Pearl Millet Seedlings Research Articles

Elemental toxicity effects on germination and growth of pearl millet seedlings1

Abstract Variability in millet stands in West Africa is clearly visible as early as three weeks after planting. The objectives of this study were to determine the influence of pH and chemical toxicities on millet germination and seedling growth and to compare varietal tolerance of toxic conditions. A nutrient solution study was carried out with a series of Hoagland‐based nutrient solutions. Germination percentage was calculated, and root and shoot lengths were measured for one week. Critical values were determined for toxic elements. The only treatment which reduced germination percentage significantly was copper (Cu) concentrations >0.05M. Solution pH values between 5 and 7 resulted in the best root growth, though shoot growth was unaffected by pH. The roots were more sensitive than the shoots to several [aluminum (Al), boron (B), zinc (Zn)] of the elemental toxicities studied. Soil Al and manganese (Mn) levels may be high enough to have toxic effects on millet roots. However, natural soil iron (Fe), Cu, and Zn levels were much lower than the critical levels determined in the nutrient solution study. The improved varieties were more tolerant of Fe and Zn toxicity than the LOCAL variety, but the LOCAL variety was more tolerant of high B concentrations.

Induced systemic resistance protects pearl millet plants against downy mildew disease due to Sclerospora graminicola

Three-day-old seedlings of pearl millet ( Pennisetum glaucum), when root-dip inoculated with different concentrations of zoospores of Sclerospora graminicola, had increasing degrees of downy mildew disease incidence with increasing inoculum load. Inoculation of plants with 6000 zoospores ml −1 caused infection in all plants but resulted in only 18% disease as evidenced by external symptom manifestation. The plants treated to this suboptimal level of zoospores, when challenged after 4–6 days with 40 000 zoospores ml −1 remained predominantly healthy compared with the controls, suggesting induction of resistance by the suboptimal dose of inoculum used. The resistance induced was systemic and protected tillers and inflorescences.

Phenylalanine Ammonia Lyase Activity in Pearl Millet Seedlings and its Relation to Downy Mildew Disease Resistance

Phenylalanine ammonia lyase (PAL) activity was studied in different genotypes of pearl millet with varying degrees of susceptibility to downy mildew disease, after inoculating with Pathotype 1 of Sclerospora graminicola. In resistant genotypes, the enzyme activity significantly increased 24 h after fungal inoculation while in the susceptible genotypes, the activity decreased. The increase or decrease in enzyme activity was well-correlated with the degree of host resistance to the pathogen. A time-course of change in activity of PAL after inoculation showed a considerable difference between resistant and susceptible genotypes. Studies on the activity of PAL in different parts of pearl millet seedlings revealed that in the resistant genotype, enzyme activity significantly increased at 24 h post-inoculation only in the shoot portion, whereas in mesocotyl and root the activity decreased. In susceptible seedlings, enzyme activity decreased at 24 h post-inoculation in shoot, mesocotyl and root. The activity of PAL was also found to be pathotype-specific. Histochemical tests for lignin were positive in infected cells in the resistant genotypes. The role of PAL in imparting resistance to pearl millet against downy mildew disease is discussed.

Role ofAcremoniumEndophyte of Fescue on Inhibition of Colonization and Reproduction of Mycorrhizal Fungi

The tall fescue endophyte, Acremonium coenophialum, is inhibitory to mycorrhizal fungi. This study was conducted to determine if Acremonium inhibits infection and the extent of colonization of roots in addition to sporulation. Fewer fescue seedlings, with or without Acremonium, were infected by single spores of Glomus macrocarpum than pearl millet seedlings. However, fescue seedlings were infected by G. mosseae single spores to the same extent as pearl millet seedlings. Roots of Acremonium-free fescue were not colonized as extensively as those of pearl millet by either fungus. The presence of Acremonium in fescue caused a further considerable reduction in extent of mycorrhizal colonization. Effects of the host on sporulation were closely correlated with extent of colonization. Each of the three hosts supported a similar total spore volume of the two mycorrhizal fungi. Acremonium apparently does not affect infection, perhaps because the seedlings were too young for extensive transport of toxic alkaloids from Acremonium-infected shoot tissues to roots free of Acremonium.

The Possible Involvement of Lipoxygenase in Downy Mildew Resistance in Pearl Millet

The downy mildew disease, incited by Sclerospora graminicola, is a major biotic constraint for pearl millet production in the semi-arid tropics. Sources of resistance to this disease have been identified. However, the mechanism of host resistance still remains obscure. The enzyme lipoxygenase (LOX) is known to play a role in disease resistance in many host-pathosystems. In the present study, LOX activity was tested in seeds of different genotypes of pearl millet with different susceptibility to downy mildew. The LOX assay of the seeds indicated a good correlation between enzyme activity and their downy mildew reaction in the field. Maximum activity was recorded in seeds of highly resistant genotypes and minimum activity was found in the highly susceptible genotypes. Seeds obtained from plants recovered from the downy mildew disease had more LOX activity than that of the original parent seeds. Thus, in seeds, the LOX activity can be used as a biochemical marker for screening different genotypes of pearl millet for downy mildew. The study, carried out in the susceptible genotype of pearl millet seedlings, showed that LOX activity decreased after inoculating with S. graminicola zoospores when compared with uninoculated controls. However, a significant increase in the enzyme activity was observed on the second and third days after inoculation in resistant seedlings. The possible role of LOX in conferring resistance to downy mildew infection of pearl millet is discussed.

