Small Number Of Plants Research Articles

Prenylated Isoflavonoids: Botanical Distribution, Structures, Biological Activities and Biotechnological Studies. An Update (1995 – 2006)

In contrast with the parent class of flavonoids, the distribution of the isoflavonoid class in the plant kingdom is relatively limited, probably owing to the sporadic occurrence of isoflavone synthase. Isoflavonoids have been mostly found in the subfamily Fabaceae/Papilionoideae of the Leguminosae family. Isoprenoid-substituted (also called complex) isoflavonoids are expressed from a smaller number of plants, as a result of the similarly restricted distribution of prenyltransferases (PT-ase). After the reviews of Tanara & Ibrahim (1995), Boland & Donnelly (1997), the Handbook of Flavonoids by Harborne & C ( Handbook of Flavonoids, 1999), and the paper by Harborne and Williams (2000) few other reports concern the distribution and the biological activity of complex isoflavonoids, except a list of isoflavonoids produced from non leguminous plants. This review deals with an update of the literature on isoprenylated isoflavonoids in the years 1995-2006 and is focused on the following highlights. 1. Natural sources of complex isoflavonoids (2000-2006); 2. Chemical structure variety: new entries (2000-2006) 3. Biological activities and a possible structure-activity relationship (1995-2006) 4. In vitro production and microbial metabolism (1995-2006).

TRENDS IN ROOTING MEDIA IN DUTCH HORTICULTURE DURING THE PERIOD 2001-2005: THE NEW GROWING MEDIA PROJECT

An overview of the developments in the area and volume of substrates used for horticultural rooting media in Holland in the period 2001 to 2005 is given. The overview is followed by a discussion of some trends in society and technology including the interest of public and society in a possible substitution of peat, an increase in the use of locally produced renewable carbon based substrates and an increase in nutrient recirculation for soil grown crops. In reaction to growing public concern about peat harvesting for horticultural purposes in parts of Europe, Dutch growers, researchers, potting soil producers, an auction and traders initiated in 2003 a research program named the New Growing Media Project. The aim was: To assess the technical and economical potential of peat alternatives. Develop experience and knowledge of growing on alternative mixtures. During 2004 and 2005, fifteen growers cultivated green and flowering container plants on alternative mixes. The 2004 season was used to test larger numbers of potting soils with relatively small numbers of plants. The 2005 season was used to test the most promising potting soils with larger numbers of plants. The results showed that for Hedera and Schefflera, the ultimate alternative mix was superior to the commercial standard used. For five species, Anthurium, Chrysanthemum, Gerbera, Spathiphyllum and Castanospermum, the alternative mix proved equal to the commercial standard. For eight species, Azalea, Guzmania, Poinsettia, Rosa, Saintpaulia, Adiantum, Crassula and Ficus, results were poorer than on the standard medium. The growers however, felt confident the alternative mixes could do better if the growing system, often the irrigation frequency, could be adapted to the experimental growing medium. Begonia gave poorer results with the new mix. The percentage peat used in the mixes was reduced from 77% on average in the commercial standard mixes to 30% on average in the new mixes. The most popular alternatives were coir products which increased from 17 to 40%. Other alternatives used were various barks, rice hulls, perlite, wood fiber, composts, and rockwool granulate. Those alternatives were used in mixtures from 5 to 30%. General conclusions include a growing interest in locally produced composts, granulates and fibers and for materials with properties such as a high initial air content combined with an improved rewetting rate.

Natural History Studies for the Preliminary Evaluation of <I>Larinus filiformis</I> (Coleoptera: Curculionidae) as a Prospective Biological Control Agent of Yellow Starthistle

