Low Germination Capacity Research Articles

Why do mixotrophic plants stay green? A comparison between green and achlorophyllous orchid individuals in situ

Some forest plants adapt to shade by mixotrophy, i.e., they obtain carbon both from photosynthesis and from their root mycorrhizal fungi. Fully achlorophyllous species using exclusively fungal carbon (the so‐called mycoheterotrophic plants) have repeatedly evolved from such mixotrophic ancestors. However, adaptations for this evolutionary transition, and the reasons why it has happened a limited number of times, remain unknown. We investigated this using achlorophyllous variants (i.e., albinos) spontaneously occurring inCephalanthera damasonium, a mixotrophic orchid. In two populations, we compared albinos with co‐occurring green individuals in situ. We investigated vegetative traits, namely, shoot phenology, dormancy, CO2and H2O leaf exchange, mycorrhizal colonization, degree of mycoheterotrophy (using13C abundance as a proxy), and susceptibility to pathogens and herbivores. We monitored seed production (in natural or experimental crosses) and seed germination. Albinos displayed (1) more frequent shoot drying at fruiting, possibly due to stomatal dysfunctions, (2) lower basal metabolism, (3) increased sensitivity to pathogens and herbivores, (4) higher dormancy and maladapted sprouting, and, probably due to the previous differences, (5) fewer seeds, with lower germination capacity. Over the growing season, green shoots shifted from using fungal carbon to an increasingly efficient photosynthesis at time of fruiting, when fungal colonization reached its minimum. Conversely, the lack of photosynthesis in fruiting albinos may contribute to carbon limitation, and to the above‐mentioned trends. With a 103× fitness reduction, albinos failed a successful transition to mycoheterotrophy because some traits inherited from their green ancestors are maladaptive. Conversely, mycoheterotrophy requires at least degeneration of leaves and stomata, optimization of the temporal pattern of fungal colonization and shoot sprouting, and new defenses against pathogens and herbivores. Transition to mycoheterotrophy likely requires progressive, joint evolution of these traits, while a sudden loss of photosynthesis leads to unfit plants. We provide explanations for the evolutionary stability of mixotrophic nutrition and for the rarity of emergence of carbon sinks in mycorrhizal networks. More broadly, this may explain what prevents the emergence of fully heterotrophic taxa in the numerous other mixotrophic plant or algal lineages recently described.

24. Willow seeds viability after imbibition, freezing and freeze-drying treatments

The conservation of labile biomolecules/structures in biological, pharmaceutical and food sciences is generally performed in frozen or dehydrated systems. Vegetal germplasm is usually conserved as seeds, which are naturally dehydrated systems. Orthodox seeds (the most common) tolerate dehydration at low water contents (wc), and remain viable for several years upon conservation at 20 °C or at 4–8 °C. Willow seeds are orthodox but show some recalcitrant characteristics: the longevity does not follow the dehydration tolerance as is shown for orthodox seeds, and they lose viability in a few weeks at 20 °C. In practice, collected seeds are usually dehydrated at 20 °C for 3 h from wc 70% to 10–12% (dry basis) and then kept at −70°C, which highly increases storage time-dependant costs. The purpose of the present work was to analyze the conservation of willow (Salix nigra L.) seeds through freezing and freeze-drying. Seed imbibition with 45%w/v trehalose or polyethylene glycol 400 – PEG – or water were conducted for 16 h at 4 °C prior to freezing or freeze-drying, in order to introduce cryo- or dehydro-protective agents in the seeds by imbibition. A comparison with vacuum drying seeds was also performed. The germination rate was measured after each treatment. Water content, water activity (aw), and differential scanning calorimetry (DSC) determinations were conducted. The control seed pool (aw of 0.745; 13%db wc) retained 77% of its original germination capacity. Priming effect (Chojnowski et al., Seed Science Research 7 (1997) 323–331) was observed during seed imbibition with water and trehalose, but only 70% of the imbibed seeds with PEG germinated after imbibition, which can be related to a certain degree of PEG toxicity toward the seeds. After freezing, a great germination capability loss was observed in trehalose and water imbibed seeds; instead, PEG seeds maintained their ability to germinate. Water crystallization was observed in all the imbibed seeds (aw ∼ 0.97), and followed the increasing order: PEG Water crystallization was not observed in control seeds. Their thermograms showed a broad lipid melting (between −40 and 10 °C) and protein denaturation (between 55 and 110 °C). Since there are no major changes in protein denaturation after freezing of imbibed seeds, membrane damage could be the major responsible of the lower germination capacity observed after freezing and freeze-drying. After freeze-drying, a 30% decrease of the germination capability was observed in the PEG imbibed seeds in comparison to the frozen ones, arriving at aw of 0.269 and wc of 5%db. Water and especially trehalose imbibed seeds subjected to vacuum drying showed better germination capability with respect to the freeze-dried ones, revealing that both the amount of crystallized water and the presence of adequate protective agents were the main critical factors involved in willow seed conservation.

