Host-specific variation in infection by toxigenic fungi and contamination by mycotoxins in pearl millet and corn.

Pearl millet is widely consumed in regions of Africa and Asia, and is increasingly being grown as an alternative grain in drought-prone regions of the United States. Pearl millet and corn were grown in dryland conditions at Tifton, Georgia, USA and grains were compared for pre-harvest infection by potentially toxigenic fungi and contamination by mycotoxins. Corn hybrids Agripro 9909 and Pioneer 3146, and pearl millet Tifgrain 102 were grown in 2000 and 2001; pearl millet HGM 100 was included in the test in 2001. Hybrids were sown on multiple planting dates in each year to induce variation in flowering time. Host species differed in the frequency of isolation of potentially toxigenic fungal species in both years. Across years, corn hybrids were more prone to infection by Aspergillus flavus Link (maximum isolation frequency = 8.8%) and Fusarium moniliforme Sheldon sensu lato (maximum isolation frequency = 72.8%), with corresponding greater concentrations of aflatoxins (maximum concentration = 204.9 microg kg(-1)) and fumonisins (maximum concentration = 34,039 microg kg(-1)). Pearl millet was more prone to infection by F. semitectum Berk. & Ravenel (maximum isolation = 74.2%) and F. chlamydosporum Wollenweb & Reinking (maximum isolation = 33.0%), and contamination by moniliformin (maximum contamination = 92.1 microg kg(-1)). Beauvericin (maximum concentration = 414.6 microg kg(-1)) was present in both hosts. Planting date of corn affected aflatoxin and beauvericin contamination in 2000, and fumonisin concentration in 2001. The observed differences in mycotoxin contamination of the grains, which are likely due to host-specific differences in susceptibility to pre-harvest mycoflora, may affect food safety when the crops are grown under stress conditions.

Reproduction of Belonolaimus longicaudatus, Meloidogyne javanica, Paratrichodorus minor, and Pratylenchus brachyurus on Pearl Millet (Pennisetum glaucum).

Pearl millet (Pennisetum glaucum) has potential as a grain crop for dryland crop production in the southeastern United States. Whether or not pearl millet will be compatible in rotation with cotton (Gossypium hirsutum), corn (Zea mays), and peanut (Arachis hypogaea) will depend, in part, on its host status for important plant-parasitic nematodes of these crops. The pearl millet hybrid 'TifGrain 102' is resistant to both Meloidogyne incognita race 3 and M. arenaria race 1; however, its host status for other plant-parasitic nematodes was unknown. In this study, the reproduction of Belonolaimus longicaudatus, Paratrichodorus minor, Pratylenchus brachyurus, and Meloidogyne javanica race 3 on pearl millet ('HGM-100' and TifGrain 102) was compared relative to cotton, corn, and peanut. Separate greenhouse experiments were conducted for each nematode species. Reproduction of B. longicaudatus was lower on peanut and the two millet hybrids than on cotton and corn. Reproduction of P. minor was lower on peanut and TifGrain 102 than on cotton, corn, and HGM-100. Reproduction of P. brachyurus was lower on both millet hybrids than on cotton, corn, and peanut. Reproduction of M. javanica race 3 was greater on peanut than on the two millet hybrids and corn. Cotton was a nonhost. TifGrain 102 was more resistant than HGM-100 to reproduction of B. longicaudatus, P. minor, and M. javanica. Our results demonstrated that TifGrain 102 was a poor host for B. longicaudatus and P. brachyurus (Rf < 1) and, relative to other crops tested, was less likely to increase densities of P. minor and M. javanica.

Species and cultivar influences on survival and parasitism of fall armyworm.

