Digitaria Milanjiana Research Articles

An Invasive Plant Parthenium hysterophorus Reduces Native Forage Cover

While some research has been conducted in sub–Saharan Africa on the alien invasive Parthenium hysterophorus, little work has assessed whether it is poses negative impact on native forages. A field survey was carried out to study the dominant co–existing plant species, and its impact on plant abundance, species, and native forage cover. We found that non–natives were the dominant co–existing plants with P. hysterophorus compared to natives. Plant species (r = -0.889, P = 0.043) and abundance (r = -0.968, P = 0.007) decreased with increasing invasive percent cover. Moreover, native forage plant (Brachiaria reptans; r = -0.922, P = 0.026), Cynodon dactylon; r = -0.972, P = 0.006, Digitaria milanjiana; r = -0.938, P = 0.018, and Indigofera spicata; r = -0.977, P = 0.004) percent cover decreased with increasing invasive percent cover. The study concludes that P. hysterophorus negatively affects plant diversity, and thus, should controlled.

Distribution of macrophytes in relation to physico-chemical characters in the south western littoral zone of Lake Tana, Ethiopia

Abstract Between October 2014 to September 2016 we investigated the distribution of macrophyte assemblages in relation to water quality in the south western littoral zone of Lake Tana. in situ measurements of physicochemical parameters (DO, pH, EC, TDS, temperature and Secchi depth) were accompanied by nutrient analyses for NO3-N, soluble reactive phosphate (SRP) and total phosphorus (TP). Macrophytes were collected manually using a belt transect method. Thirty macrophyte species belonging to fifteen families were identified. Emergent and amphibious plants had the maximum percentage composition at 53 % and 30 %, respectively and attained the highest relative frequency and density, followed by floating species and other forms. Redundancy analysis (RDA) indicated that the density of Azolla pinnata subsp. africana, Ceratophyllum demersum, Cyperus alopecuroides, Digitaria milanjiana, Pycreus macrostachyos, Pycnostachys coerulea and Scirpus pallidus was positively and strongly associated with pH, Secchi depth, SRP and TP whereas that of Amaranthus hypochondriacus, Cyperus papyrus, Echinochloa stagnina, Ipomoea aquatic, Panicum maximum, Sacciolepis Africana and Stuckenia pectinata was negatively and strongly associated with these variables but positively with NO3-N. The density of Brachiaria sp., Vossia cuspidate and Leersia hexandra was negatively and strongly associated with pH, SRP and TP whereas the density of Typha latifolia was positively and strongly associated with TDS and EC. The highest diversity index (H′ = 2.63) was recorded in Zegie Yiganda sampling site, which was better protected from anthropogenic impacts. In conclusion, Lake Tana is experiencing changes in physico-chemical parameters, which has favored a shift in species composition of macrophytes towards turbidity-tolerant emergent and amphibious species.

Convergent grazing responses of different‐sized ungulates to low forage quality in a wet savanna

AbstractWe studied how grazing intensity by small and mid‐sized ungulate grazers varied with nutritional quality and grass species composition in wet oligotrophic tallgrass savanna of coastal northern Tanzania. Average grazing intensity was low (3–15% by cover), and most grass species were scarcely used by herbivores. Only two grasses, Panicum infestum and Digitaria milanjiana, had nitrogen and phosphorus concentrations that were consistently above the minimum levels (e.g. nitrogen concentrations <7 mg g−1) required by the three commonest grazers, Bohor reedbuck, waterbuck and wildebeest. The best predictors of grazing intensity were cover of P. infestum (the most abundant grass, with a mean cover of 15%) and canopy height of ungrazed vegetation. Models did not contain separate predictors for nutritional quality, presumably because quality varied mainly at the grass species level and therefore was fully represented by the variable ‘cover of P. infestum’. Given that the three grazers differed greatly in body size and muzzle width (parameters known to influence nutrient requirements and the ability of grazers to feed selectively at the smallest spatial scale), we expected there to be strong resource partitioning that would be detectable in terms of grazing strategies and feeding sites. However, apart from minor differences in canopy height, greenness and diameter of grazed patches (albeit consistent with our expectations), feeding stations of the three grazers were similar and strongly dominated by P. infestum. We conclude that the low quality of herbage in wet oligotrophic savannas restricts foraging choices, which produces a characteristic yet impoverished grazing community that exhibits only limited resource partitioning.

