Unifoliolate Leaf Research Articles

Regulation of soybean SUMOylation system in response to Phytophthora sojae infection and heat shock

Modification of protein substrates by small ubiquitin-related modifier (SUMO) plays a vital role in plants under biotic and abiotic stresses. However, its role in the stress responses of soybean (Glycine max (L.) Merrill) is poorly understood. In this study, we explored SUMOylation in soybean in response to Phytophthora sojae race 1 infection and heat shock. We selected two soybean cultivars for these analyses; one resistant to P. sojae race 1 (SN10), and one susceptible (HF25). The transcription and expression levels of SUMOylation-related genes were detected in SN10 and HF25 after inoculation with P. sojae race 1 and after exposure to heat shock (42 °C). After inoculation with P. sojae race 1, GmSUMO2/3 and GmSAE1b accumulated in the roots. After the heat shock treatment, GmSCEd and GmE3f accumulated in the leaves. The transcript levels of GmESD4d increased in response to both P. sojae infection and heat shock. We monitored SUMOylation in the root, stem, and leaves after the stress treatments. We detected SUMO conjugates in the unifoliolate leaf, trifoliolate leaf, root, and stem after the heat shock treatment. SUMO conjugates accumulated mainly in the root and stem in response to heat shock, but mainly in the root in response to P. sojae race 1 infection. The accumulation of SUMO conjugates in response to stress indicated that SUMOylation enhanced the resistance of soybean to P. sojae and heat shock. These results provide a foundation for further research on the role of SUMOylation in resistance to P. sojae and heat shock.

Genotype x environment interaction and stability of soybean cultivars for vegetative-stage characters.

In order to obtain the certificate of cultivar protection, it is necessary to prove its distinctiveness, homogeneity, and stability. Currently, there are 37 descriptors for differentiating soybeans cultivars. However, they are still not enough and, as a result, it is necessary to create, identify, and evaluate new descriptors. This study was aimed at evaluating the genotypic and environment interaction (GxE) and determining the stability of eight soybean cultivars for five vegetative-stage descriptors. The research was done in a greenhouse of the Soybean Breeding and Genetic Studies Program of Universidade Federal de Uberlândia. The treatments were composed of eight soybean cultivars, sown in two different growing seasons (January 25, 2014 and November 27, 2014). The experiments were carried out in randomized complete blocks with three replications and each experimental plot consisted of one pot with four soybean plants. The characters evaluated were: length of hypocotyl (LH), length of epicotyl (LE), length of unifoliolate leaf petiole (LUP), length of first trifoliate leaf petiole (LTLP), and rachis length of terminal leaflet of the first trifoliate leaf (RL). The data achieved from the trials were undergone genetic-statistical analyses by the GENES software. For all analyzed characters, the existence of genetic variability was observed emphasizing the vegetative-stage descriptors' utility to differentiate soybean cultivars. The occurrence of GxE interaction was detected for all characters assessed, mainly of complex nature, except by RL, which was of simple nature. The most stable cultivars for the vegetative-stage descriptors analysed were UFUS 7415 and UFUS Impacta.

Development of leaves and shoot apex protection inMetrodoreaand related species (Rutaceae)

Most members of Sapindales are characterized by compound leaves, but several genera also (or only) produce simple or unifoliolate leaves. A few genera may bear stipules or pseudostipules. Little is known about the morphological structure and morphogenesis of these types of leaves in Sapindales, but this information is required for comparative and evolutionary studies. Metrodorea is a Neotropical genus of Rutaceae, comprising species presenting compound and unifoliolate leaves, plus heterophylly, together with an intriguing bud-protecting structure at the leaf base. The aims of the present study are: (1) to examine leaf morphogenesis in Metrodorea and in closely related species (four Esenbeckia spp., Helietta apiculata and Raulinoa echinata); and (2) to improve our understanding of the morphological evolution of leaves in Metrodorea and Rutaceae. Our data show that the hood-shaped structure at the base of the leaf in Metrodorea, usually interpreted as a sheath, is, in fact, a pair of united stipules, a synapomorphy of the genus. In the species studied, it is possible to recognize two main types of unifoliolate leaf: early unifoliolate leaves and late unifoliolate leaves. We also found that the number of leaflets in the studied species is dependent on the late or early determination of the leaf primordium, and that loss of leaflets may have been favoured by the restriction of space available for development within the cavity formed by the pair of united stipules. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 178, 267–282. ADDITIONAL KEYWORDS: anatomy – character evolution – compound leaf – leaf morphology – morphogenesis – Sapindales – stipules.

