Taproot Diameter Research Articles

Classification study of Coptis chinensis based on quantitative physical property characteristics of appearance and internal quality evaluation

Combining the quantitative physical property characteristics of the appearance with the internal quality evaluation index, its aims to provide experimental basis for the classification and quality evaluation of Coptis chinensis. Fourteen batches of C. chinensis from different areas were respectively measured in size (total length, total width, root length, taproot diameter, branch number, branch length, branch diameter, length of the bridge, weight), color (external color, internal color), content (epiberberine, coptisine, palmatine, berberine). Then the determination data were evaluated by spss principal component analysis and cluster analysis. Three principal components were extracted from the original data. The principal component analysis results showed that the characteristic elements might be the total length, main root length, taproot diameter, branch length, weight, the total color value of the appearance and content of epiberberine and berberine. The results of cluster analysis showed that 14 batches of samples could be clustered reasonably into two groups. In terms of the appearance and quality, there were some differences between in the geo-authentic and non-authentic producing areas of C. chinensis. The method which was combining the quantitative physical property characteristics of the appearance with the internal quality evaluation index, and through the processing of mathematical statistics, could be used for the the classification of C. chinensis.

Stimulation of Short-term Plant Growth by Glycerol Applied as Foliar Sprays and Drenches under Greenhouse Conditions

The effects of aqueous solutions applied as foliar spray and drench applications of glycerol were tested on the ‘Chantenay’ carrot (Daucus carota L.) family Apiaceae, corn (Zea mays L.) family Poaceae, and spearmint (Mentha spicata L.) family Lamiaceae under greenhouse conditions. Foliar sprays and drenches were administered to carrots at concentrations of 0, 1, 3, 5, 10, 25, or 50 ml·L−1. Fresh weights, dry weights, and taproot diameter from carrot seedlings sprayed with a solution containing 5 mL·L−1 (50 mm) glycerol increased 105.6%, 158.4%, and 53.8%, respectively, when compared with untreated carrots. Foliar sprays were administered to corn at concentrations of 0, 0.1, 0.3, 0.5, and 1 ml·L−1 and spearmint at concentrations of 0, 1, 5, and 10 mL·L−1. Growth responses increased in corn and spearmint by using certain glycerol concentrations. Fresh weights, dry weights, and shoot length from corn seedlings sprayed with a solution containing 0.5 mL·L−1 (5 mm) glycerol increased 83.5%, 154.6%, and 90.9%, respectively, when compared with untreated corn. Fresh weights, dry weights, and shoot length from mint plants sprayed with a solution containing 5 mL·L−1 (50 mm) glycerol increased 46.6%, 68.7%, and 102.5%, respectively, when compared with untreated plants. Glycerol applications can stimulate growth responses in diverse plant species.

The development of lucerne root morphology traits under high initial stand density within a seven year period

The root system of plants is generally regarded as a factor, which is in relation to important agronomic and ecological characteristics. The aim of this study was to investigate the effect of high initial stand density on the reduction in development of lucerne root morphology traits and how long-term this effect would be. In spring 2003, a field experiment with six lucerne entries in randomized blocks was established. Broadcast sowing was used and the seeding rate was 5000 germinated seeds per m2. In 2003–2009, the plants were sampled in each plot in autumn; the average depth of sampling was 0.2 m. The stand density reached an average value of 860 plants per m2 in the autumn of the seeding year and this strongly reduced the root weight, tap-root diameter, position and number of lateral roots. The subsequent decrease of stand density to 57 plants/m2 in 2009 was not linear but it was extremely quick from the 1st to 2nd year and, by contrast, it was extremely slow in the last three years. It indicates that older plants with larger tap-root diameter probably have a higher persistency. All evaluated root traits were developed slowly, nevertheless, they reached common values during a seven year period. The intensity of the relation of stand density to root weight or tap-root diameter increased over time whilst it decreased to the ratio of root-branched plants. Results suggest that an assessment of density in samples should be recommended for the varieties evaluation in case of irregularly-spaced plants because the differences in root morphology among varieties could be caused by the differences in density among the varieties. It is possible to conclude that lucerne stands under higher initial density provided a strongly reduced speed of root development with an impact on important agronomic traits connected with root morphology.

