Predicted and actual responses during long-term selection for chemical composition in maize

Selection for higher and lower levels of protein and oil content in maize has been conducted for 61 generations. Response to selection has been irregular, and prediction of response by extrapolation of regression trend lines proved seriously inaccurate in at least 9 of 12 predictions. Application of a selection response formula also yielded generally unsatisfactory predictions. Analysis of the morphological components of oil content led to very accurate prediction of response in the High Oil strain and to a reasonably satisfactory prediction in Low Oil. It was apparent that in the last 55 generations of selection, selection response for oil content was concentrated in two separate morphological characters — germ size in the high selection and oil content of the germ in selection for lower oil content. A satisfactory analysis of the character protein content could not be made from data available.Prepared as part of a research project while the author was a Fulbright senior research fellow at the Max-Planck-Institut für Züchtungsforschung, Köln-Vogelsang, Germany, March–July, 1961.     

Winter barley breeding in the Netherlands

Summary Various Dutch breeders have devoted themselves to winter barley breeding; the local variety Groningen Winter Barley used always to be the foundation material for breeding work. In the course of years 8 new varieties have been derived from it by line selection which demonstrates clearly the degree of variation.The varietal range (fig. 1) shows the peculiarity that the leading variety Vindicat has almost completely been superseded by Urania within some years. If ever, the slogan the Dutch farmer readily accepts new varieties applies here.Its sister variety Vinesco makes a favourable impression.The varieties of winter barley are now for 97 percent based on homebred material.     

The production of hexaploid Solanum x juzepczukii

The colchicine-grafting method of doubling the chromosome number of potato cuttings was used successfully for producing hexaploids from the triploid species, Solanum x juzepczukii. All the plants with hexaploid flowers were triploid/hexaploid sectorial chimeras. Seeds were obtained from crosses of the hexaploid parts with both an andigena-tuberosum hybrid and a tuberosum variety.     

Trials to overcome the incompatibility of crosses between Lycopersicum esculentum and Lycopersicum glandulosum by repeated grafting

In breeding tomatoes for resistance to Corky root Lycopersicum glandulosum is used as a resistant parent. Crosses of tomato with L. glandulosum are difficult to effect because of the incompatibility of the partners. To overcome this incompatibility the approach method was applied beside the conventional crosses.Repeated reciprocal grafting of tomato onto L. glandulosum and also L. glandulosum on tomato did not increase the number of effected matings. The statement that by repeated grafting the characters of the scion change under the influence of the stock could not be confirmed.     

Results of one cycle of recurrent selection in rye

A sufficiently variable rye population was subjected to one cycle of recurrent selection for combining ability in order to ascertain whether this complex property can be repatterned.Some hundreds of clones derived from this population were toperossed to an other unrelated variety used as tester. Through visual selection, more than half of these clones were rejected. The topcross progenies of the remaining clones were subjected to a comparative test whereby, as was to be expected, a considerable degree of variability was demonstrated. From the best 10% and the poorest 10% that is from those which surpassed the general average by at least 1.5 standard deviation units or remained below that average by at least 1.5 , narrowed populations were built up. This was done with the aid of reserve seed which in the year in which the top cross was made had been obtained from these clones, either through compulsory selfpollination or by allowing the clones to fertilize each other in isolation. The two subpopulations obtained through selection in opposite directions further indicated as high and low were crossed en masse with the same tester variety as the first time. In addition a large number of randomly taken individuals from the high synthetic were cloned and toperossed to this common tester. On testing the top crosses carried out en masse, the high synthetics clearly yielded more than the low ones. In one trial it was even found that the high synthetic surpassed our standard variety Petkus by approximately 20%. It is possible, therefore, to segregate a population into two fractions of different combining ability.The optimistie pieture to be derived from the foregoing trials unfortunately is shaded by the results of the individual test crosses pointing to a shift of the frequency distribution in a negative sense in regard to the original population. The influence of the year may be mentioned as a possible cause of this contrast and also the fact that in the original population a close visual selection had been practised while those obtained from the synthetic resulting after one cycle were derived from individuals which had been taken entirely at random.