Morpho-physiological parameters affecting iron deficiency chlorosis in soybean (Glycine max L.)

Background and aims Iron deficiency chlorosis (IDC) leads to severe leaf chlorosis, low photosynthetic rates, and yield reductions of several million metric tonnes each year. In order to devise breeding and genetic transformation programsthat aim at generatinghigh-yielding and IDC-tolerant soybean lines, it is necessary to better understandthe mechanismsthatenabletolerantplantsto survive under Fe-limiting conditions. Methods An in silico analysis in the USDA soybean collection allowed the identification of a set of novel efficient and inefficient soybean cultivars which can be used in future studies concerning IDC response. Plants were grown in iron deficient and iron sufficient conditions using a bicarbonate system and several IDCrelated aspects were studied. Results A new set of efficient and inefficient soybean lines were identified in silico, and their tolerance to IDC was confirmed under laboratorial conditions. New plant traits that are highly correlated to IDC scoring were identified: a negative correlation was found between SPAD valuesandstem weight,weightofthe unifoliolates and iron concentration of the first unifoliolates was found; higher SPAD values were correlated with the amount of iron in the first trifoliate leaves. Our data also show that having higher concentrations of iron in the seeds provides increased resistance to IDC. No correlation was found between root iron reductase activity and chlorosis. Conclusions Soybean differential chlorosis susceptibility between different accessions is linked to specific morpho-physiological parameters such as unifoliolate leaf size, stem weigh, concentration of iron in the seeds, and tissue iron partitioning.

Common waterhemp (Amaranthus rudis) interference in soybean

Common waterhemp has become a problem weed species in Midwest soybean production. Determining the critical interference period after soybean and common waterhemp emergence is necessary for the implementation of weed control practices before soybean seed yield loss occurs. Field experiments were conducted during 1996, 1997, and 1998 to determine the influence of duration of common waterhemp interference on soybean seed yield. Removal of common waterhemp 2 wk after soybean unifoliolate leaf expansion resulted in soybean seed yield equivalent to a season-long weed-free control. Delaying common waterhemp removal until 4 wk after soybean unifoliolate leaf expansion resulted in decreased soybean seed yield. Allowing common waterhemp interference to persist 10 wk after soybean unifoliolate leaf expansion reduced soybean seed yield by an average of 43% over 3 yr. These results suggest that soybean producers should implement common waterhemp management strategies earlier than 4 wk after soybean unifoliolate leaf expansion in order to reduce the potential loss of soybean seed yield.

Genetic analysis of mutations at loci controlling leaf form in cowpea (Vigna unguiculata.

Mutations affecting leaflet number and shape occurred at high frequencies in some cowpea crosses. Mutant plants were nonpetiolate and unifoliolate as opposed to normal plants which were petiolate and trifoliolate. Two types of unifoliolate mutants were distinguishable on the basis of leaf shape which was ovate in one mutant and orbicular in the other. The nonpetiolate and the unifoliolate traits in the two mutants are each controlled by single recessive genes, but the genes controlling the traits in the different mutants were nonallelic. The orbicular leaf shape was also under the control of a single recessive gene. In the F2 and subsequent generations of the cross IBS 2497 x IBS 2625, orbicular-shaped unifoliolate leaf mutants were regularly produced, although the two parents involved in the cross were both trifoliolate. Linkage tests showed that the genes pt-1 for nonpetiolate trait, un-2 for unifoliolate leaf, and orb for orbicular leaf shape in one of the mutants were located on the same chromosome, while the genes pt-3 and un-3 in the other were also linked on a different chromosome. The results of this study provide further evidence indicating the involvement of transposable elements in the mutations observed in the cowpea lines used in this study.

Experimental Evidence of a Plant Meridian System V.

