Two-leaf Stage Research Articles

Potential of doubled-haploid lines and localization of quantitative trait loci (QTL) for partial resistance to bacterial leaf streak (Xanthomonas campestris pv. hordei) in barley

Genetic variability for partial resistance to bacterial leaf streak in barley, caused by Xanthomonas campestris pv. hordei, was investigated in 119 doubled-haploid lines (DH) developed by the Hordeum bulbosum method from the F1 progeny of the cross between two cultivars, ‘Morex’ (resistant) and ‘Steptoe’ (susceptible). Two experiments were undertaken in a randomized complete block design with three replicates, in a controlled growth chamber. Twenty seeds per replicate were planted in plastic containers (60×40×8 cm) containing moistened vermiculite. At the two-leaf stage seedlings were inoculated with an Iranian strain of the pathogen. Genetic variability was observed among the 119 DH lines for partial resistance to the disease. Some DH lines were significantly more resistant than ‘Morex’ (resistant parent) to bacterial leaf streak. Genetic gain in percentage of resistant parent for 5% of the selected DH lines was significant (47.70% and 33.72% in the first and the second experiment, respectively). A QTL analysis of bacterial leaf streak resistance showed that three QTLs were detected on chromosomes 3 and 7. Multilocus allelic effects of the three QTLs account for almost 54% of the mean difference between the parents and nearly 30% of the phenotypic variation of the trait in the mean experiment. The resistance locus on chromosome 3, near ABG377, apprears to be a major gene.

Common Bermudagrass (Cynodon dactylon) Management in Cool-Season Turfgrass

Common bermudagrass is an invasive, perennial weed of cool-season turfgrass in California. Complete renovation of the infested area has been the only practical method of restoring desirable cool-season turfgrasses. In studies in southern and northern California, common bermudagrass was suppressed with sequential herbicide applications, allowing seedling establishment and regrowth of established cool-season turfgrass species. One application of fenoxaprop, triclopyr, or their combinations did not control common bermudagrass. Sequential applications of these herbicide treatments resulted in 99, 94, and 100% control of common bermudagrass, respectively, and resulted in establishment of seeded perennial ryegrass in Riverside, CA, over a 2-yr period. Similar results were obtained in the recovery of established tall fescue from a common bermudagrass/tall fescue turfgrass mixture in Willows, CA. Both fenoxaprop and triclopyr can reduce emergence and stunt seedling growth of perennial ryegrass and tall fescue. Greenhouse studies showed that stunting and stand loss of tall fescue and perennial ryegrass seedlings could be reduced by delaying applications from PRE to the two-leaf stage.

Growth and Yield of Eggplants Grafted by a Newly Developed Robot

Eggplant (Solanum melongena L.) at the two-leaf stage were grafted on scarlet eggplant (Solanum integrifolium Poir.) by hand or a newly developed robot. The scion and rootstock were fixed with an elastic tube for hand grafting or with an adhesive and a hardener for robotic grafting. After acclimatization, the grafted plants were planted at the three- or 11-leaf stage in a glasshouse. Plants grafted by the robot showed a higher percentage of survival, and attained the three- and 11-leaf stages 8 days earlier on average than those grafted by hand. Stems were longer, and shoot fresh mass and fruit yield of plants were higher for the three-leaf-than for the 11-leaf-stage planting, irrespective of the grafting method. Such vigorous growth and high yield by robotic grafting were absent for the 11-leaf-stage planting but obvious for the three-leaf-stage planting.