TRATAMIENTOS A SEMILLAS PARA MEJORAR LA GERMINACIÓN DE Colubrina ferruginosa Brong

El logro de la repoblación en trabajos para la rehabilitación de ecosistemas degradados depende del manejo de las semillas de especies forestales. Las semillas de Colubrina ferruginosa Brong poseen una baja capacidad germinativa (40-60 %), lo que dificulta obtener brinzales para la plantación. Se montó un experimento con el objetivo de elevar la capacidad germinativa de C. ferruginosa. El ex¬perimento se efectuó durante 60 días, utilizando semillas cosechadas en febrero de 2002, a razón de 400 por tratamiento. Se evaluaron 10 tratamientos con 4 repeticiones, bajo un diseño completamente aleatorizado; de éstos, nueve consistieron en sumergir las semillas en agua y uno en agua hirviendo por 30 s. Las semillas se colocaron en cajas germinadoras, con un sustrato formado por 30 % de arena y 70 % de aserrín de pino, se cubrieron con una capa del mismo aserrín y se humedecieron con 733 mL de agua diariamente. Los valores de germinación se transformaron con la función arco seno √x/100 y se evaluaron mediante un ANOVA simple. Se comprobó que la germinación se incrementó significa-tivamente en comparación con el tratamiento control (50 %), con inmersiones de 3, 6 y 9 h (76-80 %).

SEED GERMINATION RESPONSE TO PRETREATMENTS AND STORAGE BEHAVIOUR IN SCHLEICHERA OLEOSA (LOUR.) OKEN—INDIAN LAC TREE

ABSTRACT Schleichera oleosa or the Indian lac tree is one of the major lac host tree in India. Its fruits are edible and seed kernels yield an oil which has many industrial uses. due to its importance the forest departments and the lac cultivators are promoting the plantation of the species, but its typical germination and storage behaviour may pose some problems in its propagation. The study deals with understanding germination and storage behaviour as well as devising suitable pretreatments to enhance the germination of seeds. The seeds at the time of maturation and fall had low germination capacity (15%) which increased to 74% upon dry storage at ambient temperature for two months due to after-ripening. Mechanical scarification (removal of seed coat) proved to be best pretreatment resulting in highest (92%) and fastest germination as against 60% in untreated seeds. seeds tolerated desiccation to 7.2% moisture content and chilling (+50c) maintaining 72% viability after six months in storage. Seeds exhibited orthodox storage physiology. The results contribute to knowledge about germination and storage behaviour of the species and can be utilized for propagation and conservation of the species.

