In the field, bees and other insects are observed frequently visiting the flowers. We have estimated outcrossing rates in this species to be between 86% and 89%. Self-incompatibility occurs and is assumed to be a sporophytic multiple allele system as generally found in the Brassicaceae. Self-incompatibility limits production of selfed seed. Male sterility also occurs frequently and is characterized by varying degrees of reduced (vestigial) anthers without pollen production. The genetic inheritance of these traits is being investigated at our laboratory. Interspecific hybridization is not common among native populations found in the western U.S. and difficult to obtain from controlled greenhouse crossing. We have produced punitive hybrids between L. fendleri x L. lindheimeri and L. fendleri x L. gracilis. These three species have the same chromosome number. However, based on general affinities, Rollins and Shaw (1973) place L. fendleri into a different phylogenetic group than L. gracilis and L. lindheimeri. We have not determined if the hybrids are fertile.
This species possesses a great amount of variability. Payson (1922) referred to L. fendleri as a remarkably polymorphic species. Even within populations of native stands, there are large amounts of variability. Originally, germplasm available to our breeding program were from relatively few accessions, and did not represent the geographical range of the species (Thompson and Dierig 1993). In 1993, we initiated the collection and evaluation of as many accessions of this species as possible throughout the U.S., and incorporated useful traits into elite lines.
In the future, other species of Lesquerella and/or Physaria may also be domesticated as a source of one of the other HFA or another source of lesquerolic acid for other geographic locations where L. fendleri is not adapted. Over the past three years, we collected germplasm of these genera throughout the U.S. This includes 216 accessions of 31 different species of Lesquerella and three accessions of two species of Physaria. Individual numbers of accessions and species, along with the state of their origin, are listed in Table 1. Many of these have not been previously included in the National Plant Germplasm System. Most accessions have only small amounts of seed from the original collection. Over the 1994-96 growing seasons, we increased seed amounts and evaluated the L. fendleri accessions by planting them in caged field plots supplied with honey bees to prevent cross-pollination between accessions.
Increases in oil and fatty acid contents have been achieved through recurrent selection populations. In 1993, seed from 20 open-pollinated plants selected for high oil content, high lesquerolic acid content, and a third population selected for both high oil and lesquerolic acid yield were field grown. The oil content in 1993 ranged from 22% to 25% in the high oil population. Lesquerolic acid content in 1993 for the high lesquerolic population ranged from 58% to 64%. The high lesquerolic yield population ranged in an index for lesquerolic acid yield (oil content multiplied by lesquerolic acid content) between 15 to 18. These are the base populations which are recurrently selected each year for the three seed-oil traits. Means for subsequent years are expected to be lower since this is an open pollinated population. The ranges of values in following years should be wider because of new genetic recombinations being produced. Seeds with high values are then selected for the next generation. Means and ranges of values for oil characteristics in 1994 and 1995 populations are shown in Table 2. An unselected population was used both years for comparison.
The comparison of population means between years shows modest increases for oil and lesquerolic acid content. However, differences are greater when comparing check and recurrent populations in the same year. Environmental influences are more prevalent between years. An important result of these populations is the extremes of the ranges of values have increased each year.
Within these populations, we are concentrating on selecting for other desirable characteristics such as autofertility and upright growth habit. Autofertility is important since it would eliminate the expense of supplying bees in the field to improve seed-set. Variability for this trait is present within the available germplasm. Upright growth habits would improve combine harvesting efficiency. Yellow seed coat lines are also being developed with the prospect of use in the cosmetic industry. Oil from seed with normal orange-brown seed-coats has a pigmentation that must be removed for their applications. The yellow seed coats may have less or no pigmentation and could eliminate the extra processing step.
Lesquerella has been successfully cultivated on both raised and flat fields. However, salts may be better managed on raised beds. Flowering begins in Feb. and seeds develop and mature between Mar. and late May. Nitrogen fertilizer applied at rates of 60 to 120 kg/ha resulted in increased dry matter and seed yields (Nelson et al. 1996). A good strategy for irrigation scheduling of lesquerella in southern Arizona is to irrigate about once every 15 to 20 days starting in late Feb. through mid-Apr., then once every 10 days between late Apr. through May.
Irrigation is stopped in mid-May and the plant is allowed to dry until seed moisture has reached about 12% before harvesting. Plants should be harvested from mid to late June to avoid rainstorms. Conventional combines with suitable sieves are used for seed harvesting. Seed losses can be as little as 5% with properly equipped and operating combines. Seed yields of 1800 kg/ha have been obtained in breeding test plots. Large scale field trials have yielded about 900 kg/ha.
Weed control has been a problem with lesquerella production fields. Special use permits have been applied for using Treflan and Goal in Arizona. Permits will be obtained for Fusilade, Balan, and paraquat.
Development of an epoxy fatty acid source from plants began in the late 1950s to mid-1960s when Vernonia anthelmintica (L.)Willd., native to India, was seen as a possible candidate. Vernolic acid in this species was discovered and isolated by Gunstone (1954). Excessive seed shattering prevented further development of this species. Collections of V. galamensis and subsequent evaluation (Carlson et al. 1981; Thompson et al. 1994b, c) indicated that this species is substantially better because of the quantity and quality of the seed-oil and better seed retention. The plant is native to equatorial Africa. To develop this crop for temperate zones, the short day-length flowering requirement needed to be altered (Dierig and Thompson 1993).
