Interspecific hybridization in Cucumis (L.). I. Need for genetic variation,biosystematic relations and possibilities to overcome crossability barriers

Summary The genetic variation in pickling and slicing cucumbers (C. sativus L.) seems insufficient to enable the breeder to solve serious cultivation problems. Wild allies of C. sativus possess a wide range of interesting characters which could be incorporated by means of species crosses. In the past, attempts to achieve such crosses have failed. Important characters of Cucumis species are mentioned and biosystematic problems discussed. Results of previous research on species crosses prompted an examination of the prospects of further research.     

The significance of andromonoecism for the breeding of Asparagus officinalis L. II

Summary Following a previous publication in this periodical (3), indicating the lines along which an entirely male asparagus variety can be obtained, the above article further discusses the difficulties to be overcome. The combination of andromonoecism and homozygosis for the male sex (andromonoecious MM-plants) is discussed in more detail. These plants, some hundreds of which are now in the possession of the Institute of Horticultural Plant Breeding, have the great advantage that they can be readily used to produce large numbers of MM plants. There is the danger, however, that andromonoecism is transmitted to the commercial seed of the male variety. Although the available figures do not yet provide certainty as to the genetic behaviour of andromonoecism, transmission is likely to depend on some dominant factors. Proceeding from this assumption we could already indicate in principle how to prevent andromonoecism in commercial seed.     

Geert Veenhuizen (1857–1930), the pioneer of potato breeding in the Netherlands

Potato breeding proper in the Netherlands started in 1888 at the initiative of Geert Veenhuizen at Sappemeer. He was very successful in breeding new potato varieties and stimulated Dutch farmers to tackle potato breeding.On November 18, 1957, just 100 years from the day that Veenhuizen was born, a memorial meeting was held at Sappemeer. Veenhuizen's significance was illustrated and a portrait presented to the Agricultural University.Reproductions of the portrait and a memoir in higher, secondary and primary agricultural schools will keep alive Veenhuizen's significance for agriculture in the Netherlands.     

The history of the Plant Breeding Institute I.v.P. 1912–1962

Founded in 1912, the Plant Breeding Institute (I.v.P.) has been active in a wide field, particularly since 1923. Many projects have been initiated and developed in this time.Research and instruction in plant breeding have been important items in its working programme. They are supported by a well-organized library.Breeding work and the maintenance of varieties developed by the Institute have been carried out on a modest scale for instructional purposes. Many hybrid populations have been placed at the disposal of Dutch breeders and some important varieties were raised from them.The need of establishing and maintaining international contacts is met by the editing of Euphytica and the co-operation in the European Association for Research on Plant Breeding, Eucarpia.Advice to breeders of agricultural crops, the composition of the List of Varieties of Field Crops, legalisation of varieties and the seed inspection of these varieties were left to the authority of other institutions which were specially founded for those purposes. Close contacts with these organisations were maintained leading to much fruitful co-operation.The successive directors (O. Pitsch, C. Broekema, J. C. Dorst, J. Sneep) have aimed at developing a balanced combination of plant breeding, research on varieties and seed production.     

Breeding parthenocarpic pickling cucumbers (Cucumis sativus L.): Necessity,genetical possibilities,environmental influences and selection criteria

Summary Parthenocarpic pickling cucumbers have been selected after crossing pickling and slicing cucumbers. On the best lines 90% of the female flowers set fruit (up to 75 fruits per plant within six weeks). At declining daylength productivity decreased, mainly because of a reduced flower initiation and partly by a reduced parthenocarpic potential.The correlation between several selection criteria and the possibilities of preselection of young plants is discussed.     

