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Bij een aantal gewassen is het nog problematisch om goed biologisch zaad te produceren zonder gewasbeschermingsmiddelen. Dat beperkt de beschikbaarheid en verhoogt de kosten van biologisch zaad. Onderzoek heeft kennis opgeleverd voor zaadbedrijven om de kwaliteit te verbeteren

Verslag van het veredelingsonderzoek op het Proefstation voor de Boomkwekerij te Boskoop. De belangrijkste beoordelingscriteria van 30 bestaande cultivars en 12 selecties uit het onderzoek waren: bloeirijkheid, bloemkleur, bladkwaliteit en groeiwijze

In het eerste deel in Dendroflora nr. 32 (pag. 6-23) is een overzicht van asters gegeven en zijn de belangrijkste soorten en cultivargroepen beschreven. Als vervolg hierop worden in dit artikel de cultivars van kleinbloemige herfstasters behandeld met gegevens over gebruikswaarde, ziekten en plagen

De Commissie Kwaliteitskeuring Aardappelen heeft 5 voorschriften opgesteld aan de hand waarvan kwaliteitskeuring van aardappelen kan worden uitgevoerd

Bij een aantal gewassen is het nog problematisch om goed biologisch zaad te produceren zonder gewasbeschermingsmiddelen. Dat beperkt de beschikbaarheid en verhoogt de kosten van biologisch zaad. Onderzoek heeft kennis opgeleverd voor zaadbedrijven om de kwaliteit te verbeteren

Marktanalyse van zaadleverende bedrijven voor de groentesector in Nederland, Frankrijk, Engeland, Italie en China

Voorbeelden van hybride-zuiverheidsbepaling middels de methode STMS (Sequence-Tagged Microsatellite Site) ook wel SSR (Simple Sequence Repeat) of STR (Short Tandem Repeat) genoemd

Seeds are complex biological structures and the primary dispersal units of higher plants. They consist of nutrient reserve storage tissue(s), an embryo and encapsulating structures designated for protection and that may also regulate germination. Seeds have developed mechanisms of withstanding desiccation without losing the ability of immediate reactivation of embryo growth upon rehydration.The arrest and reactivation of cell cycle related events appear to be intimately linked to the arrest of growth during seed development and reactivation of growth during germination. In this thesis, DNA synthesis,β-tubulin accumulation and appearance of microtubular cytoskeleton are studied in relation to morphological and physiological events that are involved in seed development and germination. Biochemical techniques are used to study the relation between DNA replication andβ-tubulin accumulation in embryonic cells of germinating seeds (Chapters 2 and 3). Then, immunocytochemical techniques are applied for the detection and visualisation of DNA synthesis activity and appearance of microtubular cytoskeleton in seed tissues during development and in embryos during germination (Chapters 4, 5 and 6).The results obtained in this study show a general pattern of tomato seed development and germination based on the quantitation and distribution of nuclear DNA synthesis activity,β-tubulin accumulation and microtubular cytoskeleton appearance in cells of the seed tissues. The pattern in embryos during seed germination appeared as a "mirror image"of that during development (Chapters 4 and 5). Cell cycle activities are intense during early stages of seed development and then arrest as seeds become mature. Embryonic DNA synthesis activity, together with the presence of mitotic microtubular cytoskeleton arrays and cell divisions define the period of embryo histodifferentiation. Therafter, the presence of cortical microtubular cytoskeleton and absence of DNA synthesis acitvity defines the phase of embryo growth and completion of morphogenesis. Finally, the microtubular cytoskeleton is degraded as seeds become quiescent, defining the maturation phase. The roles of GA and ABA in seed development are evaluated in the differing developmental patterns observed for the GA-deficient ( gib1 ) and ABA-deficient ( sit w) mutants. Upon imbibition in water, the cell cycle is reactivated and becomes intense as germination is completed. Initially, the cortical microtubular cytoskeleton appears and DNA synthesis is initiated in meristematic cells of embryonic radicle tip region. Thereafter, replicated nuclear DNA is detected together with mitotic microtubular cytoskeleton arrays and cell divisions, prior to radicle protrusion through the seed coat. Both primary and secondary dormancy are characterised by a very low cell cycle activity. The depth of dormancy appears to be related to the progression of the cell cycle prior to the induction of dormancy (Chapter 6).Finally, in the form of a descriptive model, it is proposed to modify the current notion of the different phases in tomato seed development and germination.