Dehulling capacity and storability of naked oat

Harvested naked oat is not completely hulless. Hull content of various cultivars ranged between one and six percent. Genotype and environment control expression of nakedness. Using different threshing settings at different grain moisture contents, it was investigated whether grain moisture at threshing and combine harvester settings affected hull content and its relationship to germination capacity. Naked groats were stored at room temperature and analysed for protein content and fatty acid composition to determine storability. Grain moisture content at threshing had contrary effects on hull content and degree of hull retention in different years. Small grains tended to retain hulls more tightly during threshing. Grain filling capacity appears to be the dominant factor determining degree of nakedness rather than stage of maturity. The postulated protective nature of hulls was confirmed only for cultivar Lisbeth. Highly viable samples of grain of cv. Lisbeth, threshed at normal settings, contained a higher percentage of hulls than those with low germination capacity, while for cv. Bullion, a protective effect of the hulls was not evident. Grain moisture content at threshing did not affect protein content of naked cultivars, but some differences in fatty acid composition were recorded. Changes in lipid composition and volatile oxidation products during storage of groats were relatively moderate, indicating no major problems related to storage when naked oat was dried well.;

Effect of Pansy (Viola x wittrockiana gams) Seeds Colour and Size on their Germination

Four commercial seed lots from the Polish seed companies of pansy (Viola x wittrockiana Gams) with low germination capacity were sorted into 2 size fractions: small and large: below 4 mm long and above 4 mm and 3 colour fractions: yellow, brown and dark, using hands and colour catalogue of British Royal Horticultural Society. The seeds were then tested for their germination following the ISTA routine rules. The seed size did not affect neither its energy nor capacity of germination. In one of the seed lots, smaller seeds germinated slightly better than the big ones, but in the two others ones, it was opposite. The smaller seed also gave higher amount of abnormal seedlings in the tests. There was a clear effect of seed colour on the seeds' germination. The dark seeds had the highest germination capacity, whereas the yellow ones - the lowest. The carried out experiments proved that color sorting of pansy seeds can improve their germination, mostly due to eliminating light, immature seeds.

Presença de sementes esverdeadas em soja e seus efeitos sobre seu potencial fisiológico

Sementes de soja, sobretudo em Mato Grosso, região dos cerrados, tem apresentado cotilédones com degradação parcial de clorofila. A conseqüência direta desse fenômeno é o descarte de muitos lotes, resultado de sua baixa qualidade. Com o objetivo de averiguar a influência exercida pela clorofila na qualidade fisiológica em sementes de soja foi desenvolvido este estudo. Foram utilizados dois lotes comerciais (A e B) da cultivar MG/BR46-Conquista, ciclo precoce com 11,8% e 37,4%, de sementes esverdeadas, segmentados em três amostras: sementes sem manipulação (lote original), sementes esverdeadas e sementes amarelas. Cada amostra consistiu de um tratamento. Através dos testes de germinação, envelhecimento acelerado (24 horas), tetrazólio, comprimento de plântula, massa de mil sementes, condutividade elétrica e emergência em campo foi realizada a avaliação da qualidade das sementes, no momento de semeadura. As sementes esverdeadas apresentaram menor germinação, viabilidade e vigor, maiores desuniformidade de plântulas, taxa de deterioração e quantidade de lixiviados, menores comprimento de plântulas e peso de mil sementes e baixa capacidade de emergência em campo, indiferente ao índice porcentual de cotilédones com pigmentação verde, porém, o prejuízo foi maior no lote B, com 37,4% de sementes esverdeadas. Pode-se inferir que clorofila é indicativo de redução do potencial fisiológico em sementes de soja.

Germination ecology of eleven species of <I>Geraniaceae</I> and <I>Malvaceae</I>, with special reference to the effects of drying seeds

Germination and survival of water-impermeable seeds of 11 species of Geraniaceae and Malvaceae were monitored during dry storage and during burial in soil for up to 2.5 years. During dry storage, seeds of annual Geraniaceae became permeable and also lost their physiological dormancy. However, during burial in natural conditions, most seeds remained impermeable and viable, with no seasonal change in germination capacity. Germination in only one species (Geranium robertianum) was enhanced by daily alternating temperatures when seeds were exhumed in spring. Drying of exhumed seeds broke physical dormancy. Seeds of the perennial Geranium pratense gradually became permeable in a prolonged germination test of 31 weeks. Most seeds of Malva remained impermeable during dry storage. Buried seeds gradually germinated in situ, and exhumed seeds had a low germination capacity in all seasons. We concluded that dormancy of hard seeds in natural conditions may be broken by drying during summer, by specific temperature regimes or by gradual softening of the seed coat, ensuring the spread of germination over many seasons.