Performances of Some Perennial Warm Season Grasses Alfalfa (Medicago sativa L.) Mixtures under Mediterranean Conditions

This research was conducted to determine forage yield and botanical composition of duo (alfalfa + one grass) and trio ( alfalfa + two grasses) mixtures of some warm season perennial grass species such as dallis grass (Paspalum dilatatum Poir.), Rhodes grass (Chloris gayana L.), Bermuda grass (Cynodon dactylon (L.) Pers.) Guineae grass (Panicum maximum Jacq.), blue couch grass (Digitaria didactyla Willd) and finger grass (Digitaria milanjiana (Rendle) Stapf) with alfalfa (Medicago sativa L.) as well as their pure sowings under irrigated conditions of Mediterranean during the years of 2011 and 2012. In the study, green herbage yield, dry matter yield, alfalfa proportion in dry matter yields and land equivalent ratio (LER) were determined. The experimental design was completely randomized block design with three replications. According to the results, it was determined that the ratios of warm season grasses in the botanical composition of the mixtures declined with the establishment age while rate of alfalfa in the botanical composition of the mixtures increased. Increasing the rate of alfalfa in the botanical composition of the mixtures also increased hay quality of the mixtures. The mixtures gave higher dry matter yield than pure sowings of the species. The highest green herbage yield (98.14 t ha1) was obtained from the mixture of Rhodes grass + alfalfa. The highest dry matter yield (22.46 t ha1) was obtained from the mixture of dallis grass + Guinea grass + alfalfa. The highest value of land equivalent ratio (LER) (1.49) was obtained from the mixture of bermuda grass +Rhodes grass + alfalfa. From the results of the study, it was concluded that Guinea grass and finger grass did not show good adaptaion to the Cukurova conditions due to low temperatures during the winter season. Bermuda grass, Rhodes grass, blue couch grass and dallis grass could be used to establish pasture mixtures with alfalfa, having long grazing season and giving high hay yield and quality. Before the establishment of such pasture mixtures, it was needed to research proper mixture ratios and proper management techniques of the mixtures

Nutritive Value of Grasses in Semi-arid Rangelands of Ethiopia: Local Experience Based Herbage Preference Evaluation versus Laboratory Analysis.

We examined the nutritive value of common grass species in the semi-arid rangelands of Borana in southern Ethiopia using local experience based herbage preference (LEBHP) perception and laboratory techniques. Local pastoralists in the study area were asked to identify common grass species and rank them according to the species’ preferences and palatability to cattle. The pastoralists listed a total of 15 common grass species which were then sampled during the main rain and cold dry seasons and analyzed for crude protein (CP), Neutral Detergent Fiber (NDF), Acid Detergent Fiber (ADF) and ash content to verify pastoralists’ claim regarding the quality of individual species. The relative feed value (RFV) and dry matter digestibility (DMD) were also calculated using NDF and ADF contents. Spearman’s rank correlation was used to examine possible relationships between laboratory results and pastoralists’ experience on grass quality. Cenchrus ciliaris, Chrysopogon aucheri, Digitaria milanjiana, Eragrostis papposa and Panicum maximum were the top five species based on LEBHP perception. There were indications of inconsistency in terms of LEBHP perception among the different pastoral communities. The chemical composition of all grass species showed significant (p<0.05) variation between sites, seasons and species. The results showed that the CP values for the Borana rangelands were in the range of 8.7% in the main rain season to 5.1% for the cold dry season. The fiber constituents were relatively low in the main rain season compared to the cold dry season. Overall, Digitaria milanjiana had the highest CP (16.5%) content, while the least was recorded with Heteropogon contortus (10.8) and Aristida adoensis (9.8%) during the main rain season. It seems that the spatial variability of landscapes within the wider geographical regions, soil properties and texture, and land-use patterns probably contributed to site differences in species quality. Generally, the RFV of individual grass species was significantly (p<0.05) varied between and within sites. The ranking of species by pastoralists according to their preferences by cattle was highly correlated with the chemical composition of laboratory results of individual grass species with ‘r’ values for CP (0.94), ash (0.95), NDF (−0.98), ADF (−0.93) and ADL (−0.93). We suggest the complimentary use of LEBHP and laboratory techniques in evaluating the nutritive quality of rangeland forage species for sustainable animal production.