We studied the life history, geographic distribution, behavior, and ecology of Larinus filiformis Petri (Coleoptera: Curculionidae) in its native range to determine whether it is worthy of further evaluation as a classical biological control agent of yellow starthistle, Centaurea solstitialis (Asteraceae: Cardueae). Larinus filiformis occurs in Armenia, Azerbaijan, Turkey, and Bulgaria and has been reared only from C. solstitialis. At field sites in central and eastern Turkey, adults were well synchronized with the plant, being active from mid-May to late July and ovipositing in capitula (flowerheads) of C. solstitialis from mid-June to mid-July. Larvae destroy all the seeds in a capitulum. The insect is univoltine in Turkey, and adults hibernate from mid-September to mid-May. In the spring, before adults begin ovipositing, they feed on the immature flower buds of C. solstitialis, causing them to die. The weevil destroyed 25-75% of capitula at natural field sites, depending on the sample date. Preliminary host specificity experiments on adult feeding indicate that the weevil seems to be restricted to a relatively small number of plants within the Cardueae. Approximately 57% of larvae or pupae collected late in the summer were parasitized by hymenopterans [Bracon urinator, B. tshitsherini (Braconidae) and Exeristes roborator (Ichneumonidae), Aprostocetus sp. (Eulophidae), and unidentified species of Eurytomidae and Ormyridae]. This weevil may be a better choice than the other capitula insects already established in the United States, particularly in colder parts of the plant's range.

The NAFTA tide: Lifting the larger and better boats

We use panel data on Mexican manufacturing plants to study the connection between plants' responses to changes in the economic environment and their contributions to aggregate total factor productivity growth, in the period following the implementation of the North American Trade Agreement. An overwhelming share of industry-level aggregate total factor productivity growth is accounted for by a small number of plants, which were larger and more productive before the implementation of NAFTA and expanded and became more productive following the implementation of NAFTA. Plants that exported before NAFTA and exported continuously through to 2000, and new exporters, are more likely to be among the top-performing plants. The performance of plants with similar exporting experience displays, however, remarkable heterogeneity: a significant number of plants that never export have strong output and productivity performance, while many exporters display poor performance. Spending on research and development, and three variables describing plants' level of integration in the global markets – foreign direct investment, use of imported intermediary inputs, and investment in foreign capital goods – are positively correlated with output and productivity performance.

Colonization genetics of an animal‐dispersed plant (Vaccinium membranaceum) at Mount St Helens, Washington

Population founding and spatial spread may profoundly influence later population genetic structure, but their effects are difficult to quantify when population history is unknown. We examined the genetic effects of founder group formation in a recently founded population of the animal-dispersed Vaccinium membranaceum (black huckleberry) on new volcanic deposits at Mount St Helens (Washington, USA) 24 years post-eruption. Using amplified fragment length polymorphisms and assignment tests, we determined sources of the newly founded population and characterized genetic variation within new and source populations. Our analyses indicate that while founders were derived from many sources, about half originated from a small number of plants that survived the 1980 eruption in pockets of remnant soil embedded within primary successional areas. We found no evidence of a strong founder effect in the new population; indeed genetic diversity in the newly founded population tended to be higher than in some of the source regions. Similarly, formation of the new population did not increase among-population genetic variance, and there was no evidence of kin-structured dispersal in the new population. These results indicate that high gene flow among sources and long-distance dispersal were important processes shaping the genetic diversity in this young V. membranaceum population. Other species with similar dispersal abilities may also be able to colonize new habitats without significant reduction in genetic diversity or increase in differentiation among populations.

The endophytic community of Dactylis glomerata

Morphological and molecular methods were used to identify the endophytic mycobiota of the grass Dactylis glomerata. Fungal endophytes belonging to 109 different species were isolated from asymptomatic plants sampled in different ecosystems in Spain. Species accumulation curves showed that most species commonly infecting this grass have been identified, but the number of singleton species occasionally infecting the plants is likely to increase with more sampling effort. A large endophytic assemblage consisting of fungi with diverse ecological roles, and potentially unknown species was found in a small number of plants. Keywords: endophytes, Dactylis glomerata, diversity, abundance

The NAFTA Tide: Lifting the Larger and Better Boats

We use panel data on Mexican manufacturing plants to study the connection between plants' responses to changes in the economic environment and their contributions to aggregate productivity growth in the period following the implementation of the North American Trade Agreement (NAFTA). In all industries, an overwhelming share of aggregate productivity growth is accounted for by a small number of plants which were larger and more productive before the implementation of NAFTA and expanded and became more productive following the implementation of NAFTA. Plants that exported before NAFTA and export continuously through 2000 and some of the new exporters are more likely to be among the top-performing plants. Exporting activity and performance of plants with similar exporting experience, however, display remarkable heterogeneity. This heterogeneity implies that trade liberalization provided growth opportunity to larger and more productive plants irrespective of their export status and provides an explanation for the lackluster average productivity performance of exporting plants.