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Samenvatting Een voldoende variabele roggepopulatic werd onderworpen aan één ronde van cyclisch herhaalde selectic op combinatie-geschiktheid ten einde na te gaan of deze complexe eigenschap kan worden vervormd.Enige honderden klonen voortgekomen uit deze populatie werden onderworpen aan een top-cross door een als tester gebruikt ander, onverwant, ras. Op grond van visuele selectie werd meer dan de helft van deze klonen afgekeurd. De proefkruisings-nakomelingschappen van de overblijvende klonen werden aan een vergelijkende toets onderworpen waarbij zoals viel te verwachten een aanzienlijke variabiliteit in opbrengstvermogen aan het licht trad. Uit de beste 10% en de slechtste 10%, d.w.z. die welke het algemeen gemiddelde met minstens 1,5 overschreden resp. daar minstens 1,5 beneden bleven, werden vernauwde populaties opgebouwd. Dit geschiedde met behulp van reservezaad dat in het jaar waarin de top-cross werd verricht van deze klonen was gewonnen, hetzij door gedwongen zelfbestuiving, hetzij door de klonen in isolatie aan onderlinge bestuiving over te laten. De op deze wijze verkregen twee in tegenovergestelde richting geselecteerde sub-populaties-aangeduid als high en low-werden en masse gekruist met hetzelfde tester ras als de eerste keer. Bovendien werd een groot aantal willekeurig uit het high syntheticum genomen individuen tot klonen gemaakt en onderworpen aan een top-cross door het zoëven genoemde tester ras. Bij de toetsing van en masse uitgevoerde proefkruisingen bleek de combinatie high x tester duidelijk meer op te brengen dan low tester. In een proef werd zelfs gevonden dat high x tester ons standaardras Petkus met ongeveer 20% overtrof. Het blijkt dus mogelijk een populatie te splitsen in 2 fracties van uiteenlopende combinatie-geschiktheid.Het optimistische beeld dat men uit de zo juist vermelde proeven krijgt wordt helaas verduisterd door de resultaten van de individuele proefkruisingen welke wijzen op een verschuiving van de frequentieverdeling in negatieve zin ten opzichte van de oorspronkelijke populatie. Als mogelijke oorzaken van deze tegenstelling kunnen worden aangewezen jaarinvloeden en tevens het feit dat onder de klonen uit de oorspronkelijke populatie een scherpe selectie op het oog werd toegepast terwijl die uit het na één cyclus verkregen syntheticum werden afgeleid van volkomen willekeurig genomen individuen.

     

“Production et fixation des variétés” by Carrière, 1865

The author draws our attention to the book Production et fixation des variétés dans les végétaux published 100 years ago.This book gives us a clear picture of the knowledge and ideas prevailing in plant breeding at that time.

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Production et fixation des variétés by Carrière, 1865

     

The influence of modifier genes on the intensity and stability of self-incompatibility in cabbage

Summary Four inbred cabbage lines have been derived from a single parental plant through several generations of selfing. Two inbreds have been found homozygous for an S ₁ allele while the other two are each homozygous for S ₂. Each inbred is self-incompatible, cross-incompatible with the inbred carrying the same S allele, and fully cross-compatible with inbreds carrying the other S allele. The S ₁ and S ₂ pairs of inbreds were each found to consist of one inbred with very high self-incompatibility (mean seed set of 0.15–0.25 seeds per pod) and one inbred with less intense self-incompatibility (mean seed set of 1.25–1.70 seeds per pod). For the S ₁ pair, flower to flower and plant to plant variation in seed set per pod was much larger for the less incompatible inbred that for the highly incompatible inbred. Further, incompatibility expression of the less incompatible inbred was influenced by temperature variation while that of the highly incompatible inbred was stable under different temperature regimes. The F₁ between the two inbreds of high and low incompatibility with the common S ₁ allele behaved like the less incompatible parent. F₂ plants showed intermediate intensities of selfincompatibility as well as variation for both lesser and greater intensities than those exhibited by the parents. The variations of self-compatibility and the sensitivity to environmental differences are considered to be conditioned by genes which modify incompatibility expression of the S alleles.     