Gradients in fracture force and grazing resistance across canopy layers in seven tropical grass species

AbstractIn reproductive swards, stems can act as a barrier that affects the grazing behaviour of ruminant livestock. The barrier effect of stems is closely associated with both the force required to fracture the stems and the density of these stems (in combination, these make up grazing resistance), and these factors need to be considered when making predictions about the forage intake of ruminants grazing reproductive pastures. Differences in grazing resistance between sward canopy layers of different grass species are thought to affect bite dimensions, but data are scarce. In this study, we assessed the grazing resistance for three canopy layers of seven tropical grass species. Species differed significantly in grazing resistance for every canopy layer, with a general ranking order for grazing resistance, in ascending order: Cenchrus ciliaris (‘American' buffel), Digitaria milanjiana (‘Jarra’ finger grass), Setaria surgens (annual pigeon grass), Setaria sphacelata (‘Narok’ setaria), Dichanthium sericeum (Queensland bluegrass), Chloris gayana (‘Callide’ Rhodes grass). In the top canopy layer, grazing resistance did not appear to create a barrier for any of the species, but in the bottom canopy layer, it did for all species. Species also differed in the relative contribution of fracture force and density to grazing resistance. The results highlight the importance of managing the grazing systems to minimize the barrier effect of the stems, which can be done by controlling the phenological stage of the pasture and the grass species and animal size used in the system.

Tensile fracture properties of seven tropical grasses at different phenological stages

AbstractThe intake of forage grasses by grazing ruminants is closely related to the mechanical fracture properties of grasses. The relationship between the tensile fracture properties of grasses and foraging behaviour is of particular importance in tropical reproductive swards composed of both stems and leaves. This study (i) quantified and compared the tensile fracture properties of stems and leaves of seven tropical grass species and (ii) provided insight into the underlying plant traits that explain differences in fracture properties between species. Fracture force, tensile strength, fracture energy and toughness of stems (in various phenological stages) and leaves were measured and compared among five introduced tropical grasses (Cenchrus ciliaris, Chloris gayana, Digitaria milanjiana, Megathyrsus maximus (syn. Panicum maximum), Setaria sphacelata) and two native tropical grasses (Setaria surgens and Dichanthium sericeum). Species differed significantly in fracture force and fracture energy, with stems and leaves of C. ciliaris and S. surgens requiring less force and energy to fracture and stems and leaves of M. maximus and S. sphacelata requiring more force and energy to fracture in comparison with the other species. Differences in tensile strength and toughness were less pronounced. The differences among species in fracture force and energy mainly resulted from differences in cross‐sectional area of plant parts rather than from differences in tensile strength and toughness.

Biological Control of Leaf‐Cutting Ants Using Forage Grasses: Nest Characteristics and Fungus Growth

One of the major pasture pests in the neotropics is the leaf‐cutting ant Acromyrmex landolti, which cuts monocots to nourish a symbiotic fungus as a food source. The objective of the present study was to characterize ant nests and to test the effect of six forage grasses on grass consumption and fungus properties of A. landolti nests. Grasses tested in a 7‐week field experiment during March and April 1997 in the Paraguayan Chaco were Cynodon nlemfuensis, Panicum maximum, Cenchrus ciliaris, Brachiaria brizantha, Digitaria milanjiana and Urochloa mosambicensis. In a bioassay, grass species were evaluated with regard to fungus growth in the laboratory. Results showed that ant nests at that time of year were deeper and had more chambers than often reported in the literature. The two least and most preferred grasses were B. brizantha and C. ciliaris, and C. nlemfuensis and D. milanjiana, respectively. Consumption of the first two grasses was strongly reduced during the second half of the experiment, approaching zero in the last week. The highest fungus weights were found in nests fed with C. nlemfuensis and D. milanjiana. Fungus colony weight and colour proved to be adequate parameters with which to rate the vigour of the fungus; weight was lowest in nests fed with B. brizantha and C. ciliaris. In the bioassays, B. brizantha and D. milanjiana plant saps reduced the fungal growth most and least, respectively. In conclusion, D. milanjiana and C. nlemfuensis can be regarded as highly susceptible to A. landolti, and B. brizantha as resistant; the other grasses cannot be assigned to either group. The bioassay proved to be a quick way of testing the ability of a grass species to inhibit fungal growth.