Severity of root rot in mature subterranean clover and associated fungal pathogens in the wheatbelt of Western Australia

Pasture decline is considered to be a serious challenge to agricultural productivity of subterranean clover across southern Australia. Root disease is a significant contributing factor to pasture decline. However, root disease assessments are generally carried out in the early part of the growing season and in areas predominantly sown to permanent pastures. For this reason, in spring 2004, a survey was undertaken to determine the severity of root disease in mature subterranean clover plants in pastures located in the wheatbelt of Western Australia. DNA-based soil assays were used to estimate population density in the soil of a variety of soil-borne pathogens known to commonly occur in the Mediterranean-type environments of southern Australia. The relationships between severity of disease on tap and lateral roots and root diameter, root length, nodulation, and total rainfall were determined. The survey showed, for the first time, that severe root disease is widespread in spring across the wheatbelt of Western Australia. There was a positive correlation between rainfall and tap root disease, and between tap root disease and average root diameter of the entire root system. Despite the high levels of root disease present across the sites, the DNA of most root disease pathogens assayed was detected in trace concentrations. Only Pythium Clade F showed high DNA concentrations in the soil. DNA concentrations in the soil, in particular for Phytophthora clandestina and Rhizoctonia solani AG 2.1 and AG 2.2, were higher in the smaller autumn sampling in 2006. This study suggests that the productivity of subterranean clover-based pastures is severely compromised by root rot diseases throughout the growing season in the wheatbelt of Western Australia.

Shifts in plant nutrient use strategies under secondary forest succession

In evergreen broad-leaved forests (EBLFs) in Tiantong National Forest Park, Eastern China, we studied the soil chemistry and plant leaf nutrient concentration along a chronosequence of secondary forest succession. Soil total N, P and leaf N, P concentration of the most abundant plant species increased with forest succession. We further examined leaf lifespan, leaf nutrient characteristics and root–shoot attributes of Pinus massoniana Lamb, the early-successional species, Schima superba Gardn. et Champ, the mid-successional species, and Castanopsis fargesii Franch, the late-successional species. These species showed both intraspecific and interspecific variability along succession. Leaf N concentration of the three dominant species increased while N resorption tended to decrease with succession; leaf P and P resorption didn’t show a consistent trend along forest succession. Compared with the other two species, C. fargesii had the shortest leaf lifespan, largest decay rate and the highest taproot diameter to shoot base diameter ratio while P. massoniana had the highest root–shoot biomass ratio and taproot length to shoot height ratio. Overall, P. massoniana used ‘conservative consumption’ nutrient use strategy in the infertile soil conditions while C. fargesii took up nutrients in the way of ‘resource spending’ when nutrient supply increased. The attributes of S. superba were intermediate between the other two species, which may contribute to its coexistence with other species in a wide range of soil conditions.

Effects of climatic factors, fluctuating water availability and partial defoliation on the diurnal radial growth pattern of carrot (Daucus carota) taproots

Carrot taproots are prone to radial longitudinal tissue fractures (splitting). The longitudinal alignment of the fractures is consistent with the tangential stress induced by radial growth in the annular cambium. In this study linear variable differential transformers were used to monitor the diurnal radial growth pattern of mature carrot taproots. The diurnal growth pattern was characterised by rapid expansion during the night (dark) period and small shrinkage during the light period. The magnitude of the daily shrinkage was positively correlated with both vapour pressure deficit and global radiation. A positive correlation between the rate of taproot expansion during the night period and global radiation level the preceding day was also recorded. Water stress reduced the taproot night time expansion rate, but the taproot of water stressed plants expanded rapidly when watered to field capacity. Partial defoliation of plants at midday resulted in immediate expansion of the taproot, however, the daily growth rates of the partially defoliated plants was less than untreated control plants over the following 3 days. It was concluded that the short-term changes in taproot diameter could be used to infer changes in tangential stresses and therefore taproot splitting propensity.