Cylindrocladium pauciramosum causes root and collar rot of Polygala myrtifolia in Spain

Polygala myrtifolia (Polygalaceae), or milkwort, is an evergreen shrub commonly found in Mediterranean gardens. In November 2004, plants of P. myrtifolia showing foliar chlorosis and wilting of the shoots with collar and root rot were observed in Valencia, eastern Spain. A Cylindrocladium sp. was isolated from the infected parts. Single conidial isolates were grown on carnation leaf agar under near-UV light at 25°C for 7 days (Crous & Wingfield, 1994). The macroconidiophores were septate, 115–185 (170) µm long, with a terminal pear-shaped vesicle, measuring 4–8 (7) µm in width. Phialides (12 × 4 µm) were doliform to reniform, with conidia 40–58 × 3·5–5 µm, cylindrical with rounded ends and one-septate. Chlamydospores were brown and formed microsclerotia. These features agree with the description of Cylindrocladium pauciramosum (Schoch et al., 1999). Further confirmation was obtained by sequence analysis. The 5′ end of the β-tubulin gene was amplified using the primers T1 and Bt2b (Henricot & Culham, 2002). The sequence of the amplified product was deposited in GenBank (accession number AY923867). Comparison with other sequences in GenBank revealed that the isolates described here were identical with C. pauciramosum (DISTEF-G 192) from P. myrtifolia in Italy. To confirm pathogenicity, wounds made at the base of the stems of 1-year-old plants of P. myrtifolia were inoculated with an aqueous suspension of 2 × 105 conidia mL−1. Control plants were treated with sterile distilled water. Inoculated plants developed symptoms similar to those observed in natural infections. Cylindrocladium pauciramosum was reisolated from the diseased parts of the inoculated plants. This disease was first reported in Europe only recently, affecting P. myrtifolia in Italy (Polizzi & Crous, 1999). Cylindrocladium pauciramosum has a wide host range and attacks many other ornamentals, although this is the first record on any known host from Spain. The disease affects relatively small numbers of plants at present, with reports of 3% losses in nurseries.

A new species of Oreomyrrhis (Apiaceae) from southern South Island, New Zealand, and comparison of its limestone and ultramafic habitats

Oreomyrrhis basicola is described as a new species from southern New Zealand. O. basicola is segregated from the O. rigida complex by its grey‐green to blue‐grey leaves, fewer primary pinnae, and primary pinnae that are only occasionally further divided with secondary pinnae. It is known from two base‐rich habitats: ultramafic substrates in northern Southland and limestone in northern Otago. These substrates have very high base saturations, but differ in that the exchange complex of limestone substrates is dominated by calcium and that of the ultramafics is dominated by magnesium. O. basicola is known from three subpopulations, each with small numbers of plants, and is, therefore, considered to be Nationally Endangered.