First Reports of Soilborne wheat mosaic virus and Wheat spindle streak mosaic virus in Africa.

During 1997 and 1998, virus symptoms similar to those of Soilborne wheat mosaic virus (SBWMV) and Wheat spindle streak mosaic virus (WSSMV) were observed on nine wheat cultivars (Triticum aestivum cvs. Deka, Gamtoos, Lorie II, MM2, Nata, Nkwazi, P7, Scepter, and Scan) in the Central, Copper-Belt, Lusaka, and Southern provinces of Zambia. Symptoms were observed between June and August on wheat, which in Zambia is an irrigated crop grown during the cooler months (May to August). In fields suspected to be infected with SBWMV, irregularly distributed, circular patches of severely stunted sparse plants were observed. Because of these symptoms, the syndrome is described in Zambia as the "crater disease." Infection was more common on light to medium sandy-loam clay soils, and affected patches were particularly common along the field edges and in poorly drained areas. Such waterlogged conditions are conducive to the multiplication and spread of Polymyxa graminis, the protist vector of SBWMV (1). Affected plants initially showed chlorotic streaks on all leaves, which became uniformly yellow and eventually necrotic. The roots of these plants were slightly swollen and enlarged and are likened to "Rastafarian pleats" locally. In fields suspected to be infected with WSSMV, symptomatic plants were observed in the border rows of affected fields. Chlorotic streaks and mosaics were observed on the leaves of affected plants, and the tips of these leaves were also frequently twisted. Using double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA), SBWMV and WSSMV were positively identified in symptomatic plants. In total, 81 plants from the four provinces were tested, and 72 and 37% were infected with SBWMV and WSSMV, respectively. Identification was confirmed by DAS-ELISA using antisera from W. Huth (BBA-Braunschweig, Germany) and C. Rubies-Autonell (Bologna University, Italy) for SBWMV and using antisera from W. Huth (BBA-Braunschweig, Germany) and G. Bergstrom (Cornell University, New York) for WSSMV. Further confirmation of the identity of the two viruses was provided by the reaction of 12 indicator species (Chenopodium amaranticolor, C. quinoa, C. hybridum, Digitaria milanjiana, Eleusine indica, Oryza sativa (cv. IITA 212), Panicum maximum, Rottboellia cochinchinensis, Setaria verticillata, Sorghum bicolor(cv. Sima), S. halepense, and Triticum aestivum (cvs. Lucal, Kwale, Lorie II, Nkanga, 128, and GV 4-12) in mechanical transmission studies using infected leaf sap. This is the first report of SBWMV and WSSMV not only in Zambia but also Africa. The area of wheat grown in Zambia has risen in the past several years to approximately 18,000 ha per annum. However, annual wheat yield (60,000 tons) has not risen to match this increase. The effect of SBWMV and WSSMV on yield in Zambia has not yet been measured, but both viruses cause serious losses in other countries (1-3) and the severity of the symptoms suggests that significant yield reductions are likely. Furthermore, no Zambian wheat cultivars are known to be resistant to either virus. Generally, wheat production fails to meet demand in the country and therefore further yield losses due to virus infection could be disastrous.

Yield, in vitro digestibility, crude protein, and mineral concentration of eight Digitaria introductions in Puerto rico

Abstract Dry matter (DM) yield, in vitro organic matter digestibility (IVOMD), crude protein (CP) and mineral composition of eight Digitaria accessions were compared between long‐ and short‐day seasons in the semiarid southern region of Puerto Rico and evaluated in relation to grazing ruminant requirements. Digitaria milanjiana 6416 was consistently among the highest DM yielding accessions in both seasons. The mean IVOMD was similar in both seasons for most accessions. Concentrations of CP, magnesium (Mg), copper (Cu), zinc (Zn), cobalt (Co), and selenium (Se) were below the recommended levels for grazing ruminants in both seasons. This study suggests the need for livestock mineral supplementation, even under conditions of high pasture fertilization (NPK) and forage‐growing conditions in the semiarid southern region of Puerto Rico.