A Diclofop-methyl-ResistantAvena sterilisBiotype with a Herbicide-Resistant Acetyl-coenzyme A Carboxylase and Enhanced Metabolism of Diclofop-methyl

An Avena sterilis biotype was found to be highly resistant to aryloxyphenoxypropionate (APP) herbicides, especially diclofop-methyl. At the enzyme level, this biotype contained a modified acetyl-coenzyme A carboxylase (ACCase) with six-fold resistance to diclofop acid. Absorption and translocation of [14C]diclofop-methyl applied to the leaf axil of the two-leaf stage plants were similar in both susceptible and resistant biotypes. However, the rate of metabolism of [14C]diclofop was increased 1·5-fold in this resistant biotype compared to the susceptible. Experiments with tetcyclacis, a cytochrome P450 monooxygenase inhibitor, indicated that inhibition of this enhanced diclofop metabolism increased diclofop-methyl phytotoxicity in this biotype. Studies with ten individual families of the resistant biotype indicated that both mechanisms of resistance, an altered target site and enhanced metabolism, are present in each individual of the population. Hence, it is likely that these two mechanisms of resistance both contribute to resistance in this biotype. © 1997 SCI.

A Diclofop‐methyl‐Resistant Avena sterilis Biotype with a Herbicide‐Resistant Acetyl‐coenzyme A Carboxylase and Enhanced Metabolism of Diclofop‐methyl

An Avena sterilis biotype was found to be highly resistant to aryloxyphenoxypropionate (APP) herbicides, especially diclofop-methyl. At the enzyme level, this biotype contained a modified acetyl-coenzyme A carboxylase (ACCase) with six-fold resistance to diclofop acid. Absorption and translocation of [14C]diclofop-methyl applied to the leaf axil of the two-leaf stage plants were similar in both susceptible and resistant biotypes. However, the rate of metabolism of [14C]diclofop was increased 1·5-fold in this resistant biotype compared to the susceptible. Experiments with tetcyclacis, a cytochrome P450 monooxygenase inhibitor, indicated that inhibition of this enhanced diclofop metabolism increased diclofop-methyl phytotoxicity in this biotype. Studies with ten individual families of the resistant biotype indicated that both mechanisms of resistance, an altered target site and enhanced metabolism, are present in each individual of the population. Hence, it is likely that these two mechanisms of resistance both contribute to resistance in this biotype. © 1997 SCI.

Activation of Systemic Acquired Disease Resistance in Cucumber Seed during Germination

Systemic acquired disease resistance (SAR) involves the activation of the natural physiological defense mechanisms against pathogen infection in a systemic manner within plants. A series of experiments were conducted in which `Beit Alpha' cucumber seed were treated with 2,6-dichloro-isonicotinic acid (INA) during osmotic conditioning or imbibition in water. Following germination and emergence, seedlings were challenge inoculated at the two-leaf stage with Colletotrichum lagenarium and incubated as a bioassay for expression of SAR. INA (289 μm) treatment of imbibed seeds reduced the number of anthracnose lesions per leaf by >90% as compared to untreated controls. Interactions were observed between INA treatment and the solute used for osmotic conditioning. Priming in 0.5 m KH2PO4 or 0.49 m sorbitol in combination with INA resulted in rapid seedling emergence and a 65% to 80% reduction in disease lesion incidence relative to primed controls. Increases in solute concentration, so as to lower the osmotic potential of the priming solution and thus extend the period of exposure to INA, did not result in enhanced SAR expression. Maximum SAR induction occurred when imbibed seeds were exposed to INA at the onset of expansive radicle growth. This study demonstrates that SAR can be abiotically induced in cucumbers during seed germination.

Postemergence herbicides and application time affect wheat yields

Experiments conducted on wheat grown in the Sacramento and San Joaquin valleys found that two of the most critical factors in reducing plant injury are choice of postemergence herbicide and the growth stage at which the herbicide is applied. To minimize risk of wheat injury and to maximize yields, the optima! time to apply postemergence herbicides is at the tillering growth stage. The two-leaf stage is most sensitive to 2,4-D. Moderate or severe injury caused by 2,4-D and dicamba + MCPA on one-third to one-half of spikes can cause yield losses of up to 27%.