Early growth of Brazilian pine (Araucaria angustifolia[Bertol.] Kuntze) in response to soil compaction and drought

Soil compaction leads to changes in soil physical properties such as density, penetration resistance and porosity, and, by consequence, affects root and plant growth. The initial growth of Brazilian pine is considered as being more affected by soil physical than chemical conditions, and the presence of a well-developed tap root system has been associated with this fact. A greenhouse experiment was conducted in order to evaluate the impact of soil compaction on the growth of Brazilian pine seedlings and on their susceptibility to a simulated drought period. In the first phase of the experiment, the effects of three levels of soil compaction on root morphology and plant growth were examined. Soil cylinders were artificially compacted in PVC tubes. Pre-germinated seeds were planted, and 147 days later 10 plants from each treatment were harvested for analysis. Higher values of soil density were associated with a shorter and thicker tap root. Growth of lateral roots and shoots remained unaffected at this stage. In the second phase, half of the plants (12) in each compaction treatment were drought-stressed by withholding water for a period of 77 days. Increased soil compaction again resulted in reduced length and increased diameter of the main tap root. This time, the effects were also extended to the lateral roots. Shoot extension growth and overall plant mass, however, increased with soil compaction. This greater mass accumulation in plants growing under increased soil compaction may be attributed to a more intimate contact between roots and soil particles. Drought stress reduced both root and shoot growth, but root mass was more negatively affected by drought stress in plants growing under high levels of soil compaction. Future investigations on the effects of soil compaction on the initial growth of Brazilian pine should include a wider range of compaction levels to better establish the relationship between soil physical parameters and plant growth.

Influence of nutrient solution concentration and a root pathogen ( Pythium aphanidermatum) on tomato root growth and morphology

Young roots, especially those in the root hair zone, are most important for nutrient uptake. However, these roots are also sensitive to high nutrient solution concentration and root pathogens, major problems in soilless culture systems. Supply of nutrient solution at a constant electrical conductivity (EC) can increase the EC in the root environment up to 10 dS m −1. Pythiaceae are among the most important root pathogens in soilless systems. Therefore, investigations were carried out to quantify and compare root damage by high nutrient solution EC and by Pythium aphanidermatum (Edson) Fitzp. Three tomato plants at two-leaf-stage ( Lycopersicon esculentum [Mill] L. cv. Counter) were transferred to a 2 l container filled with aerated nutrient solution. They grew in climate chambers for 14 days (16 h light 600 μmol m −2 s −1, 30/25 °C day/night). In one experiment, a basic nutrient solution of 1.5 dS m −1 was supplemented with either NaCl or macronutrients to give an EC of 1.5, 5 or 9 dS m −1. In another experiment, plants were inoculated with P. aphanidermatum (0, 10 2, or 10 4 oospores ml −1 solution). All treatments were replicated five and four times, respectively. On days 3, 7, 10, and 13 after treatment one plant was sampled from each container. Fresh and dry mass of shoots and roots, total root length, number of adventitious roots and of all tap root laterals decreased with increasing nutrient solution EC. Dry matter content of roots and tap root diameter were not influenced while shoot dry matter content increased with increasing EC. NaCl enhanced root fresh matter, tap root diameter, total root length and number of adventitious roots compared with the macronutrient treatment. On the contrary shoot dry matter content and number of all laterals were reduced by NaCl. Three days after inoculation with P. aphanidermatum the number and length of roots were reduced significantly by the treatment 10 4 oospores ml −1. P. aphanidermatum effects were greatest on young and thin roots, particularly those of the second and third laterals. Reduction increased with time and increasing number of inoculated oospores. Root diameters were greatest in the treatment with 10 4 oospores ml −1. Results confirm that attempts to extrapolate results obtained on average root systems to single root formation could be misleading. Furthermore, a tomato plant can compensate to some extent its water uptake of a root system reduced by nutrition or pathogen effects.

