True Leaf Stage Research Articles

Juvenility and Photoperiodic Flowering Requirements of Chrysanthemum ×superbum `G. Marconi' and `Snow Lady' Grown under Short- and Long-day Conditions

Juvenility and flowering requirements of Chrysanthemum ×superbum Bergmans ex J. Ingram `G. Marconi' and `Snow Lady' were examined by growing plants under short days (SDs) and transferring them to long days (LDs) upon reaching specific true leaf stages. `G. Marconi' plants did not flower in continuous SDs and only sparse flowering occurred in plants transferred to LDs. `Snow Lady' plants transferred from SDs to LDs at the cotyledon stage flowered fastest from seeding (75 days) and had the fewest number of main stem leaves and total leaves (9 and 15, respectively) at the time of first flower. Plants moved from SDs to LDs at the 24 true leaf stage flowered 123 days after seeding and averaged 28 leaves on the main stem and 37 total leaves at the time of first flower. To examine apical floral initiation, plants were distributed between SDs and LDs following transplanting and five plants per treatment were sampled each week thereafter. Microscopic examination revealed floral initiation in plants sampled after just 1 week in LDs and, after 5 weeks, macroscopic terminal flower buds were present. Under SDs, apical floral initiation began after 5 weeks, yet, 9 weeks were required for floral initiation in all five plants sampled.

Efficacy of Fumigants for Controlling the Root Aphid, 1994

Abstract Fumigants were tested to control a new root aphid found in the farming area of Kula located on the Hawaiian Island of Maui. The field trial was installed on a cooperating grower’s farm at Kula, Maui in a field that contained broccoli heavily infested by the pest. The experimental plots were adjacent to a broccoli planting that was also heavily infested by the root aphid. The adjacent broccoli crop was removed by the grower 5 weeks after the field trial began. The four treatments tested were Telone II (30 gal/A), Vapam (60 gal/A), Di-Syston 15G (13.4 lbs/A) as a treated check, and an untreated check. The field site was plowed on 24 Nov 1994 and fumigants were applied 2 weeks later using a tractor mounted injector. Head cabbage seedlings in the 6-8 true leaf stage were planted 2 weeks after fumigants were applied. The Di-Syston treatment was applied in-furrow immediately prior to transplanting. A randomized block plot design with three replications was used. Each treatment replication consisted of four rows of cabbage with 25 plants per row at 18 inches inter plant spacing. Treatment plots were separated by a 3 feet buffer. The treatments were evaluated at 3, 7, and 12 weeks after planting to assess aphid populations on the roots. During each evaluation, the roots of 15 plants were taken from each treatment plot and individually bagged. Each root sample was washed in a calcium chloride solution (1 tablespoon/gallon water). The aphids floated to the surface and were counted.

Pepper Transplants Are Excessively Damaged by Brushing

`Jupiter' or `Marengo' pepper (Capsicum annuum L.) seedlings maintained under 0%, 30%, 50%, or 80% shade in a greenhouse were brushed 80 strokes twice daily beginning at the cotyledonary, first true leaf, or second true leaf stage. Averaged across shade environments, brushing reduced `Jupiter' and `Marengo' stem length 25% to 36% and 6% to 28%, respectively. However, the percentage of plants exhibiting mechanical damage by brushing ranged from 86% to 93% and 48% to 90% for `Jupiter' and `Marengo', respectively. Transplant quality tended to decrease as brushing was delayed. When brushing of `Marengo' was reduced to 40 strokes twice daily in 1992, plant growth reduction decreased, but the percent damage was about the same. The damage severity, however, was reduced as indicated by higher plant-quality ratings. Pepper plant damage was excessive for the small amount of growth regulation provided by brushing.