Selection of perennial grasses as a component of legume-based pastures on light-textured soils in the dry tropics of Queensland

Adaptation indices for introduced perennial grasses were derived for a site in the seasonally dry tropics of North Queensland to determine the suitability of grasses as a component of sown legume pastures. Grasses are required to replace native species that are intolerant of the heavy grazing pressure imposed on these legume-based pastures. Agronomic, production, morphological, and reproductive data on 143 accessions of 20 perennial grass genera were compared from 1983 to 1987. The grasses were grown in rows in a grazed Seca and Verano stylo pasture. The seed production potential of 40 Digitaria accessions grown in swards under irrigation was also assessed. The stoloniferous species Bothriochloa pertusa, Digitaria milanjiana, D. taatalensis, B. insculpta, and Urochloa mosamhicensis had the highest adaptation indices under continuous grazing. Digitaria accessions with the ability to produce appreciable viable seed were identified. Andropogon gayanus, a tussock species, had the highest yield and most spread in the first 2 years in the absence of wet season grazing. The potential of B. pertusa and D. milanjiana for stabilising legume pastures has been identified, and the need for wet season grazing management of tussock species has been shown. The range of genetic material in D. milanjiana requires further environmental evaluation.

Selecting for nutritive value in Digitaria milanjiana. 3. Relation of chemical composition and morphological and anatomical characteristics to the difference in digestibility of divergently selected full sibs, and comparison with D. eriantha ssp. pentzii

Comparisons were made of the dry matter digestibility (DMD) and yield of plant fractions harvested from long-established swards of 6 genotypes of Digitaria milanjiana selected from 3 F1 families for high and low leaf digestibility, and D. eriantha ssp. pentzii (pangola grass). Defined leaf blade, sheath and stem internode fractions were collected at different sward development stages and analysed for DMD, chemical composition, and tissue morphological and anatomical characteristics. The leaf blade of each high-digestibility genotype was consistently superior (1.9-4.5 percentage units) in DMD to that of its low digestibility counterpart, and to pangola grass, at both vegetative and reproductive -- stages. For leaf sheath and stem, the superiority in DMD of the high digestibility group was not evident or was less pronounced. The high DMD selections had green leaf dry matter yields comparable to those of the low DMD group but higher than those of pangola grass. The gain in DMD for leaf blade of the high over the low digestibility selection was consistently correlated with a decrease in cell wall content, acid detergent fibre or lignin, and poorly correlated with other chemical and leaf morphological characteristics. High and low DMD genotypes did not differ in the proportion of cell types in leaf or stem, or in other measured anatomical characteristics.

Selecting for nutritive value in Digitaria milanjiana. 4. Milk production from an elite genotype compared with Digitaria eriantha ssp. pentzii (pangola grass)

An elite genotype of Digitaria milanjiana, which had been selected on the basis of improved leaf digestibility, was compared with pangola grass (Digitaria eriantha ssp. pentzii, formerly Digitaria decumbens) in terms of milk production, at Mutdapilly in south-eastem Queensland. Unsupplemented Holstein-Friesian cows grazed nitrogen-fertilised, irrigated swards of 2 grasses using a switch-back experimental design. Pasture management and stocking rate were adjusted to provide the animals with 15 kg of green leaf (on a dry matter basis) per cow per day, so that any differences in milk yield could be attributed to differences in leaf quality rather than to total dry matter yield. Cows grazing the selected genotype produced 0.9 kg more milk, 0.07 kg more butterfat and 0.05 kg more protein per cow per day (5.8, 13.0 and 10.9%, respectively) than those grazing pangola grass. These increases were associated with a small increase in leaf digestibility, a faster rate of breakdown of leaf (in an artificial masticator) and a higher proportion of leaf in the diet chosen by the cows grazing the selected genotype. The results of this experiment demonstrate that a tropical grass selected on the basis of digestibility increased milk production of grazing cows. However, factors other than higher digestibility (such as leafiness) contributed to the improvement in production over that from pangola grass.