The seed head (capitula) contains hermaphroditic, protandrous florets. The range in number of florets per capitula, also representing the number of potential seeds per capitula, is between 50 and 150. The pistil is completely surrounded by an anther sheath, which dehisces as the stigma is emerging through. As the stigma opens and becomes receptive, the under side is covered with pollen by rubbing past this sheath. However, self-incompatibility is prevalent. The chromosome number of all subspecies is 2n = 18. Subspecies readily hybridize among themselves (Thompson et al. 1994a).
Although the arrangement of the flower structure makes controlled crossing and selfed seed production difficult, we have been able to accomplish crossing with a washing process. Central florets are chosen from the seed head. The anther sheath is gently removed from each floret. The remaining stigmata are washed with distilled water from a water bottle. Stigmata at this stage of development are still in an unforked position. We manually separate the lobes of the stigma approximately three-fourths to the base. Stigmata are then washed again and dried after one to three minutes. They can then be pollinated and bagged.
Since V. galamensis is native to equatorial areas, flowering in most of the germplasm is controlled by short day-lengths. As a result, most of the native germplasm cannot be grown in the U.S. for seed production. Plants will remain vegetative during the entire growing season. Plants begin to flower as days become shorter, which is also accompanied by colder temperatures, and senescence occurs. Day-neutral germplasm in one of the accessions, V. galamensis ssp. galamensis var. petitiana, flowers and produces seed during the normal growing season, but lacks other desirable characteristics. Transfer of the day-neutral flowering trait from this variety into var. ethiopica and other germplasm resulted in more desirable plant growth characteristics. These hybrids have been evaluated and selections made over the past four years at various locations across the U.S.
Petitiana is not strictly day-neutral since flowering increases under short-days compared to long-day treatment. The hybrids followed the same trend since flowering significantly decreased under long-days, and when compared to petitiana under this treatment, flowering was less. Our breeding objective now is to increase the quantity of flower heads per plant and maintain other characteristics of the short-day germplasm. These include larger flower-head size, which corresponds to the number of seeds per flower-head, increased seed weight, seed retention, and removing seed dormancy.
In 1994, seeds were planted at five locations in the U.S., and one in Argentina to evaluate oil content, seed weight, and seed yields. Eight hybrid lines and one parent line petitiana were compared. The U.S. locations included Phoenix, Arizona; Fort Stockton, Texas; Medford, Oregon; Columbia, Missouri; Petersburg, Virginia; and Salta, Argentina. The results are summarized by line across the six locations in Table 4 and combined lines results from each location in Table 5. Severe white fly and disease pressure at the Phoenix location resulted in only flowering data being collected at this location. Results showed that location affected all traits with Virginia and Missouri higher in yield, and Argentina higher in 1000 seed-weight and total oil content. Line 29E-OR2-14 and 66C-1-9 had higher yields; 15D-10-12, 29E-OR2-14 and 66C-1-9 had larger seed-weights; and 29E-OR2-14 had higher oil content (Table 4). Significant location x entry interactions for number of plants flowering at 81 days after planting, yield and total oil content were present indicating variability in stability for these traits among the populations. Lower yields, higher oil contents, and 1000 seed weights in Argentina may be due to the harvest method of picking ripe seed instead of combining plants.
A planting density study at Maricopa, Arizona was made in 1994 with hybrid lines by varying plant spacing within rows, which were 1 m apart. Plant populations were established at 15,000, 30,000, and 60,000 plants/ha using spacings of 15, 30, and 60 cm, respectively in a randomized complete block design with four replications. Although plants flowered earlier in the 0.60 m spacing, these plants appeared to be the poorest performers toward the end of the season. As plants mature, the stems become brittle. There is an advantage to space plants closer to provide support for other plants. The closer spacing may also force flowering on the top and outside canopy, achieving better plant architecture for harvesting.
Hybrid lines of Vernonia galamensis have been identified that will flower under both short and long-days. Further improvements are still necessary for commercialization. Backcross populations have successfully increased the number and size of flower-heads per plant. Comparison of F1 plants to hybrids from later generations for flower head and seed size indicates that some inbreeding depression occurs. High yielding lines adapted to various locations should soon be available.
|L. fendleri||New Mexico||22|
|L. gracilis var. nutt.||Oklahoma||4|
|L. gordonii||New Mexico||2|
|L. ovalifolia ssp. alba||Oklahoma||3|
|L. ovalifolia ssp. oval||Oklahoma||6|
|L. ovalifolia ssp. oval||Arizona||10|
|L. ovalifolia ssp. oval||Texas||7|
|P. floribunda||New Mexico||1|
|Mean (and range)|
|Population||Year||Oil (%)||Lesquerolic acid (%)||Lesquerolic yield (%)|
|High oil population|
|High lesquerolic population|
|High lesquerolic yield population|
|Mean number of flower heads per plant|
|14 h day||10 h day|
|Var. petitiana (day-neutral parent)||7||28.1||13-64||60.5||38-101|
|Var. ethiopica (short-day parent)||9||0||0||4.9||2-5|
|Seed wt |
|Seed wt |