Seed Potassium Concentration Decline During Maturation Is Inversely Related to Subsequent Germination of Primrose

It has been reported previously that seed potassium (K) concentrations were negatively correlated with the seed's germination capacity in randomly sampled commercial seed lots of primrose (Primula vulgaris Huds.). To explain this relationship, hypotheses about a causal role for the seed maturation level at harvest date and the possible environmental and genetic stability of the correlation were explored. Mineral composition and quality of Primula seeds were investigated (1) as to how they were affected by maturation stage with weekly seed harvests from the 7th to the 15th week post-anthesis (WPA), and (2) using a nutrient solution culture of gonophores varying in K supply (0, 1.5, 3, and 6 mmol K L−1) during reproductive growth. Concentrations of minerals [K, nitrogen (N), phosphorus (P), calcium (Ca), and magnesium (Mg)] in leaves and whole seeds were analyzed, as were selected seed characteristics (embryo and endosperm development, seed mass, viability, and germination) of two parental lines (pin and thrum morph of genotypes 45 and 48) for hybrid-seed generation. Leaf-mineral composition and vegetative growth were mostly affected by K supply. In contrast, mineral concentrations per gram dry seed mass of seeds harvested at mature stage (15 WPA) were not influenced (i.e., K, Mg), or only slightly so (i.e., N, P, Ca), by differential K supply to gonophore plants. However, seeds harvested at the premature stage (8 WPA) revealed concentrations of K, Ca, and Mg at evidently increased levels, with K and Mg clearly reflecting the differential K availability. During further maturation, the seed N and P concentrations remained relatively constant in respect to the considerable growth in single seed mass. In contrast, concentrations of K, Ca, and Mg decreased markedly and simultaneously with rapid seed growth. Irrespective of the different growth rates of seed mass between the genotypes, the decreasing seed concentrations (31% decline) strongly correlated with increasing percentage germination (40% rise) from 9 to 14 WPA (r = −0.81; n = 21; p < 0.01). However, weaker negative correlations between germination and seed Ca or Mg concentrations resulted from pronounced genotypic differences in levels of these two seed elements. Taken together, seed K concentration is the most reliable measure to indicate maturity and to act as a marker for low germination capacity due to premature seed harvest. In addition, possible interactions between climate impact, phytohormones, and seed mineral dynamics during maturation should be explored.

Influence of Triterpene Glycosides of the Holothurian Cucumaria japonica on Root Growth in Cucumis sativus L. Seedlings

We have shown that triterpene glycosides of the Far Eastern edible holothurian Cucumaria japonica (monosulfated subfractions A2 and A4, disulfated subfraction A6, trisulfated subfraction A7, and the total fraction of monosulfated glycosides including subfractions A0, A1, A2, and A4) inhibited growth of the main root of Cucumis sativus seedlings. Cucumariosides were arranged as follows according to their inhibitory activity: subfraction A2 (ED50 = 53.1 ± 3.6 μg/ml) > total fraction of monosulfated glycosides (ED50 = 127.4 ± 5.8 μg/ml) > subfraction A4 (ED50 = 346.5 ± 15.2 μg/ml) > subfraction A6 (ED50 = 375.7 ± 17.2 μg/ml) > subfraction A7 (ED50 = 539.4 ± 11.5 μg/ml). The average length of the main root decreased with the increase of glycoside concentrations as a result of a growing amount of seedlings with low germination capacity and the absence of seedlings with high germination capacity.