Effect of end-border condition on small-plot yield of cucumber

Summary Twelve or 14 cultivars and breeding lines (collectively referred to as lines hereafter) of pickling and fresh-market cucumbers (Cucumis sativus L.) were evaluated in 1.5 m long plots. The plots were harvested once when the check lines reached the 10% oversized fruit stage, and total, marketable, and early (oversized) number of fruits per plot was counted. The plots were planted with or without 1.5 m long end-borders to determine whether end-borders can be eliminated in small-plot trials where seed numbers and field space are limiting. Yield in unbordered plots was inflated 5 to 21% over bordered plots, but there was generally no significant effect in the analysis of variance for line x end-border condition. Therefore, end-borders are not needed when comparing different lines.     

Optimum plot size determination and its application to cucumber yield trials

Summary Methods of estimating Smith's b and, thereby, optimum plot size are compared from a theoretical viewpoint. For estimating b, generalized least squares is recommended over Smith's (1938) original method and other methods because the points used to fit the required regression are correlated and have unequal variances.Optimum plot size for once-over-harvest trials measuring yield (as number of fruits per plot) of pickling and frest-market cucumbers (Cucumis sativus L.) was estimated to be 0.7 to 3.8 m² (0.5 to 2.5 m of row for rows 1.5 m apart) for conventional harvesting, and 1.0 to 5.6 m² (0.7 to 3.7 m of row) for simulated harvesting using paraquat to defoliate plots before evaluation. Estimates of optimum plot size were calculated from a number of uniformity trials differing in year (1982 or 1983), planting date (early or late), and field. The estimates were sufficiently stable to suggest that they have useful generality.For multiple-harvest yield trials, optimum plot sizes for determining yield of pickling (expressed in $/ha or q/ha) or fresh-market cucumbers (i.e. USDA Fancy and No. 1 grade fruit combined or USDA Fancy, No. 1, and No. 2 grade fruit combined, in q/ha) were estimated from experimental data to be 6.4 to 10.3 m² (4.3 to 6.8 m of row).     

Phylogenetic studies in Citrus reticulata and related types

Summary Sixteen types of mandarins were screened for their leaf flavonoid patterns with the help of cellulose thin-layer chromatography. In general, Tanaka's classification of mandarins into 36 species is untenable, as was already concluded by Swingle (1948), Hodgson (1965) and Singh (1967). It is likely that a fine loose skinned mandarin was first evolved. Later, it hybridized with wild mandarin to give rise to numerous types and forms.Contribution No. 474 of Indian Institute of Horticultural Research, Bangalore-6, India.     

Gummy stem blight resistance of cucumbers (Cucumis sativus L.)

Summary A start was made with breeding for resistance to gummy stem blight in cucumber. A method has been development for screening plants in a young stage. Using this method a distinct level of resistance was found in plants of Leningradsky, Wjarnikovsky,a P.I. entry from Birma, Rheinische Vorgebirge and a P.I.entry from Turkey. Lines developed from this material show a higher level of resistance than Dutch slicing and pickling cucumber varieties.     