Possibilities for regulation stem growth of tobacco seedlings by treatment with some growth retardants

Abstract Some growth retardants, structural analogues of Alar, such as the monomethyl ester of itaconic acid (MEIA), the monoethyl esters of adipinic (MEEAdA) and of succinic acids (MEESA) were tested as possible regulators of stem growth of tobacco seedlings. The compounds, in concentrations of 500, 1000, 1500 and 2000 mg/1, were sprayed on the leaves of oriental tobacco cv. Plovdiv 5 at the fourth true leaf stage and produced an obvious retarding effect. This effect was well expressed on the tenth day after treatment, when the compounds ranked as follows: Alar, MEIA, MEESA, MEEAdA, according to their retarding effect. The stems of treated plants were shorter, their fresh and dry weights were reduced and they were characterized by higher amounts of lignin and phenols. Two weeks after transplanting, the differences observed in height, weights and amounts of lignin and phenols decreased. The conclusion is reached that treatment of tobacco seedlings with Alar, MEIA, MEEAdA and MEESA can temporarily inhibit growth through transplanting period, but has bo influence on subsequent growth rates. The use of these retardants may be suitable for protecting tobacco seedlings from overgrowth in cases when the climatic conditions do not permit their planting in the fields in time.

Sensitivity of Tobacco (Nicotiana tabacum) and Vegetable Crop Seedlings to Fluridone in Irrigation Water

The sensitivities of tobacco, tomato, pepper, and cucumber seedlings to an aquatic herbicide, fluridone, were examined in growth chamber and greenhouse studies. New leaves of tobacco seedlings became chlorotic after 6-d exposure to fluridone concentrations of 5 μg/L or greater in hydroponic float culture, and dry weights were significantly reduced at 100 μg/L or greater. When treated only once at the beginning of a 2-wk evaluation period, all crops except cucumber exhibited injury symptoms at 100 μg/L. When grown in sand, pepper and tomato were injured at 25 μg/L; tobacco injury occurred at 10 μg/L. Dry weights of pepper, tobacco, and tomato seedlings decreased significantly at 250, 50, and 250 μg/L, respectively, on potting mix; effects on dry weights were not significant for plants on sand. Cucumber was injured by treatment at 100 μg/L or greater in sand, but there were no effects on dry weights in either sand or potting mix. When treated three times weekly for 2 wk with fluridone, pepper, tobacco, and tomato grown in potting mix were injured by 50, 25, and 100 μg/L; when grown in sand, injury occurred at 10, 5, and 10 μg/L, respectively. Dry weights of pepper, tobacco, and tomato were reduced by 50,50, and 100 μg/L, respectively, in potting mix; effects on dry weights were not significant for plants in sand. Cucumber seedlings were damaged by 250 μg/L or higher on potting mix and 100 μg/L or higher on sand, but there were no effects on dry weights regardless of substrate. Threshold injury levels for plants grown in potting mix to the second true leaf stage and then treated three times weekly were 25 μg/L for pepper and tobacco and 50 μg/L for tomato; dry weights were significantly reduced in pepper at 25 μg/L and in tobacco and tomato at 50 μg/L. Cucumber seedlings were not injured by any treatment in this test.

532 PB 008 DEVELOPMENT OF ROOT RESTRICTION STRESS IN WATERMELON TRANSPLANTS

Seeds of `Mirage' and `Starbrite' watermelon [Citrullus lanatus (Thunb.) Matsum. and Nakai] were sown in TODD planter flats with root cell volumes of 20, 28, 39, 49, or 83 cm3. Plants were harvested for growth measurement at 5, 10, 15 and 20 days after seeding (DAS). Data were regressed over root cell volume for each harvest date. The effect of root volume restriction (RVR) was determined by comparing the slopes of the regression lines. All measurements of growth increased with increasing root volume at each harvest date. Generally, the slopes of all regression lines increased with each successive harvest, i.e., plant growth was limited more in the smaller root volumes than in larger volumes at each successive harvest. The greatest increase in the slopes of the regression lines occurred between 10 and 15 DAS for most measurements of both cultivars. This indicates that RVR became significantly more limiting to seedling growth after 10 DAS which corresponded to the second to third true-leaf stage.