When the first unifoliolate leaf of Phaselus vulgaris L. cv. Kentucky wonder pole bean was at the expended stage, two needles were inserted into opposite sides of the stem near the unifoliolate bud and left there for the entire experiment. Changes of the period of circumnutation movement at the shoots of Phaselus vulgaris L. pole bean were measured. Results from two separate experiments are reported in this communication. In the first experiment, the mean period of the ultradian rhythms of the horizontal circumnutation movement of shoots was reduced significantly (p = 0.0022) from 124.2 minutes in controls to 116.3 minutes in the treated plants. The average period of the ultradian rhythms of circumnutation movement in the treated and the untreated groups from the second experiments were 96.7 and 132.1, minutes respectively, which was statistically significant (p < 0.0001). This study demonstrates for the first time that acupuncture markedly shortens the period lengths of the ultradian rhythms of circumnutation movement of the shoots of the Phaselus vulgaris L. pole bean.

Seedling White Clover Response to Defoliation

Defoliation during the early stages of seedling development can influence growth of white clover (Trifolium repens L.). Our objective was to determine the response of cultivars with diverse leaf sizes to defoliation across a range of seedling growth stages. ‘Regal’ (large‐leaf), ‘Louisiana S‐1’ (medium‐large‐leaf), ‘Grasslands Huia’ (medium‐smallleaf), and ‘Aberystwyth S184’ (small‐leaf) were grown in the greenhouse and were initially clipped to remove all leaf (except cotyledons) and petiole tissue (1.0‐cm stubble) when seedlings attained a unifoliolate leaf or one, two, four, and eight trifoliolate leaves. Seedlings were subsequently clipped in the same manner every 7 or 28 d for the next 28 d. Plant response to defoliation was assessed 7, 14, 21, and 28 d after the last clipping. Seedling shoot dry weight of all cultivars increased linearly in response to initial leaf stage when subsequent clipping occurred every 7 d after the initial defoliation. When subsequent clipping was delayed 28 d, defoliation after the four‐trifoliolate stage did not influence shoot weight of any cultivar except Regal. Despite fewer numbers of leaves after regrowth, seedling leaf area of Regal was always greater than that of the other cultivars. Number of stolon branches of Regal and Louisiana S‐1 increased in response to leaf stage at initial defoliation (0.15 branches stage−1), while that of Grasslands Huia and Aberystwyth S184 was relatively unchanged after the four‐ to six‐trifoliolate stage. Permitting white clover seedlings to attain advanced leaf stages before initial defoliation and increasing the time interval before subsequent defoliation will enhance seedling growth and potential survival.

Determination of the distribution of three nitrate reductase isoforms in soybean seedlings by chromatography and a simple method based on assay conditions

Blue Sepharose affinity chromatography was used to study the distribution of the constitutive NAD(P)H‐nitrate reductase (EC 1.6.6.2: Cl‐NR) and of the constitutive and inducible NADH‐nitrate reductases (EC 1.6.6.1; C2‐NR and i‐NR, respectively), in the unifoliolate leaf (F0), the first and the second trifoliolate leaves (F1 and F2) and the roots of urea‐ and nitrate‐grown soybean (Glycine max [L.] Merr.) plants. The C1‐NR eluted by NADPH is present in the F0 and F1 leaves and nearly absent in the F2 leaf. The activity pattern of this isoform is not modified by nitrate nutrition. The C2‐NR eluted by NADH is high in the F0 leaf, low in the F1 leaf and nearly absent in the F2 leaf of urea‐grown plants. The NADH elution from leaves of nitrate‐grown plants is a mixture of C2‐NR and i‐NR, requiring careful interpretation of results. However, i‐NR appears the principal isoform in the leaves especially in the F2 leaf. This i‐NR is the only NR present in the roots.The pH effect on the assay of the 3 partially purified isoforms was studied using LNR2 and LNR5 soybean mutants to remove the cross contamination. It appears that C1‐NR and C2‐NR activities are negligible at pH 8.5, which allows the assay of only the i‐NR in a crude extract at this pH, even when C1‐NR and C2‐NR are present. It appears also that the assay of C1‐NR activity at pH 6.5 with NADPH is free of interference by the i‐NR. To estimate the C2‐NR activity with NADH at pH 6.5 in a crude extract in the presence of C1‐NR and i‐NR, we propose a simple calculation using the coefficient from the pH responses. These calculations are used to compare the development of C1‐NR, C2‐NR and i‐NR activities in the F0 and F1 leaves of plants previously grown on urea and transferred to nitrate. Only the activity of the inducible isoform is modified by the nitrogen treatment. Activity of the constitutive isofroms appear stable during the 48 h treatment, with only a slight decrease in C1‐NR activity being observed with time.