Polyploid Distribution and Seed Dormancy in Relation to Provenance Rainfall in the Digitaria milanjiana Complex

Chromosome numbers were counted in 72 accessions in the Digitaria milanjiana complex and 2 of D. macroblephara from contrasting climates in Africa; 18 were diploids, 38 tetraploids, and 18 hexaploids. Higher polyploids were mostly from lower rainfall provenances. Diploids were mostly accessions which had been attributed to other species in pre-1982 classifications but which are now considered to be synonyms of D. milanjiana. Some 29 accessions, including diploids, tetraploids and hexaploids from low-rainfall and high-rainfall provenances at equatorial or near-tropical latitudes were grown and seed was harvested on 2 occasions (Jan. and Mar. 1987). Seed was treated at alternating temp. of 30/25°C or constant 60°C for 0, 2, 6, 10 or 16 weeks and then germinated. Percentage germination increased over time for all accessions, from 1% at harvest to 26% at 16 weeks. Germination was markedly lower in accessions from low-rainfall (14%) than high-rainfall (33% at 16 weeks) provenances. Similarly, percentage germination was lower in hexaploids (16%) than tetraploids (26%) and lower in tetraploids than diploids (38% at 16 weeks). High temp. treatment increased germination percentage but the effect was only marked in accessions with comparatively high levels of germination at low temperatures. Percentage dormancy (estimations based on live but ungerminated seed after germination treatment following 16 weeks at 60°C) was significantly and negatively correlated with rainfall of provenance. It was concluded that seed dormancy in D. milanjiana is related both to polyploidy and rainfall of provenance and that genetic adaptation to arid regions has been associated with polyploidisation and increasing dormancy.

Selecting for nutritive value in Digitaria milanjiana. 2. Intake and digestibility of divergently selected full-sibs compared with Digitaria decumbens

We compare the voluntary intake and digestibility of 6 genotypes selected from 3 F1 families of Digitaria milanjiana for high or low leaf digestibility, and D. decumbens (pangola grass). Swards were harvested on 6 occasions (4 by 4-week regrowths, 1 by 10-week and 1 by 14-week regrowth) and fed to sheep in metabolism cages. Averaged over families and regrowths, high digestibility selections were significantly superior to low digestibility selections in digestibility, voluntary dry matter intake and intake of metabolisable energy. There was a large range in leafiness of the genotypes. Correlations between leafiness and in vivo digestibility, dry matter (DM) intake and intake of metabolisable energy were positive and statistically significant. Comparison of full-sibs at the same percentage stem (80 and 100%) suggested a higher DM intake, digestibility and intake of metabolisable energy of stem from genotypes selected for high leaf digestibility. Averaged over harvests, none of the selected genotypes was significantly superior to pangola grass in digestibility but all were superior in DM intake and 5 in intake of metabolisable energy. The best selected genotype was 35% better than pangola grass in terms of intake of metabolisable energy. Differences in in vitro digestibility of young leaves from vegetative tillers of full sibs, the characteristic on which the genotypes had been selected, were maintained under sward conditions, although differences were reduced.

Selecting for nutritive value in Digitaria milanjiana. 1. Breeding of contrasting full-sib clones differing in leaf digestibility

Nineteen F1 families were produced by pair-crossing 7 stoloniferous genotypes of Digitaria milanjiana. Progenies and parents were grown as spaced plants (0.5 by 0.5 m microswards) and plucked samples were taken from vegetative regrowth in 2 successive seasons for estimation of digestibility using the in vitro cellulase method. Stolon number, herbage yield (one, 9-week regrowth), flowering date and leaf width were also assessed. Parental clones differed significantly in plucked sample digestibility (range 4.1 units) and there was no significant clonexyear interaction. Heritability, based on parent-progeny regression, was 0.86. The occurrence in progenies of a low percentage (4.9%) of genotypes with plucked sample digestibility significantly higher than that of the higher parent suggested that genetic improvement of plucked sample digestibility may be possible. However, such segregates did not occur in the progeny of high digestibility parents. Digestibility of plucked samples was not correlated with any of the agronomic attributes measured. This, together with the high heritability for stolon number (h2 = 0.86) indicates that it is feasible to breed a genotype of D, milanjiana with high yield, high leaf digestibility and vigorous stolon development for clonal propagation. Genotypes with a mean plucked-sample digestibility of &gt;70.0% occurred in 11 families. For these families highest and lowest digestibility genotypes were further sampled; only the top 2 fully expanded leaves were analysed. Conclusions derived from plucked samples were confirmed, showing that full-sibs differed genetically in leaf digestibility. Three pairs of full-sibs, which differed in leaf digestibility by 5.0-7.2 units, were selected for in vivo and physiological comparison.