Modeling in-situ pine root decomposition using data from a 60-year chronosequence

Because the root system of a mature pine tree typically accounts for 20–30% of the total tree biomass, decomposition of large lateral roots and taproots following forest harvest and re-establishment potentially impact nutrient supply and carbon sequestration in pine systems over several decades. If the relationship between stump diameter and decomposition of taproot and lateral root material, i.e., wood and bark, can be quantified, a better understanding of rates and patterns of sequestration and nutrient release can also be developed. This study estimated decomposition rates from in-situ root systems using a chronosequence approach. Nine stands of 55- to 70-year-old loblolly pine (Pinus taeda L.) that had been clear-cut 0, 5, 10, 20, 25, 35, 45, 55, and 60 years ago were identified on well-drained Piedmont soils. Taproot and lateral root systems were excavated, measured, and weighed. Although more than 50% of the total root mass decomposed during the first 10 years after harvest, field excavations recovered portions of large lateral roots (>5 cm diameter) and taproots that persisted for more than 35 and 60 years, respectively. Results indicate that decomposition of total root biomass, and its component parts, from mature, clear-cut loblolly pine stands, can be modeled with good precision as a function of groundline stump diameter and years since harvest.

Herbicides, weeds and endangered species: management of bitou bush ( Chrysanthemoides monilifera ssp. rotundata) with glyphosate and impacts on the endangered shrub, Pimelea spicata

Environmental weed invasion threatens the biodiversity of native species. Unfortunately, managing these weeds may also affect biodiversity adversely. A recent example occurred when glyphosate, a herbicide used to control the highly invasive weed, bitou bush ( Chrysanthemoides monilifera ssp. rotundata), accidentally drifted over a small population of an endangered shrub, Pimelea spicata. Following concerns that the affected population would not recover and, thereby, cause the local extinction of P. spicata, we conducted a series of glasshouse and field experiments to explore the impacts of glyphosate on this endangered species. Seedlings and young plants of P. spicata, in which the tap root was undeveloped, were killed by a single application of glyphosate. Older plants with a well developed tap root also died back initially, but about 50% of individuals re-sprouted. This re-growth was associated with a significant decrease in tap root diameter, implying that further disturbance, including repeated treatment with glyphosate, would kill plants by impairing their potential for recovery. Unlike some sclerophyllous native shrubs, the tolerance of P. spicata to glyphosate was limited, even when its growth was slowed artificially by limiting water availability. Winter applications of glyphosate to manage infestations of bitou bush will impact adversely on populations of P. spicata and may also affect the other rare and endangered species whose survival is threatened by this species, even though some natives are unaffected by the herbicide. Protecting native biodiversity from bitou bush will involve sustainable weed management that minimises impacts on non-target native species.

Root distribution of Senna siamea grown on a series of derived-savanna-zone soils in Togo, West Africa

Although crucial for assessing the functioning of alley cropping systems, quantitative information related to the hedgerow tree root distribution remains scarce. Soil mapping and destructive soil sampling was used to assess the impact of soil profile features on selected root characteristics of Senna siamea hedgerows, growing in alley cropping systems in three sites (Glidji, Amoutchou, and Sarakawa) representative for the derived savanna of Togo, West Africa. While the soil profiles in Glidji and Sarakawa contained a clay accumulation horizon, the Amoutchou profile was sandy up to 1 m. The number of small roots (diameter < 2 mm), quantified on a soil profile wall, decreased with depth in all sites. For most soil depths, the abundance of small roots tended to be higher near the tree base, e.g., ranging from 5.3 dm−2 in Amoutchou to 21.4 dm−2 in Glidji for the 0–20 cm layer, than in the middle of the alley, e.g., ranging from 3.1 dm−2 in Amoutchou to 13.8 dm−2 in Glidji for the 0–20 cm layer. Root length density (RLD) of the 0–10 cm and 10–20 cm layers was significantly higher in Glidji than in Amoutchou (P < 0.05) and in Sarakawa (P = 0.08). Differences in RLD between sites were not significant for layers below 30 cm. For each layer, root weight densities (RWD) were similar in all sites, e.g., ranging from 0.44 mg cm−3 in Amoutchou to 0.64 mg cm−3 in Glidji in the 0–10 cm layer, indicating that the roots in the Glidji topsoil had a smaller overall diameter than in Amoutchou. In Amoutchou, the relative RLD was lower than in Glidji or Sarakawa for the top 40 cm of soil, while the inverse was observed for the layers between 50 and 100 cm deep and this was related to the sandy soil profile in Amoutchou. Another consequence of the sandy profile was the larger tap root diameter below 50 cm in Amoutchou compared to Sarakawa. For all sites, significant (P < 0.001) linear regressions were observedbetween RLD's, RWD's, and the abundance of small roots, although the variation explained by the regression equations was highest for the relationship between RLD and RWD. The potential of the hedgerows to recover nutrients leached beyond the reach of food crops or the safety-net efficiency was evaluated for the tree sites.