Interactions between host plant resistance and biological control may benefit or hinder pest management efforts. Turfgrass cultivars have rarely been tested for extrinsic resistance characteristics such as occurrence and performance of beneficial arthropods on plant genotypes with resistance to known turf pests. Parasitism of fall armyworm, Spodoptera frugiperda (J.E. Smith), among six turfgrass genotypes was evaluated. The six grasses tested [Sea Isle-1 and 561-79 seashore paspalum, Paspalum vaginatum Swartz; TifSport and TifEagle hybrid Bermuda grass, Cynodon dactylon (L.) x C. transvaalensis (Burtt-Davy); and Cavalier and Palisades zoysiagrass, Zoysia japonica von Steudel and Z. matrella (L.) Merrill, respectively] represented a range in resistance to S. frugiperda. Differential recovery of larvae released as first instars reflected this gradient in resistance of Cavalier > or = Palisades > or = TifSport = TifEagle > or = 561- = Sea Isle-1 Larval recovery (percentage of initial number released) was greatest in May, less in July and August, and least in October, probably reflecting the increase in activity of on-site predators and disease pressure. Parasitism of the fall armyworm by the braconid Aleiodes laphygmae Viereck varied among turfgrass genotypes. Parasitism was greatest during July. In total, 20,400 first instars were placed in the field; 2,368 were recovered; 468 parasitoids were subsequently reared; 92.2% were A. laphygmae. In the field, the greatest percentage of reduction in S. frugiperda larvae by A. laphygmae occurred on the armyworm-susceptible seashore paspalums (51.9% on Sea Isle-1 in July). Cotesia marginiventris Cresson and Meteorus sp. also were reared from collected larvae. No parasitoids were reared from larvae collected from resistant Cavalier zoysiagrass. A. laphygmae and C. marginiventris were reared from larvae collected from the other five grass cultivars. No parasitoids of older larvae or pupae were observed.

Ploidy variation among herbicide-resistant bermudagrass plants of cv. TifEagle transformed with the bar gene.

A protocol was developed for biolistic transformation of hybrid bermudagrass cv. TifEagle using the bar gene. TifEagle is an ultradwarf used exclusively on golf greens. Herbicide resistance should serve as a useful management tool, especially if methyl-bromide is unavailable for fumigation prior to plant establishment. Hybrid bermudagrass is completely sterile, which should limit the chance of gene escape via out-crossing. Sliced nodes were used to initiate embryogenic tissue cultures on MS medium supplemented with 1 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D) and 0.01 mg/l 6-benzylaminopurine (BA). Embryogenic tissue was bombarded with the bar gene, and herbicide-resistant tissue was selected in the dark on medium supplemented with 0.75 mg/l 2,4-D, 0.01 mg/l BA and 5-15 mg/l phosphinothricin (PPT). Resistant somatic embryos were induced to germinate in the light on MS medium supplemented with 0.13 mg/l 2,4-D and 0.5 mg/l BA. Plants were transferred to the greenhouse after rooting in the presence of 10-15 mg/l PPT and testing positive in a chlorophenol red assay. A total of 89 herbicide-resistant plants were recovered from at least nine independent events from six separate bombardments, although the number of independent transformation events was not confirmed for the entire group. Flow cytometry indicated that most of the plants (82/89) were hexaploid and that the remaining seven plants were triploid. The hexaploid plants were a darker green than the triploids or TifEagle control. Other variation, present only in the hexaploids, included an increased leaf width and length. Southern blot hybridization confirmed genomic integration of the bar gene in triploid and a subset of hexaploid herbicide-resistant plants. AFLP analysis did not indicate changes in DNA profiles using [33P] and a sample of 32 hexaploid plants recovered from a single bombardment. DNA profiles were very similar to that of the TifEagle control with a semi-automated fluorescence-based AFLP.

Fertile transgenic pearl millet [ Pennisetum glaucum (L.) R. Br.] plants recovered through microprojectile bombardment and phosphinothricin selection of apical meristem-, inflorescence-, and immature embryo-derived embryogenic tissues.