The breeding of peas in the Netherlands

Summary The varietal assortment of Dutch round blue pea varieties has changed considerably. At the beginning of this century their cultivation was based entirely on the varieties bred by Dr R. J. Mansholt at Westpolder (Gr.). Since 1937 the Unica pea produced by P. J. Hijlkema, Mensingeweer (Gr.), has gained ground. Mansholt's G.E.K. and Unica were dominant for many years, and were also used abroad.A remarkable change in the varietal assortment of the round blue peas occurred since the appearance of varieties less susceptible to the Fusarium solani foot disease. Particularly the Rondo C.B. pea of the Plant Breeding Station C.B. (Dir.: Ir C. Koopman) at Hoofddorp has become widely grown (Fig. 2).In addition, it was this same station that succeeded in breeding a variety entirely resistant to fusarium wilt.It is clear that, in the course of the past few years, new varieties have been bred by the breeders. The new varieties excelled the established ones in one or more respects.Some varieties were widely distributed, others were discarded by the breeders after a couple of years, or (since 1924, the year when the first List of Varieties appeared) written off the List.Widely cultivated varieties had to retire in their turn when better ones came on the market.Even at present time Dutch plant breeders are working hard to improve the yield, quality and reliability of peas.     

Interspecific crosses in the genus lycopersicum

The agene of the corky root disease of Dutch glasshouse tomatoes is a non-sporulating fungus of the group Mycelia sterilia. The breeding programme for corky root resistance is based on the resistance derived from Lycopersicum glandulosum. To test the best way of backcrossing we made backcrosses in all possible combinations between tomato, triploid F ₁ hybrid (tomato × Lycopersicum glandulosum) and Lycopersicum glandulosum. Our experiments showed that the shortest way from the wild resistant Lycopersicum back to the commercial type of the tomato possessing the desired resistance was backcrossing the F ₁ triploid hybrid to Lycopersicum glandulosum.     

Effect of some environmental factors on the appearance of “June Yellows” in strawberries and its significance for the development of a test method

Summary The symptoms of June Yellows in strawberries only appear in spring and autumn, and vary in extent from year to year. In order to find a test method for June Yellows which would make it possible to produce yellows symptoms independently of the weather conditions, an investigation of the climatic factors favouring the appearance of yellows was started.It proved possible to produce in apparently normal plants of the varieties Auchincruive and Blakemore symptoms of both Transient Yellows and Streak by growing them at 5°C and providing artificial light of about 7000 lux for at least 12 hours per day.For plants from an environment with a relatively low temperature a treatment of about two months proved sufficient to produce a maximum effect. For plants from an environment with a relatively high temperature a treatment of about three months was necessary to obtain a maximum reaction.

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Samenvatting De symptomen van voorjaarsbont bij aardbeien treden uitsluitend op in het voorjaar en najaar, maar in verschillende jaren in verschillende mate. Teneinde de beschikking te krijgen over een toetsmethode op Voorjaarsbont, waarbij onafhankelijk van toevallige weersomstandigheden bontsymptomen kunstmatig geproduceerd kunnen worden, is een onderzoek ingesteld naar klimaatsfactoren welke het optreden van bont begunstigen.Het bleek mogelijk om bij uiterlijk normale planten van de rassen Auchincruive Climax en Blakemore symptomen zowel van Transient Yellows als van Streak te voorschijn te roepen door ze te plaatsen in een omgeving met een temperatuur van 5°C en een belichting van ±7000 lux gedurende minstens 12 uren per etmaal. Voor planten afkomstig uit een koude omgeving bleek een behandeling van ongeveer twee maanden voldoende te zijn om een maximaal effect te bereiken, bij planten uit een warme omgeving was voor een maximale reactie een behandeling van ongeveer drie maanden nodig.