Reversal of Heat-induced Resetting in Eustoma grandiflorum with Low Temperatures

The effects of seedling age and temperature regimes and durations on the reversal of Eustoma grandiflorum (Raf.) Shin. heat-induced rosette formation were clarified. When E. grandiflorum seedlings were grown in a natural-light phytotron (600-800 μmol·m-2·s-1) for 4 weeks at 33/28C (12-h day/12-h night) from germination to the four true-leaf stage, the optimum temperature and duration required to break rosette formation was 15C for 4 weeks with continuous illumination (35 μmol·m-2·s-1). However, when seedlings were grown for 12 weeks at 33/28C from germination to the eight true-leaf stage. shoot elongation required 6 weeks at 10C.

Importance of tolerance and growth rate in the resistance of oilseed rapes and mustards to flea beetles, Phyllotreta cruciferae (Goeze) (Coleoptera: Chrysomelidae)

The resistance of oilseed rapes and mustards to crucifer flea beetles, Phyllotreta cruciferae (Goeze), is known to vary, and tolerance to feeding damage may be a factor in the resistance shown by two of the species. The tolerance of Brassica juncea L., Brassica napus L., Brassica rapa L. and Sinapis alba L. was compared in field and laboratory studies. The growth rates of damaged and undamaged plants were measured at four early growth stages, and the level of antixenosis was determined to ascertain the relative importance of tolerance and antixenosis and the relationship between tolerance and growth rate. Antixenosis was confirmed to be a factor in the resistance of S. alba, but this species also proved to be most tolerant of feeding damage and showed rapid compensatory growth at three early growth stages. Brassica juncea showed no antixenosis, but it was tolerant of damage particularly at germination, the cotyledon stage, and the first true leaf stages, which probably accounts for its resistance to moderate flea beetle damage. Brassica rapa showed only a very low level of tolerance, and B. napus was intolerant of damage at all four growth stages. The level of tolerance was species specific and growth-stage specific and was not related to the rates of growth of the species. Key words: Insecta, antixenosis, canola, crucifer flea beetles

Efficacy of Systemic Aphicides for Control of Melon Aphid on Cantaloupe, 1993

Abstract Two greenhouse trials were conducted sequentially to evaluate rates of systemic aphicides for control of melon aphid on cantaloupe. Methods of both trials were the same with the exceptions of the cultivars used, number of replicates and sample intervals. In the first trial, ‘Top Mark’ cantaloupe were planted 16 Aug and arranged in a RCB design with 4 replications. In the second trial, ‘Perlita’ cantaloupe were planted 4 Oct and arranged in a RCB with 3 replications. In both trials, cantaloupe were seeded in 6-inch pots with Metro Mix® Redi Earth growing medium (40-50% peat moss; 50-60% medium vermiculite), thinned to 1 plant per pot when plants reached the 1st true leaf stage, and maintained in a greenhouse at 65°F a 85°F during the trial. Untreated cantaloupe and watermelon plants colonized with melon aphid were interspaced between treated plants as an infestation source during the trial. A general purpose fertilizer was applied at the recommended greenhouse rate, triadimefon was misted over plants with a spray bottle at the recommended rate for powdery mildew control, and plants were irrigated as needed by adding water to plastic trays used to hold each pot. All treatments were applied as a soil drench around the base of each plant after pretreatment counts. Four oz total volume was used for each treatment and the untreated control received 4 oz of water alone. The total number of aphids were counted on three leaves per plant, and each leaf was marked and resampled 3 (1st trial); 4, 6, 8, and 10 DAT (2nd trial). Linear regression analysis was used to determine relationships between aphicide rate and mean number of aphids per leaf. Data were analyzed for treatment differences using analysis of variance and means were separated with Ryan-Einot-Gabriel-Welsch multiple range tests (P ≤ 0.10).