Pearl millet [ Pennisetum glaucum (L.) R. Br.] is a drought-tolerant cereal crop used for grain and forage. Novel traits from outside of the gene pool could be introduced provided a reliable gene-transfer method were available. We have obtained herbicide-resistant transgenic pearl millet plants by microprojectile bombardment of embryogenic tissues with the bar gene. Embryogenic tissues derived from immature embryos, inflorescences and apical meristems from diploid and tetraploid pearl millet genotypes were used as target tissues. Transformed cells were selected in the dark on Murashige and Skoog medium supplemented with 2 mg/l 2,4-D and 15 mg/l phosphinothricin (PPT). After 3-10 weeks in the dark, herbicide-resistant somatic embryos were induced to germinate on MS medium containing 0.1 mg/l thidiazuron and 0.1 mg/l 6-benzylaminopurine. Plants were transferred to the greenhouse after they were rooted in the presence of PPT and had passed a chlorophenol red assay (the medium turned from red to yellow). Transgenic plants were recovered from bombardments using intact pAHC25 plasmid DNA, a gel-purified bar fragment, or a mixture of pAHC25 plasmid or bar fragment and a plasmid containing the enhanced green fluorescent protein ( gfp) gene (p524EGFP.1). Analyses by the polymerase chain reaction, Southern blot hybridization, GFP expression, resistance to herbicide application, and segregation of the bar and gfp genes confirmed the presence and stable integration of the foreign DNA. Transformed plants were recovered from all three explants, although transformation conditions were optimized using only the tetraploid inflorescence. Time from culture initiation to rooted transgenic plant using the tetraploid inflorescence ranged from 3-4 months. Seven independent DNA/gold precipitations were used to bombard 52 plates, 29 of which produced an average of 5.5 herbicide-resistant plants per plate. The number of herbicide-resistant plants recovered per successful bombardment ranged from one to 28 and the frequency of co-transformation with gfp ranged from 5% to 85%.

Evaluation of turfgrass species and cultivars for potential resistance to twolined spittlebug (Hemiptera: Cercopidae).

Potential resistance to the twolined spittlebug, Prosapia bicincta (Say), was evaluated among 56 turfgrass genotypes. Greenhouse, laboratory, and field bioassays identified differences in spittlebug survival and development, host preference and damage levels, and turfgrass tolerance to and ability to recover from pest induced injury. All centipede grasses demonstrated high levels of susceptibility, followed by bermudagrasses, seashore paspalums, and zoysiagrasses. Average nymphal survival to the adult stage ranged from 1.5 to 78.1%. Development required 38.1-62.0 d under greenhouse conditions, depending on plant taxa. Among seashore paspalums, nymphal survival to the adult stage was lowest and duration of development was longest on HI-1, 'Sea Isle 2000', 561-79, and 'Mauna Kea'. Reduced spittlebug survival and increased developmental times were also observed on the bermudagrasses BERPC 91-15 and 'Tifway'. Although zoysiagrasses supported spittlebug development and survival to the adult stage, developmental times were extended on the zoysiagrass cultivars 'Emerald' and 'El Toro'. Spittlebug preference varied with generation evaluated. First-generation spittlebugs inflicted the greatest damage on TC201 (centipede grass), 'Primavera' (bermudagrass), and 'Emerald' (zoysiagrass) in choice tests. In the fall, second-generation spittlebugs damaged TC201 (centipedegrass) and 'Sea Isle 1' (paspalum) most severely, whereas 561-79 (paspalum) and 'Emerald'(zoysiagrass) were less severely affected. Among taxa included in field trials, HI-1, 'Mauna Kea', 'Sea Isle 2000',and AP-14 paspalums, 'Tifway' bermudagrass, and 'Emerald' zoysiagrass were most tolerant (demonstrated the best regrowth potential following twolined spittlebug feeding).

Grass species and endophyte effects on survival and development of fall armyworm (Lepidoptera: Noctuidae).

Grass selections including 10 zoysiagrasses, 18 paspalums, 34 Bermuda grasses, tall fescue, creeping red fescue, and perennial ryegrasses with and without endophyte were evaluated for potential resistance to fall armyworm, Spodoptera frugiperda (J. E. Smith), larvae. Laboratory evaluations assessed the degree of antibiosis among >70 grass lines to first-instar fall armvworms. When all parameters measured were considered, the trend in resistance to fall armyworm among endophyte-infected (E+) and endophyte-free (E-) cool season grasses from greatest to least was: 'Dawson' E+ > APR 1234 > 'Dawson' E- > 'Rosalin' E+ > Lp 5425, 'Rosalin' E-, ATF 480 > 'Tulsa' or: E+ slender creeping red fescue > E+ turf- type perennial ryegrass > E- slender creeping red fescue > E+ forage-type perennial ryegrass > E- forage-type perennial ryegrasses, and E+ tall fescue > E- turf-type tall fescue. Among warm season grasses larval weight gain was reduced on all zoysiagrasses. Larval weight gain also was lower on the Bermuda grasses 'Tifsport', 'Tifgreen', 97-4, 97-14, 97-22, 97-28, 97-39, 97-40,97-54, 98-15, 98-30, and 98-45 than when larvae were fed 'Tulsa' tall fescue or the diet control. Only APR1234 and 'Dawson' creeping red fescue reduced larval survival to the same extent that was observed for zoysiagrasses. Survival on Bermuda grasses was least on 97-8. Seashore paspalums were only rarely less susceptible to fall armyworm than tall fescue, although pupal weights were consistently lower on 'Temple 1' and 'Sea Isle 1' paspalums than that on 'Tulsa' tall fescue. Genetic resistance to key grass pests can reduce insecticide use and simplify management of these cultivars.