Caracterización de la pubescencia acicular en las hojas de genotipos de habichuela

Se estableció una escala para estimar la densidad de pubescencia acicular en el envés de las hojas de la habichuela (Phaseolus vulgaris L.). La escala varía de 1 a 9; el grado 1 equivale a hojas glabras y el 9 a hojas con alta densidad de pubescencia acicular. Se sembraron 14 genotipos de habichuela en un invernadero para determinar la relación entre el grado de densidad de pubescencia acicular y tricomas unciformes en la hoja cotiledonar y en las primeras cuatro hojas trifoliadas. Se hizo una lectura visual y un conteo de densidad de pubescencia acicular y de tricomas unciformes en un microscopio de disección con una magnificación de 10 y 70%, respectivamente. Se encontró que la pubescencia acicular varió en tamaño y densidad dependiendo del genotipo y la posición de la hoja en la misma planta. La lectura visual y el conteo de densidad de pubescencia acicular al microscopio fueron similares. En la hoja cotiledonar y en la primera trifoliada casi todas los genotipos carecían de pubescencia acicular. Se observó que la densidad de pubescencia acicular aumentó a partir de la segunda hoja trifoliada hasta la cuarta hoja, siendo esta última donde se encontró la mayor densidad. Además, el grado de densidad de pubescencia acicular fue mayor cuando la hoja estaba menos expandida. Se clasificaron los genotipos de habichuela Pompadour-E, representativo del grado 1 en la escala propuesta, José Beta en el grado 3, Pompadour- X en el grado 5 y Pompadour-XB en el grado 7. La escala se debe usar cuando el envés de la cuarta hoja trifoliada está completamente expandida, aproximadamente 30 días después de la siembra. Treinta y tres genotipos de habichuela de color rojo moteado se sembraron en Isabela y Juana Díaz, Puerto Rico y en El Zamorano, Honduras, para determinar la similitud de lecturas de densidad de pubescencia acicular en tres ambientes distintos. Las correlaciones encontradas fueron positivas y altamente significativas (r &gt; 0.85), lo que indica que esta escala para la densidad de la pubescencia acicular se podría usar en diferentes ambientes. Las lecturas también fueron similares (r &gt; 0.95) cuando las tomaron distintas personas. En el conteo de densidad de tricomas unciformes ocurrió lo contrario de la pubescencia acicular. En la hoja cotiledonar y las primera y segunda trifoliadas, se encontraron las mayores densidades. En las tercera y cuarta hojas, los tricomas unciformes desaparacen en los genotipos que tienen una alta densidad de pubescencia acicular.

Nitrogen Nutrition of Nodules in Relation to `N-Hunger' in Cowpea (Vigna unguiculata L. Walp)

