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Yingmou Yao and Peter M.A. Tigerstedt

Genetic variation in growth rhythm, hardiness and height of 24 populations from 3 subspecies in sea buckthorn (Hippophae rhamnoides) were studied in a field test. The relative variance component of subspecies varied from 26.2% to 73.7% of total variance. Subspecies turkestanica had a growth mode of late start-late finish, ssp. rhamnoides, intermediate start-early finish and ssp. sinensis, early start-intermediate finish. Subspecies rhamnoides had a growth period of 129 days, ≈30 days shorter than the two Asian subspecies. The average height of ssp. rhamnoides was 43.7 cm, about one-third of that for ssp. tarkestanica and sinensis. Subspecies rhamizoides was more hardy than ssp. sinensis, which was still more hardy than ssp. turkestanica. The variance among populations was generally comparable with within population variance. Except for hardiness, variations for all characters were much larger in ssp. rhamnoides than in ssp. sinensis. The total genetic variance (subspecies plus population) varied from 50% to 84% of total variance for all characters, except 37% for secondbracts. Later growth cessation was correlated with longer growth period, taller plants, more severe frost and winter damage. Strong clinal variation showed that the higher the latitude, the earlier the growth cessation, the shorter the growth period and plant height, the more hardy the population. -The results indicated that population selection should bean efficient way for growth rhythm and plant height. Clinal variation provides guidelines for seed and plant transfer as well as plant introduction. With limited collection and management capacity in germplasm conservation, the recommendation is to collect fewer individuals in each population but more populations along latitude.

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J. Roger Harris, Nina L. Bassuk, Richard W. Zobel, and Thomas H. Whitlow

The objectives of this study were to determine root and shoot growth periodicity for established Fraxinus pennsylvanica Marsh. (green ash), Quercus coccinea Muenchh. (scarlet oak), Corylus colurna L. (Turkish hazelnut), and Syringa reticulata (Blume) Hara `Ivory Silk' (tree lilac) trees and to evaluate three methods of root growth periodicity measurement. Two methods were evaluated using a rhizotron. One method measured the extension rate (RE) ofindividual roots, and the second method measured change in root length (RL) against an observation grid. A third method, using periodic counts of new roots present on minirhizotrons (MR), was also evaluated. RE showed the least variability among individual trees. Shoot growth began before or simultaneously with the beginning of root growth for all species with all root growth measurement methods. All species had concurrent shoot and root growth, and no distinct alternating growth patterns were evident when root growth was measured by RE. Alternating root and shoot growth was evident, however, when root growth was measured by RL and MR. RE measured extension rate of larger diameter lateral roots, RL measured increase in root length of all diameter lateral roots and MR measured new root count of all sizes of lateral and vertical roots. Root growth periodicity patterns differed with the measurement method and the types of roots measured.

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S. Pérez, S. Montes, and C. Mejía

A wide range of peach [Prunus persica (I,.) Batsch] germplasm was collected from the most important peach growing regions in Mexico and some Latin American countries, as well as from breeding programs in the United States, Europe, and South Africa. Budded trees, seedlings derived from selfing cultivars and selections, and seed samples from various growing regions were propagated and planted in central Mexico. Twenty eight morphological or phenological variables were recorded on 52 accessions representing different geographic regions. The highest degree of variability was observed for traits related to bud density and distribution, and to phenological variables associated with temperature requirements such as budbreak and harvest seasons, leaf fall, fruit development, and seed stratification period. Principal component analysis (PCA) integrated groups of phenotypes based mainly on growth habit, shoot diameter, bud and leaf size, as well as resistance to powdery mildew, rust, and frost. PCA provides support for the development of objectives and breeding strategies in the search for germplasm and cultivars for nontraditional peach growing regions.

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L.J. Grauke and J.W. Pratt

Seven open-pollinated pecan [Carya illinoinensis (Wangenh.) K. Koch] stocks were grown in a nursery in blocks. Bud growth of ungrafted seedlings was influenced by rootstock, with growth being more advanced on `Curtis', `Elliott', `Apache', and `Sioux' seedlings than on `Moore', `Riverside', and `Burkett'. Bud growth of grafted trees was influenced by scion, with growth of `Candy' being most advanced, while `Cape Fear' trees were more advanced than `Stuart'. Growth of `Candy' grafted trees was affected by rootstock, with growth being more advanced on `Elliott' and `Curtis' seedling rootstock as compared to `Apache', Sioux', `Riverside', and `Burkett' seedling rootstock. Tree damage caused by a May freeze was directly related to bud growth and was influenced by scion and rootstock.