Evaluation of Pearl Millet Grain Hybrids for Resistance to Meloidogyne spp. and Leaf Blight Caused by Pyricularia grisea.

Pearl millet, Pennisetum glaucum, has potential as a grain crop in the southeastern United States. Our objectives were to (i) determine the resistance and/or tolerance of pearl millet hybrids to Meloidogyne incognita race 3 and M. arenaria race 1; (ii) compare reproduction of Meloidogyne spp. on pearl millet and corn; and (iii) determine the disease severity of leaf blight caused primarily by Pyricularia grisea. In a field naturally infested with M. incognita, experimental pearl millet hybrids with inbreds 114 and 117 as the pollinators had fewer numbers of second-stage juveniles and more severe leaf blight than did HGM-100, a nematode-susceptible hybrid; hybrids with inbred 115 as the pollinator were similar to HGM-100 in both nematode numbers and foliar disease severity. Grain yields in pearl millet were greater in plots treated with 1,3-dichloropropene than in control plots and were negatively correlated with leaf blight severity. In a greenhouse experiment, both M. incognita and M. arenaria produced fewer eggs on pearl millet hybrids with pollinators 114, 117, 101, 102, and 103 than on hybrid HGM-100. Reproduction of M. incognita was less on the resistant pearl millet hybrids than on corn. Because both M. incognita and P. grisea can reduce grain yield of pearl millet, hybrids developed for the southeastern United States should be resistant to both pathogens.

Resistance to Striga hermonthica in Wild Accessions of the Primary Gene Pool of Pennisetum glaucum.

ABSTRACT Resistance to Striga hermonthica in 274 wild Pennisetum glaucum subsp. monodii and stenostachyum accessions was evaluated at Samanko, Mali in 1997 and 1998, and at Cinzana, Mali and Sadoré, Niger in 1998. Data recorded included number of striga plants per plot at least three times during the season, date of striga emergence, number of Pennisetum plants, Pennisetum anthesis date, and downy mildew incidence (caused by Sclerospora graminicola). Across trials, the average maximum number of striga per host plant ranged from 0.9 to 8.3. Average days to striga emergence ranged from 54 to 68 days across trials, and was negatively correlated (P < 0.01) with maximum striga within trials. Days to Pennisetum flowering ranged from 54 to 74 days across trials. Host flowering was correlated (P

First Report and Epidemics of Buffelgrass Blight Caused by Pyricularia grisea in South Texas.