Seeds are complex biological structures and the primary dispersal units of higher plants. They consist of nutrient reserve storage tissue(s), an embryo and encapsulating structures designated for protection and that may also regulate germination. Seeds have developed mechanisms of withstanding desiccation without losing the ability of immediate reactivation of embryo growth upon rehydration.The arrest and reactivation of cell cycle related events appear to be intimately linked to the arrest of growth during seed development and reactivation of growth during germination. In this thesis, DNA synthesis,β-tubulin accumulation and appearance of microtubular cytoskeleton are studied in relation to morphological and physiological events that are involved in seed development and germination. Biochemical techniques are used to study the relation between DNA replication andβ-tubulin accumulation in embryonic cells of germinating seeds (Chapters 2 and 3). Then, immunocytochemical techniques are applied for the detection and visualisation of DNA synthesis activity and appearance of microtubular cytoskeleton in seed tissues during development and in embryos during germination (Chapters 4, 5 and 6).The results obtained in this study show a general pattern of tomato seed development and germination based on the quantitation and distribution of nuclear DNA synthesis activity,β-tubulin accumulation and microtubular cytoskeleton appearance in cells of the seed tissues. The pattern in embryos during seed germination appeared as a "mirror image"of that during development (Chapters 4 and 5). Cell cycle activities are intense during early stages of seed development and then arrest as seeds become mature. Embryonic DNA synthesis activity, together with the presence of mitotic microtubular cytoskeleton arrays and cell divisions define the period of embryo histodifferentiation. Therafter, the presence of cortical microtubular cytoskeleton and absence of DNA synthesis acitvity defines the phase of embryo growth and completion of morphogenesis. Finally, the microtubular cytoskeleton is degraded as seeds become quiescent, defining the maturation phase. The roles of GA and ABA in seed development are evaluated in the differing developmental patterns observed for the GA-deficient ( gib1 ) and ABA-deficient ( sit w) mutants. Upon imbibition in water, the cell cycle is reactivated and becomes intense as germination is completed. Initially, the cortical microtubular cytoskeleton appears and DNA synthesis is initiated in meristematic cells of embryonic radicle tip region. Thereafter, replicated nuclear DNA is detected together with mitotic microtubular cytoskeleton arrays and cell divisions, prior to radicle protrusion through the seed coat. Both primary and secondary dormancy are characterised by a very low cell cycle activity. The depth of dormancy appears to be related to the progression of the cell cycle prior to the induction of dormancy (Chapter 6).Finally, in the form of a descriptive model, it is proposed to modify the current notion of the different phases in tomato seed development and germination.

The research described in this thesis aimed at increasing insight into the sources of variation in quality attributes of individual seeds within a soybean seed lot, into the relations between physical attributes and performance of seeds in seed tests and in controlled seed production conditions, and into the importance of the seed lot quality for crop performance including quality of seeds produced. Cv. IAS-5 (determinate growth habit) was used in all studies. Differences in characteristics within and between plants proved to be important sources of variation in size, weight, shape, viability, and performance of individual seeds in the seed lot produced. Seeds from earlier pods were larger, heavier, more spherical but less viable than from later pods. Seeds from main stems or from the top of the plants were larger and heavier than seeds from the branches or from the bottom of the plants. At these positions also pod set was earlier. Shorter times to emergence and longer periods from first pod set to harvest were associated with larger sizes of seeds produced per plant. Longer periods between first flower and first pod, and shorter periods between first pod and harvest were related to a higher viability of seeds produced per plant, but only under high air temperatures during pod growth and maturation. Within the seed lot studied, different physical seed attributes were associated. Etching and cracking were more frequent in larger and heavier seeds, yellow seeds were larger than greenish seeds. Taking into account these associations was essential to correctly assess the actual contribution of individual attributes to seed performance. Distinct tests assessed different attributes as being important. The tetrazolium test detected etched, cracked, greenish and wrinkled seeds. Conductivity per seed was affected by seed size, weight, cracking and wrinkling. Conductivity on a seed area projection basis (μA/mm 2) was shown to minimize size and weight effects. In this case, also higher conductivity values for greenish seeds were detected. Some individual physical seed attributes affected distinct stages of seedling growth differently. Therefore, conclusions on the importance of physical attributes for seed performance in seedling growth tests may depend on the stage of seedling growth at the time of analysis. Size, weight, shape, etching and wrinkling of seeds planted in soil were not related to emergence under favourable conditions, but fewer seedlings emerged from cracked and from greenish seeds. Within a crop, yield components per plant (number of pods or seeds, total weight of seeds) decreased with increasing size, weight and cracking of the seeds planted. In none of the crops physical attributes of individual seeds planted were associated with quality attributes of the seeds produced by them. Effects of seed lot grading for physical attributes on crop uniformity, and on quality, uniformity and yield of the seeds produced could not be shown.&nbsp

