Atypical Branching of Foxtail (Setaria spp.) Panicles in West-Central Kansas.
ABSTRACT.--Taxonomists describe panicles of green and yellow foxtail (Setaria viridis (L.) and S. glauca (L.) Beauv., respectively) as dense, contracted, narrow and cylindrical. However, a 6-y survey near Hays, Kansas documented inflorescences of green and yellow foxtail that were divided into two to four or more elongated segments. Those panicles were forked or digitate rather than a single compact cylinder. Anomalous panicles were always found on plants having several normal heads. Branched morphology was infrequent (<1 head in 10,000), but was observed in 1993 and 1995-1998. Before 1998 Kansas collections of foxtail specimens with abnormal panicles were limited to a 1600 X 3200 m area in central Ellis County. Observations during 1998 increased the known geographic distribution in Kansas to a 3200 X 3600 m area. Seed collected from branched panicles of both species and grown in greenhouse conditions did not produce plants with any aberrant inflorescences. Occurrence of deviant green or yellow foxtail panic les did not correlate with herbicide usage or drift.
During August 1992 a green foxtail (Setaria viridis (L.) Beauv.) plant with an unusual inflorescence was found at the Kansas State University Agricultural Research Center near Hays (Fig. 1). One panicle was split into four distinct segments, producing an inflorescence with a digitate appearance. Because hundreds of typical nonbranched foxtail heads were present within a few meters, that specimen was dismissed as a freak occurrence with an unknown cause. However, during 5 of the next 6 y repeated occurrences of that phenomenon were documented.
Green and yellow foxtail (Setaria glauca (L.)) are important weeds in cropland of the central plains region of North America. Both species are found throughout Nebraska, but yellow foxtail is most abundant in wetter central and eastern areas (Stubbendieck et al., 1994). Green foxtail is more common in drier western portions of Nebraska. This moisturerelated distribution pattern also occurs in Kansas (Barkley, 1983). In west-central Kansas we have observed that yellow foxtail infestations are usually restricted to moist sites such as roadside ditches, field borders and low areas in cropland where water accumulates. Green foxtail also is found in wet sites, but is more common in spring-planted crops and fallow fields.
Hitchcock (1950) described the morphologies of green and yellow foxtail inflorescences as cylindric, spikelike and, in the case of green foxtail, tapering toward the summit. Recent taxonomic work has maintained Hitchcock's original concepts of cylindric, contracted, spike-like yellow and green foxtail inflorescence structure (Great Plains Flora Association, 1991; Holm et al., 1997). Panicles of green foxtail in Nebraska were described by Stubbendieck et al. (1994) as cylindric with short branches and those of yellow foxtail as dense, erect and cylindric, which agreed with descriptions of foxtail plants collected in Kansas (Gates, 1936, 1941). Those citations consistently indicated that a typical green or yellow foxtail panicle has a single, undivided central rachis with short; spikelet-hearing secondary branches closely appressed to it. Likewise, the term 'dense panicle' denotes an arrangement in which spikelets and spikelet branches are clustered tightly into an area immediately adjacent to the rachis. None of those citations indicated green or yellow foxtail panicles divided into two or more secondary segments. Fairbrothers (1959) examined inflorescence characteristics of 100 green foxtail plants from New Jersey and 62 specimens from New England herbaria and did not mention any examples of branched panicles. Branched panicles with secondary branches up to 25 cm long are known within Setaria subgenus Ptychophyllum (Rominger, 1962), but that monograph contained no information indicating green or yellow foxtail specimens with a forked or digitate rachis were observed.
Substantial variability in green foxtail morphology was documented by Schreiber and Oliver (1971). They developed an identification key distinguishing four varieties of green foxtail. Two varieties were reported with primary culm heights of 2 to 3 m (robust green foxtails: Setaria viridis var. robusta-alba Schrieber and S. viridis var. robusta-purpurea Schreiber) and were differentiated by purple or white panicle bristles. Primary culm heights of typical green foxtail ranged from 0.5 to 1.5 m. An intermediate variety with culm heights of 1.5 to 2.5 m was called giant green foxtail (S. viridis var. major (Gaudin) Pospichel). Wang et al. (1995) also noted the wide array of morphological heterogeneity in green foxtail, but results from their isozyme analyses indicated minimal genetic differences among populations of green foxtail. Thus, they questioned whether current taxonomic varietal divisions among green foxtail morphological types are valid.