     

Inheritance of tolerance to leaf iron deficiency chlorosis in tomato

By using two tomato genotypes, 227/1 (Fe chlorosis susceptible) and Roza (Fe chlorosis tolerant), and their reciprocal F₁, F₂ and BC₁ generations, the inheritance of tolerance to leaf Fe deficiency chlorosis of Roza was studied. Plants were grown in a nutrient solution and subjected to 2.0 × 10^–6 M Fe EDDHA and 10 mM NaHCO₃ to induce Fe deficiency stress by stabilization of pH to 7.8–8.2. A rating scale of 1–3 for chlorophyll was used and both monogenic and polygenic inheritance hypotheses were tested. Better responses to Fe deficiency, as measured by SPAD meter values, were obtained from the cross Roza × 227/1 than from the reciprocal cross. Data from F₂ and BC₁ suggest Fe chlorosis tolerance of Roza is to be controlled by polygenic loci with a relatively high additive effect.     

Numerical taxonomy of Portuguese Tronchuda cabbage and Galega kale landraces using morphological characters

Summary A morphological study was carried out to determine the relationships among Portuguese cole landraces using 58 accessions belonging to: (i) Portuguese Tronchuda cabbage (Brassica oleracea var. tronchuda Bailey syn. var. costata De Candolle, Couve Tronchuda); (ii) Portuguese Galega kale (B. oleracea var. acephala De Candolle, Couve Galega); and (iii) other economically less important coles such as Algarve cabbages (B. oleracea var. capitata L., Couve do Algarve or B. oleracea var. sabauda L., Couve Repolho-lombarda do Algarve). The cole accessions were collected from the growers, studied under field conditions during two consecutive years, and characterized using 46 morphological characters from seedling stage to ripe silique. Morphological data were analysed by numerical taxonomy techniques using UPGMA (Unweighted Pair Group Method Using Arithmetic Averages) and by principal component analysis (PCA). Phenograms based on correlation and distance coefficients showed the existence of 8 main groups (A-H). Five of these groups correspond to Tronchuda cabbage landraces: (A) Couves de Trás-os-Montes; (B) Couves do Minho; (C) Couves from Central Portugal; (D) Couve Portuguesa; (E) Couves from Southern inland Portugal. The three other groups correspond to: (F) cabbages; (G) miscellaneous coles; and (H) Galega kales. Landrace groups are primarily associated with morphological differences among accessions and secondly with accession geographical origin. The interannual character variation did not affect the clustering patterns of the accessions and therefore the stability of landrace classification. PCA was congruent with the landrace groups defined by the phenograms and gave supplementary information on the usefulness of the characters for the definition of the various groups.     

Investigation on the susceptibility to club root

Summary Club root (Plasmodiophora brassicae) is a destructive disease of several cruciferous crops in practically all countries. The cultivation of resistant varieties offers the best possibility for control.This disease causes in some areas of the Netherlands considerable damage to turnips which are frequently grown as a catch crop in many regions; other cruciferous crops are generally grown on a much smaller scale.On badly infested plots we found a yield reduction ranging from 35–80%, depending on the method of calculation. In foreign literature (Findley, Van Slijcken andLindfors) figures ranging between 15–100% are reported.Crops and varieties with an abundant foliage give with an equal infection a smaller yield reduction than crops and varieties with a smaller amount of leaves.The affected part has a somewhat higher dry matter content and a higher N-content in the dry matter. The content of sugar is considerably lower.Resistance of some crops and of many turnip and swede varieties has been investigated by means of field experiments, carried out in several years. The infection by club root fluctuates, so that a great many replications are required.Table 1 gives a summary of the susceptibility of some fodder crops. Contrary toKarling and others we found that Chinese radish is not immune.As to the turnip types we refer to Table 2. The varieties belonging to the types Halflong green top yellow, Halflong purple top white, Flat round yellow turnip, and Round yellow-fleshed turnip are less susceptible than varieties belonging to the other types. Within the type Halflong purple top white to which the principal varieties of the Netherlands can be ranged, there appears to exist the greatest variation in susceptibility. Several foreign varieties stated as resistant were more or less badly affected (Table 3).The percentage of destroyed plants correlates with the percentage of affected plants.Resistance may correlate with sweet taste. Some resistant varieties are now being investigated in the Netherlands.The results of some of our trials suggested the existence of physiological strains of club root within the crop turnips. Several examples of such physiological races in various crops have been mentioned in literature.In breeding work we consider it advisable to allow for the existence of physiological strains of club root within the crop turnips.