Effect of ammonium sulfate on the phytotoxicity, foliar uptake, and translocation of imazamethabenz in wild oat

Experiments were conducted in greenhouse, growth chamber, and laboratory conditions to determine the effect of ammonium sulfate [(NH4)2SO4] on the phytotoxicity, foliar uptake, and translocation of imazamethabenz on wild oat. Rates of (NH4)2SO4 up to 5% (w/v) applied with a greenhouse sprayer did not affect the phytotoxicity of the herbicide when the mix was applied at the one- to two-leaf stage. However, inclusion of 1 and 2% (NH4)2SO4 increased the phytotoxicity of the herbicide when the mix was sprayed at the two- to three-leaf, or the three- to four-leaf stage. At 10%, (NH4)2SO4 decreased the phytotoxicity of the sublethal dosage of the herbicide. When the herbicide was applied as individual drops to the growth chamber-grown plants, inclusion of (NH4)2SO4 at 1% did not affect phytotoxicity as measured by shoot growth. The presence of (NH4)2SO4 did not affect the amount of imazamethabenz retained by wild oat foliage, but it decreased [14C]imazamethabenz absorption, slightly antagonized acropetal translocation, and increased the basipetal translocation of [14C]imazamethabenz. It was concluded that application methods greatly modify the effect of (NH4)2SO4 on imazamethabenz phytotoxicity. Herbicide absorption and translocation as determined by one method do not necessarily represent the absorption and translocation patterns when different application methods are used. Absorption and translocation were not the factors that were responsible for the observed effect of (NH4)2SO4 on the herbicide phytotoxicity.

Barley Chromosome Location and Expression of Dwarf Bunt Resistance in Wheat Addition Lines

Barley (Hordeum vulgare) is resistant to dwarf bunt of winter wheat (Triticum aestivum) caused by Tilletia controversa. Nine wheat-barley addition lines were utilized to determine which barley chromosomes and chromosome arms carry resistance genes. The lines included six disomic addition lines, WB1, WB2, WB3, WB4 WB6, and WB7, and three ditelosomic addition lines, WB5S (containing the short arm of barley chromosome 5), WB6S (containing the short arm of barley chromosome 6), and WB6L (containing the long arm of barley chromosome 6). These lines, their parent cultivars, and susceptible winter wheat cv. Wanser were inoculated with spores of T. controversa at the two-leaf stage. The barley parent, Betzes, showed no infection and only 5 of 401 heads of addition line WB6 were infected. Lines WBI, WB2, WB3, WB4, and WB7, and cvs. Wanser and Chinese Spring showed a high incidence of infection. WB6S had significantly lower bunt incidence (0 to 1%) than WB6L or WB5S. Lines WB6L and WB5S had a high incidence of infection. This suggests that the short arm of barley chromosome 6 carries the dwarf bunt resistance gene(s). The incidence of bunt infection in wheat-barley hybrid plants was examined. Hybrids were regenerated from embryo rescue followed by F 1 inflorescence culture of wheat-barley crosses and by embryo rescue followed by induction of somatic embryos directly from culture of the immature embryos. Both methods resulted in production of amphiploid plants as well as haploid hybrids (n = 28). Infection incidence in crosses with zero, one, and two copies of the barley genome in a wheat background was 64, 30, and 1%, respectively, suggesting a dosage effect associated with the resistance gene(s). The female wheat parent influenced the expression of barley resistance gene(s) in these wheat-barley hybrids.

Responses ofEchinochloaSpecies and Rice (Oryza sativa)to Indigenous Pathogenic Fungi