No green foxtail plants with culms [greater than]2 m have been observed in west-central Kansas. If robust varieties are present, field conditions prevent full expression of their growth potential in western Kansas; thus, they are indistinguishable from standard green foxtail. During seasons with above-normal rainfall in early summer Kansas green foxtail plants occasionally reach heights of 1.7 m and have panicle lengths exceeding 12 cm, which is within the range of giant green foxtail plants of Indiana and Illinois.
According to Gould (1968), pearl millet (Pennisetum glaucum (L.) R. Br.) is a member of the grass tribe Paniceae, as are green and yellow foxtail. Like foxtails, pearl millet typically has a compact, cylindrical spikelike panicle. However, occurrences of basal branching and forked panicle tips have been documented and their cause attributed to recessive genes (Kumar and Andrews, 1993). Schreiber and Oliver (1971) also reported occasional branching in panicles of robust foxtail varieties in Indiana and Illinois, but not in other varieties or other states. Green foxtail specimens with forked or divided panicles are known from Ontario, Canada (Dore and McNeil, 1980).
This descriptive exploratory study documented unusual panicle morphologies of green and yellow foxtail from Kansas.
Surveys for atypical foxtail panicles were conducted on the Kansas State University Agricultural Research Center-Hays, within Hays city limits (Ellis Co.), and along rural roadsides adjacent to research center property. Sites with extensive foxtail populations included rural roadsides, water drainage ditches, fence-rows, gardens, vacant lots, railroad rights-of-way, pastures and fallow croplands. Fields containing sorghum, corn, sunflower and soybean crops on research center property also were explored. Surveys were done in 1993 and 1995 through 1998.
Field searches were conducted by pacing through hundreds of yellow and green foxtail colonies and inspecting foxtail seed heads for branched specimens. Colony sizes varied from a dozen plants in a residential flower bed to several 100,000 plants in a summer-fallowed field. Sites most commonly infested with foxtail plants were rights-of-way along rural gravelsurfaced roads and fence-row borders immediately adjacent to cultivated fields. Such areas were periodically disturbed by cultivation or roadside maintenance (especially mowing). Thus, narrow strips (0.5 to 2.0 m wide) along edges of rural roads and borders of cultivated ground were common refuges for weedy annual grasses in western-central Kansas.
Additional observations of foxtail panicle morphology were obtained from areas of Kansas State University property dedicated to herbicide efficacy tests. During each growing season 400 to 600 summer crop or summer fallow plots (usually 2 X 6.7 m) were sprayed with numerous herbicide products. Normal summer crop planting dates ranged from mid-April to mid-June. Herbicide treatments were applied from 30 d before seeding until mid-July. Thus, foxtail response to a diverse assortment of herbicide products and application dates was examined during six growing seasons.
When a branched rachis was found the entire plant was removed from the soil and atypical tillers, including leaves and roots, were separated from tillers with normal panicles. Samples with anomalous panicles were preserved as herbarium specimens and donated to herbaria at Kansas State University, Manhattan; Fort Hays State University, Hays, Kansas; Utah State University, Logan; Purdue University, West Lafayette, Indiana; Northern Arizona State University, Flagstaff; University of Nebraska, Omaha and University of Wyoming, Laramie. The majority of specimens were donated to the University of Kansas herbarium at Lawrence. Letters were sent in 1995 to seven of those herbaria asking if their collections of green or yellow foxtail had divided panicles. Specimens at Fort Hays State University were checked by the authors.
A study was initiated to determine whether seeds from branched panicles produced plants with anomalous inflorescences. Seeds were removed from branched panicles of both green and yellow foxtail specimens collected in 1993 and germinated in a petri plate (30-33 C with 24 h of light). Germinated seed were transferred to greenhouse pots, grown to maturity during May through November 1996 and panicle morphology examined. After the initial flush of panicles matured plants were clipped to a height of 7 to 10 cm to simulate mowing that frequently occurs on roadside rights-of-way.
Green and yellow foxtail plants having the primary axes of their panicles divided into two or more prominent segments were collected and preserved during the summers of 1993 and 1995 to 1997 (Table 1). All cases of atypically branched panicles from west-central Kansas occurred on plants with several typical nonbranched panicles.