Dry biomass distribution in a cerrado sensu stricto site in Brazil central

The Cerrado has been the main source of firewood and charcoal in Brazil, but despite being one of the hot spots for conservation of the world's biodiversity, neither plantations of native species nor sustainable management has been adopted in the region. The aim of this work was to investigate the biomass distribution and the potential for energy production of the cerrado species. The study was conducted in a cerrado sensu stricto site at the Água Limpa Farm (15º 56'14'' S and 47º 46'08'' W) in the Cerrado Biosphere Reserve. An area of 63.54ha was divided in 20 x 50m plots and, a random sample consisting of ten of these plots, representing 1.56% of the study-site, was assessed. All woody individuals from 5 cm diameter at 30 cm above ground level were identified and measured. Each individual was felled, the twigs thinner than 3cm were discarded while the larger branches and the trunks, both with bark, were weighted separately. After that, 2.5cm transverse sections of the trunk with bark were taken at 0, 25, 50, 75 and 100% of the length. A similar sample was also taken at the base of each branch. A total of 47 species in 35 genera and 24 families were found, with an average density of 673 individuals per ha. The diameter distribution showed a reversed-J shape with 67% of the individuals up to 13cm, while the maximum diameter was 32.30cm. Seven species represented 72% of the total biomass. In general, the species with higher production per tree were among those with higher production per ha. This content was distributed by diameter classes, reaching a maximum of 2.5ton/ha between 9 to 13cm and then, decreasing to 0.96 ton/ha between 29 to 33cm diameter. Carbon sequestering was 6.2ton/ha (until the actual stage of cerrado) based on an average 50% carbon content in the dry matter. The heat combustion of the wood varied from 18,903kj/kg to 20,888kj/kg with an average of 19,942kj/kg. The smaller diameter classes fix more carbon due to the large number of small plants per ha. But, for a species that reached larger dimensions and contained individuals in all diameter classes, Vochysia thyrsoidea, one can verify an increase in carbon fixation from 1.41 kg/ha in the first class (5 to 9cm) to 138,3kg/ha in the last (25 to 33cm). That indicates that it is possible to select species that reach larger size with a higher capacity of carbon accumulation per plant. The species that reached larger dimensions, with a production per tree above average and had high calorific power values were Dalbergia miscolobium, Pterodon pubescens and Sclerolobium paniculatum. These species have potential for use in fuelwood plantations and sustainable management.

Irrigated wheat response to population density and planting date in bed planting in Northwest Mexico

Irrigated wheat response to different population densities and planting dates when it is planted on raised beds is not well defined. A field study was carried out at the Yaqui Valley Agricultural Experimental Station in Sonora, Mexico during fall-winter 1992–1993, in a split plot design with three planting dates: Nov 10, Dec 10 and Jan 10; and six population densities: 50, 100, 150 200, 250 and 800 thousand plants per hectare (TPPH), in a complete randomized block design, with four replications. The fertilization used was 150-40-0 kg ha −1 of N-P 2 O 5 -K 2 O; the wheat variety used was Altar C85. Results indicated that wheat response to population density (PD) was different at different planting dates. At an early date, the plants grew taller and more vigorous and the field area could be covered with a small number of plants. The optimal PD was around 150 TPPH (15 plants m −2 ) when planted on Nov 10, which represents less than 10 kg ha-1 of seed. After this date, it was required to increase the PD as th...

Temporal and host‐related variation in frequencies of genes that enable Phyllotreta nemorum to utilize a novel host plant, Barbarea vulgaris

AbstractThe flea beetle, Phyllotreta nemorum L. (Coleoptera: Chrysomelidae), is an intermediate specialist feeding on a small number of plants within the family Brassicaceae. The most commonly used host plant is Sinapis arvensis L., whereas the species is found more rarely on Cardaria draba (L.) Desv., Barbarea vulgaris R.Br., and cultivated radish (Raphanus sativus L.). The interaction between flea beetles and Barbarea vulgaris ssp. arcuata (Opiz.) Simkovics seems to offer a good opportunity for experimental studies of coevolution. The plant is polymorphic, as it contains one type (the P‐type) that is susceptible to all flea beetle genotypes, and another type (the G‐type) that is resistant to some genotypes. At the same time, the flea beetle is also polymorphic, as some genotypes can utilize the G‐type whereas others cannot. The ability to utilize the G‐type of B. vulgaris ssp. arcuata is controlled by major dominant genes (R‐genes). The present investigation measured the frequencies of flea beetles with R‐genes in populations living on different host plants in 2 years (1999 and 2003). Frequencies of beetles with R‐genes were high in populations living on the G‐type of B. vulgaris ssp. arcuata in both years. Frequencies of beetles with R‐genes were lower in populations living on other host plants, and declining frequencies were observed in five out of six populations living on S. arvensis. Selection in favour of R‐genes in populations living on B. vulgaris is the most likely mechanism to account for the observed differences in the relative abundance of R‐genes in flea beetle populations utilizing different host plants. A geographic mosaic with differential levels of interactions between flea beetles and their host plants was demonstrated.