Six pathogenic fungal species were isolated from naturally infected Echinochloa species and evaluated as biological control agents of Echinochloa species in rice. Curvularia lunata var. aeria and Exserohilum oryzae were pathogenic to both rice and Echinochloa species and were not evaluated further. Bipolaris sacchari, Curvularia geniculata, Dactylaria dimorphospora, and Exserohilum monoceras were pathogenic only to Echinochloa species and were further compared for virulence under controlled environment conditions in the greenhouse. When provided a 24-h dew period, Exserohilum monoceras killed seedlings of all three Echinochloa species tested: E. crus-galli, E. colona, and E. glabrescens; B. sacchari resulted in 100% mortality of seedlings of E. colona and E. glabrescens; C. geniculata killed seedlings of only E. colona; and D. dimorphospora did not cause any plant death. When given a 12-h dew period, Exserohilum monoceras still killed the three Echinochloa species, whereas the other fungi did not cause plant death. Echinochloa seedlings at the one- and two-leaf stages were more susceptible to these fungi than were seedlings at the three- and four-leaf stages. B. sacchari, Exserohilum monoceras, and E. oryzae produced phytotoxins that caused 100% leaf area chlorosis and wilting of intact seedlings of the Echinochloa species placed in cell-free culture filtrates.

Plant height as a factor in competition between black nightshade and two horticultural crops (tomato and pepper)

SummaryIn a glasshouse experiment the differential competitive relationship between black nightshade, tomato and pepper was investigated at four times of weed emergence. Thus, the weed emerged at the six, four and two-leaf stages of both crops and simultaneously with them. Black nightshade competed for light and nutrients with tomato only when the weed height exceeded that of the crop from the beginning of tomato flowering onward, as it was the simultaneous emergence that reduced tomato fruit yield (36.5%), number of fruits and N, P and K uptake. Competition between the weed and pepper for light and nutrients was more severe, even when weed emergence was delayed until the six-leaf stage of the crop which reduced fruit yield, number of fruits and N, P and K uptake. The earlier the weed emerged relative to the pepper, the less the crop height and yield. Pepper yield was reduced by 29, 44 and 62% when the weed emerged at the six, four and two-leaf stages respectively. Black nightshade that emerged simultaneo...

Postemergence Green Foxtail (Setaria viridis) Control in Corn (Zea mays) in Western Canada

Field research was conducted to determine the effectiveness of DPX-79406 (a 1:1 mixture of nicosulfuron and rimsulfuron) for green foxtail control in field corn. Green foxtail control was similar when DPX-79406 was applied postemergence compared to preplant incorporated EPTC/dichlormid or metolachlor. DPX-79406 gave similar green foxtail control to that of cyanazine and better control than inter-row cultivation following soil-applied herbicides. Green foxtail control was greatest when DPX-79406 was applied at the one- to two-tiller stage compared to the one- to two-leaf stage, suggesting that green foxtail is more susceptible to DPX-79406 at later growth stages. DPX-79406 injured ‘Pioneer 3995’ corn in all trials but injured ‘Pride K020’ corn in only one treatment. DPX-79406 between 15 and 25 g ai/ha gave 85% control of green foxtail with minimal corn injury. Adjuvants tended to increase both corn injury and green foxtail control with Scoil and Merge increasing DPX-79406 activity the most. DPX-79406 provides an effective postemergence alternative for green foxtail control in field corn, for either preplant incorporated herbicides or postemergence cyanazine.

Frequency of post-emergence harrowing effects wild oat control and spring wheat yield

Crops grown by organic producers or others choosing not to use herbicides require alternative weed control methods. In a 3-yr study at Scott, Saskatchewan, several harrowing frequencies were applied to emerged wild oats infesting spring wheat. Two passes with diamond tooth harrows at the one- to two-leaf stage of wild oats reduced panicle density and fresh weight in 2 of 3 yr. Multiple harrowings reduced wheat culms, fresh weight, and yield in 2 of the 3 yr. In 1992, four harrowings reduced wheat culms and yield, but had no effect on wild oat. In 1993, two harrowings reduced wild oat panicles and fresh weight, but had no effect on wheat culms and fresh weight, suggesting that moisture conditions at and immediately following harrowing have a differential effect on the ability of the two species to recover. Key words:Avena fatua L., Triticum aestivum L., cultural control, organic production

Response of Durum Wheat Kernels and Leaves at Different Growth Stages toPyrenophora tritici-repentis

Fourteen durum wheat genotypes were evaluated for the reaction of leaves at different growth stages and kernels to Pyrenophora tritici-repentis. Plants were artificially inoculated with P. tritici-repentis at the two-leaf stage and after emergence of the flag leaf, and were rated for tan spot reaction by percent leaf area with symptoms and lesion type or length. At two locations in southern Saskatchewan, the same genotypes were rated in the field for leaf spots at late milk to early dough in 1991 and 1992. There was no correlation among trials in percent leaf area with symptoms at the seedling stage. Lesion type was considered the best method to determine tan spot reaction at the seedling stage [...]