Flax scorch

Summary Scorch is a soilborne disease of flax which as far as known only occurs in the Netherlands, Belgium and Northern France. Due to the publication of Marchal (1900) the fungus Asterocystis radicis de Wild had for a long time been considered as the causal organism. In later years, however, Dutch investigators (v. d. Meer, 1928, and Diddens, 1931) proved that the disease is caused by the fungus Pythium megalacanthum de Bary and that Asterocystis is quite harmless to flax.The only way of controlling the disease has been the breeding of resistant varieties. As early as 1888 Prof. L. Broekema established that resistance occurs and attempted to raise scorch-resistant varieties. In later years also other investigators and breeders worked on the same problem.The breeding for flax scorch resistance forms part of the working programme of the S.V.P. (Foundation for Agricultural Plant Breeding). Though different isolates of the scorch-fungus were tested by the author, no physiological specialization was found. He evolved a laboratory method for investigating flax scorch resistance and studies the heredity of the resistance. On page 204 the resistance of some varieties is expressed n relative figures.It is attempted to promote breeding work of Dutch private breeders by providing them with resistant populations and lines.Vlasbrand is een bodemziekte welke, voor zoverre bekend, alleen voorkomt in Nederland, België en Noord-Frankrijk. Op grond van de publicatie van Marchal (1900) werd de schimmel Asterocystis radicis de Wild lange tijd als de veroorzaker van deze ziekte beschouwd. In latere jaren bewezen Nederlandse onderzoeksters (v. d. Meer, 1928 en Diddens, 1931) echter dat de ziekte door de schimmel Pythium megalacanthum de Bary veroorzaakt wordt en dat Asterocystis ongevaarlijk is voor vlas.Het kweken van resistente rassen vormt de enige mogelijkheid de ziekte te bestrijden. Prof. L. Broekema stelde reeds in 1888 vast, dat resistentie voorkomt en trachtte vlasbrand resistente rassen te kweken. In latere jaren legden ook anderen zich hierop toe.Het kweken op vlasbrand resistentie vormt een onderdeel van het werkprogramma van de S.V.P. Hoewel verschillende isolaties door de schrijver onderzocht zijn, werd geen physiologische specialisatie aangetroffen. Hij werkte een laboratoriummethode uit voor onderzoek op vlasbrandresistentie en bestudeert de erfelijkheid van de resistentie. Op blz. 204 is de resistentie van enige rassen in verhoudingscijfets uitgedrukt.Door de Nederlandse kwekers te voorzien met resistente populaties wordt getracht de kweekarbeid te bevorderen.     

Frequencies of genetical factors determining male sterility in onion (Allium cepa L.) and their significance for the breeding of hybrids

Summary In selections of some more or less commonly grown onion varieties in the Netherlands the frequencies of genetical factors governing male sterility were determined. In the leading Dutch variety Rijnsburger the chromosomal factor ms was found to occur in a frequency of over 0.95 and the cytoplasmic factor S in a frequency of less than 0.01.As a consequence, a programme of breeding hybrid onions with the aid of this variety can be started in a simple way by selfing selected plants to produce B lines. Simultaneously seed is harvested from male-sterile plants in the same variety. Subsequently in the third, fifth or seventh year, backcrossing can be started to obtain corresponding A lines. For backcrossing the progenies of the initially selected male-sterile plants are used.The choice of the year in which backcrossing will be started depends mainly on circumstances and on one's personal views.     

Effects of selection in tetraploid green gram varieties

A comparative study of the effect of tetraploidy in three varieties of green gram (Phaseolus aureus Roxb.) and selection of plants with high, medium and low vigour showed that the reduced leaflet size and height at the time of flowering can be considerably improved by selection. It appeared that the diploid level can be approached or even exceeded.The reduced fruit setting can also be improved considerably but not the size of fruits and number of seeds per pod. The increased seed weight was further improved in two varieties. The increase in protein content of the tetraploid seeds was greatest in the variety with the lowest protein content at the diploid level.Though for vegetative growth selection alone would suffice to bring the tetraploids up to the diploid level, if not higher, the reduced fruit and seed setting, though responding well to selection, are unlikely to be overcome unless other breeding methods are introduced.     

The use of a modified bulk segregant analysis to identify a molecular marker linked to a scab resistance gene in apple

Almost two-hundred random sequence decamer-primers were used to screen a pair of bulked samples and the donor parent Malus floribunda clone 821 for markers linked to the V_f gene conferring resistance to apple scab (Venturia inaequalis (Cke.) Wint.). A single primer was identified which generated a PCR fragment, OPK16/1300, from the donor parent M. floribunda clone 821 and the scab-resistant selections/cultivars bulk, but not from the scab-susceptible recurrent parent bulk. Co-segregation analysis using a segregating apple progeny and polymorphism analysis of individual scab-resistant Coop selections/cultivars confirmed that this marker was linked to the scab-resistance gene V_f with a recombination frequency of 4.3%. OPK16/1300 was then cloned and sequenced. Sequence-specific primers of 25 oligonucleotides based on the marker were synthesized, and used in turn to screen M. floribunda clone 821, scab-susceptible apple cultivars, scab-resistant apple cultivars, and scab-resistant Coop selections. A pair of sequence-specific primers of clone OPK16/1300 amplified a distinct single band of the same size as the RAPD clone. Thus, a sequence characterized amplified region (SCAR) marker was developed which can be used to identify polymorphisms of OPK16/1300 based on the presence or absence of a single band. This revised version was published online in July 2006 with corrections to the Cover Date.     