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Samenvatting Knolvoet (Plasmodiophora brassicae) is in praktisch alle landen een belangrijke ziekte voor verschillende kruisbloemige gewassen. De verbouw van resistente rassen biedt nog de beste perspectieven voor de bestrijding, omdat andere maatregelen vaak op practische bezwaren stuiten.Deze ziekte veroor zaakt in sommige streken van Nederland nogal schade bij het gewas stoppelknollen, dat in tal van streken veelvuldig wordt verbouwd; andere kruisbloemige gewassen worden gewoonlijk minder intensief verbouwd.Op zwaar besmette percelen constateerden wij een opbrengstderving van 35–80 %, afhangende van de wijze van berekening. In de buitenlandse literatuur (Findley, van Slijcken enLindfords) vindt men opgaven van 15 %– 100 %, verband houdende met vatbaarheid der rassen en zwaarte van besmetting. Schade kan veroorzaakt worden door wegvallen van zeer jonge planten, groeiremming, aantasting van het te oogsten deel of door snelle rotting.Bladrijke gewassen en bladrijke rassen geven bij gelijke aantasting een geringere oogstderving dan minder bladrijke gewassen en rassen.Het aangetaste deel heeft een wat hoger drogestofgehalte en een hoger N-gehalte in de drogestof. Het suikergehalte is belangrijk lager.Door middel van veldonderzoek op een achttal percelen, uitgevoerd in verschillende jaren, is de resistentie van enkele gewassen en bij stoppelknollen en koolrepen van vele rassen nagegaan. De besmetting door knolvoet is per perceel wisselvallig, zodat zeer veel herhalingen gewenst zijn.Tabel 1 geeft een indruk van de vatdaarheid van enkele voedergewassen.In tegenstelling metscKarling en anderen voden wij, dat Chinese zomeramenas niet immuun is. Bij koolrapen waren de ,,Gele groenkoppen enigszins resistent in vergelijking met andere rassen.Voor de stoppelknollentypen zij verwezen naar tabel 2. De rassen behorend rot de typen ,,Halflange gele groenkop, ,,Halflange witte blauwkop, ,,Platronde gele, Platronde gele en Ronde gele (Gele boterknollen) zijn minder vatbaar dan ressen behorende tot de overige typen. Binnen het type Halflange witte blauwkop, waaronder de belangrijkste rassen in Nederland gerangschikt kunnen worden, blijkt de grootste variatie in vatbaarheid te bestaan. Verschillende buitenlandse, als resistent beoordeelde rassen werden meer of minder zwaar aangetast (tabel 3).Het percentage weggevallen planten correleert met het percentage aangetaste planten.Resistentie lijkt wel verenigbaar met zachte smaak. In Nederland zijn thans enige resistente rassen in onderzoek.Op enkele proefvelden gaven de uitkomsten ons aaleiding tot de veronderstelling, dat er physio's bestaan binnen het gewas stoppelknollen.Er zijn verschillende voorbeelden in de literatuur vermeld van physio's bij verschillende gewassen.Er is verder nog een voorbeeld gegeven, waaruit blijkt, dat men voorzichtig moet zijn met conclusies hierover.Bij de veredeling lijkt het ons gewenst met de mogelijkheid van het bestaan van verschillende physio's binnen het gewas stoppelknollen rekening en houden.

     