The mechanism and inheritance of adult plant leaf rust resistance in 12 wheat lines

Twelve lines of wheat (Triticum aestivum L.) were developed that had susceptible infection types to leaf rust (Puccinia recondita Rob. ex Desm. f.sp. tritici) race UN 15 in the seedling stage but were resistant in the adult plant stage in the field. The lines were developed from four crosses, each involving four parents (eight in total) that had originally been selected for adult plant or field resistance to stem rust (Puccinia graminis Pers. f.sp. tritici Eriks, and Henn.). The objectives of the present study were to determine the mechanism of resistance to leaf rust and its inheritance in the 12 lines. The 12 lines were grown in an artificially inoculated field nursery in Saskatoon, coefficients of infection (CI) were determined at four dates, and the areas under the disease progress curve (AUDPC) were calculated. Four representative lines were grown in a growth chamber to measure the latent period and pustule size at the two-leaf and flag-leaf stages. Eight lines were crossed and backcrossed to a susceptible check and the parents, F1, F2, F3, and BC1F2 generations were grown in a field nursery. The 12 lines showed wide ranges in CI and AUDPC but all were significantly more resistant than the susceptible check. The four lines studied in the growth chamber had longer latent periods and smaller pustules than the susceptible check at both stages. The differences tended to be greater at the flag-leaf stage. The inheritance studied showed that resistance was recessive or partially recessive and was controlled by two or more genes in each line of the eight lines. In three of the eight lines, Lr34 may be one of the genes and in the other five both Lr13 and Lr34 could be present. However, additional genes are clearly involved. A single gene by itself had only a small effect, but in two and three gene combinations the effects appeared to be greater. This type of resistance appears to occur frequently and may be durable because its complex inheritance may make it more difficult for the rust fungus to overcome. It should be used in breeding wheat for areas where leaf rust is a major problem.

Effects of imazamethabenz on the main shoot growth and tillering of wild oat (Avena fatua L.)

Foliar application of imazamethabenz at sublethal doses of 100 and 200 g a.i./ha to wild oat plants at the two-leaf stage without tillers greatly inhibited the growth of the main shoot but increased tillering. The near cessation of sheath and the main stem elongation indicated that the major effect of imazamethabenz on the main shoot was inhibition of intercalary growth. Low doses of imazameth-abenz treatment resulted in more leaves (including leaf primordia) in the main stem but did not affect mature first and second leaves. Sublethal doses of imazamethabenz only briefly inhibited tiller growth. A later increase in tillering in treated plants resulted from the stimulated resumed growth of tillers and the increased initiation of tiller buds. Such enhanced tillering mainly resulted from the release of apical dominance due to the inhibition or cessation of the main stem growth with imazamethabenz treatment. Both doses of imazamethabenz (100 and 200 g a.i./ha) significantly reduced the biomass of shoots and roots, but increased the ratio of roots/ shoots dry weight.

Interactions of Plant Size and Squash Bug (Hemiptera: Coreidae) Density on Growth of Seedling Squash

An investigation to delimit the influence of feeding by adult squash bug, Anasa tristis (De Geer), on squash, Cucurbita pepo var. melopepo L. ‘Hyrific’, was done during the summers of 1988 and 1989. When two or more adult squash bugs were allowed to feed on plants at the two-leaf stage for 200 DD (base 15.6°C), yield reductions were caused primarily by seedling mortality. Plants surviving the infestation period were typically unable to make up for growth delays induced by squash bug feeding. The size of the plants at infestation influenced yield, with four-leaf plants producing lower yields at maturity than those with six leaves.