A cheap method of testing spinach plants for blue mould resistance during the summer months

A device (tent) is described which makes it possible, by using a cheap cooling plant, to test spinach plants for blue mould throughout the year, with 100% success. It is also suitable for testing other crops for fungus diseases. The use of these tents has been adopted not only by the Institute of Horticultural Plant Breeding but also by the Dutch seed trade.

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Samenvatting Er wordt een apparaat (tent) beschreven dat het mogelijk maakt d.m.v. een weinig kostbare koelinstallatie, ook gedurende de droge, hete zomermaanden, spinazieplanten een wolftoets te geven, die 100% kans van slagen biedt. Behalve voor het toetsen van spinazie op wolfresistentie, bleek het ook mogelijk andere gewassen op diverse schimmelziekten te toetsen. De tent is niet alleen in gebruik bij het Instituut voor de Veredeling van Tuinbouwgewassen, maar ook reeds bij Nederlandse selectiebedrijven.

     

A mechanism for inhibiting cross-fertilization in pigeonpea (Cajanus cajan (L.) Millsp.)

Summary Natural out-crossing imposes considerable costs and inefficiencies in breeding, evaluation and commercialization of pigeonpea (Cajanus cajan (L.) Millsp.). This note reports identification of a modification of floral morphology which inhibits cross-fertilization. Floral morphology and possible mechanisms of action of this character are discussed.On leave from International Crops Research Institute for the Semi-Arid Tropics (ICRISAT). Hyderabad, India.     

Some remarks on the breeding of field crops in the Netherlands

Summary In the Netherlands the home-bred varieties are developed almost entirely by private establishments. The Government institutes (Institute of Agricultural Plant Breeding and Foundation for Agricultural Plant Breeding) at Wageningen give advice to the breeders of field crops.The private plant breeders are informed of the results obtained and the working methods. They receive plant material for their breeding programme.The List of Varieties is the reference guide not only for the farmers but also to the plant breeders and the seedsmen. In the case of field crops it forms the basis for the seed inspection. A close connection exists between the breeding, variety-list and seed inspection.     

On bacterial wilt of alfalfa (Medicago sativa L.) caused by Corynebacterium insidiosum (McCull.) Jensen,in Italy

Bacterial wilt of alfalfa (Medicago sativa L.) caused by Corynebacterium insidiosum (McCull) Jensen was unknown in Italy until 1957. The authors established in that year in the province of Bologna this dangerous disease in 2–3 year-old stands of alfalfa which appeared uniformly and extensively thinned.They started a breeding programme with the use of bacterial wilt resistant material from the U.S.A., while also studies on methods of testing for resistance under Italian conditions are in progress.     

Unravelling the inheritance,QST and reproductive phenology attributes of the tetraploid tropical grass Brachiaria ruziziensis (Germain et Evrard)

The autotetraploid forage Congo signal grass (Brachiaria ruziziensis) is an important component in the Brachiaria breeding programme. As with other tropical forage grass species, the association between flowering and seed yield components, the mode of inheritance and the effects of population structure on phenotypic breeding are lacking. Seventeen characteristics evaluated in 59 half‐sib progeny of seven subpopulations were analysed using a mixed model methodology. According to the commonality analysis, the total seed yield (0.67) and number of days to flowering (0.22) had a greater influence on the filled‐seed yield. The flowering synchrony, total number of panicles, filled‐seed yield, green matter yield and dry matter yield presented statistically significant additive genetic variance between and within the subpopulations. The Q_ST estimates ranged from 0.09 for the flowering synchrony index to 0.31 for the filled‐seed yield. The effects of population structure and its use in breeding programmes are further discussed.