Juvenility, Flowering, and the Effects of a Limited Inductive Photoperiod in Coreopsis grandiflora and C. lanceolata

Juvenility and flowering requirements of Coreopsis grandiflora Hogg ex Sweet. `Sunray' and C. lanceolata L. `Early Sunrise' were examined by growing plants under short days (SD) and transferring them to long days (LD) upon reaching the designated true leaf stages. Neither cultivar flowered in continuous SD, and `Sunray' remained vegetative in LD. However, LD induced flowering in `Early Sunrise' plants in each leaf count treatment and the loss of juvenility was gradual, with most rapid flowering occurring when plants were transferred to LD at the 16 leaf stage. The limited inductive photoperiod (LIP) inhibited stem elongation of `Early Sunrise' plants in all LD treatments and selectively inhibited axillary flower bud development compared to plants grown in continuous LD. LIP did not affect scape length at first flower even though plant height was significantly diminished if given relatively few LD before transfer to SD. Height reduction was attributed to LIP inhibition of stem elongation with no significant loss of axillary flower bud potential.

Relationships between turnip root fly (Delia floralis) larval development and the sugar content of swede (Brassica napus ssp. rapifera) roots

SummaryEight genotypes of swede (Brassica napus L. ssp. rapifera [Metz.] Sinsk.) at the 8–10 true leaf stage were inoculated with five, 10 or 20 eggs of the turnip root fly Delia floralis (Fall). The roots were sampled, with control roots, after 6 weeks of larval development. D. floralis root damage, as measured by reduction in root weight, was found to be linked to inoculation level. Neither D. floralis egg numbers nor swede genotype had a significant effect on the percentage of larvae developing to pupation. Mean pupal weight varied by a factor of ×1.4 and consistently decreased with increasing egg inoculation level. Changes in the root concentrations of glucose, sucrose and fructose were measured. All swede genotypes showed a similar response in their sugar concentrations after root damage. Glucose and fructose concentrations were reduced whilst sucrose concentration remained unaffected. The concentrations of glucose and fructose were highly correlated. Pupal weight, used as a measure of larval development, was significantly correlated with the concentrations of individual and total sugars in the roots. The implications of sugar responses to damage in brassicas, and the correlation between sugar concentrations in the roots and D. floralis pupal weights are discussed.

INTERACTION BETWEEN IRRADIANCE AND PHOTOPERIOD ON ANTIRRHINUM MAJUS L. FLOWER INITIATION.

Antirrhinum majus L. cv `Winchester' seedlings (first true leaf stage) were placed in controlled environment chambers maintained at 20C under 8, 10, 12 or 14 hr photoperiods for flower induction. Seedlings were grown at irradiance levels of 240, 315, 380 or 460 μmol s-1 m-2 within each chamber. Plants were removed after 7, 14 or 21 days and were placed in a glasshouse maintained at 20 ± 2C under natural photoperiod and irradiance levels for flower development. Data were collected on flower number and number of nodes below the first flower when all flowers were visible on the inflorescence. Node number decreased from 67 to 43 nodes as photoperiod increased from 8 to 14 hrs. Increasing irradiance hastened flowering on plants grown under 8-12 hr photoperiods only and had no effect on flower number. Flower number increased from 23 to 30 as photoperiod length increased from 8 to 14 hrs. Node number decreased from 57 to 44 nodes and flower number increased from 22 to 31 flowers as the time of treatment increased from 7 to 21 days under the 14 hr photoperiod. Time of treatment had no effect on node number or flower number when plants were grown under 8 or 10 hr photoperiods.

GROWTH AND DEVELOPMENT OF CATHARANTHUS ROSEUS UNDER VARIOUS ENVIRONMENTAL CONDITIONS

In recent years, Catharanthus roseus has become a popular bedding plant, but at present there is little cultural information available for growers. This study examines the effects of four different temperature regimes and two light levels on three cultivars of Catharanthus. Average daily temperature regimes ranged from 15.3°C to 27.3°C; light intensities were 125 μmolm-2s-1 and 250 μmolm-2s-1. Plants were harvested as each successive pair of true leaves reached 1.5 cm in length, from the first true leaf stage until flowering. Measurements included internode length, leaf length, leaf area, dry weight of stem and leaves, and number and length of shoots. The plants grown at the lowest temperature regime took four times as long to flower as those grown at the highest temperature regime. Plants grown at the coolest temperature also exhibited chlorosis, stunting, and unusual flower formation. Information obtained from this study should assist growers in determining their planting schedule and the optimum greenhouse temperature for desired plant habit.