A blight on buffelgrass, Cenchrus ciliaris L., has been observed for several years in south Texas and Mexico. The disease did not reach epidemic proportions until 1996. The causal agent, identified as Pyricularia grisea (Cooke) Sacc., is a common pathogen of grasses and other cultivated crops. Several Pennisetum spp. have been reported as hosts of Pyricularia spp.; this is the first report of buffelgrass as a host of this pathogen (1,2). Pathogenicity of P. grisea on buffelgrass was confirmed by greenhouse inoculations of 2-month-old buffelgrass plants with conidia washed with distilled water from monoconidial isolations of the pathogen, grown on potato dextrose agar, from infected leaves collected in several locations in south Texas and Mexico. Plants were placed for 8 h every night inside a plastic enclosure with a humidifier, simulating the high relative humidity conditions prevalent during the epidemic. Typical lesions developed after 7 days. The pathogen was re-isolated from the lesions after 10 days, fulfilling Koch's postulates. Conidia harvested from the sporulating samples were hyaline, transversely septate, with one to three septa, most of them having two. Conidia were obpyriform, with hylum often protuberant, measuring 20.6 to 26.3 µm in length and 8.5 to 10.1 µm wide. These measurements are consistent with those given for Pyricularia spp. by Ellis (1). Conidiophores were hyaline, single, slender, and unbranched. Initial symptoms were dark, discolored spots on the leaf that developed into tan, round to elliptical, necrotic lesions with a dark red border and a yellow, chlorotic halo. With increasing severity, lesions can coalesce, killing the entire leaf blade. Under heat and moisture stress, leaves with few lesions and yellow discoloration will wilt completely. Except for the presence of distinct lesions, wilted plants appear to be suffering from severe drought stress or herbicide injury. Losses vary from a few lesions to wilted whole plants and entire pastures. The pathogen also reduces the quantity and quality of seed by infecting involucres of the head. In the absence of the disease, even under severe moisture or drought stress, buffelgrass is able to thrive. Common T-4464 buffelgrass, which is highly susceptible to P. grisea, was introduced into south Texas in the late 1940s and is currently grown on 8 to 10 million acres in south Texas and Mexico. Buffelgrass reproduces by obligate apomixis, in which seeds are formed without sexual fertilization. Consequently, the progeny are genetically identical to the maternal parent. The monoculture of this grass with its unique type of reproduction encompasses millions of acres with genetically identical plants. Interaction of inoculum with weather conditions (nights with 8 to 10 h of more than 75% relative humidity) in 1996, 1997, and the late summer of 1998 produced epidemics of buffelgrass blight throughout south Texas and northern Mexico. P. grisea was also isolated from lesions on grassburr Cenchrus incertus M. A. Curtis collected throughout the area. References: (1) M. B. Ellis 1971. Dematiaceous hyphomycetes. Commonwealth Mycological Institute, Kew, Surrey, England. (2) D. F. Farr et al. 1989. Fungi of Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN.

Protein and energy value of pearl millet grain for mature goats.

We conducted two studies to assess the protein and energy value of pearl millet grain (Pennisetum glaucum [L.] R. Br.) for mature goats. In Exp. 1, 15 2-yr-old male castrated goats were gradually introduced over a 4-mo period to three all-grain diets consisting of 100% corn (Zea mays L.), 50:50 corn:pearl millet, and 100% pearl millet. After the adjustment to all-grain feeds, the goats were fed the diets in metabolism crates for 2-d adjustment and 7-d total collection periods. For Exp. 2, complete diets containing the three grain treatments (corn, 50:50 corn:pearl millet, and pearl millet) as 40% of the total DM as fed (the remainder was mainly alfalfa meal and mineral supplement) were balanced to contain 16% crude protein (CP) and 2.24 Mcal digestible energy (DE)/kg on an air-dry basis. Twelve mature (4- to 6-yr-old) buck goats were randomly assigned to diets and fed in pens for 14 d and then moved to metabolism crates for 10-d adjustment and 10-d total collection periods. In Exp. 1, DM intake was unaffected by dietary treatment, but digestibility of DM and organic matter was lowest (P < .10) in goats fed 100% pearl millet. Digestibility of complete diets also decreased (P < .10) as corn was replaced by 50 or 100% pearl millet, but DM intake increased (P < .10) on the 100% millet diet. In both experiments, substituting pearl millet for corn had no effect on nitrogen retained by the goats. Metabolizable energy of pearl millet was only 92% that of corn, but ME intake was similar when the grains were fed as 40% of the dietary DM. Pearl millet has potential as a major energy feed for goats in areas where it can be economically produced.

Tight clustering and hemizygosity of apomixis-linked molecular markers in Pennisetum squamulatum implies genetic control of apospory by a divergent locus that may have no allelic form in sexual genotypes.