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Dennis E. Deyton, Carl E. Sams, Jim R. Ballington, and John C. Cummins

`Legacy' southern highbush blueberry plants at the Middle Tennessee Research and Education Center were sprayed on 22 Feb. 2005 with 0%, 6%, 9%, or 12% soybean oil. The treatments were arranged in a randomized complete-block design with five replications. Flower bud abortion was evaluated by sampling 25 flower buds/plant on 21 Mar., dissecting, and visually examining buds for browning of ovaries. Flower bud phonology was rated periodically until first bloom and then percentage of open bloom was rated every 2 to 3 days. Fruit were harvested for yield and 50-berry samples taken weekly for the first 4 weeks to determine berry size. Sprays of 6%, 9%, and 12% soybean oil delayed the 50% open bloom date of `Legacy' by 2, 4, and 9 days, respectively, but also caused 9%, 35% and 87% mortality of flower buds. `Legacy' bushes sprayed with 0%, 6%, 9% and 12% soybean yielded 11.6, 13.7, and 10.3, and 4.5 lb/bush, respectively. Berry size was increased by 14% to 23% by oil sprays. In a second experiment, `Climax' blueberries in a commercial planting in Spring City, Tenn., were sprayed on 4 Mar. with water, 5% TNsoy14 (96% soybean oil, a.i.), 500 ppm abscisic acid (ABA) (Valent BioSciences Corp., Long Grove, Ill.), or the combination of oil and ABA (seven replications). Flower bud development and bloom were rated as previously described. Spraying 5% TNsoy14 or 500 ppm ABA delayed the 50% open bloom date by 1 day and the combination of the two delayed bloom by an additional day. On 5 Apr., `Climax' bushes sprayed with 5% TNsoy14, 500 ppm ABA, and 5% TNsoy14 plus 500 ppm ABA had 49%, 41%, and 20% open bloom compared to 70% open bloom on control plants. The 5% oil, 500 ppm ABA, and the oil plus ABA treatments did not significantly affect crop load or berry size.

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B.T. Scully and D.H. Wallace

A diverse set of 112 common bean (Paseolus vulgaris L.) accessions were evaluated for variation in eight traits related to yield over a 2-year period. Days to flower, days of pod fill, and days to maturity ranged from 25 to 66, 44 to 83, and 70 to 133, respectively, in upstate New York: Yield and biomass ranged from 81 to 387 and 270 to 1087 g•m-2, respectively. Harvest index ranged from 12% to 65%. The biomass (biomass/days to maturity) and seed (yield/days of pod fill) growth rates ranged from 3.2 to 9.3 and 1.2 to 9.5 g•m-2 -day-1, respectively. The economic growth rate (yield/days to maturity) extended from 0.6 to 5.7 g•m-2 -day-1. The growth rates, biomass, and days of pod fill were linearly and positively related to yield. Biomass and the growth rates explained a large amount of the variation in yield, with r 2 values between 0.71 and 0.84; days of pod fill explained the least, with r 2 = 0.09. Yield followed a curvilinear relationship with days to flower and days to maturity; yield was maximized at 48.5 days to flower and 112.2 days to maturity. Yield was a quadratic function of harvest index and maximized at 57.2%. Among these three curvilinear traits, days to flower explained 80% of the variation in yield, while days to maturity and harvest index accounted for 25% and 12.5%, respectively. The “ideal” genotype for New York was defined at these maximum values for harvest index, days to maturity, days to flower, and at 63.7 days of pod fill. Additionally, a simple equation is proposed to aid breeders in the selection of common bean accessions with strong sink strength. It is defined as “relative sink strength”: RSS = seed growth rate/biomass growth rate. Values > 1.0 implied strong sink capacity in common beans.

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P.A.W. Swain and R.L. Darnell

Two cultivars of southern highbush blueberry (Vaccinium corymbosum L. interspecific hybrid), `Sharpblue' and `Wannabe', were container-grown outside in either a dormant or nondormant production system to determine how the two production systems affected carbohydrate (CH2O) status, growth, and development. Plants were maintained in the nondormant condition by continuous N fertilization throughout winter (average maximum/minimum temperatures of 17/5 °C). Plants in the nondormant system retained their foliage longer into the winter compared with plants in the dormant system. Flower bud number, density, fruit number, and total fruit fresh weight (FW) per plant were greater in the nondormant compared with the dormant system plants for both cultivars. Mean fruit FW was greater in dormant compared with nondormant `Wannabe' plants, while in `Sharpblue', mean fruit FW was similar in both systems. Cane and root CH2O concentrations in nondormant system plants were generally similar to or lower than those measured in dormant system plants. Assuming that longer leaf retention in nondormant system plants increased CH2O synthesis compared with dormant system plants, the patterns of reproductive/vegetative development and root/shoot CH2O concentrations indicate that the increased CH2O in nondormant system plants was allocated to increased reproductive growth in lieu of CH2O reserve accumulation. It is probable that this increased CH2O availability, combined with longer perception of short days due to longer leaf retention, were major factors in increasing flower bud initiation and yield in the nondormant compared with the dormant system plants.

