Inhibition of Abscission of Bean Petiole Explants by Lepidimoide

The effect of lepidimoide on the process leading to abscission was studied in bean (Phaseolus vulgaris L. cv. Masterpiece) petiole explants. The assays, involving observations on the junction of the petiole of primary leaves and the pulvinus, were conducted in the light. Lepidimoide, at concentrations of 1 μm or higher, delayed the abscission process; however, the progression of abscission proceeded at normal rates, and complete abscission resulted. On the other hand indoleacetic acid inhibited the normal senescence resulting in greatly decreased abscission during the observation period. These observations show that lepidimoide only delays abscission, and the kinetics seem to indicate that lepidimoide and indoleacetic acid affect abscission through different mechanisms. Received March 1, 1996; accepted November 4, 1996     

Involvement of Abscisic Acid and Indole-3-acetic Acid in the Flowering of Pharbitis nil

The involvement of abscisic acid (ABA) and indole-3-acetic acid (IAA) in the regulation of flowering of Pharbitis nil was investigated through exogenous applications and analyses of endogenous levels. Both hormones inhibited the flowering of P. nil when they were applied before or after a single 15-h dark treatment. The inhibitory effect of ABA and IAA was significant when they were applied before the dark treatment, and the application to plumules was more effective than that to cotyledons. In all applications, the inhibitory effect of IAA was stronger than that of ABA. Endogenous levels of ABA and IAA in the plumules were compared between flower-inductive (15-h dark treatment) and noninductive (continuous light) light conditions. There was no significant difference in the ABA level between light and dark conditions, whereas the level of IAA was decreased by the dark treatment. These results suggest that biosynthesis and/or catabolism of IAA is affected by the light treatment and therefore may be involved in the regulation of early flowering processes in the apex. The inhibitory effects of ABA and IAA were reversed by an application of gibberellin A₃, indicating that gibberellin A₃ counteracts the flowering processes affected by ABA and IAA. Application of aminoethoxyvinylglycine restored the flowering response inhibited by IAA, which suggests the possibility that the inhibitory effect of IAA is the result of enhanced ethylene biosynthesis. Received November 22, 1996; accepted February 17, 1997     

Effect of Pot Size and Timing of Plant Growth Regulator Treatments on Growth and Tuber Yield in Greenhouse-Grown Norland and Russet Burbank Potatoes

The effects of pot size, timing of the application of paclobutrazol (PTZ) and gibberellic acid (GA₃), and the counteractive effect of these two compounds on growth and tuber yield of greenhouse-grown Norland and Russet Burbank potatoes were investigated. Plants were grown either in 1.5-liter pots (15 cm deep) or 3.0-liter pots (18 cm deep) and received a foliar application of either 1.5 mm PTZ or 9 × 10⁻³ mm GA₃ at early or late stolon initiation. Some plants that had been foliar treated with 1.5 mm PTZ at early stolon initiation were foliar treated with 9 × 10⁻³ mm GA₃ at late stolon initiation. PTZ reduced haulm length in both cultivars significantly, particularly when the treatment was applied at early stolon initiation, but the late treatment reduced haulm length only when growing in 3.0-liter pots. Irrespective of the timing of treatment, GA₃ increased haulm length in Norland growing in both pot sizes, but the treatment increased haulm length in Russet Burbank only when applied at late stolon initiation. GA₃ applied after PTZ did not overcome the growth-inhibiting effect of the PTZ treatment. The PTZ treatment effectively increased usable tuber number/plant (UTN) in Norland, but PTZ had no effect on UTN in Russet Burbank. PTZ reduced usable tuber weight/plant (UTW) only in Norland growing in 1.5-liter pots. By contrast, GA₃ increased UTN only when treated at late stolon initiation of 1.5-liter pot-grown Norland, whereas the same treatment was effective when applied only at early stolon initiation for Russet Burbank. For Norland, the increase in UTN by early applied PTZ was reduced by the subsequent application of GA₃. The use of 3.0-liter pots for minituber production in both Norland and Russet Burbank appears to have no advantage over growing in 1.5-liter pots, particularly when PTZ or GA₃ is used to enhance tuberization. Received May 30, 1997; accepted February 3, 1998     