Theoretical studies on the methodological procedures of radiation breeding

Radiation breeding for the introduction of additional desirable characters into improved varieties in autogamous plants, especially in cereals, would be much more feasible if more efficient screening methods could be found. Such methods are proposed in this report. From the standpoint of the theory of probability, it is intended to establish effective screening methods by which a desirable X₂ mutant can be detected in a minimum total of X₂-plants, and/or X₁- and X₂-plants in the aggregate.The relative efficiencies of four new methods and the standard method are compared, the improved ear-to-row method (method B), the one-plant-one-grain method (method C), the one-plant-two-grain method (method D) and one-plant-three-grain method (method E) all of which are more effective than the conventional ear-to-row method (method A). In method B, the total number of X₂-plants required to recover at least one desirable X₂-plant is obtained when the probability of detecting at least one X₂-line with one or more desirable mutants among X₂-lines is equal to the probability of detecting at least one desirable mutant among plants in that X₂-line. In methods C, D and E, one, two or three grains respectively, taken from each of the X₁-plants of the number required to detect at least one desirable X₂-plant, are sown to obtain corresponding X₂-plants.The number of X₁-plants, total X₂-plants, and X₁- and X₂-plants in the aggregate required to obtain at least one desirable mutant (m, mn and m+mn respectively) shows the following relations: method C>D>A>E>B for m, ABED>D>C for mn and ABC>D>E (the last two being very close to each other) for m+mn.Each of the new methods B, C, D and E will be applicable in radiation breeding. When the discrimination of a mutant is difficult method B will be useful. On the contrary, when a mutant is easily distinguishable, method C, with dense planting in X₁, will frequently be much better. In some cases methods D and E, especially D, will be more useful in the practice of radiation breeding than method C. Method A should not be used in any case.     

The genetical control of the everbearing habit and three other characters in varieties of fragaria vesca

A genetical study was made of three diploid varieties of Fragaria vesca, namely, wild type and two cultivated Alpine varieties, Baron Solemacher and Bush White. The varieties differ in several characters, including flowering habit, runnering habit, branching habit and fruit colour. Wild type is seasonal flowering, produces runners, has a simple branching habit and has red fruit. Both the Alpine varieties have a perpetual flowering (everbearing) habit and produce no runners. Buron Solemacher resembles wild type in branching habit and fruit colour, whereas Bush White has a very bushy habit (i.e., has a large number of crowns per plant) and has white fruit.Wild type F. vesca was crossed with the two Alpine varieties, and the F₁ progenies were selfed and back-crossed to the Alpine parents. The results indicate that the differences in flowering habit are controlled by a single major gene, seasonal flowering being dominant to perpetual flowering, the recessive alleles in the two perpetual flowering varieties apparently being identical. Differences in runnering habit also appear to involve a single gene locus but non-runnering is associated with the bushy habit in Bush White and therefore either the three alleles of the same gene occur or the gene controlling bushiness in separate but closely linked with the gene controlling runnering. Fruit colour is controlled by one major gene locus, red being dominant to white fruit. All three major genes segregate independently. In all cases the characters of the wild type are dominant. The possible nature of the physiological process controlled by the gene for flowering habit is discussed.     

Swedish land-races of red clover

The collection of Swedish local red clover strains, owned by the Swedish Seed Growers' Association, may serve as an attempt to organize a gene bank for land-races of red clover in Northern Europe. From all 43 strains seed is available and it is hoped that seed of satisfactory germination capacity can be kept available for the future. It may be obtained for research purposes in samples of not larger than 100 grams from the Swedish Seed Association, Uppsala 1, Sweden.     

Vaktijdschriften op het gebied van de plantenveredeling

Summary The English abstracting journal Plant Breeding Abstracts gives a satisfactory synopsis of books on plant breeding and of articles in this field that have appeared in general and professional journals.In the above survey are mentioned the following periodicals: Sveriges Utsädesföreningstidskrift (1891 ), Zeitschrift für Pflanzenzüchtung (1913 ), Der Züchter (1929 ), Agri Hortique Genetica (1943 ), Indian Journal of Genetics and Plant Breeding (1941 ), Melhoramento (1948 ), Annales de l'Amélioration (1951 ) and Euphytica, Netherlands Journal of Plant Breeding (1952 ).

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Vaktijdschriften op het gebied van de plantenveredeling

     

Theoretical studies on the methodological procedures of radiation breeding

If the expectation of the number of desirable mutants for equal size of X ₂-populations decreases with decreasing number of plants per X ₂-line, the one-plant-one-grain method (method C), the one-plant-two-grain method (method D), and the one-plant-three-grain method (method E), especially method C, would be disadvantageous in comparison with the improved ear-to-row method (method B) and the conventional ear-to-row method (method A).From theoretical considerations it can be shown that a probability of occurrence of an X ₂-line containing desirable mutant (p ₁) and a conditional probability of occurrence of such desirable mutant for each one of the plants in such an X ₂-line (p ₂) are not affected by the number of X ₂-lines (m), but by the number of plants per X ₂-line (n). Consequently, the expectation of the number of desirable mutants in an X ₂-population, E(I), can be given by E(I) = mp ₁(1– q ₂ n · n p ₂/(1 –q ₂ n) = mn p ₁ p ₂ where p ₁+q ₁=1 and p ₂+q ₂=1.Therefore, with respect to E(I), method A=B=C=D=E for equal size of X ₂-populations. However, method ABE>D>C for different sizes of X ₂-populations.Most of this work was carried out in the National Institute of Agricultural Sciences, Hiratsuka, Japan.     