Potato is an important crop in sub-tropical Southwest China, where it is double-cropped in diverse ecological systems. Yields are higher at higher elevation. Spring crops show higher yields but lower light use efficiencies than autumn crops, especially at higher altitudes. The gaps between the actual and potential yields are mainly due to insufficient utilization of radiation and low light use efficiency of the actual crops.Earlier planting in spring increased yield at 500 m asl. At 1200 m asl effects of planting time on yield were absent. In autumn, these effects were generally absent at all elevations, although plant stands were consistently and often severely reduced by early planting.For spring crops, seed tubers should be older at lower altitude and younger at higher altitude than those commonly used. For autumn crops, seed tubers should be relatively old, both at low and high altitudes. Manipulation of seed sources can be done through selecting progenies of previous spring or autumn crops produced either at low or high altitudes, or from early harvest of the seed crop. The observed long-term after-effects of seed origins may have been associated with (unknown) effects on seed health.Heavier seed tubers gave higher yields in all conditions in the range from 20 to 124 g. When numbers of sprouts were set equal per unit area, the effect of weight of seed tubers on final tuber yield per unit area was absent. Tuber numbers per stem increased as seed tuber weight decreased when the seed tubers used were young.Cutting of seed tubers generally promoted plant emergence and increased stem numbers per plant in comparison with the whole seed tuber, per unit seed weight planted; cutting also spread a wilting disease probably mainly caused by Pseudomonas solanacearum, especially at lower altitude.The results of seed or plant density in combination with the effects of planting time, seed tuber weight and intercropping showed that a denser spacing up to 10 seed tubers/m 2consistently increased tuber yields. Plant stand was reduced by higher seed density in most experiments, but not at the expense of yield.Higher total yield of combined potato and maize was obtained when one row of maize was alternated with two rows of potato than when two rows of maize were alternated with two rows of potato. Results suggest that planting dates of the two species can be more closely synchronized in the current intercropping system, to achieve a more efficient use of space and time.Viruses, late blight and bacterial wilt caused varying degrees of yield loss in Sichuan, and they were closely associated with a number of biotic, abiotic and agronomic factors. Varietal resistances to the diseases, especially to late blight and bacterial wilt, were found. Parasitic nematodes were found in variable population densities. Defoliation by 28-spot beetle sometimes was severe.This thesis provides some basic information on crop production and agronomic measures required for further crop improvement in this complex agro-ecological region.

Verslag van het veredelingsonderzoek op het Proefstation voor de Boomkwekerij te Boskoop. De belangrijkste beoordelingscriteria van 30 bestaande cultivars en 12 selecties uit het onderzoek waren: bloeirijkheid, bloemkleur, bladkwaliteit en groeiwijze