Influence of 2,3,5-Triiodobenzoic Acid and 1-N-Naphthylphthalamic Acid on Indoleacetic Acid Transport in Carnation Cuttings: Relationship with Rooting

³H-IAA transport in excised sections of carnation cuttings was studied by using two receiver systems for recovery of transported radioactivity: agar blocks (A) and wells containing a buffer solution (B). When receivers were periodically renewed, transport continued for up to 8 h and ceased before 24 h. If receivers were not renewed, IAA transport decreased drastically due to immobilization in the base of the sections. TIBA was as effective as NPA in inhibiting the basipetal transport irrespective of the application site (the basal or the apical side of sections). The polarity of IAA transport was determined by measuring the polar ratio (basipetal/acropetal) and the inhibition caused by TIBA or NPA. The polar ratio varied with receiver, whereas the inhibition by TIBA or NPA was similar. Distribution of immobilized radioactivity along the sections after a transport period of 24 h showed that the application of TIBA to the apical side or NPA to the basal side of sections, increased the radioactivity in zones further from the application site, which agrees with a basipetal and acropetal movement of TIBA and NPA, respectively. The existence of a slow acropetal movement of the inhibitor was confirmed by using ³H-NPA. From the results obtained, a methodological approach is proposed to measure the variations in polar auxin transport. This method was used to investigate whether the variations in rooting observed during the cold storage of cuttings might be related to changes in polar auxin transport. As the storage period increased, a decrease in intensity and polarity of auxin transport occurred, which was accompanied by a delay in the formation and growth of adventitious roots, confirming the involvement of polar auxin transport in supplying the auxin for rooting. Received April 19, 1999; accepted December 2, 1999     

Effect of the Herbicide Atrazine on the Bean Leaf Lipids

Eight-day-old bean plants, grown in a nutrient solution, were sprayed with 10⁻⁵, 10⁻⁴, 10⁻³, and 10⁻² M atrazine. The lipid changes in primary and trifoliate leaves were studied 6 d after the herbicide application. The atrazine treatment inhibited the growth of the trifoliate leaves, and decreased photosynthetic and transpiration rates, the stomatal conductance, and the total lipid content. Atrazine treatment increased 16:0 and 18:3 acids and decreased trans-3-hexadecenoic and 18:2 acids in the phospholipids. The herbicide also increased 16:0 and 18:1 acids in glycolipids and decreased 18:3 acid in monogalactosyl diacylglycerols and digalactosyl diacylglycerols. In most cases the marked changes in fatty acid composition of the main lipid classes were observed at 10⁻⁴ and 10⁻³ M atrazine. This revised version was published online in June 2006 with corrections to the Cover Date.     

A Possible Role for Jasmonic Acid in Adaptation of Barley Seedlings to Salinity Stress

The changes caused by NaCl salinity and jasmonic acid (JA) treatment (8 days) on growth and photosynthesis of barley plants (Hordeum vulgare L., var. Alfa) have been studied. Gas exchange measurements and analysis of enzyme activities were used to study the reactions of photosynthesis to salinity and JA. Both 100 mm NaCl and 25 μm JA treatment led to a noticeable decrease in both the initial slope of the curves representing net photosynthetic rate vs intercellular CO₂ concentration and the maximal rate of photosynthesis. The calculated values of the intercellular CO₂ concentration, CO₂ compensation point, and maximal carboxylating efficiency of ribulose-1,5-bisphosphate carboxylase support the suggestion that biochemical factors are involved in the response of photosynthesis to JA and salinity stress. The activities of phosphoenolpyruvate carboxylase and carbonic anhydrase increased more than twofold. Pretreatment with JA for 4 days before salinization diminished the inhibitory effect of high salt concentration on the growth and photosynthesis. The results are discussed in terms of a possible role of JA in increasing salinity tolerance of the barley plants. Received September 8, 1997; accepted May 19, 1998     

Possible Involvement of Altered Gibberellin Metabolism in the Induction of Tomato Irregular Ripening in Dwarf Cherry Tomato by Silverleaf Whitefly