Early growth, nodule development, and nitrogen fixation by two cultivars of cowpea (Vigna unguiculata L. Walp), one large-seeded (Vita 3; 146.0 +/- 0.9 milligrams seed dry weight, 4.1 +/- 0.2 milligrams seed N), the other small-seeded (Caloona; 57.5 +/- 2.5 milligrams seed dry weight, 1.8 +/- 0.1 milligrams seed N), were compared under conditions of sand culture with nutrient solution free of combined N. The seed stocks used had been obtained from plants uniformly labeled with (15)N, thus enabling changes with time in distribution of cotyledon and fixed N among plant parts to be measured by isotope dilution. Caloona, but not Vita 3, showed physiological symptoms of ;N hunger,' i.e. transient loss of chlorophyll (visible yellowing) and N from the first-formed unifoliolate leaves at or around the onset of symbiotic functioning and N(2) fixation. The smaller-seeded Caloona showed higher early nitrogenase activity than the larger-seeded Vita 3 and by 28 days had fixed 6.6 milligrams of N per milligram of seed N [mg N . (mg seed N)(-1)] versus only 3.5 mg N . (mg seed N)(-1) in Vita 3. Both cultivars lost around 30% of their initial seed N at germination, mostly as fallen cotyledons. Abscised cotyledons of Caloona contained 1.21 +/- 0.17% N; those of Vita 3 contained 2.61 +/- 0.37% N. When compared on the basis of cotyledon N available for seedling growth, Caloona was shown to have fixed 10.6 mg N . (mg seed N)(-1) and Vita 3 only 5.3 mg N . (mg seed N)(-1). Most of the cotyledon N withdrawn from the unifoliolate leaf pair of Caloona during ;N-hunger' was committed to early nodule growth and, in total, 20 to 25% of the cotyledon N resource of this cultivar was ultimately invested in establishment of symbiosis compared with only 7% in Vita 3.

Photoperiodically Sensitive Interval in Time to Flower of Soybean

In order to accurately model the flowering process, it is essential to determine which environmental factors are affecting development at any point in time. The purpose of this research was to determine when different soybean [Glycine max (L.) Merr.) genotypes first become sensitive to photoperiod and how long photoperiod continues to influence the appearance of the first flower under optimal temperature conditions. Controlled‐environment experiments were conducted in which plants were switched at intervals between emergence and flowering from long‐day (22 h) to short‐day (9 h) treatments and from short‐ to long‐day treatments. AH photoperiod chambers were maintained at 26 °C both day and night. Six cultivars from six maturity groups were used: ‘Dawson’, ‘Williams’, ‘Ransom’, ‘Forrest’, ‘Davis’, and ‘Jupiter’. Two nearly isogenic breeding lines differing in response to inductive conditions were also evaluated. All cultivars tested were sensitive to photoperiod by the time the unifoliolate leaf was fully expanded. The experimental line bred for a lengthened juvenile phase exhibited apparent insensitivity to photoperiod for 11 d longer than any of the other genotypes. After flowering was induced, further inductive nights hastened flowering. for all cultivars, photoperiod during the last 6.3 to 8.7 d prior to expression of the first flower had no effect on time to first flower. Thus, for modeling purposes, the interval between emergence and first flower can be divided into four phases: (1) a purely vegetative phase (absent in most of the cultivars tested); (2) a photoperiod‐sensitive inductive phase; (3) a photoperiod‐sensitive post‐inductive phase; and (4) a photoperiod‐insensitive post‐inductive phase.

Chloroplast structure in normal and pigment‐deficient soybeans grown in continuous red or far‐red light

Clark L1, a normal green soybean [Glycine max (L.) Merrill] and Clark y9y9, a backross‐developed isoline exhibiting pigment deficiency, were grown under continuous red (11 W m−2 and far‐red (9 W m−2) light. Chloroplast thylakoids from the unifoliolate leaf (9–10 days old) were isolated and analyzed for pigments, pigment‐protein, membrane polypeptides, electron transport and ultrastructural differences. Chloroplasts of soybean plants grown under far‐red light have decreased chlorophyll a to chlorophyll b ratio, increased light‐harvesting complexes, and grana structure with few stroma‐type thylakoids. Photosystem II/photosystem I ratios (PSII/PSI) are higher in far‐red due to decreased synthesis of PSI reaction center and/or less antenna associated with PSI.

Control of Cowpea (Vigna unguiculata) in Soybean (Glycine max) with Acifluorfen

Acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} applied 7 days after cowpea [Vigna unguiculata(L.) Walp.] emergence (unifoliolate leaf stage) gave better control than later applications. Cowpea control was obtained with one acifluorfen application at 7 days after cowpea emergence in 1981, but in 1980 and 1982, applications at 7 and 14 days were necessary for acceptable control (&gt; 80%). Acifluorfen reduced cowpea plant dry weights relative to the weedy control. A single application 7 days after emergence reduced cowpea plant growth more than one at 21 days after emergence. Of all times of application, the greatest soybean [Glycine max(L.) Merr.] injury occurred when acifluorfen was applied at 7, 14, and 21 days after emergence, but seed yields were not reduced relative to the untreated weed-free control. There was no difference in response among three weedy cowpea cultivars to acifluorfen.