GENETICS OF RESISTANCE TO ALTERNARIA BRASSICICOLA IN BRASSICA OlERACEA

Initial screening indicated that 20° C and 100% RH using a 50,000 spores/ml concentration produced a severe test, but it was still possible to identify potential resistance. More than 600 Brassica spp. were screened at the 3-5 true leaf stage for resistance to Alternaria brassicicola, and selections were then subjected to a field screen. Disease severity scores ranged from 1 to 9, with 1 being most resistant and 9 most susceptible. Fourteen B. oleracea accessions representing cabbage, broccoli, cauliflower, kale, kohl rabi, brussels sprouts and chinese kale were selected as having potential resistance or tolerance. One B. napus accession was also selected for tolerance. Nine of the B. oleracea selections and three susceptible checks were included in a complete diallel. Resistance appears to be quantitative and partially dominant. Both general and specific combining ability effects were significant, but GCA is apparently more important in predicting the performance of the hybrid. The inheritance of resistance will be discussed.

Control of Flea Beetles on Canola with Insecticides Applied as Seed Treatments, 1992

Abstract This test was designed to evaluate fungicide and insecticide seed treatments against naturally occurring populations of plant pathogens and insects. The treated seed was planted at the MSU Post experiment farm near Bozeman on 4 May. Four row plots measuring 1.3 m x 6 m and seeded at 160 seeds/m2 were arranged in a randomized block design with 4 replicates. Flea beetle damage was assessed on young cotyledons 24 d after seeding. Stand density counts were made after the 4 true leaf stage. Three applications of Sevin insecticide were applied at approximately 2 wk intervals, starting at the time the plots were rated for flea beetle damage. Data collected were analyzed using analysis of variance. The statistical relationship between means was determined with Student-Newman-Keuls multiple comparison test at P = 0.05. In this test, the fungicides were chosen to control a wide spectrum of disease organisms.

Evaluation of Insecticide Efficacy for Spwf Control on Cucurrits, 1992

Abstract A small plot study was conducted to evaluate selected insecticides and combinations of insecticides for their efficacy against the SPWF in cucurbits. Cucumbers were planted in 40 inch beds with one guard row planted to sudan grass between each row. Experimental plots measuring one row by 25 feet were established shortly after plant emergence. Plots were arranged in a random complete block design with four replications. Insecticide applications were initiated at the three true leaf stage, with applications made on 1, 7 and 12 Oct, 1992. Insecticides were applied with the CO2 pressurized backpack sprayer (40 PSI), with three lOx hollow cone nozzles per row (1 overtop, 2 on drops), in a total volume of 50 GPA. Adult SPWF were monitored 24 hours after each application by counting the number of adults on the first fully expanded leaf from the growing terminal on three randomly selected plants per plot. For evaluation of immatures the 5th and 7th leaf were sampled on two randomly selected plants per plot. All immature SPWF were counted on two 2.2 cm diameter disks cut from each leaf (8 disks per plot).

Evaluation of Jojoba Oil Formulations for Spwf Control on Cucumbers, 1992

Abstract A small plot study was conducted in Weslaco, Texas to evaluate two formulations of jojoba oil for control efficacy against the SPWF on cucumbers. Experimental plots measured one row (40 in.) by 25 feet. Plots were separated by single row wind breaks of sudan grass. Treatments were initiated when plants were in approximately the 3 true leaf stage. Treatments consisted of jojoba oil mixed with lauryl sulfate and a premix jojoba oil. Applications were made with a CO2 pressurized backpack sprayer at 40 PSI, with 3 lOx hollow cone nozzles per row (1 overtop, 2 on drops) in a total volume of 50 GPA. Applications were made on 1, 7 and 12 Oct 1992. Adult SPWF were monitored 24 hours after each application by counting the number of adults on the first fully expanded leaf from the terminal on three plants in each plot. Immature stages were monitored on 9 and 14 Oct on two randomly selected plants per plot. Two leaves were removed from each plant (4th and 6th leaf from the terminal on 9 Oct; 5th and 7th leaf from the terminal on 14 Oct) and brought into the laboratory for counting. Two 2.2 cm diameter disks were cut from each leaf using a cork borer and the total number of immatures were counted on these disks (8 disks per plot).