External and internal tomato irregular ripening (TIR) symptoms were associated with the feeding of silverleaf whitefly (SLW), Bemisia argentifolii Bellows and Perring. Four experiments consisting of various soil drench applications of GA₃ (100 ppm) and cycocel (CCC, an inhibitor of GA biosynthesis; 1,000 and 2,000 ppm) were applied to dwarf cherry tomato cv. Florida Petite in the presence and absence of SLW in an attempt to mimic the disorders induced by the SLW. The application of GA₃ induced external and internal TIR symptoms similar to the SLW-induced disorder. Minimal TIR-like symptoms also occurred in the control and CCC treatments. Internal TIR symptoms in GA₃, GA₃ plus SLW, and GA₃ plus CCC treatments ranged from 66% to 97% throughout the experiments. The incidence of external TIR symptoms was highest in the GA₃ plus SLW treatment compared with the other treatments. CCC reduced the incidence of external TIR symptoms induced by GA₃ or GA₃ plus SLW treatments. However, CCC-treated plants also attracted more oviposition and higher populations of SLW and consequently induced a greater incidence of TIR symptoms than SLW treatment alone. Furthermore, although low SLW populations may be associated with low external TIR symptoms, internal TIR symptoms almost always remained high in infested plants. The results suggest that the TIR disorder in dwarf cherry tomato which is induced by the SLW may be a gibberellin-regulated disorder. Received May 27, 1997; accepted September 26, 1997     

Effect of Wild-Type and Mutant Plant Growth-Promoting Rhizobacteria on the Rooting of Mung Bean Cuttings

Mung bean cuttings were dipped in solutions of wild type and mutant forms of the plant growth-promoting rhizobacterium Pseudomonas putida GR12-2 and then incubated for several days until roots formed. The bacteria P. putida GR12-2 and P. putida GR12-2/aux1 mutant do not produce detectable levels of the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, whereas P. putida GR12-2/acd36 is an ACC deaminase minus mutant. All bacteria produce the phytohormone indole-3-acetic acid (IAA), and P. putida GR12-2/aux1 overproduces it. Treatment of cuttings with the above-mentioned bacteria affected the rates of ethylene production in the cuttings in a way that can be explained by the combined effects of the activity of ACC deaminase localized in the bacteria and bacterial produced IAA. P. putida GR12-2 and P. putida GR12-2/acd36-treated cuttings had a significantly higher number of roots compared with cuttings rooted in water. In addition, the wild type influenced the development of longer roots. P. putida GR12-2/aux1 stimulated the highest rates of ethylene production but did not influence the number of roots. These results are consistent with the notion that ethylene is involved in the initiation and elongation of adventitious roots in mung bean cuttings. Received October 21, 1998; accepted January 3, 1999     

Prehistoric Chronology of the Common Bean in the New World: The Linguistic Evidence

Glottochronology and the comparative method of historical linguistics provide a linguistic approach for dating the common bean ( Phaseolus vulgaris L.) that both complements and supplements archaeological dating techniques such as accelerator mass spectrometry (AMS). For example, the comparative approach reveals that prehistoric languages of eastern North America having glottochronological dates earlier than 700 B.P., such as Proto-Iroquoian (2700 B.P.), lacked words for bean. Protolanguages of the region with glottochronological dates younger than 700 B.P. had bean terms. These linguistic results accord with the AMS finding that beans do not become archaeologically visible in the region until around C.E. 1300. The earliest AMS date for beans of Mesoamerica is around 2300 B.P. This date is considerably younger than glottochronological dates for prehistoric languages of the area, such as Proto-Mayan (3400 B.P.), for which bean terms are posited. Linguistic findings for protolanguages of Mesoamerica suggest that the regional bean chronology is considerably older than that indicated through archaeological dating.     

Gibberellic Acid3 Modifies Some Growth and Physiologic Effects of Paclobutrazol (PP333) on Wheat

Gibberellic acid₃ (GA₃) modification of some growth and physiologic effects of paclobutrazol (PP₃₃₃) was studied by applying PP₃₃₃ alone and in combination with GA₃ at the tillering stage of wheat. Results showed that GA₃ weakened the effect of PP₃₃₃ on tillering and shortening the plant, increased the dry matter accumulation of different tillers, improved plant nitrogen metabolism by favoring nitrogen translocation into tillers at late growth stage, and stimulated tiller development. All of these reduced the difference in spike weight among tillers and the main stem. Compared with control, there were more spikes per plant and fewer grain per spike in the PP₃₃₃ treatment, but all yield components developed positively in the treatment consisting of the mixture of GA₃ and PP₃₃₃. Received May 22, 1996; accepted November 14, 1996     

Role of the Ring Methyl Groups in Abscisic Acid Activity in Erucic Acid Accumulation in Oilseed Rape (Brassica napus L.)