Apomixis is a naturally occurring mode of reproduction that results in embryo formation without the involvement of meiosis or fertilization of the egg. Seed-derived progeny of an apomictic plant are genetically identical to the maternal parent. We are studying a form of apomixis called apospory that occurs in the genus Pennisetum, a taxon in the grass family. A cultivated member of this genus, pearl millet (Pennisetum glaucum), reproduces sexually. A wild relative of pearl millet, Pennisetum squamulatum, that is an obligate aposporous species, is cross-compatible with pearl millet when used as a pollen donor in the interspecific cross. We present herein the genetic mapping of 13 molecular markers in an interspecific hybrid population of 397 individuals that segregates for apomixis and sexuality. Surprisingly, 12 of the 13 markers strictly cosegregated with aposporous embryo sac development, clearly defining a contiguous apospory-specific genomic region in which no genetic recombination was detected. Lack of or suppression of recombination may be coincidentally associated with the chromosomal context of the apomixis locus or it may be a consequence of its evolution that is essential for preservation of gene function as has been previously shown in studies of complex loci in both plant and animal species.

Molecular markers for rust and pyricularia leaf spot disease resistance in pearl millet.

Pearl millet [Pennisetum glaucum (L.) R.Br.] is a warm-season grass used for food, feed, fodder and forage, primarily in countries of Africa and India but grown around the world. The two most-destructive diseases to pearl millet in the United States are rust (caused by Puccinia substriata var. indica) and pyricularia leaf spot (caused by Pyricularia grisea). Genes for disease resistance to both pathogens have been transferred into agronomically acceptable forage and grain cultivars. A study was undertaken to identify molecular markers for three rust loci and one pyricularia resistance locus. Three segregating populations were screened for RAPDs using random decamer primers and for RFLPs using a core set of probes detecting single-copy markers on the pearl millet map. The rust resistance gene Rr 1 from the pearl millet subspecies P. glaucum ssp. monodii was linked 8.5 cM from the RAPD OP-G8350. The linkage of two RFLP markers, Xpsm108 (15.5 cM) and Xpsm174 (17.7 cM), placed the Rr 1 gene on linkage-group 3 of the pearl millet map. Rust resistance genes from both Tift 89D2 and ICMP 83506 were placed on linkage-group 4 by determining genetic linkage to the RFLP marker Xpsm716 (4.9 and 0.0 cM, respectively). Resistance in ICMP 83506 was also linked to the RFLP marker Xpsm306 (10.0 cM), while resistance in Tift 89D2 was linked to RAPD markers OP-K19350 (8.8 cM) and OP-O8350 (19.6 cM). Fragments from OP-K19 and OP-O8 in the ICMP 83506 population, and Xpsm306 in the Tift 89D2 population, were monomorphic. Only one RAPD marker (OP-D11700, 5.6 cM) was linked to pyricularia leaf spot resistance. Attempts to detect polymorphisms with rice RFLP probes linked to rice blast resistance (Pyricularia oryzae; syn=P. grisea) were unsuccessful.

Nutritional value of pearl millet for lactating and growing goats.

Studies were conducted to assess nutritional value of pearl millet grain (Pennisetum glaucum [L] R. Br.) for lactating and growing goats. Three complete diets containing either 40% corn, 40% pearl millet, or 40% corn and pearl millet mixed 1:1 (wt/wt) were balanced to contain 16% crude protein and 2.24 Mcal DE/kg on an air-dry basis. Forty-five does were blocked by kidding date and randomly assigned to diets for a 7-wk investigation. Feed intake and milk production were unaffected (P > .25) by treatment, and they averaged 2.86 and 2.47 kg daily, respectively. Thirty-three growing goats were blocked by sex and fed the same diets for 15 wk. Daily growth rate and feed to gain ratio were depressed (P < .05) by 25.4 and 19.0%, respectively, when corn was completely replaced with pearl millet. Digestion coefficients for DM, GE, CP, and NDF were reduced by over 10 percentage units with partial or complete replacement of corn by pearl millet. Ruminal acetate and ratio of acetate to propionate increased (P < .05) but butyrate, propionate, and ammonia were depressed (P < .05) with the pearl millet diets. Growing goats consumed 43 meals daily. They consumed 26.9, 32.6, 27.4, and 13.1% of their ration during the morning (0600 to 1200), afternoon (1200 to 1800), evening (1800 to 2400), and night (2400 to 0600), respectively. Pearl millet is a useful energy feed for mature, but not for growing, goats.

Digestibility and utilization of pearl millet diets fed to finishing beef cattle.