A method to characterize root morphology traits in alfalfa

Productivity in alfalfa (Medicago sativa L.) has been shown to be influenced by root morphology. Our objectives were to identify the optimum age, cultural practices, and environmental conditions to characterize taproot diameter (TD), lateral root number (LRN), fibrous root mass (FRM), and determinate taproot percentage (DTP) in alfalfa. No correlations were found between greenhouse-cultured plants and 21-wk-old field-grown plants for LRN or FRM, while TD showed low to moderate correlations between greenhouse and field environments. Fourfold more plants with determinate taproots were identified in transplanted plots compared to seeded plots. All root traits were affected by plant spacing but, no germplasm × plant spacing interactions were found. Solid seeded plants needed more time to show maximum expression of root traits and scored lower for LRN and FRM and had smaller TD than spaced plants. Only TD had a significant germplasm × location interaction. Both TD and LRN increased with N fertilizer and between the seeding and first production years, but no germplasm × N rate or germplasm × year interactions were found. Rankings of alfalfa germplasms were the same at the end of the seeding year (22 wk after planting) and at the end of the first production year (74 wk after planting). Characterization of LRN and FRM in alfalfa should be conducted in seeded field plots with uniform plant spacing at one location, with or without N fertilizer at least 22 wk after planting. A similar protocol with evaluation at more than one location would be more appropriate for characterization of TD. Key words: Medicago sativa L., root morphology, alfalfa

Gain from Two Cycles of Divergent Selection for Root Morphology in Alfalfa

Alfalfa (Medicago sativa L.) has been identified for use in phytoremediation. Phytoremediation is defined as the use of green plants to remove or contain environmental contaminants. Alteration of root morphology would increase the degradative efficiency of alfalfa for phytoremediation. Root morphology traits in alfalfa are heritable, but are strongly influenced by dormancy and geographic origin. Our objective was to create alfalfa source germplasms that differ in root morphology within the same genetic background. Four experimental alfalfa germplasms differing in dormancy and genetic origin were evaluated after two cycles of divergent selection for root morphology traits. Two sources were selected for few vs. many lateral roots and the other two sources were selected for few vs. many fibrous roots followed by one subsequent cycle of selection for few vs. many lateral roots. These divergent populations were evaluated using two fertilizer rates (0 and 200 kg N ha−1) and were established twice at each of two locations. Plants from one experiment at each location were dug at the end of the establishment year and from the second experiment at the end of the first production year. All plants were evaluated for number of lateral roots, fibrous root mass, taproot diameter, plant count per plot, and plot root weight. Two cycles of divergent selection for root morphology traits in all four source germplasms produced alfalfa populations that differed in root morphology. Realized heritabilities from all germplasm sources ranged from 21 to 48% for fibrous root mass and from 11 to 43% for lateral root number. Response to selection varied among the four source germplasms and indicated that the choice of parent germplasm will be a factor for success in producing alfalfa populations that differ in root morphology within a single genetic source.