The research described in this thesis aimed at increasing insight into the sources of variation in quality attributes of individual seeds within a soybean seed lot, into the relations between physical attributes and performance of seeds in seed tests and in controlled seed production conditions, and into the importance of the seed lot quality for crop performance including quality of seeds produced. Cv. IAS-5 (determinate growth habit) was used in all studies. Differences in characteristics within and between plants proved to be important sources of variation in size, weight, shape, viability, and performance of individual seeds in the seed lot produced. Seeds from earlier pods were larger, heavier, more spherical but less viable than from later pods. Seeds from main stems or from the top of the plants were larger and heavier than seeds from the branches or from the bottom of the plants. At these positions also pod set was earlier. Shorter times to emergence and longer periods from first pod set to harvest were associated with larger sizes of seeds produced per plant. Longer periods between first flower and first pod, and shorter periods between first pod and harvest were related to a higher viability of seeds produced per plant, but only under high air temperatures during pod growth and maturation. Within the seed lot studied, different physical seed attributes were associated. Etching and cracking were more frequent in larger and heavier seeds, yellow seeds were larger than greenish seeds. Taking into account these associations was essential to correctly assess the actual contribution of individual attributes to seed performance. Distinct tests assessed different attributes as being important. The tetrazolium test detected etched, cracked, greenish and wrinkled seeds. Conductivity per seed was affected by seed size, weight, cracking and wrinkling. Conductivity on a seed area projection basis (μA/mm 2) was shown to minimize size and weight effects. In this case, also higher conductivity values for greenish seeds were detected. Some individual physical seed attributes affected distinct stages of seedling growth differently. Therefore, conclusions on the importance of physical attributes for seed performance in seedling growth tests may depend on the stage of seedling growth at the time of analysis. Size, weight, shape, etching and wrinkling of seeds planted in soil were not related to emergence under favourable conditions, but fewer seedlings emerged from cracked and from greenish seeds. Within a crop, yield components per plant (number of pods or seeds, total weight of seeds) decreased with increasing size, weight and cracking of the seeds planted. In none of the crops physical attributes of individual seeds planted were associated with quality attributes of the seeds produced by them. Effects of seed lot grading for physical attributes on crop uniformity, and on quality, uniformity and yield of the seeds produced could not be shown.&nbsp

The thesis describes the genetic bases of 2n-pollen formation. A comparison was made of the frequencies of 2n-pollen production in a different environment using the progeny of diallel crosses between five well-known diploid clones and three clones of Solanum phureja. It was evident that this character has a complex type of inheritance; through repeated cycles of selection for 2n-pollen a four-fold increase could be achieved at population level. Through proper selection of diploid male parents it was established that 2n-pollen genotypes can be effective for transferring useful characters, like bacterial wilt resistance, in 4x-2x crosses. The progenies derived from 4x-2x, 4x-4x and 4x-selfings were compared to find the optimal breeding approach for the production of TPS varieties. There were clear indications that it was possible to breed TPS varieties directly by 4x-2x crosses. This means that the advantages of breeding at diploid level and the effective transfer of desirable Units by 2n-gametes can be used in the TPS breeding.

The thesis describes the genetic bases of 2n-pollen formation. A comparison was made of the frequencies of 2n-pollen production in a different environment using the progeny of diallel crosses between five well-known diploid clones and three clones of Solanum phureja. It was evident that this character has a complex type of inheritance; through repeated cycles of selection for 2n-pollen a four-fold increase could be achieved at population level. Through proper selection of diploid male parents it was established that 2n-pollen genotypes can be effective for transferring useful characters, like bacterial wilt resistance, in 4x-2x crosses. The progenies derived from 4x-2x, 4x-4x and 4x-selfings were compared to find the optimal breeding approach for the production of TPS varieties. There were clear indications that it was possible to breed TPS varieties directly by 4x-2x crosses. This means that the advantages of breeding at diploid level and the effective transfer of desirable Units by 2n-gametes can be used in the TPS breeding.

In a broad based study, various aspects of the control of the diseases Rhizoctonia solani and Phytophthora infestans were studied in a biological cultivation system. Experiments were carried out on organic farms. In addition a farm study was carried out in which the cultivation of seed potatoes was followed and recorded for a period of three years on 15 organic farms

In het eerste deel in Dendroflora nr. 32 (pag. 6-23) is een overzicht van asters gegeven en zijn de belangrijkste soorten en cultivargroepen beschreven. Als vervolg hierop worden in dit artikel de cultivars van kleinbloemige herfstasters behandeld met gegevens over gebruikswaarde, ziekten en plagen

In a broad based study, various aspects of the control of the diseases Rhizoctonia solani and Phytophthora infestans were studied in a biological cultivation system. Experiments were carried out on organic farms. In addition a farm study was carried out in which the cultivation of seed potatoes was followed and recorded for a period of three years on 15 organic farms