EFFECT OF DIFFERENT DAMAGE FACTORS ON SOYBEAN SEED QUALITY

Poor quality in soybean seed can be due to physiological, pathological or mechanical causes. Seed morphological and anatomical features also make soybean more susceptible to damage factors than other plant species. The purpose of this paper was to evaluate the effects of the different damage factors upon soybean seed quality and its longevity during storage. In two trials, carried out in La Plata (Prov. Buenos Aires, Argentina), soybean seed samples from 7 pre-trading lines, obtained in two consecutive crops, were analysed. Assessments were performed on day 40 and day 160 after harvesting for the first trial and on day 50 and day 150 after harvest in the second. The method employed was the blotter test, following the International Seed Testing Association (ISTA) rules. The parameters evaluated were: damaged cotyledons, rotten seed, fungal contamination and germination capacity. The damage factors had different influences on seed quality. The presence of pathogenic fungi did not necessarily mean low germination capacity. Their effect depended on the degree of infection, the presence of seed-borne pathogens and the time of sample analysis. Rotten seeds and damaged cotyledons caused by moisture had a striking influence on seed quality and preservation during storage.

Comparative regeneration ecology of three leguminous timber species in a Bolivian tropical dry forest.

A comparative study of the regeneration ecology ofthree lesser-known leguminous timber species wasconducted in the seasonally dry forests of SantaCruz, Bolivia to determine species regenerationstrategies and make silvicultural recommendationsfor these species. The study included arepresentative from each subfamily of Leguminosae:Anadenanthera colubrina (Vell. Conc.) Benth.(Mimosaceae), Copaifera chodatiana Kunth.(Caesalpinaceae), and Centrolobium microchaeteC. Martius (Fabaceae). After production in themid-late dry season, seeds of all species sufferedhigh (>30%) rates of predation. For seedssurviving predation, Anadenanthera germinatedwithin three days after the first rains and a highgermination capacity (82%), but most seedlings diedfrom inadequate light or during subsequent periodsof drought. Copaifera germinated more slowlybut had high germination capacity (85%). Centrolobium had very low germination capacity(4%) and germinative energy. Most successfulregeneration of Centrolobium occurred viasprouting from damaged roots on or near loggingroads where it had a density of 261 root sprouts/ha.Anadenanthera regenerated best from seedin areas with soil disturbance or burning. Theregeneration of these species will likely increaseunder more intensive logging and/or post-harvestcompetition control treatments in logging gaps. Themore shade-tolerant Copaifera is most suitedto the current regime of light selective logging,but all three species are likely to be responsive topost-harvest competition control treatments. Impacts of controlled and natural fire were mixed,but generally seedling regeneration and growth wereeither not significantly affected or were increasedby fire.

Differentiation in adaptive traits between neighbouring bog and mineral soil populations of Scots pine Pinus sylvestris

I used a reciprocal sowing experiment in the field to reveal differentiation in adaptive traits between two neighbouring northern populations of Scots pine Pinus sylvestris. 1 compared a peat bog population with a mineral soil population. Seedling survival was monitored during seven growing seasons and the plants were then harvested to obtain data on pine traits associated with growth and resource allocation, i.e. height, needle length, total dry weight, relative growth, proportion root and proportion needles. Seeds from the peat bog populations had lower germination capacity and were smaller than those from the mineral soil population. Despite their smaller size, the seeds from the bog population were superior for establishment of pines on the bog. On the mineral soil, the traits were strikingly similar in the two pine populations. In contrast, the traits were more variable and differentiated on the bog. Here, the native bog pines grew faster and had a larger proportion root than those originating from the population on the adjacent mineral soil. It is suggested that the differentiation between peat bog populations and mineral soil populations might represent a major direction of differentiation in northern Scots pine populations.

Malting Quality of Hexaploid Triticale in Comparison with That of Barley, Wheat and Rye.