Root Morphology of Alfalfa Plant Introductions and Cultivars

Alfalfa (Medicago spp.) root morphology has a critical role in plant persistence and productivity traits. The objectives of this research were to evaluate root morphological traits for 1067 plant introductions (PIs) from diverse geographic origins and from 110 North American cultivars. All entries were grown in 2-m rows at the University of Minnesota Agricultural Experiment Station at Rosemount, MN. Plants from both studies were evaluated during autumn of the establishment year for taproot diameter (TD), lateral root number (LRN), lateral root diameter (LRD), lateral root position (LRP), and fibrous root mass (FRM). Variability was observed among PIs and North American cultivars for all traits. The range for all traits were greater in the PIs than in the cultivars. Discriminant analysis using root morphological traits to generate canonical functions separated PIs assigned to germplasm groups from different geographic origins. Among the PIs, TD and LRD were positively correlated and LRN, LRP, and FRM were negatively correlated with fall dormancy. Discriminant analysis using root traits to generate canonical functions separated the very fall dormant from the non-dormant classes. Semi-dormant classes for cultivars released before 1980 had some overlap, but some individual classes could be distinguished by root traits. Semi-dormant classes for cultivars released after 1979 could not be separated. Fall dormancy was negatively correlated with LRN, LRD, LRP, and FRM for cultivars released before 1980, but FRM was the only root trait correlated with fall dormancy for cultivars released after 1979. Our results suggest that recent plant breeding strategies for semi-dormant alfalfa has influenced the relationship between fall dormancy and root morphology. Variation observed for root morphological traits among all alfalfa entries evaluated indicated that selection for specific root modifications could be effective.

Structural root form and fine root distribution of some woody species evaluated for agroforestry systems

Fine root distribution and structural root characteristics of four-years-old multipurpose woody species with potential for use in agroforestry systems were investigated on an Alfisol in the forest savanna transition zone of south-western Nigeria. Rooting patterns of woody species studied differed considerably. Lonchocarpus sericeus had the lowest percentage (21%) of total fine roots confined to the upper (0 to 30 cm) soil layer, compared to 84% with Tetrapleura tetraptera. Despite the superior tap root system of Enterolobium cyclocarpum and the fine root form of Nauchlea latifolia however, their extensive distribution and very large lateral woody root volume density may pose a major problem for seedbed preparation and tillage operations in simultaneous agroforestry systems. Lonchocarpus sericeus appears to have the most desirable structural and fine root architecture among the species studied for simultaneous agroforestry systems. The total root density below the underlying distal soil layers was linearly related to the sum of square of tap root diameter and the corresponding soil depths.

The effect of grazing on seed production in Echium plantagineum

SummaryThis study measured the effect of livestock grazing on the seed production and the seed‐bank of the annual weed, Echium plantagineum L., by comparing six sites across south‐eastern Australia. Maximum taproot diameter predicted seed production of ungrazed plants irrespectiveof site. Seed losses to flowering plants grazed in spring were calculated using the taproot diameter relationship. Moderate continual grazing pressure throughout the seeding period (December‐January) reduced seed production by at least 87%, although grazing was most destructive per unit of time in the first half of this period (peak seed production of the infestation). E. plantagineum has a strong c apacity to compensate for stock grazing should the stock be removed too early. Seedbanks generally increased following significant seed rain, although this trend was not always consistent. In manipulated quadrats, where seed production was reduced by atleast 90% for 4 years, germination of E. plantagineum was lower relative to controls from the second year and the seedbank was 10 times lower when measured in the fourth year. The implications of these results are discussed in relation to existing control strategies for this weed.