Modification of the structure of abscisic acid (ABA) has been reported to result in modification of its physiologic activity. In this study we tested the effect of removing methyl groups from the ring and of chirality of ABA on activity in microspore-derived embryos of oilseed rape (Brassica napus L.). The natural (+)-ABA molecule induced growth inhibition and an increase in the amount of erucic acid accumulated in the oil at medium concentrations less than 1 μm. (−)-ABA showed similar effects. Removing the 7′-methyl group resulted in a dramatic decrease in activity: (+)-7′-demethyl-ABA retained some activity as a growth inhibitor; a 10–100 μm concentration of this compound was needed for a response, and (−)-7′-demethyl-ABA was almost completely inactive. Similar effects were observed with regard to elongase activity, which catalyzes erucic acid biosynthesis from oleic acid. Removal of the 8′- and 9′-methyl groups resulted in a more complex response. These compounds all showed intermediate activity; for growth inhibition, the presence of the 9′-methyl was the more important determinant, whereas chirality dominated the response on erucic acid accumulation, with the (+)-enantiomers being more active. Received July 25, 1997; accepted October 31, 1997     

Uptake, Distribution, and Metabolism of 1-Naphthaleneacetic Acid and Indole-3-Acetic Acid During Callus Initiation From Actinidia deliciosa Tissues

1-Naphthaleneacetic acid (NAA) and 6-benzyladenine (BA) were required for in vitro callus formation at the basal edge of kiwifruit (Actinidia deliciosa [A. Chev] Liang and Ferguson, cv. Hayward) petioles. The uptake, metabolism, and concentration of NAA and indole-3-acetic acid (IAA) content were examined in the explants during the callus initiation period. After 1, 6, 12, 24, 48, and 96 h of culture in the presence of [H³]NAA, petioles were divided into apical, middle, and basal portions and analyzed. Except for a high IAA level measured at 12 h, IAA content decreased in tissues during a culture period of 96 h. NAA uptake was higher in petiolar edges than in the middle portion, and NAA was rapidly conjugated with sugars and aspartic acid inside the tissues. The amide conjugation was triggered in apical and basal portions from 12 h and in the middle part from 48 h, with α-naphthylacetylaspartic acid being the major metabolite. Free-NAA concentration in cultured petioles achieved an equilibrium with the exogenously applied NAA (0.27 μm) from 12 h, and it remained constant thereafter. The relationships between the role attributed to NAA and BA in the initiation and the maintenance of disorganized growth of callus in kiwifruit cultures are discussed. Received December 21, 1998; accepted July 20, 1999     

Involvement of Abscisic Acid in Mesocotyl Growth in Etiolated Seedlings of a Foxtail Millet Dwarf Mutant

Etiolated seedlings of foxtail millet (Setaria italica Beauv.) dwarf mutant CH84113 were treated with various concentrations of abscisic acid (ABA), mefluidide, mannitol, or polyethylene glycol (PEG) 6000. It was found that these chemicals, at suitable concentrations, could increase mesocotyl length significantly, whereas these chemicals at higher concentrations had an inhibitory effect. Endogenous levels of ABA in mesocotyl were measured by enzyme-linked immunosorbent assay. It was found that endogenous ABA increased progressively in a chemical (ABA, mefluidide, mannitol, or PEG 6000) concentration-dependent manner, indicating that the effects of these chemicals on mesocotyl growth may be mediated by increased endogenous ABA levels. On the other hand, S-3307, an inhibitor of the oxidative reactions in gibberellin (GA) biosynthesis, inhibited the elongation of mesocotyl significantly. When ABA and GA₃ were applied simultaneously, the effect on mesocotyl growth was additive. These results imply that ABA and GA may control different processes in the regulation of mesocotyl growth. Received October 27, 1997; accepted May 11, 1998     