INTERACTION BETWEEN CHLOROPLAST BIOGENESIS and PHOTOREGULATION OF AMYLASES IN Pennisetum americanum LEAVES

In pearl millet (Pennisetum americanum) seedlings, light acting via phytochrome stimulates amylase activity in the leaves. The maximum photostimulation of amylase is observed in the segment proximal to the leaf base. This photostimulation mainly results from an enhancement in β-amylase activity (EC 3.2.1.2.), which constitutes80–90% of leaf amylase activity. The subcellular fractionation studies revealed that while p-amylase is localized only in the extraplastidic compartment, a-amylase (EC 3.2.1.1.) is localized both in the cytosol and in the chloroplasts. The mesophyll cells contained both a- and β-amylase activity, but only a-amylase activity was present in the bundle sheath cells. The Norflurazon-mediated photooxidation of chloroplasts during leaf development also eliminated plastidic α-amylase activity, confirming dependence of its photoregulation on the chloroplast biogenesis.

Temperature Parameters Useful for Modeling the Germination and Emergence of Pearl Millet

The modeling of germination and seedling emergence is required for the construction of a simulation model of pearl millet [Pennisetum americanum (L.) Leeke]. This study provides the temperature parameters necessary to model these processes. Seed of BJ104 pearl millet were germinated in incubators at six controlled temperatures (15, 20, 25, 30, 35 and 40 °C). Germination percentage and coleoptile lengths were measured over time in each temperature regime. Germination percentage at 5 d after the commencement of imbibition was not affected by temperature. Cubic polynomials described the rates of development for germination and coleoptile elongation over the temperature range of 15 to 40 °C. The relationships between rate of development for germination and the lag stage prior to linear elongation of the coleoptile and temperature were linear only between a base of 16 °C and an optimum of 35 °C. The thermal time for the growth stages from planting to 50% germination, germination to the start of linear coleoptile extension, and the duration of linear coleoptile elongation from seed depth until 50% emergence were 5.3 ± 0.4, 7.5 ± 0.4, and 0.82 ± 0.06 degree‐days (°C‐d)mm−1, respectively. It is proposed to use these parameters in a crop simulation model to predict emergence of pearl millet seedlings.

Mechanisms of Starvation Tolerance in Pearl Millet

The response of pearl millet (Pennisetum glaucum [L.]) seedlings to prolonged starvation was investigated at the biochemical and ultrastructural level. After 2 days of darkness the bulk of the seedling carbohydrate reserves were depleted. After 8 days in the dark the respiratory rate had declined to less than 50% of its initial value and the plants had lost half of their total protein content. Unlike the situation with carbohydrate depletion, protein loss was restricted to specific organs. The secondary leaf and stem (including the apical meristem) showed little or no protein loss during this period. In the primary leaf, seed, and roots, protein loss was substantial. In spite of the high rate of protein degradation in the primary leaf and roots, these organs showed no ultrastructural changes suggestive of tissue, cellular, or subcellular degradation. In addition, ribulose bisphosphate carboxylase was not preferentially degraded during starvation and only a small decline in chlorophyll content was observed after 8 days in the dark. During the period from 8 to 14 days, cell death started at the tip of the primary leaf and gradually spread downward. Both shoot and root meristems remained alive up to 14 days. Consequently, the eventual death of the plant was due to the loss of the carbohydrate-producing regions rather than the meristems. We suggest that these results provide an explanation for the high degree of starvation tolerance exhibited by pearl millet.

Carbon monoxide sensitivity of cytochrome c oxidase in male sterile seedlings of pearl millet

The redox state of cytochrome a 3 during in situ respiration of leaves of young seedlings of pearl millet was assessed by in vivo aerobic assay of nitrate reductase, after one min exposure to carbon monozide (CO). Cytoplasmic male sterile (CMS) line 81A derived from Tift 23 DB and its maintainer 81 B were found to be completely insensitive to CO, indicating that cytochrome a 3 was in a highly oxidised state during steady-state respiration. Treatment of these leaves with DNP (2,4-dinitrophenol) however, rendered them responsive to CO. The uncoupler probably facilitated electron flow from cytochrome a to a 3. Four other CMS lines and their maintainers, restorers and hybrids were all found to be highly responsive to CO, indicating that cytochrome a 3 was largely reduced. Hybrid MH-179 obtained from CMS 81 A and restorer ICM P-451, was found to be highly sensitive to CO, probably because of the influence of the male parent.