Evaluation of emmer wheat and other Triticeae for resistance to Russian wheat aphid

During the winters of 1990/91 and 1991/92, 181 accessions of Triticum dicoccon Schrank from the CIMMYT gene-bank were screened in the field for resistance to Russian wheat aphid, Diuraphis noxia (Kurdjumov). Accessions were sown in hill plots of 10 seeds and artificially infested with D. noxia at the two-leaf growth stage. Hills were visually assessed for damage at tillering, booting and heading. Entries differed significantly in their reaction to D. noxia, and severity of symptoms increased with time. Twenty four of the entries were highly resistant to the aphid. In winter 1991/92, 807 accessions of wild and cultivated wheats (26 species) and synthetic hexaploids were screened similarly for resistance to D. noxia. A large number of A-genome species were resistant, while few D-genome species were identified as resistant. These newly discovered sources of resistance can be used to expand the genetic base of resistance to D. noxia in both bread (T. aestivum L.) and durum wheats (T. turgidum L. convar. durum (Desf.) Mackey).

Induced systemic resistance to Alternaria cassiae in sicklepod

Localized infection of the weed Cassia obtusifolia L. (sicklepod) by Alternaria cassiae Jurair and Khan led to the development of induced systemic resistance (ISR) in the host. Using plants in the two-leaf stage of growth, infection (induction) of the first compound leaf with a spore suspension (52800 spores ml −1) resulted in 43 ± 10% ( n = 6) reduction in infection on the second leaf upon challenge 3 days after induction. The threshold number of lesions for optimum induction of ISR was 17 per 0·25 cm 2. The degree of ISR expression was dependent on the induction dosage; full expression occurred within 24 h of induction but persisted for only about 9 days. ISR comparable to that achieved with an average of 52800 spores ml −1 was induced by salicylic acid and oxalic acid but not with the other chemicals tested. In addition to ISR, the sicklepod plants developed resistance to A. cassiae as a function of age, i.e., they exhibited an increasing gradient in resistance from top to bottom of the plant after the two-leaf stage of growth. The characteristics of ISR in sicklepod would not be expected to substantially limit the efficacy of A. cassiae as a bioherbicide.

Modification of Petunia Seedling Carbohydrate Partitioning by Irradiance

Petunia × hybrida Villm. `Red Flash' plants received either 10 or 20 mol·day-1 photosynthetic photon flux (PPF) in growth chambers at: 175 μmol·m-2·s-1 for 16 hours, 350 μmol·m-2·s-1 for 8 or 16 hours, or 350 μmol·m-2 s-1 for 8 hours plus 8 hours of incandescent photoperiod extension (5 μmol·m-2·s-1 PPF). The irradiation components of peak, total, and duration were examined. Doubling total PPF increased total carbohydrate (CHO) production by 60%, seedling dry weight (DW) by 30%, rate of seedling growth by 25%, and acid invertase activity by 50% compared to the other treatments, once the seedlings had reached the two-leaf stage. Seedlings receiving 20 mol·day-1 PPF partitioned 14% more CHO into ethanol soluble sugars rather than starch, which may explain the increase in relative growth rate observed with supplemental irradiance treatments. Extending the photoperiod for 8 hours with 5 μmol·m-2·s-1 PPF reduced total CHO production by 50% compared to the same treatment without photoperiodic lighting. Treatment with 350 μmol·m-2·s-1 for 8 hours resulted in the highest O2 evolution (8.8 μmol O2/min per dm2). Increasing the photoperiod from 8 to 16 hours gave the lowest rate of O2 evolution (4.5 μmol O2/min per dm2). Previous reports of the importance of photosynthetic period in controlling partitioning between starch and sugars may have simply observed a decreasing rate of starch accumulation due to increased total PPF.