Malting quality of hexaploid triticale ( × Triticosecale Wittmack) was analysed in comparison with that of barley as a standard, and wheat and rye as parental species, by using the micro-malting method. Triticale malt had higher diastatic power than rye and wheat, and was particularly higher than barley. Malt extract and extract yield of triticale were almost as high as the levels for rye, while those of barley were rather low. An average value of total malting loss obtained from 11 cultivars of triticale was lower than that of hexaploid wheat and malting loss from shoot and root was lower than that of barley and hcxaploid wheat. Total and soluble nitrogen were high in triticale. Steeping period of triticale was shorter than that of barley by about four-fold. The high diastatic power, high malt extract, and short steeping period in triticalc malt seemed to be advantageous industrial brewing characteristics, while high total nitrogen and low germination capacity appeared to be disadvantageous.

Wheat‐bug damage in New Zealand wheats: The feeding mechanism of nysius huttoni and its effect on the morphological and physiological development of wheat

AbstractAdult Nysius huttoni White were placed in separate cages containing cultivars Rongotea and Karamu at the late anthesis, watery ripe and milky ripe stages of development. Between 84 and 99 % of the matured kernels were injured with the characteristic visible markings of bug‐damaged wheat. All the samples contained strong wheat‐bug proteinase activity as shown by the incubated SDS‐sedimentation test and the disappearance of HMW glutenin subunits from electrophoretograms. Grain infested at late anthesis was most severely affected with shrivelled kernels, high screenings, protein, free amino acids and α‐amylase, and low kernel weight, germination capacity and carbohydrate content. Grain infested at the watery ripe and milky ripe stages had values for the above properties closer to uninfested control wheat values.It was suggested that N huttoni sucked sap from lateral sieve tubes in the wheat ovary at late anthesis causing severe disruption to physiological development of the grain. Two commercial lines of wheat showed some characteristics of this effect.

Studies in Hibiscus

1. Intra- and inter-specific crosses were made in four arboreal species of the East Asian Group of Hibiscus, mutabilis, sino-syriacus and para-mutabilis, and six perennial herbaceous species of the North American Group, coccineus, incanus, lasiocarpus, leucophyllus, militaris and moscheutos.2. Intraspecific crosses:The species of the Asian Group except mutabilis showed remarkable self-incompatibility. Self-pollination yielded only a few capsules without seeds, whereas the crosses between different strains produced capsules containing many fertile seeds.Self-incompatibility was not found in mutabilis and the American Group. Self-pollination in these species always proved highly fertile.3. Interspecific crosses:Reciprocal crosses between six herbaceous species of North American origin produced abundant capsules containing a number of fertile seeds with high germination capacity.Reciprocal crosses between syriacus, sino-syriacus and para-mutabilis resulted in low percentages of capsule setting, The capsules contained few fertile seeds with low germination capacity. Mutual crosses between mutabilis and the other arboreal species were all unsuccessful.Crosses between mutabilis and six American species were successful only when the former was the mother plant. The percentages of fruit setting, the number of seeds obtained, and the viability of the seeds were all inferior to the corresponding figures in the mutual crosses within the American group.Reciprocal crosses between the Asian species other than mutabilis and the American herbaceous species proved unsuccessful in every case.

Lucerne investigations: III. Effect of heat treatment on germination and field establishment of lucerne seed