Effects of pretransplant nutrient conditioning on elemental accumulation in tomato seedlings

Tomato seedlings ( Lycopersicon esculentum Mill. H2653, ‘Heinz Canada’), grown in 288 cell (6.4 cm 3 volume) plug trays, were fertilized daily with solutions containing (mg l −1) either 75 nitrogen (N), 32 phosphorus (P) and 62 potassium (K) or 150 N, 64 P and 124 K up to the four true leaf stage. Thereafter, seedlings were pretransplant nutrient conditioned (PNC) for up to 12 days with solutions containing N, P and K at concentrations (mg l −1) of: 0, 0 and 0; 75, 32 and 62; 150, 64 and 124; 300, 128 and 248; and 450, 194 and 374. Shoot tissue soluble NO 3-N and total N, P and K concentrations changed significantly within only 3–5 days of PNC in response to modification of elemental concentration in nutrient solutions. Differences in shoot dry weight were not apparent until 8–12 days after alteration of PNC concentrations. The withholding of nutrients significantly depleted the pool of soluble nitrate with as few as 5 days. PNC of small plug tomato seedlings with nutrient solution containing (mg l −1) 300 N, 128 P and 248 K for approximately 5 days resulted in maximal enhancement of elemental content and concentration in shoot tissue with minimal effect on shoot growth rate.

Effect of Application Rate, Weed Species, and Weed Stage of Growth on Imazethapyr Activity

Field experiments were conducted in 1986, 1987, and 1988 to evaluate imazethapyr rate and time of application on postemergence control of 24 weed species. Contour graphs were developed that predicted imazethapyr rates required for various levels of weed control based upon weed leaf number at application. Rates below the labeled rate (70 g ha−1) provided 90% or greater control of common cocklebur, smallflower morningglory, and smooth pigweed if applied to 3 true-leaf or smaller weeds and of barnyardgrass, seedling johnsongrass, and Palmer amaranth if applied while weeds were in the cotyledon or 1 true-leaf stage. A rate of 70 g ha−1provided 90% control of large crabgrass in the 1 true-leaf stage. Entireleaf morningglory, red rice, pitted morningglory, and velvetleaf are not susceptible enough to imazethapyr for 90% or greater control to be obtained with rates lower than 70 g ha−1at the 1 true-leaf growth stage. These data demonstrate how control data can be used for developing effective reduced-rate herbicide recommendations based on weed leaf number.

INHERITANCE OF CHILLING RESISTANCE IN CUCUMBER

Cucumber (Cucumis sativus L.) is one of the more chilling sensitive crops. Chilling resistance could provide growers with protection against late spring frost. Significant differences for chilling resistance were observed among a set of 9 diverse cucumber cultigens when grown at 22 C to 1st true leaf stage, then given a chilling treatment of 4 C for 7 hours in full light (PPFD 500 μmol.m-2.s-1). Two populations, NCWBP and NCES1, were used to measure narrow-sense heritability (estimated as twice the parent-offspring regression coefficient) for chilling resistance. Sets (256/population) of parents and offspring were evaluated in separate tests for seedling resistance. Plants were rated for damage 0 (none) to 9 (dead) on the cotyledons and 1st true leaf, 3 and 5 days after chilling. Ratings were corrected for position in the Phytotron chamber, and log transformations used to normalize the data. Generally, correction reduced the heritability estimates and transformation improved them. Heritability was highest for cotyledon ratings made 5 days after chilling, ranging from 0.35 for NCWBP to 0.70 for NCES1. Ratings of the 1st true leaf were more difficult to make, and produced lower estimates of heritability. Breeders should be able to make good progress in selecting for chilling resistance using this seedling test.