Multiline as a Strategy to Reduce Damage Caused by Colletotrichum lindemuthianum in Common Bean

The aim of the study was to verify whether a mixture of lines containing equal amounts of seven lines of Carioca‐type common bean, all agronomically uniform but each presenting different patterns of resistance to Colletotrichum lindemuthianum, would be less damaged by anthracnose than the individual pure lines. Plants cultured in experimental plots in Lavras, Minas Gerais, Brazil, in the dry harvest seasons of 2007 and 2008 were inoculated with a mixture of races 65, 81, 87, 89 and 337 of the pathogen, and the severity of anthracnose was evaluated at 10‐ day intervals commencing 12 days after inoculation. The progress of the disease was estimated from the coefficients of the linear regression equations (b₁) and from the areas under the disease progress curves (AUDPC). The mean grain yields were determined in both experimental periods. The value of b₁ for the multiline was not different from that presented by the resistant line MA‐II‐22 and indicated a slower progress of the disease over time compared with susceptible lines. There were no differences in AUDPC values between the multiline and the resistant lines. The multiline presented a grain yield that was similar to those of the most productive lines even though susceptible lines comprised more than 28% of the mixture and such lines showed the lowest yields of grain. It is concluded that the use of the mixture of lines represents a good strategy for reducing the progress of anthracnose in the field and, as a consequence, reducing loss of grain yield.     

Changes of Respiration Rate, Ethylene Evolution, and Abscisic Acid Content in Developing Inflorescence and Young Fruit of Olive (Olea europaea L. cv. Konservolia)

Simultaneous measurements of respiration, ethylene production, and abscisic acid (ABA) concentrations, as well as the growth parameters length, fresh weight (FW), and dry weight (DW) of olive (Olea europaea L. cv. Konservolia) inflorescence were carried out at short intervals (3–7 days) during the period from bud burst until the 3rd week after full bloom (AFB), when young fruit reached 8 mm in length. The axis of inflorescence elongated remarkably during the 3rd week after bud burst (ABB), massive bract shedding occurred during the 4th week ABB, full bloom (FB) was observed 7 weeks ABB, and massive floral organ abscission 1 week AFB. The results showed a continuous increase in inflorescence FW and DW from bud burst until 4 days before FB. Respiration rate, ethylene production, and levels of ABA were relatively high during the first 3 weeks ABB. After this period, respiration and ethylene followed a similar pattern of changes, inversely to that of ABA concentration. An accumulation of inflorescence ABA 6 and 4 days before FB was associated with the minimum values of respiration and ethylene production on the same dates. The sharp decrease in the ABA concentration during FB and 3 days later was followed by a high rise in ethylene and an increase in respiration rate, which both rose further 1 week AFB. The results suggest a possible correlation of ABA with the early stage of floral abscission, whereas ethylene production seems to be correlated with the terminal separatory activity in olive inflorescence abscission processes. Received May 28, 1998; accepted November 17, 1998     

Growth Responses and Allocation of Assimilates of Rice Seedlings by Paclobutrazol and Gibberellin Treatment

Paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)methyl-4,4-dimethyl-2-(1h-1,2,4-trizol-1-yl)penten-3-ol] effectively decreased vegetative growth of rice (Oryza sativa L.) seedlings and increased the chlorophyll content. The number of veins in a leaf, the calculated number of stomata per leaf, and the length of guard cells were not altered by the paclobutrazol treatment, suggesting an effect on cell elongation. The allocation pattern of carbohydrates was changed by either gibberellin (GA) or paclobutrazol treatment. GA₃ induced more shoot growth and less accumulation of starch than the control and paclobutrazol-treated seedlings. Photosynthetic ability was not affected by either paclobutrazol or GA₃ treatment. Paclobutrazol-treated plants allocated a smaller amount of photosynthates for vegetative shoot growth and stored more as starch in the crowns than the control and GA₃-treated plants. The same starch degrading activity in the crown tissue of paclobutrazol-treated seedlings as in control plants suggests that the accumulated starch is utilized in a normal activity for growth including leaf emergence, tiller formation, and root production, resulting in improved seedling quality. Received May 30, 1996; accepted December 10, 1996     