Outbreak of Iris yellow spot virus in Onion Seed Crops in Central Oregon.

Iris yellow spot virus (IYSV) of the genus Tospovirus, family Bunyaviridae is considered an emerging or reemerging pathogen affecting onions in the United States. The virus has been endemic to the Treasure Valley of southern Idaho for more than a decade (4). Reports of its further spread came from several states in the region, most recently from New Mexico and Washington (1,3). During the 2004 growing season, a few onion seed crops near Madras (Jefferson County) in central Oregon showed symptoms suggestive of IYSV infection, including characteristic diamond-shaped scape lesions (2). By July, scapes in one-half of a 4-ha field were 100% symptomatic and 95% lodged, leading to nearly total crop failure; in the other half, scapes were 30 to 40% symptomatic and 15% lodged, with symptoms and lodging increasing weekly at 8 weeks before harvest. The half of this crop with greater incidence was immediately adjacent to a field where very limited IYSV-like symptoms were noticed in a 2002-2003 onion seed crop that was harvested in mid-August 2003, after the highly symptomatic 2003-2004 onion seed crop was planted next to it in early July 2003. Both crops were planted from true seed. In another onion seed crop located 1,000 m away, IYSV-like symptoms were abundant around the field edges in July and through the field in August 2004, with approximately 5% lodging by mid-August. A small number of plants with IYSV-like symptoms were present in a few more distant fields, but not in most onion seed fields in central Oregon. Symptomatic plants were collected and tested in the laboratory for confirmation of IYSV infection. IYSV was confirmed using enzyme-linked immunosorbent assay (ELISA) with a commercially available antiserum (Agdia Inc., Elkhart, IN). Total nucleic acids were extracted, and using primers specific to the nucleocapsid (N) gene of IYSV (3), reverse transcription-polymerase chain reaction (RT-PCR) was done. RT-PCR gave DNA amplicons of the expected size. The DNA amplicons were cloned and sequenced. Nucleotide sequence comparisons with known IYSV N gene sequences confirmed virus identity. The rapid spread of IYSV in the Pacific Northwest and its severity of incidence often leading to 100% incidence is a cause for concern for onion growers and industry. Efforts to identify management practices to reduce its impact have to be undertaken on a regional basis because of its widespread occurrence across several states in the northwestern United States.

Farmers' practices, metapopulation dynamics, and conservation of agricultural biodiversity on-farm: a case study of sorghum among the Duupa in sub-sahelian Cameroon

In many traditionally managed agroecosystems, populations of domesticated plants maintain high levels of genetic diversity. The threat of erosion of this diversity is a current conservation concern, motivating studies of how diversity can be maintained by in situ conservation measures. Precisely how the biological traits of plants and the cultural practices of farmers act on fundamental evolutionary forces – drift, migration, selection, and mutation – to create and maintain crop plant diversity has been little investigated in detail. We develop some elements of the framework required for studying such biocultural interactions, focusing on one component of management: farmers' decisions on what to plant, and the structure of germplasm exchange among farmers. We illustrate the approach with a study of Duupa farmers in northern Cameroon. Our results suggest that sorghum populations managed by the Duupa function like source–sink metapopulations. Fields of older farmers, larger and containing a greater number of varieties, act as sources, whereas fields of younger farmers act as sinks, becoming sources as their owners mature. In each field, seeds for sowing are selected from a small number of plants. The frequent exchange of germplasm among fields may counteract the genetic bottlenecks associated with the small number of genitors within each field. Identifying key processes and key individuals should facilitate the design of in situ conservation measures to maintain crop plant diversity against the threat of genetic erosion.

Transpositional behaviour of an Ac/Ds system for reverse genetics in rice.