Inheritance of Root Traits in Alfalfa

Root growth patterns influence nutrient uptake, productivity, and persistence in alfalfa (Medicago sativa L.). Inheritance of traits affecting root growth patterns in alfalfa are not well understood. Objectives of this research were to determine the affects of plant spacing and geographic location on root traits in alfalfa, to determine the inheritance of seven root morphological traits of alfalfa, and to evaluate the association between root traits, fall dormancy, and seedling year herbage yield. Progenies of diallels and design II matings were planted during May 1991 at two locations in 30‐cm rows with 2.5 cm between plants within the row. Plants were evaluated for seedling year herbage yield and fall dormancy. During October 1991, they were dug and evaluated for taproot diameter (TD), lateral root number (LRN), lateral root diameter (LRD), lateral root position (LRP), fibrous mass (FRM), percentage of determinate taproots (PDT), and determinate taproot position (DTP). Border effects were determined by evaluating single plants from the ends of the plots separately from plants in the middle of the plots. Extra space on plot borders affected root morphology, but few progeny × border interactions were found. Location affected root morphology, and a few location × cross interactions were observed for TD and LRP. Additive genetic effects were important in controlling inheritance for TD, LRN, LRD, LRP, and FRM. These traits had moderate (45) to high (87) heritabilities. genetic variances were detected for PDT or DTP. Taproot diameter was the root trait most highly correlated with fall dormancy (0.46–0.50) and seedling year herbage yield (0.61–0.75). Selection for LRN, LRD, and FRM at one location with uniform plant spacing should be successful. Multiple location selection programs may be more appropriate for TD and LRP.

Response to selection for increased taproot diameter

Increased taproot diameter is an important component in maintaining white clover (Trifolium repens L.) growth, nitrogen fixation and persistence during short-term moisture stress. Previous reports indicated selection for large taproot diameter would result in commensurate increases in leaf size and poorer growth habit. The current research investigates the response to selection for taproot diameter and the association between taproot diameter and leaf size in large-leaved clovers suited to dairy grazing systems. Taproot diameter increased by 2.4% per cycle while leaf size and growth habit were not significantly altered. Furthermore, while taproot diameter did not increase between cycle 2 and 3, the root index which measures the ratio of taproot diameter to leaf size increased linearly across all three cycles. These results suggest it is possible to select white clovers for dairying which have larger taproot diameter while maintaining a suitable growth habit. Keywords: dairying, drought, genetic improvement, root morphology, Trifolium repens L., white clover,

Effects of stand age on agronomic, morphological and chemical characteristics of alfalfa

Iroquois alfalfa (Medicago sativa L.) was seeded every spring from 1978 to 1988, and the established stands were maintained until the fall of 1988. Agronomic, morphological and chemical characteristics of the stands were compared among different age groups. A drastic reduction of alfalfa population occurred in the seeding year and during the first winter. There were about 40 plants m−2 in the 2nd yr which gradually decreased to 25 plants m−2 in the 8th yr, and between 12 and 24 plants m−2 in the 10th yr. There were more grass weeds in older stands. Total dry matter yield of forage, including weeds, did not decrease significantly with age of alfalfa stand Alfalfa yield, however, decreased with age, and the reduction in older stands was more evident in cut 1 than cut 2. There was little or no difference in cold hardiness among different stand ages in postseeding years. Root development pattern changed from vertical extension in the seeding year to lateral development of branched roots in postseeding years. Shoot number, crown diameter, crown decay taproot diameter, root depth, and number and spread of branched roots were associated with aging. Concentrations of total nonstructural carbohydrates (TNC) in the crown and roots decreased slightly with age. In the root, concentrations of K, Ca, B, and Fe increased, and Ca was most closely associated with age. No significant association of P, Mg, S, Mn, Cu, or Zn with age was found. Concentrations of minerals in the crown did not change with age, except B which increased slightly. Key words: Medicago sativa L., persistence, longevity, plant density, yield, minerals

Estimates of heritability for, and relationships between, root and shoot characters of white clover II. Regression of progeny on mid-parent

White clover genotypes were selected for high and low values of leaf size, taproot diamater, number of taproots, proportion of total root and taproot dry weight. Crosses within selected groups of genotypes resulted in 14 seed lines, which were compared with parent genotypes in field tiles. Selections for taproot diameter and proportion taproot were more successful than those for taproot number and proportion root.