Pearl millet grain was blended with corn in 1:1 or 2:1 ratios in beef finishing diets fed in two metabolism and two feedlot trials. In Exp. 1, diets contained 1) 79.5% corn and 4.5% soybean meal (C-SBM), 2) 28% corn, 54.5% sorghum, and 1.5% soybean meal [GSC(2:1)], and 3) 28% corn and 56% pearl millet [PMC(2:1)]. In Exp. 2, diets contained 1) 81.5% corn and 3.5% soybean meal (C-SBM) or 2) 42.5% corn and 42.5% pearl millet [PMC(1:1)]. Diets fed to steers in metabolism trials in Exp. 1 and 2 had similar (P > .10) apparent digestion coefficients for OM, crude fiber, NDF, and ADF. However, ether extract digestibility was higher (P < .05) for C-SBM than for GSC(2:1) and PMC(2:1) in Exp. 1, and it was higher (P < .10) for C-SBM than for PMC(1:1) in Exp. 2. In both experiments CP digestibility was higher (P < .10) for C-SBM diets, and N retention was similar (P > .10) for diets within each experiment. In each experiment, TDN calculated from apparent digestion coefficients was converted to NEm and NEg. The TDN, NEm, and NEg were lower (P < .10) for GSC(2:1) and PMC(2:1) than for C-SBM in Exp. 1. Experimental diets were fed to steers (n = 45; 396 +/- 19 kg initial BW; 70-d ad libitum feeding) in Exp. 1 and to heifers (n = 30; 318 +/- 15 kg initial BW; 92-d ad libitum feeding) in Exp. 2. The ADG, empty body weight gain (EBG), and predicted EBG were not different (P > .10) for diets composed of the different grain sources. Feed DMI and DM per gain were higher (P < .05) for PMC(1:1) than for C-SBM in Exp. 2. Pearl millet supplied approximately 88% as much NEm and 85% as much NEg as the corn-SBM portion of diets having similar CP concentrations.

Effects of irrigation, nitrogen, and a nematicide on pearl millet.

Pearl millet is used mainly as a temporary forage crop in the southern United States. A new pearl millet hybrid has potential as a major grain crop in the United States. The effects of nematodes, irrigation, a nematicide, and nitrogen rates on a new pearl millet grain hybrid, HGM-100, and nematode population changes were determined in a 2-year study. Root-knot nematodes (Meloidogyne incognita race 1) entered the roots of pearl millet and caused minimal galling, but produced large numbers of eggs that hatched into second-stage juveniles. Root-gall indices ranged from 1.00 to 1.07 on a 1-5 scale and were not affected by irrigation or rates of nitrogen. Yield of pearl millet was up to 31% higher under no supplemental irrigation than under irrigation, 16% higher in fenamiphos-treated plots than untreated plots, and 56% higher in plots treated with 38 kg nitrogen/ha than plots treated with 85 kg nitrogen/ha. In southern Georgia, pearl millet appears to be resistant to ring nematode (Criconemella ornata) but favors development and reproduction of M. incognita.

Molecular markers shared by diverse apomictic Pennisetum species.

Two molecular markers, a RAPD (randomly amplified polymorphic DNA) and a RFLP/STS (restriction fragment length polymorphism/sequence-tagged site), previously were found associated with apomictic reproductive behavior in a backcross population produced to transfer apomixis from Pennisetum squamulatum to pearl millet. The occurrence of these molecular markers in a range of 29 accessions of Pennisetum comprising 11 apomictic and 8 sexual species was investigated. Both markers were specific for apomictic species in Pennisetum. The RFLP/STS marker, UGT 197, was found to be associated with all taxa that displayed apomictic reproductive behavior except those in section Brevivalvula. Neither UGT197 nor the cloned RAPD fragment OPC-04600 hybridized with any sexually reproducing representatives of the genus. The cloned C04600 was associated with 3 of the 11 apomictic species, P. ciliare, P. massaicum, and P. squamulatum. UGT197 was more consistently associated with apomictic reproductive behavior than OPC04600 or cloned C04600, thus it could be inferred that UGT197 is more closely linked to the gene(s) for apomixis than the cloned C04600. The successful use of these probes to survey other Pennisetum species indicates that apomixis is a trait that can be followed across species by using molecular means. This technique of surveying species within a genus will be useful in determining the relative importance of newly isolated markers and may facilitate the identification of the apomixis gene(s).