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B.T. Scully, D.H. Wallace, and D.R. Viands

One-hundred-twelve common bean (Phaseolus vulgaris L.) lines of diverse origin were grown in three environments in 1986 and two environments in 1987. The purpose was to estimate broad-sense heritabilities of nine yield-related traits and the phenotypic, genetic, and environmental correlations among them. The traits and their heritabilities were seed yield (0.90), biomass (0.93), harvest index (0.92), days to maturity (0.96), days to flower (0.98), days of pod fill (0.94), biomass growth rate (biomass/days to maturity) (0.87), seed growth rate (seed yield/days of pod fill) (0.87), and economic growth rate (seed yield/days to maturity) (0.86). These high heritabilities were attributed to the broad genetic diversity and the comparatively small variances associated with the genotype × environment interactions. Genetic correlations of yield were: with biomass, 0.86; harvest index, 0.42; days to maturity, 0.40; days to flower, 0.33; days of pod fill, 0.24; biomass growth rate, 0.92; seed growth rate, 0.84; and the economic growth rate, 0.85. The concomitant phenotypic correlations were mostly equal to the genetic correlations for biomass and the three growth rates, but lower for the phonological traits (days to maturity, flower, and pod fill). Harvest index had the lowest correlations with yield. Correlations were also reported for the other 28 pairwise combinations among these nine traits. Indirect selection was explored with yield as the primary trait and the other eight as secondary traits. Estimates of relative selection efficiency (p) suggested that indirect selection was not a viable option for increasing common bean yields or identifying superior parents.

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Georgios Psarras, Ian A. Merwin, Alan N. Lakso, and John A. Ray

A 2-year field study of `Mutsu' apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] on `Malling 9' (M.9) rootstock was conducted to observe root growth in situ, and compare patterns of root growth, root maturation and turnover rates, and soil-root respiration. Rhizosphere respiration was monitored with a portable chamber connected to an infrared gas analyzer; root emergence, browning, and turnover rates were measured by direct observation through minirhizotron tubes inserted in the root zone. Negligible root growth was observed before the onset of shoot growth in mid-May. In both years, a main peak of new root emergence in late June and early July coincided partially with major phases of shoot and fruit growth. A smaller peak of root emergence during August to September 1997 consisted primarily of new roots at 20 to 45 cm soil depths. Most roots remained <1 mm in diameter and developed in the upper 25 cm soil profile; no roots were observed at any time below 50 cm, due to a compacted soil layer at that depth. The cumulative survivorship of new roots was 38% in 1996 and 64% in 1997, and 50% of emergent white roots turned brown or senesced within 26 days in 1996 and 19 days in 1997. Root turnover rates were highest in mid-August both years. Rhizosphere respiration was correlated (r 2 = 0.36 and 0.59, P = 0.01 and 0.004) with soil temperatures in 1996 and 1997, with Q10 values of 2.3 in both years. The Q10 for root-dependent respiration (the difference between soil only and combined soil-root respiration) in 1997 was 3.1, indicating that roots were more sensitive than soil microflora to soil temperature. The temporal overlap of high rates of shoot, root and fruit growth from late May to mid-July suggests this is a critical period for resource allocations and competition in temperate zone apple trees.

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Robert J. Dufault, Brian Ward, and Richard L. Hassell

The objective of this study was to determine the best combination of planting dates (PDs) and cultivars on yield and quality for long-term production of romaine lettuce. `Green Forest' (GF), `Apache' (AP), `Darkland' (DK), `Green Tower' (GT), `Ideal Cos' (IC), and `Tall Guzmaine' (TG) were successfully grown to harvest maturity on 19 PDs from September 1998 to April 2001. Lettuce planted in September and April PDs (pooled over cultivars and year), required as little as 47 and 49 days, respectively, to reach harvest (all cultivars harvested on the same day). Lettuce planted in October, November, February, and March PDs (pooled over cultivars and year), required on average 64, 66, 75, and 67 days to reach harvest, respectively, but in the coldest PDs of December and January, 90 and 98 days, respectively, were needed to reach maturity. Of the eight PDs evaluated, marketable numbers/plot (pooled over cultivars and years) were greatest in the September PD, followed by April (–8% decrease from September PD) > March (–13%) > October (–17%) > November (–21%) > December = January = February (about –30%) and heads weighed the most in September > January = February (–7% decrease from September PD) > March = April (–14%) > October (–21%) > December (–25%) > November (–31%). Cull heads/plot (pooled over cultivars and years) were greatest in April > December (–5% decrease from April PD) > January = February (–16%) > November (–27%) > October (–34%) > March (–44%) > September (–49%). Two out of three November PDs were lost to freezing damage and this PD should be avoided. Significant bolting occurred primarily in the September and October PDs (in 1 of 3 years) with negligible bolting in the November, December, and January PDs, but bolting recurred again in the February, March and April PDs. Marketable numbers/plot (pooled over all PDs and years) were greatest for GF > GT (–7% decrease from GF) > AP (–8%) > IC (–9%) > DK (–11%) > TG (–21%). The interaction effect of cultivar × PD indicated that GF yielded the most marketable heads in 6 out of 8 PDs. The best performing cultivars by PD (pooled over years) were September and February = GF and IC; October = TG; November = AP; December, January, March, and April = GF.