Soybean Mutants Lacking Constitutive Nitrate Reductase Activity

Nitrogen assimilation in three nitrate reductase (NR) mutants of soybean (Glycine max L. Merr. cv Williams) was studied in the growth chamber and in the field. These mutants, LNR-2, LNR-3, and LNR-4, lack the non-NO(3) (-)-inducible or constitutive fraction of leaf NR activity found in wild-type plants, but this had no effect on the concentration of nitrogen accumulated when grown on NO(3) (-) in the growth chamber. Dry weight accumulation of two of the mutants (LNR-3 and LNR-4) was decreased relative to LNR-2 and wild type. In the field, LNR-2 had dry weights and nitrogen concentrations similar to the wild type at 34 and 61 days after planting, and at maturity. Acetylene reduction activities were also similar at 61 days.Urea-grown LNR-2 seedlings lack both inducible and constitutive NR activity, and were resistant to four days of treatment with 0.5 mm ClO(3) (-). Urea-grown wild-type seedlings, having only constitutive NR activity, developed ClO(3) (-) toxicity symptoms and suffered decreases in unifoliolate leaf NR activity and chlorophyll concentration. This suggests that (a) the reduction of ClO(3) (-) to ClO(2) (-) by NR is the major cause of ClO(3) (-) toxicity in soybeans and (b) the constitutive NR is active in situ.Segregation of the F(2) of reciprocal crosses between the wild type and the mutants indicated that absence of constitutive NR activity was controlled by a single recessive nuclear gene. Evolution of NO((x)) gas was also absent in these mutants, and this was found to be inherited jointly with constitutive NR activity: in 346 segregants, no recombinants were found. Allelism tests between LNR-2 and LNR-3, and LNR-2 and LNR-4, indicated that the constitutive NR mutation was at the same locus in each mutant.

Frost Tolerance in Soybeans1

Additional frost tolerance in soybeans (Glycine max (L.) Merr.] would be a useful trait. Our research was conducted to test the effects of prefrost temperatures, stages of plant development, and genotype on frost tolerance in soybeans. In one experiment, 30 genotypes were tested for frost tolerance. Plants were grown in controlled environments at prefrost day/night temperatures of 15/9, 20/14, and 25/19 C, then subjected to advective white frosts of − 2, − 2.5, and − 3 C. at the cotyledon, unifoliolate, or first trifoliolate leaf stage in a factorial design, for a total of 27 treatments. Lower frost temperatures caused a greater percentage of the tissue to be damaged and a greater percentage of plant kill. Plants grown at 25/19 C before frost exhibited more damage than plants grown at lower temperatures. Frosts at the cotyledon stage killed fewer plants (P&lt;0.1) than at the unifoliolate leaf stage, with plants at the first trifoliolate leaf stage intermediate in susceptibility to frost. Most plants grown to the cotyledon stage at 15/9 C could survive frosts of − 3 C. Significant (P&lt;0.05) differences were measured in frost tolerance among genotypes, but the temperatures tolerated varied only about 0.2 C.In a second experiment, 40 genotypes collected in the People's Republic of China were grown at 25/19 C and subjected to − 2.5 and − 3 C at the first trifoliolate leaf stage. No differences in frost tolerance were detected among genotypes. The results suggest that little variability exists among genotypes of G. max for frost tolerance.

Response of Pinto Bean Plants Exposed to O3, SO2, or Mixtures at Varying Temperatures1

Abstract Pinto bean plants (Phaseolus vulgaris L. cv. Pinto 111) in the unifoliolate leaf stage were exposed for 3 hours to 0.8 ppm SO2, 0.25 ppm 03, or a mixture of the 2 pollutants at these concentrations at 15, 24, or 32° C. Foliage exposed to O3 alone developed adaxial stipple and leaves exposed to SO2 alone developed interveinal necrosis. The mixture of O3 and SO2 induced O3-type symptoms at 32° and SO2-type symptoms at 15°. Both symptom types were present at 24°. Some abaxial glazing or silvering was also induced by the mixture, and was most common at 15° and 24°. Ozone and SO2 each induced greater foliar injury at 15° or 32°, as compared to 24°. The mixture of O3 and SO2 induced greatest macroscopic foliar injury at 15°. The degree of adaxial vs abaxial leaf surface injury varied with temperature.