A collection of transposon Ac/ Ds enhancer trap lines is being developed in rice that will contribute to the development of a rice mutation machine for the functional analysis of rice genes. Molecular analyses revealed high transpositional activity in early generations, with 62% of the T0 primary transformants and more than 90% of their T1 progeny lines showing ongoing active transposition. About 10% of the lines displayed amplification of the Ds copy number. However, inactivation of Ds seemed to occur in about 70% of the T2 families and in the T3 generation. Southern blot analyses revealed a high frequency of germinal insertions inherited in the T1 progeny plants, and transmitted preferentially over the many other somatic inserts to later generations. The sequencing of Ds flanking sites in subsets of T1 plants indicated the independence of insertions in different T1 families originating from the same T0 line. Almost 80% of the insertion sites isolated showing homology to the sequenced genome, resided in genes or within a range at which neighbouring genes could be revealed by enhancer trapping. A strategy involving the propagation of a large number of T0 and T1 independent lines is being pursued to ensure the recovery of a maximum number of independent insertions in later generations. The inactive T2 and T3 lines produced will then provide a collection of stable insertions to be used in reverse genetics experiments. The preferential insertion of Ds in gene-rich regions and the use of lines containing multiple Ds transposons will enable the production of a large population of inserts in a smaller number of plants. Additional features provided by the presence of lox sites for site-specific recombination, or the use of different transposase sources and selectable markers, are discussed.

Evaluation of the control of beet armyworm, Spodoptera exigua, with baculoviruses in greenhouses using a process-based simulation model

Abstract Scenario studies were carried out with a process-based model for control of wild-type and genetically modified baculoviruses in populations of Spodoptera exigua in glasshouse chrysanthemum (BACSIM). These scenario studies were used to evaluate the effectiveness of different spraying regimes, concentrations, UV-protection agents, and mean time to kill insect. In simulations on concentration and timing of S. exigua multicapsid nucleopolyhedrovirus (SeMNPV), good control efficacy was obtained with SeMNPV concentrations of 1×107 polyhedra/m2 or higher. An early timing of virus applications, soon after egg deposition, is essential for effective control, especially at high temperatures, when the developmental rate of larvae is high and the window of opportunity for virus control is short. UV-protection agents contribute only marginally to effective biological control in the glasshouse because the decay rates of SeMNPV and Autographa californica multicapsid nucleopolyhedrovirus already ensure a period of exposure to active virus that is long enough for caterpillars to acquire a lethal concentration under practical conditions. The effect of genetic improvement towards shortening the survival time of infected larvae depends on the ability to time virus applications accurately and the mean time to kill the unmodified virus. Recombinant viruses with a lower mean time to kill are more effective than wild-type viruses when applied against second, third, and fourth instars because in these stages S. exigua infests a considerable number of plants and the rate of foliage consumption increases rapidly. When applied against first instars that infest only a small number of plants and have low consumption rates, recombinants will only be slightly more effective than wild-type viruses. In the case of an unmodified virus that already has a relatively high mean time to kill, a further reduction in the time to kill will not result in improved control. Thus, accurate monitoring followed by virus application is indispensable for adequate control and may even alleviate the need for fast killing viruses.

Genetics of qualitative traits in domesticated chia (Salvia hispanica L.).

In Salvia hispanica L., several changes in qualitative characters, including seed coat color, stem pigmentation, and shattering, have evolved with cultivation and domestication. Three F(2) segregating generations from crosses between wild and domesticated parents were scored for three qualitative traits. A single recessive gene, designated scc, was found to govern the white seed characteristic. A single dominant gene, designated SSP, was found to control striated stem pigmentation. A complete dominance of open calyx over closed calyx was observed in F(1) generations and small numbers of plants with closed calyxes were observed in F(2) generations, not conforming to Mendelian ratios. For this non-shattering trait, a complementation test was conducted between two lines representative of geographically and morphologically divergent domesticated varieties. Complementary gene action was not observed in any F(1) plants, and all F(2) plants were homogeneous with respect to the trait, suggesting the same genetic control for non-shattering among domesticated varieties. An analysis of limited data for linkage of SSP and scc indicated that the two loci segregate independently.