Minitubers are small seed potato tubers that can be produced year-round in glasshouses on in vitro propagated plantlets planted at high density. The research reported in this thesis studied the agronomical and physiological principles of the production of minitubers and their performance under Dutch field conditions. The minitubers had fresh weights between 0.125 and 4.000 g.More than 3000 minitubers per m 2were produced in 10 weeks (average fresh weights 1 - 2 g), when tubers were harvested 4, 7 and 10 weeks after planting, using a non-destructive harvesting technique in the first two harvests. Removing tubers in the first harvest resulted in initiation of new tubers because more potential tuber sites became available that were not subjected to the dominance of rapidly growing tubers. Part of the newly initiated tubers grew to a harvestable size within three weeks, but the number of tubers in harvestable sizes did not increase thereafter, whereas part of the undersized tubers was resorbed. The second harvest stimulated growth of tubers that otherwise would have been resorbed or would have remained too small.Almost all minitubers≥0.5 g survived storage at 2 °C for 1.5 years. After 6 months of storage, growth of plants from minitubers was still poor. Largest leaf areas were achieved after 10 - 11 months of storage, highest stem numbers, progeny tuber weights and harvest indices after 14 - 15 months of storage for cv. Agria and after 18 - 19 months for cv. Liseta.The performance of minitubers was affected considerably by their weight. Lighter tubers had a longer dormant period, partly because of a slower sprout growth up to 2 mm (used to assess the end of dormancy). Plants from lighter tubers took longer to emerge and at emergence had thinner stems, lower root weights, and higher shoot:root ratios. Crops from lighter minitubers produced lower yields because of less radiation intercepted (slower ground cover) and a lower harvest index. Multiplication factors per planted tuber were lower in crops from lighter minitubers because fewer plants emerged or survived, and fewer progeny tubers and lower weights were produced per plant. Yield variation within a crop was higher in crops from lighter minitubers, but - when properly nursed - variation in yield over years was not affected by the weight. Effects of minituber weight generally became less clear in the higher weight ranges. Differences in performance between minitubers and conventional tubers were attributed to weight and age of seed tubers, presprouting method and crop husbandry.Minitubers can be used in the first year of potato seed production programmes to speed up multiplication and to increase the quantity of seed from new cultivars.

Minitubers are small seed potato tubers that can be produced year-round in glasshouses on in vitro propagated plantlets planted at high density. The research reported in this thesis studied the agronomical and physiological principles of the production of minitubers and their performance under Dutch field conditions. The minitubers had fresh weights between 0.125 and 4.000 g.More than 3000 minitubers per m 2were produced in 10 weeks (average fresh weights 1 - 2 g), when tubers were harvested 4, 7 and 10 weeks after planting, using a non-destructive harvesting technique in the first two harvests. Removing tubers in the first harvest resulted in initiation of new tubers because more potential tuber sites became available that were not subjected to the dominance of rapidly growing tubers. Part of the newly initiated tubers grew to a harvestable size within three weeks, but the number of tubers in harvestable sizes did not increase thereafter, whereas part of the undersized tubers was resorbed. The second harvest stimulated growth of tubers that otherwise would have been resorbed or would have remained too small.Almost all minitubers≥0.5 g survived storage at 2 °C for 1.5 years. After 6 months of storage, growth of plants from minitubers was still poor. Largest leaf areas were achieved after 10 - 11 months of storage, highest stem numbers, progeny tuber weights and harvest indices after 14 - 15 months of storage for cv. Agria and after 18 - 19 months for cv. Liseta.The performance of minitubers was affected considerably by their weight. Lighter tubers had a longer dormant period, partly because of a slower sprout growth up to 2 mm (used to assess the end of dormancy). Plants from lighter tubers took longer to emerge and at emergence had thinner stems, lower root weights, and higher shoot:root ratios. Crops from lighter minitubers produced lower yields because of less radiation intercepted (slower ground cover) and a lower harvest index. Multiplication factors per planted tuber were lower in crops from lighter minitubers because fewer plants emerged or survived, and fewer progeny tubers and lower weights were produced per plant. Yield variation within a crop was higher in crops from lighter minitubers, but - when properly nursed - variation in yield over years was not affected by the weight. Effects of minituber weight generally became less clear in the higher weight ranges. Differences in performance between minitubers and conventional tubers were attributed to weight and age of seed tubers, presprouting method and crop husbandry.Minitubers can be used in the first year of potato seed production programmes to speed up multiplication and to increase the quantity of seed from new cultivars.

De Commissie Kwaliteitskeuring Aardappelen heeft 5 voorschriften opgesteld aan de hand waarvan kwaliteitskeuring van aardappelen kan worden uitgevoerd