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Project description

Reproductive biology and population genetics of fountain grass (Pennisetum setaceum Forskal), an invasive species in California. (01XN024)
Program Exotic Pests and Diseases Research Program
Principal
investigator
J.G. Waines, Botany and Plant Sciences, UC Riverside
Host/habitat Wildland
Pest Fountain Grass Pennisetum setaceum
Discipline Weed Science
Review
panel
Natural Systems
Start year (duration)  2001 (Three Years)
Objectives Collect plant and/or seed germplasm of fountain grass (Pennisetum setaceum), growing along the coast and in inland valleys of California.

Survey the population genetic structure of these naturalized weeds using isozyme markers.

Test whether expansion of fountain grass populations is correlated with population genetic diversity.

Determine the extent of seed production in naturalized fountain grass populations and whether the seed is apomictically or sexually produced using cytogenetic procedures.

Examine whether ornamental cultivars produce viable seed under natural conditions.

Determine the method of spread of fountain grass populations in California and suggest ways to limit this.

Final report Plants and mature spikes of naturalized populations of fountain grass were collected in coastal and inland valleys of San Diego, Orange, Los Angeles, Ventura, and Santa Barbara counties; and in western and central Riverside County. The plant forms invasive monoculture populations, especially near the coast, but also they are common in inland valleys, and they are now invading the low-elevation desert near the Palm Springs tramway. The green-leaved naturalized form grows vigorously in the spring and fall, and dies down in the cool, wet winter, or hot, dry summer. It will grow vigorously in the hot summer months if a source of irrigation water is available, such as in ornamental plantings. Populations vary as to their time of flowering, especially in winter-spring, so there may be genetic variation for photoperiod response in naturalized California populations. We did find genetic variation for isozyme alleles, which again points to some genetic variation among populations. Pollen production among the green- leaved form varied with season, and it could be almost sterile in winter, if produced at all. In spring, up to 70% fertile pollen was produced by green-leaved plants, which produced 30% to 70% fertile seed. The green-leaved plants can be very fertile. Reproduction is mostly by seed, although tillers are produced and in older plants these bunch grasses could separate into ramets, especially on the outer circumference of the clump. All of the invasive populations that we saw on the coast and in the desert are of the green-leaved form.

In contrast, the red-bronze leaved forms appear to be more or less pollen sterile. They do not produce viable seed, and any reproduction is vegetative by tillers or ramets. There are several different named cultivars, some tall and robust, others dwarf and slender. All have attractive red-bronze leaves and reddish flower spikes. We did not encounter green-leaved types in this group, but they should be searched for or produced. Seed-sterile green-leaved types in the bronze group could take over from the seed fertile green-leaved types that are so invasive. They would be just as attractive in terms of ornamental horticultural value.

We sowed several thousand spikelets of the bronze-leaved forms, and found almost 100% seed sterility. Several seedlings (5-6) did germinate and always grew into fertile green- leaved plants. The simplest explanation is that the mature spikelets of the green-leaved type will float around on a wind current and could have landed on a bronze-leafed spike, and have been sown along with bronze-leaved spikelets. Hence, they would be a contaminant. There are other more complicated explanations. We never germinated seedlings that grew into bronze-leaved plants.

Third-year
progress
We have collected two commercial varieties (cultivars), namely setaceum and rubrum, and have grown these plants in five-gallon pots in the glass house. We have monitored these for seed production. Var. setaceum has green leaves and light purple spikes. It is the most common variety in the horticultural trade and has been much planted by CALTRANS and by landscapers. It is invasive in both coastal and desert communities. This variety is supposed to be triploid and sterile. But at certain times of the year, especially in the spring and early summer months, it produces abundant pollen, some of which is fertile. It also produces many small fertile seeds, mostly by nucellar embryony. Thus, spread of this invasive species appears to be by apomictic seed production, which is abundant under appropriate temperature, moisture, and day-length conditions. At other times of the year, the mature spikes can have no seed, or plants do not flower at all, as in winter. Presumably, these sterile spikes are the source of the popular notion in the horticultural trade that fountain grass is sterile and does not reproduce by seed.

Variety rubrum has dark red to purple leaves and spikes, and is less common in the commercial trade, although its popularity in landscape plantings in Riverside County appears to be increasing. It is supposed to be hexaploid and have sterile anthers and no seed production. We found that the anthers are largely sterile, though perhaps not completely so, and that the florets produce only a few seeds. However, when variety rubrum is planted next to variety setaceum with fertile pollen, the latter can pollinate and fertilize the rubrum flowers and seed production increases.

We have extensively surveyed coastal and inland valleys of San Diego, Imperial, Riverside, Orange, Los Angeles, San Bernardino, Santa Barbara, and Ventura counties. The invasive populations all appear to be of the green leaf variety. We have yet to find an invasive red leaf form.

Second-year
progress
The commercial plants are continuing to be monitored for seed production. The red cultivar appears to be quite sterile, but the green cultivar produces much seed at certain times of the year.

A total of 22 populations have been identified in Riverside, San Diego, and Imperial counties. These are being visited periodically for observation and collection.

Greenhouse populations from each collection site are being developed as seed becomes available.

Initial isozyme data have been collected for plants from six of the populations plus the cultivars. A limited amount of genetic variation has been detected.

First-year
progress
Since February 2002, we collected the two commercial varieties (viz., rubrum, setaceum) and have been growing these plants in five-gallon pots in a glass house. We have been monitoring these plants for seed production.

We extensively surveyed coastal and inland valleys of San Diego, Imperial, and Riverside counties and identified 15 fountain grass populations. We are monitoring these populations for seed and clonal productions.

We standardized eight electrophoretic enzymes (ADP, CAT, EST, IDH, MDH, PGI, 6PGD, and PGM) for fountain grass species.

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