Morphology ranged from bifurcate panicles (simple fork with two segments) to trifurcate to less common multiple divisions with four or more digitate segments (Fig. 2). Overall frequency of branched panicles was extremely low ([less than]1 in 10,000 heads). At least 250,000 panicles were surveyed per year, but only 57 specimens were collected during this study and another 10 to 15 branched heads were not preserved. A typical section of roadside habitat on the Kansas State University Agriculture Research Center near Hays contained more than 100 foxtail panicles per square meter in September and October 1998.
Before 1998 all specimens were found on research center land within a 3200 by 1600 m area. During October 1998 two branched green foxtail panicles were observed, but not collected, within the city limits of Hays. No anomalous foxtail inflorescences were found in fields or rural roadsides adjacent to research center property. Searches of green and yellow foxtail collections in selected herbaria during 1995 did not uncover any specimens with unusual branching morphologies in six of seven herbaria listed in the Materials and Methods section. Specimens of robust green foxtail varieties with branched panicles were present in the Purdue University collection as reported by Schreiber and Oliver (1971).
No plant grown from seed on branched panicles collected in 1993 produced any atypical inflorescences. Nine green foxtail and 17 yellow foxtail plants produced 74 and 537 normal heads, respectively. By mid-June green foxtail plants stopped producing panicles and began dying, but yellow foxtail panicles continued to emerge until early October. Furthermore, none of the panicles produced after plants recovered from clipping were branched. Therefore, seeds produced on branched panicles did not acquire parental panicle morphology. Dore and McNeil (1980) obtained the same results when they planted green foxtail seed produced on panicles with anomalous branching.
Field observations did not indicate foxtail panicle branching was a response to herbicides. Most specimens were collected along roadsides that received no herbicide treatments during summer growing seasons. Furthermore, hundreds of typical foxtail panicles were in the immediate area surrounding each branched head, which suggests herbicide drift was not involved. Plants with branched panicles also had unaffected panicles and no herbicide symptoms were discernible on leaves, culms, crowns or roots of tillers having branched panicles. Branching of foxtail inflorescences appears to be a consistent, but infrequent, event within the Kansas State University field research area near Hays. However, our observations did not ascertain what caused any foxtail rachis to divide. Due to the infrequent noninherited nature of forked and digitate green foxtail panicles, Dore and McNeil (1980) did not consider this branching phenomena to be of any taxonomic importance.
Acknowledgements--Contribution No. 98-392-J, Kansas Agric. Exp. Stan., Manhattan, Kansas 66506.
(1.) Corresponding author: Telephone (785)625-3425 ext. 522; FAX (785)623-4369; e-mail: email@example.com
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Records of yellow and green foxtail plants from west-central Kansas having inflorescences divided into 2 or more primary segments Latin binomial/common name Year Collection dates Branching pattern Setaria glauce (L.) Beauv/yellow foxtail  1993 11 Aug.; 8 Sep. bifurcate 1996 14, 19, 21 Jul. bifurcate 21 Jul. trifurcate 1997 29, 30 Jul. bifurcate Setaria viridis (L.) Beauv/green foxtail  1993 12 Jul.; 11 Aug. bifurcate 26, 29 Jul.; 11 Aug. multibranched 1995 30 Jul.; 13 Aug. trifurcate 30 Jul. bifurcate 30 Jul. multibranched 1996 29 Jun.; 5, 14, 21 Jul. bifurcate 5, 9, 14 Jul. trifurcate 8, 14 Jul. multibranched 1997 29 Jul. bifurcate 29 Jul. multibranched Latin binomial/common name Year No. of plants Setaria glauce (L.) Beauv/yellow foxtail  1993 2 1996 10 2 1997 5 Setaria viridis (L.) Beauv/green foxtail  1993 2 3 1995 2 1 1 1996 10 6 5 1997 7 1 (1.)All plants collected from sections 4, 8, 9 or 10 or Range 18W, Township 14S Ellis Co. by F.E. Northam
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|Author:||NORTHAM, FRANCIS E.; STAHLMAN, PHILLIP W.|
|Publication:||The American Midland Naturalist|
|Article Type:||Statistical Data Included|
|Date:||Apr 1, 2000|
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