PERFORMANCE OF HUMAN EXPERTS GRADING POT ROSES IN A COMMERCIAL ENVIRONMENT

In Denmark, ornamental products are graded by manual labour. The task is very demanding regarding labour and training of the employees. This paper addresses the characteristics of manual grading of pot-roses, with its variance and bias of plant evaluation, within and between experts. Evaluations from three experts were gathered for 2800+ pot roses. From these 2800 five additional experts, resulting in a total of eight evaluations per plant evaluate plants 300. The evaluations were given in a natural work environment that means that the estimate of performance by the single expert should reflect the consistency to be expected of commercial products. The reason for this investigation is to establish knowledge of the current consistency of product grading, to evaluate future automatic grading systems, based on computer vision. A very important issue in relation to subjective evaluation is the determination of an appropriate correct classification of the products. Pros and cons of the majority voting scheme is considered in relation to pot plant grading. The performance of each individual expert is analysed with respect to the majority decision, and the analysis covers overall error rates, class-specific error rates, certainty of the expert statement and hit-rate. Expert statements are merged to form expert-panels. The theory of panels is explained and the performance is compared with the performance of an individual expert. Further, the maximum achievable classification rate is estimated based on expert-panels and the correlation between these. The single expert classification rate varies between 84% and 92%, but the errors are not equally distribution between classes. The performance of expert-panels formed by single expert statements varies between 90.9% and 98.6%, which is a significant improvement. A conservative estimate of the maximum achievable classification rate is between 98.5-99.5%. This implies that an almost perfect classifier can be developed, if the same level of information is available for an automatic grading system, as for the human grader. This paper identifies the lower qualities (B) as the most difficult to grade. It is uncertain whether the low performances of grade B plants are caused by the small number of plants or the fact that the variance of class B plants is much larger than that of high quality plants (A). It is also found that a considerable improvement can be obtained by employing expert panels. They can be implemented in an automatic grading system, providing a good knowledge base.

ATTEMPTS TO OBTAIN VIROID-FREE HOP PLANTS IN POLAND

Studies on the occurrence of hop latent viroid in plants of different hop cultivars growing in hop gardens in the Lublin region have shown this pathogen to be widespread in plants of all hop cultivars. The pathogen was detected in cones by dot-blot hybridisation. No infection was detectable in small numbers of plants from among each cultivar. The 108 cuttings of these plants were taken in the spring and then planted in a glasshouse in the Hop Experimental Station at Jastkow. In the spring of the following year these plants were replanted on the field near the glasshouse and then were tested for the presence of HLVd by RT-PCR technique. The results of the test were positive for plants of most tested cultivars. Only 7 out of 30 plants from among one cultivar Lomik, gave negative results. The test for detection of HLVd in these plants was repeated in the spring of this year. All tested plants were infected.

Some Limiting Factors and Improvement for the Overwintering Ability of Spring Wheat Sown before Continuous Snow Cover.

It has been known that spring wheat sown immediately before continuous snow cover has higher quality and yield than that sown in spring in the heavy snowfall areas of Hokkaido. To increase the stability of the overwintering of spring wheat sown before continuous snow cover, some limiting factors for overwintering and improvement of wintering ability were studied. The number of germinated seeds increased from the 30th day under snow, and thereafter seminal root and coleoptile elongated. Though the seeds reached their germination percentage measured at 20°C before the 40th day under snow, the percentage of overwintering plants after snow thaw largely decreased. Under snow, snow mold (Typhura ishikariensis) on plants sown before continuous snow cover was observed, which seems to affect the overwintering ability. Germinating seeds at 20°or 2°C before sowing did not improve their overwintering ability. A low germination percentage did not affect overwintering ability, but a smaller number of plants and number of panicle per area decreased grain yield. These results suggest that overwintering ability was not related with the germination process, but it was limited by injury after germination under snow. Overwintering ability was improved by the use of large seeds, more than 2.2mm in diameter, which also affected rapid growth after snow thaw and increased grain yield. It was suggested that large seeds containing much nutrient can enhance plant growth under snow and especially regrowth after snow thaw.