the plant will be either male or female. Cross pollination is natural for these grasses.
  3. The grass may be monoecious where the florets are imperfect, having only one sex represented; male florets are born separately from the female as in maize and buffalo grass. Such plants are highly cross-pollinated.
  4. The grass may be dichogamous, such that the male and female organs mature at separate times. If anthesis (pollen shedding) occurs before the stigma is mature the grass is said to be protandrous. If the stigma is receptive before anthesis, the grass is protgynous. In either case, self-pollination is largely prevented.
  5. The grass floret may be cleistogamous where the lemma and palea remain closed until such time as anthers have released pollen. This is common to several of the cereal grains ensuring a high degree of self pollination and maintenance of varietal purity.
  6. The floret remains closed until anthers are about to rupture and stigmas are highly receptive. This system is called chasmogamy. It allows both cross and self pollination.
  7. Sexual reproduction may not be necessary for seed production if the grass species is apomictic (see previous discussion). Apomixis ensures exactness in propogation of the species."

Also from Oregon State University, Chromosome Number: The Implication of Cytogenetics. From that article:

"If one attempts to crossbreed different, but closely related grass species, there often will be varying levels of pairing among related chromosomes. This phenomenon is known as homeologous or imperfect pairing, and produces partial fertility in hybrids of closely related but diverging grass species (Jauhar, 1993). Hybrid plants can persist in a vegetative state if they are perennial, but most often they are partially or completely sterile. A technique commonly used by grass breeders to restore proper chromosome pairing and fertility is to treat fertilized embryos with the chemical colchicine, which promotes a doubling of the chromosome complement. In effect, the result is a perfectly pairing homologous chromosome set, allowing the hybrid to carry out normal meiosis."

On a brighter note, both Bouteloua curtipendula (Sideoats grama) (Plant Profile Map) and Bouteloua gracilis (Blue grama) (Plant Profile Map) are native to Cochise County, as well as Muhlenbergia porteri (Bush muhly). It would seem to us that repopulating your property with 3 native grasses would be by far the better course to take, especially in view of the many complications in cross pollination.

 

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