Inter‐and intracontinental sexual compatibility in Sclerospora graminicola

Oospore collections of Sclerospora graminicola, obtained from diverse locations in West Africa and India, were used to infect susceptible pearl millet plants. Asexual spores, collected from five infected plants from each collection were used as individual isolates to inoculate pearl millet seedlings, alone and in every possible combination to test for sexual compatibility type. Oospores were produced with some combinations of isolates but not others, indicating the presence of two compatibility types, designated g1 and G2 These were found in approximately equal proportions. There were also some isolates which produced a few oospores when inoculated alone. Tests for cross‐compatibility were made by combining isolates of opposite sexual compatibility types from different collections. Not only were collections from within continents cross compatible but there was also cross‐compatibility between isolates from different continents. The implications of such extensive outbreeding capacity in S. graminicola are considered.

Inhibition of Abscisic Acid Accumulation in Seedling Shoots of Pearl Millet (Pennisetum americanum [L.] Leeke) Following Induction of Chlorosis by Norflurazon

Summary Shoots from four-day old light-grown pearl millet (Pennisetum americanum [L.] Leeke) seedlings, grown continuously in the presence of 1.32 × 10-5M norflurazon (NF), lacked chlorophyll and failed to accumulate abscisic acid (ABA) when water stressed. Chlorophyll and stress-induced ABA contents were significantly correlated (r = 0.82, P No inhibitory effect on ABA accumulation by NF occurred if seedlings were grown at low light intensity ( The results suggest that norflurazon had no «direct» effect on ABA accumulation. The possibility that structurally and functionally intact chloroplasts are required for this process is discussed.

Pearl Millet Tolerance to Selected Herbicides

Pearl Millet Tolerance to Selected Herbicides

Metal Content of Plants and Soils in a Tree Nursery Treated with Composted Sludge

AbstractDigested sewage sludge compost from Washington, D.C., was applied to a Downer sand at rates of 0, 56, 112, 224, and 448 dry metric tons/ha. A fertilized control treatment was also utilized. Pearl millet (Pennisetum americanum [L.] K. Schum.) was grown as a summer cover crop prior to fall tree seeding. Leaf samples of red oak (Quercus ruba L.) and black walnut (Juglans nigra L.) seedlings were taken the summer of the first growing season. The total metal contents (µg/g) of the compost were 2,154 Zn, 517 Cu, 13.9 Cd, and 69 Ni. The treated soils were monitored for DTPA extractable Zn, Cu, Cd, and Ni throughout the 2.4 years of the experiment.No visual, foliar effects were noted on the growth of pearl millet or tree seedlings from the increasing rates of compost, however, pearl millet tissue Cd levels were significantly increased with increasing levels of compost from about 0.40 to about 1.62 µg/g. Metal contents of the tree seedlings were low and within normal levels recorded in the literature. Extractable soil Zn, Cd, and Cu decreased with time, however, soil Ni extractability tended to increase with time. Compost additions resulted in an increased soil pH which was maintained throughout the experiment.Poor correlations (r2 ranged from 0.002 to 0.543) were obtained between DTPA extractable metals and metal concentrations of pearl millet, red oak, or black walnut.

Effect of Supplemental Irrigation with Sea Water on Growth and Chemical Composition of Pearl Millet (Pennisetum typhoides S. et H.)

Summary Pearl millet seedlings were raised as a rainfed crop in pots containing sea shore sand. Forty days old plants were irrigated with 10,000 ppm sea water alone and supplemented with various nutritive salts and with 15,000 ppm sea water. The crop received nine irrigations at intervals of three to five days. Irrigation with sea water alone reduced the growth and yield of the crop, but some of the modifications to the 10,000 ppm sea water resulted in increased yield. The main constituents of the seeds were not greatly affected, although a slight accumulation of sodium took place in the seeds. There was, however, a considerable accumulation of minerals in the leaves and stem. Supplemented 10,000 ppm sea water led to a still greater accumulation of minerals, especially in the leaves and stem. Salt accumulation in the sand in the root zone was negligible even after nine irrigations with diluted sea water. The experiment shows that pearl millet is tolerant of diluted sea water and the deleterious effects of irrigation with sea water can be reduced to a certain extent by appropriate supplementing with nutritive salts.

Resistance to Greenbug in Three Millet Species1

AbstractPearl millet, Pennisetum typhoides (Burn.) Stapf and C. E. Hubb.; foxtail millet, Setaria italica L.; and proso millet, Panicum miliaceum L. were evaluated for resistance to the C‐biotype greenbug, Schizaphis graminum (Rondani), a recent serious pest of sorghum, Sorghum bicolor (L.) Moench. All trials were conducted in growth chambers at 27 C. Survival and reproduction of adult greenbugs confined to seedling and mature plants were greater on sorghum than on the millet species. The millets were also more resistant than sorghum on the basis of plant injury scores. Pearl millet seedlings were slightly more resistant than mature plants. Pearl millet supported the most greenbugs and proso the least in seedling trials with greenbugs confined to the three millet species individually and in all possible paired combinations. Since the millet species evaluated were highly resistant, they could serve as substitute crops for sorghum until greenbug‐resistant sorghum cultivars become commercially available.