1. Lucerne seed samples of known harvest history were treated by dry heat at various temperatures and durations; their germination capacity, emergence and establishment were tested by laboratory, greenhouse and field establishment tests on heavy Boil during 1952–6 at Cambridge.2. A successful and safe heat treatment was 42° C. for 5 days, increasing the germination by as much as 44% up to about 90% at the cost of hard seed.3. The establishment obtained on heavy soil from treated seed samples, although varying from season to season, was significantly higher (P &gt; 0·001) at all seed rates than that obtained from untreated control samples.4. Significant differences were obtained in germination capacity and establishment between samples harvested at different conditions. High moisture content of seed and high percentage of dark brown seeds was associated with late harvest. Brown seeds had a significantly lower germination capacity than yellow seeds. Only samples with a high initial moisture and high percentage of brown seeds showed a substantial decrease in germination capacity during the storage period of 3 years.5. Although the mean number of plants established is significantly higher for higher seed rates the mean percentage of plants established decreases significantly with higher seed rates and the greatest wastage of seeds occurred at the high seed rate of 15 lb; per acre.6. The viability of seed and speed of germination and of emergence were the most important factors in determining the successful establishment of a crop on heavy soil.7. Hard seed is viable and could germinate and produce seedlings by the end of the season, but only a very small percentage of it could normally be established under field conditions. With untreated seed no significant correlations were established between laboratory germination and field establishment or between laboratory germination and greenhouse emergence, yet there were highly significant correlations in these cases for treated seed. With increased duration of laboratory germination test, corresponding to a decrease in the proportion of hard seed, values of r increased. Correlations between field establishment at three seed rates and greenhouse emergence were significant in the case of both untreated and treated seeds.8. When the hard seeds were added to germination or establishment the relationships between the results of these tests were very close and highly significant correlations were established for both lots of seed, untreated and treated. The high proportion of hard seeds was the main limiting factor preventing a close relation between tests for untreated seed.

Differential Insecticide Damage in Maize Varieties

A MIXTURE of three parts of ethylene dichloride and one part of carbon disulphide (by volume) applied at the rate of 0.6 c.c./litre of storage space by pouring the liquid on to the surface has been effective for some years in preventing insect damage to maize grain (var. Tsolo) stored in closed bins for subsequent sowing. In 1956 the variety Mexican Elite was grown instead of Tsolo, and the grain after storage was found to have a very low germination capacity. A series of experiments was carried out to test the hypothesis that the insecticide was affecting the grain adversely, and that some varieties of maize were more susceptible than others to this treatment.

Studies in the cold storage of peanuts

AbstractShelled and unshelled peanuts packed in small gunny bags were stored at four temperature ranges, viz., 32–35° F, 42–45° F, 52–55° F and room temperature (71–92° F) for 9 months. The relative humidities ranged between 85% to 90% in the cold‐storage chambers and 50–82% at the room temperature.A parallelism was observed between the changes during storage in the moisture contents of the kernels and the acid values of the extracted oils and to a less degree, the changes in peroxide values. So far as germination capacities are concerned, shelled nuts should be stored at 32–35° F and unshelled ones at room temperatures (71–92° F). A free fatty acid content exceeding 1% was found to be associated with seeds of low germination capacity.

Taproot-problems in the breeding of root vegetables

1. In most breeding programs of root vegetables the thickness of the taproot is an important but somewhat confusing factor. The reason is that there is not a clear idea of how genetic and physiological influences interact. Here a report is given of the results of a series of field experiments on this interaction in red garden beet. 2. It is shown that, as a rule, there is a close correlation between the foliage weight per plant and the size of the taproot. This means that a variety with a large top also has a relatively thick taproot. There may be genetic factors influencing the differences in the ratios of the taproot diameter to the foliage weight. Usually the influence of these factors is rather small. 3. The opinion is forwarded that there are two different activities in the beet plant, which may operate at the same time as long as the plant grows. But under the influence of the age of the plant and of the growth conditions one of them may dominate over the other. The first is the growth activity of the primary axis (leaf rosette + taproot). The second is the activity of root thickening. When the plants are very young the growth activity of the primary axis dominates. Later on there is a changeable equilibrium between the two activities. 4. Low germination capacity of the seeds, short day length or an acid soil retard both activities. Under these conditions root thickening is slow but also the growth of the primary axis. Consequently, reduction of the growth rate in these cases does not result in an uncommonly heavy taproot. 5. Relatively low temperature and (or) a relatively dry soil retard root thickening more than the growth of the primary axis. The result is a thick taproot. 6. Relatively high temperatures and a satisfactory water content of the soil favour a quick root thickening. The result is an early root thickening and a small primary axis. The taproot becomes thin and the top will be relatively small. 7. This explains why large top types of beet are more popular in areas with a warm, continental climate, and short top types in areas with a cool marine climate.