Pathogenic Variability of Isolates of Pseudocercospora griseola, the Cause of Common Bean Angular Leaf Spot, and its Implications for Resistance Breeding

The pathogenic variability was evaluated of 48 Pseudocercospora griseola isolates collected in the State of Minas Gerais, Brazil. Isolates were inoculated to a set of 12 international differential cultivars in a greenhouse. Ten pathotypes (55-15, 63-7, 63-15, 63-23, 63-25, 63-27, 63-31, 63-47, 63-55 and 63-63) were identified, showing the great pathogenic variability of this fungus in Minas Gerais State. Pathotypes 55-15, 63-15, 63-25 and 63-27 had not previously been reported in the State. Of the 48 isolates, all except pathotype 55-1547 induced a compatible reaction with all cultivars from the Andean group. Isolates were highly pathogenic in both Andean and Mesoamerican cultivars, thus being classified as Mesoamerican pathotypes. Pathotype 63-63 was the most widespread, and overcame the resistance genes present in all differential cultivars.     

Common Bean Reaction to Fusarium oxysporum f. sp. Phaseoli, the Cause of Severe Vascular Wilt in Central Africa

During the September‐December season of 1990, severe symptoms of Fusarium wilt were for the first time observed on a popular climbing bean (Phaseolus vulgaris L.) cultivar. G 2333. introduced within the previous 5 years. Seventy‐three bean genotypes were screened for resistance lo the disease, using artificial inoculation. The effect of inoculation density on the reaction of four selected genotypes was also investigated. Of the 29 climbing bean genotypes evaluated, 19 were resistant, including 11 of the 15 pre‐release or released cultivars. Of the 44 bush bean cultivars evaluated, 28 were resistant, five were intermediate and 11 were susceptible. All susceptible cultivars showed vascular discoloration. In both susceptible and resistant genotypes, the fungus spread almost equally from the entry points in inoculated roots to the base of the plants, but colonization and vertical spread within the vascular system were markedly less in resistant than in susceptible cultivars. At 20 and 30 cm above soil level, the fungus was only recovered from susceptible cultivars. Increasing inoculum density from 10² to 10⁷ conidia/ml did not affect the resistance of cultivars RWR 950 and G 685 but. in the susceptible cultivars G 2333 and MLB‐48‐89 A. it resulted in early appearance, high incidence and severity of the disease.     

Potential Role of Abscisic Acid in Cotton Fiber and Ovule Development

Fibers and ovules of a cotton cultivar (Gossypium hirsutum L. Trambak-108) were analyzed for growth and free abscisic acid (ABA) content by indirect enzyme immunoassay. An inverse correlation between fiber elongation and ABA content was observed. In the seed, accumulation of ABA was observed during secondary thickening and the maturation phase. The potential role of ABA in fiber and seed development is discussed. Received June 25, 1997; accepted October 15, 1997     

Resistance of Common Bean (Phaseolus vulgaris) to Bacterial Wilt Caused by Curtobacterium flaccumfaciens pv. flaccumfaciens

Bacterial wilt caused by Curtobacterium flaccumfaciens pv. flaccumfaciens is an important new disease of common bean (Phaseolus vulgaris) in western Canada. Both yellow and orange variants of the pathogen were found in the region. A controlled environment study was conducted to assess 124 common bean cultivars and lines from eight market classes for resistance to the yellow and orange variants of the pathogen, using the hilum injury/seed inoculation method. Results of the screening tests showed significant (P < 0.05) differences in resistance to bacterial wilt among the cultivars or lines. The great northern line L02E317, the great northern cultivar Resolute and pinto lines L02B662 and 999S‐2A, were highly resistant to both variants of the pathogen, with disease severity indices of 0 on a rating scale of 0 (no wilt symptoms) to 5 (dead seedling). Resistant cultivars or lines were found among black, great northern, pink, pinto, small red and Flor de Mayo bean market classes. The study concludes that new bacterial wilt‐resistant germplasm exists among Canadian bean cultivars and lines, and constitutes a valuable resource for breeding common beans for resistance to both yellow and orange variants of C. flaccumfaciens pv. flaccumfaciens.