Genetic variation in sodium and potassium concentration in herbage of Digitaria milanjiana, and its relation to provenance

Sixty-five accessions, including diploids, tetraploids and hexaploids, of the African grass Digitaria milanjiana, were grown in a grass garden in south-eastern Queensland, and sodium (Na) and potassium (K) concentrations of herbage were determined after regrowth periods of either 6 weeks or 6 months. The accessions were originally obtained from sites in Africa from l�S. to 25�S., and over 400-1700 mm mean annual rainfall. The Na concentration of herbage ranged from 0.01 to 2.30% (w/w) and was inversely correlated with K concentration. There was a clearly defined geographic distribution of accessions which had high or low Na concentrations. Accessions from coastal sites had high concentrations of Na in the dry matter (&gt;0.25% DM), those from inland sites south of 20�S. had low concentrations of Na (usually &lt;0.24% DM), and all those from inland sites north of latitude 20' S. were invariably very low in Na concentration (&lt;0.09% DM). Accessions with high and low levels of Na occurred at all three ploidy levels. Genetic studies at the diploid level, using generation means analysis, showed differing patterns of inheritance of Na and K concentration for two crosses, even though they had one parent in common. Both additive and dominance effects were evident for Na and K; in addition, significant inter-allelic interactions occurred, especially involving dominance. The results are discussed in relation to the adaptive significance of Na accumulation, to its significance in animal production, and to the possibilities of breeding cultivars that have adequate Na concentration and are adapted to low rainfall regions.

Genetic Variation in Seed Dormancy in Digitaria milanjiana in Relation to Rainfall at the Collection Site

SUMMARY (1) Digitaria milanjiana (Rendle) Stapf, is a highly variable grass species which occurs in regions of low (450 mm) to high (1700 mm) rainfall in central and eastern Africa. (2) Studies of dormancy characteristics of seed of a range of accessions grown under uniform conditions revealed three different classes, apparently genetic in origin. Ecotypes from high rainfall regions had relatively short dormancy, ecotypes from low rainfall tropical regions had an extended dormancy which could be broken by treatment at 60 0C for several months, and an ecotype from a low rainfall equatorial site had an intermediate length dormancy which was not affected by heat treatment. (3) Dormancy in all cases was broken by removal of the palea and lemma. Leaching of entire disseminules in running water had no effect and short-duration, high-temperature treatment (100 or 120 OC for 15 s) had a variable and inconsistent effect. Treatment of dormant accessions at low temperatures (10 OC for 9 months) prolonged dormancy. Treatment of all dormancy-class accessions at 60 OC for 25 weeks had no immediate effect on viability, but resulted in a much more rapid fall in viability than treatment at 30-25 OC or 10 OC for 25 weeks. (4) Hybridization experiments showed that the dormancy of the low-rainfall equatorial ecotype, although due to the presence of the lemma and palea, was controlled by an interaction between embryo and maternal genotype. No such interaction was evident in low-rainfall tropical ecotypes. (5) The adaptive significance of these dormancy patterns is discussed in relation to the distribution of rainfall in the provenance sites. The extended dormancy of tropical accessions is clearly adaptive to a long dry season and the requirement for long periods of high temperature to break dormancy prevents seed from germinating following occasional dry season showers. The absence of dormancy in high rainfall equatorial ecotypes is consistent with the absence of a dry season in their region of origin.