Origin of the main class of repetitive DNA within selected Pennisetum species.

In an attempt to identify relationships among genomes of the allotetraploid Pennisetum purpureum Schumach and closely related Pennisetum species with which it can be successfully hybridized, repetitive DNA sequences were examined. Digestion with KpnI revealed two highly repetitive fragments of 140 bp and 160 bp. The possibility that these sequences could be used as genome markers was investigated. Average sequences were determined for the 140 bp and 160 bp KpnI families from P. purpureum and P. squamulatum Fresen. Average sequences (based upon four or five repeats) were determined for the P. glaucum (L.) R. Br. 140 bp KpnI family and the diploid P. hohenackeri Hochst. ex Steud. 160 bp KpnI family. The average sequences of the 160 bp KpnI families in P. purpureum and P. squamulatum differ by only nine bases. The 140 bp KpnI families of the three related species, P. purpureum, P. squamulantum, and P. glaucum are nearly identical, and thus likely represent a recent divergence from a common progenitor or a common genome. Each repetitive sequence may contain internal duplications, which probably diverged following amplification of the original sequence. The 140 bp KpnI repeat probably evolved from the 160 bp KpnI repeat since the missing 18 bp segment is part of the internal duplication that is otherwise conserved in the subrepeats. Tandemly arrayed repetitive sequences in plants are likely to be composed of subrepeats which have been duplicated and amplified.

Transmission of the apomictic mode of reproduction in Pennisetum: co-inheritance of the trait and molecular markers.

Apomixis, asexual reproduction through seed, is an obligate mode of reproduction in several species from the genus Pennisetum. Transfer of apomixis to sexual, cultivated pearl millet (P. glaucum) from a wild species P. squamulatum has resulted in an obligate apomictic backcross line with a low, but unknown number, of chromosomes from the wild species. Molecular markers (restriction fragment length polymorphisms and random amplified polymorphic DNAs) have been identified that unequivocally demonstrate the presence of P. squamulatum DNA in BC3. Three of the informative RFLP clones have been sequenced and converted to sequence-tagged sites that can be amplified by the polymerase chain reaction. Molecular genetic analysis of more advanced back-cross individuals, using the two types of polymerase chain reaction-based molecular markers, has demonstrated co-inheritance of apomictic reproduction and two of the molecular markers. The remaining five molecular markers generally co-segregate with each other but are not linked with the mode of reproduction. These results suggest that genes for apomixis apparently can be transmitted by a single chromosome. Chromosome-specific markers will provide a starting point for the mapping of this genetically intractable reproductive trait.

Nutritive characteristics of pearl millet grain in beef cattle diets.

Two trials were conducted to compare pearl millet grain with corn and grain sorghum in cattle diets. Grain portions of diets in metabolism and feedlot experiments contained 73% corn and 6% soybean meal (C); 76.2% grain sorghum and 2.8% soybean meal (GS); and 79% pearl millet (PM). In the metabolism trial (replicated 3 x 3 latin squares; six steers), apparent digestibilities of DM and OM were higher (P less than .05) for C than for GS or PM diets. Ether extract and CP digestibilities were higher (P less than .05) for C and PM than GS. Dietary TDN was higher (P less than .05) for C compared with GS or PM diets. Fecal N was higher (P less than .05) for GS than for C or PM, urinary N was higher (P less than .05) for PM than C or GS, but retained N was similar (P greater than .05) for C, GS and PM diets. In a 90-d feedlot trial (18 individually fed heifers), a trend was observed for higher (P less than .20) ADG on C compared with PM; however, feed/gain was similar for C, GS and PM diets (8.2, 9.1 and 8.5 kg feed/kg gain, respectively). Ruminal fluid acetate:propionate ratios were lower (P less than .05) at 3.5 and 7 h postfeeding for PM compared with C or GS diets on d 83. Pearl millet grain may be used as a feed grain for beef cattle, but diets should be formulated to efficiently utilize the high quantity of protein (about 14% of DM) in this grain as a substitute for supplemental protein.