Unifoliolate leaf: A mutant in cowpeas

Unifoliolate leaf: A mutant in cowpeas

PRELIMINARY STUDIES ON THE COLD TOLERANCE OF SOYBEAN SEEDLINGS

Emergence experiments were conducted on 32 soybean (Glycine max (L.) Merrill) cultivars at a 2.5-cm depth in Guelph loam soil at 10, 20 and 30 C. Differences in emergence were found among cultivars at 10 C but not at 20 and 30 C. Results of the emergence experiment at 10 C permitted classification of cultivars into cold tolerant, intermediate and intolerant groupings. There was no close relationship between maturity group and degree of cold tolerance. Differences in speed of germination were found among cultivars at 10 C. A correlation coefficient (r = +0.616) between germination and emergence indicates that germination at 10 C would be effective in the selection of cold tolerant types. Growth analysis studies on seedlings up to the unifoliolate leaf stage showed that cold tolerant cultivars had a higher fresh weight at a specific age at 10 C. This was attributed to the faster emergence of the cold tolerant cultivars.

Herbicidal Effects of Tebuthiuron and Glyphosate1

AbstractThese studies were conducted to gain a better understanding of the differences in activity of two new herbicides with three commonly used herbicides with regard to their effects on growth, phytotoxicity and germination. This information is necessary for the further evaluation of the new compounds. New herbicides N‐[5‐(1,1‐dimethylethyl)‐1,3,4‐thiadiazol‐2‐yl ]‐N,N′dimethylurea (tebuthiuron) and N‐(phosphonomethyl)glycine (glyphosate) were compared with 1,1′‐dimethyl‐4,4′‐bipyridinium ion (paraquat), alkanolamine formulation of 2,4‐dichlorophenoxyacetic acid (2,4‐D), and 7‐oxabicyclo[2.2.1.] heptane‐2,3 dicarboxylic acid (endothall). Growth and phytotoxic effects were evaluated on cowpea [Vigna unguiculata (L.) Walp.] and sorghum [Sorghum bicolor (L.) Moench] seedlings. Germination effects were studied on seed of sorghum, cowpea, and wheat (Triticum aestivum L.)Greenhouse grown seedlings of cowpea (10 to 12‐days old) and sorghum (25 to 28‐days‐old) were treated by applying 100 μ1 aqueous solution of the test compounds to one unifoliolate leaf of cowpea or to the partially unfurled true leaf of sorghum. Rates ranged from 1.4 to 1,434 μg/plant depending on the herbicide. Evaluation of phytotoxic and growth responses was made 10 to 12‐days post‐treatment. In cowpea, the growth response was determined by measuring the length of the first internode. In sorghum, fresh weight served as a measure of the growth response. Cowpea phytotoxicity was determined on percent dead plants per six‐plant replicate. For sorghum, phytotoxicity was measured as percent desiccation/ plant. Absorption times were determined by washing treated seedlings at intervals for a 6‐hour period. All experiments were repeated six to eight times with each treatment being replicated six and 10 times, cowpea and sorghum respectively.The order of decreasing effectiveness of the five herbicides for growth and herbicidal effectiveness for cowpea and sorghum was paraquat, glyphosate, tebuthiuron, 2,4‐D, and endothall. Endothall‐glyphosate mixtures were synergistic in inhibiting growth of cowpea. Endothalltebuthiuron mixtures were generally synergistic in killing and inhibiting growth of sorghum.Absorption of growth‐inhibiting levels of all five herbicides occurred within the first 60 min. of exposure. Phytotoxic levels of tehuthiuron, paraquat, and endothall were absorbed within 5, 30, and 60 min, respectively. Glyphosate showed rapid action and resistance to removal by washing.Glyphosate and tebuthiuron had little inhibitory effect on germination of sorghum, wheat, or cowpea. Paraquat severely inhibited germination of all three species; endothall and 2,4‐D inhibited only cowpea.