Título en español

Un experimento en un suelo Ultisol de la región húmeda montañosa de Puerto Rico se realizó para evaluar el potencial de producción de forraje y proteína bruta de cinco selecciones de la leguminosa Stylosanthes guianensis, una de Stylosanthes gracilis y la gramínea Digitaria milanjiana USDA PI 299699. En el primer período experimental, las forrajeras se cortaron nueve y seis veces cada 45 y 65 días, respectivamente. Durante el segundo período, se cortaron 5 y 4 veces cada 65 y 79 días respectivamente. Las parcelas de leguminosas recibieron 112 kg por ha y año de fósforo y potasio en una sola aplicación. Las de la gramínea recibieron 3,360 kg por ha y año de un abono 15-5-10; se aplicó la cantidad indicada después de cada corte, según el intervalo asignado. Las parcelas no se regaron en ninguno de los períodos experimentales. La gramínea D. milanjiana sobrepasó significativamente en producción de forraje verde y seco las seis selecciones de Stylo a los 3 intervalos de 45, 65 y 79 días. La gramínea produjo 29,574 y 29,920 kg/ha en 13.5 meses cuando se cortó cada 45 y 65 días, respectivamente. A intervalos de 79 días, produjo 25,046 kg por ha en un período de 10.5 meses. Las leguminosas más productivas de forraje seco fueron la cultivar Fine Stem (IRFL-1416), S. guianensis USDA PI 361877 y las cultivares comerciales Endeavour y Schofield. La cultivar Fine Stem produjo rendimientos de 18,522 y 18,936 kg/ha en 13.5 meses, que pueden considerarse altos para una leguminosa tropical. Cuatro de las cultivares produjeron casi tanta proteína bruta como la D. milanjiana al cortarse cada 45 días, mientras que a intervalos de corte de 65 y 79 días todos se acercaron a la gramínea en este criterio. En la época lluviosa surgió un brote de antracnosis que redujo el crecimiento de las seis leguminosas, pero en menor grado a las cultivares Endeavour y Fine Stem. Se sugiere cortar la leguminosa cada 65 días. Al cortarse cada 45 días, los yerbajos tienden a invadirla despues del año. A intervalos de 79 días, la leguminosa tiende a producir menos forraje y proteína bruta que cuando se corta cada 65 días. Se presenta el contenido en nitrógeno, fósforo, potasio, calcio y magnesio de las leguminosas y la gramínea para los tres intervalos de corte estudiados. En general, las cultivares arrojaron marcadamente mayores contenidos en nitrógeno, calcio y magnesio que la gramínea D. milanjiana.

Título en español

Se realizaron 2 pruebas de 1 año cada una, en la Subestación Experimental Agrícola de Corozal para determinar la disponibilidad de cinco pastos: Tanner (Brachiaria radicans), Signal (Brachiaria decumbens), Pangola (Digitaria decumbens), Digitaria milanjiana y Guinea (Panicum maximum), como fuentes de forraje pastado para novillas Holstein en crecimiento. Los efectos de las diversas especies en la ganancia diaria media (ADG) (amplitud de .43 a .51 kg) no fueron significativos. El pasto Digitaria milanjiana fue el mejor en ganancia diaria media, siendo el Signal el que se estima que más cabezas puede mantener, 5.87 versus 5.2 a 5. 7 cabezas/ha y año para los otros cuatro pastas. Se obtuvieron variaciones altas en GOP, tanto entre especies como entre meses. De diciembre a enero, la ADG fue aproximadamente 50% mas baja debido a efectos de temperatura en el crecimiento de los pastos. Se consideran los cinco pastos como aceptables para el crecimiento de las novillas. Sin embargo, el pasto Tanner no se recomienda por su posible toxicidad. Los contenidos de materia seca (DM) y de proteína bruta (CP) fueron más altos en abril pero más bajos en septiembre. El contenido de DM varió de &lt;20 a &gt;30, demostrando su influencia en el consumo. En julio y agosto, los tres pastos arrojaron un medio de &lt;7% CP, lo cual posiblemente afectó el consumo. Con temperatura y lluvia normales, la temperatura máxima se correlaciona positiva y significativamente (P &lt; .01) (.64 a .87) con el contenido de DM y negativamente (- .26 a -. 79) con el contenido de CP. Sin embargo, la precipitación anormal tuvo un efecto marcado en estas relaciones. Se obtuvieron carrelaciones variables entre el contenido de DM o de CP en muestras cosechadas y la ADG, indicando que estas medidas eran relativamente poco confiables para producir ganancia. El consumo estimado de DM en términos de porcentaje peso corporal varió de 2.9 a 3.1%. En promedio, se utilizó &lt;6% de DM de pasto disponible. Con relación a costos, una razón de uso tan baja no parece económica, por lo cual, se sugiere más investigación en el manejo y abonamiento de pastos tropicales para un uso más eficiente de la biomasa disponible.