A new,useful flowering characteristic in Beta vulgaris L.

In a culture of Beta vulgaris L., Czechoslovak semi-sugar-beet variety Choovka, one plant was found of which all flowers came into flower simultaneously; they were distributed with regular density; all glomerules—even at the twig tips—were of the same size and ripened at the same time. These properties which are of a great economic value were fixed by further cultivation.     

Large-scale use of F1 hybrids in „Vorstenlanden” tobacco

Summary In the preceding pages an outline has been given of the methods used in breeding of Vorstenlanden tobacco. The new tobacco strains introduced on a large scale have been obtained by:1. Individual selection in old populations.2. Individual selection in F₂ and following generations, after crossing several true-breeding Vorstenlanden types.3. Individual selection in F₂ and following generations, after crossing of a Timor strain with Vorstenlanden tobacco and repeated backcrossing with Vorstenlanden strains. Through this practice,Phytophthora resistance could be combined with good Vorstenlanden quality.4. Artificially induced mutations by means of X raying young flower buds. This gave a tobacco strain with an exceptionally bright leaf color. This latest new strain could only be introduced through growing of F₁ hybrid mutant × typica, by doing so the bright color of the leaves could be combined with the normal number of leaves per plant.By growing various F₁ hybrids on a large scale, viz. of thePhytophthora resistant tobacco strain crossed with several other tobacco strains, selected for quality characteristics, combinations have been obtained, in whichPhytophthora resistance has been saved, while the advantage of growing different types of tobacco has not been lost.Because of a decrease in the variation of quality types, through the loss of seed of many selected strains at the reopening of the tobacco plantings, it is highly recommendable to pay full attention in the future to the possibilities, created by the large scale use of F₁ hybrids.Samenvatting Het op grote schaal gebruik maken van F₁ planten bij de Vorstenlandse tabak.De in de practijk op grote schaal verbouwde nieuwe tabakslijnen werden verkregen door:1. Individuele selectie in de oude populatie.2. Individuele selectie in de F₂ en volgende generaties na kruising van verschillende zaadvaste Vorstenlandse typen.3. Individuele selectie in de F₂ en volgende generaties na kruising van een resistent Timor-type met Vorstenlandse tabak en herhaalde terugkruising met Vorstenlandse lijnen. Hierdoor konPhytophthora-resistentie worden gecombineerd met zeer goede Vorstenlandse kwaliteit.4. Kunstmatig opgewekte mutaties door middel van Röntgenbestraling van de jonge bloemknoppen. Dit leverde een voor de practijk zeer gewaardeerde tabakslijn op met uitzonderlijk heldere bladkleur. Deze laatste lijn kon in de practijk uitsluitend worden geintroduceerd door het planten van de F₁ mutant × typica, waardoor de heldere bladkleur kon worden gecombineerd met het normale aantal bladeren per plant.Door op grote schaal gebruik te maken van F₁ planten, verkregen door dePhytophthora-resistente tabakslijn te kruisen met verschillende andere op kwaliteitseigenschappen geselecteerde lijnen, werden belangrijke resultaten verkregen. DePhytophthora-resistentie werd behouden en het voordeel om tabak van verschillend type aan de markt te kunnen brengen, ging niet verloren.Doordat de variatie in kwaliteitstypen, door het verlies van het zaad van vele geselecteerde lijnen, is verminderd, verdient het aanbeveling in de toekomst, bij herstel van de tabakscultuur, alle aandacht te besteden aan de mogelijkheden, welke door het op grote schaal gebruik maken van F₁ planten worden geschapen.