Mutation research in canary grass

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   Irradiations with X-rays and neutrons of normal dry seeds (humidity 12.0%) of canary grass showed, depending on the dosage, typical differences in their influence on germination and survival of seedlings.     
   
   

Neutronic mutations in peas

Pea seeds were irradiated with neutrons. At least 9 mutations have been found. Probably all are recessive. Some are undesirable, some have practical value. At least one mutant represents a completely new characteristic. One mutation occurred more than once. Three times two mutations occurred in one seed. Irradiation with neutrons is considered to present a valuable means in plant breeding.     

Resistance to early browning in peas

Early browning is a virus disease of peas occurring in the Netherlands on light soils, mainly in coastal regions. Numerous varieties have been tested for resistance on an infested field. A limited number, reported here, are classified sufficiently resistant.     

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.     

Qualitative resistance to powdery mildew in hybrid sweet peas

Lathyrus odoratus L. × Lathyrus belinensis L. hybrids were produced using L. belinensis as the pollen parent, with fertile seed produced by the L. odoratus parent. The F1 hybrid plants were completely self-sterile, but produced viable seeds when backcrossed to L. odoratus. The plants produced by backcrossing resembled L. odoratus, the flower colour being purple/magenta, and were self-fertile. Both hybrid plants and those produced by back crossing to L. odoratus were resistant to Erysiphe pisi DC that causes powdery mildew in sweet peas. Continued backcrossing resulted in hybrid plants, that closely resembled the L. odoratus parent, but segregated for complete resistance/susceptibility to E. pisi,with a ratio of 2.46:1 resistant to sensitive plants. This suggests the presence of a single dominant gene that confers resistance. When resistant and sensitive plants were inoculated with E. pisi and their leaf surfaces examined,using a Scanning Electron Microscope, it was found that although spores germinated on the leaves of both resistant and sensitive plants, spores present on resistant plants collapsed shortly after germination. Possible reasons for this are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic distance and its association with heterosis in peas

Summary The relationship between the genetic distance of parents and both the heterosis of F₁ hybrids and the variance of F₅ lines was investigated in 72 crosses of pea (Pisum sativum L.). The genetic distance between each pair of parents was estimated, using isozyme (GDi), morphological (GDm) or quantitative (GDq) markers and finally a combination of isozyme and morphological markers (GDi+m). GDm was poorly correlated with the other measures of genetic distance, which in turn were strongly correlated with each other. Genetic distance was moderately correlated with the level of heterosis for yield over midparent in the F₁ generation, with the highest correlation obtained from GDi+m. GD was not significantly correlated with heterosis for yield over the better or best parent but it was significantly correlated with all three measures of heterosis for pods per plant and hundred seed weight. There was no correlation between genetic distance and the level of heterosis for yield and total dry matter in the F₂ generation, but GDi, GDi+m and GDq were predictive for the level of inbreeding depression in grain yield and total dry matter. When parents were high in genetic distance, crosses produced highly transgressive segregants for basal branches per plant, hundred seed weight, harvest index and onset of flowering. Genetic distance between parents was thus a useful measure for predicting a portion of hybrid performance and also of the variance of derived inbred lines. It was concluded that when choosing parents for a cross, consideration should be given to their genetic distance as well as their overall adaptation and their yield. There is considerable potential for optimising choice of parental combinations in the development of improved pea cultivars.     

Tapetal behaviour, gene action and breeding value in male-sterile peas

Eight non-allelic male-sterile mutants controlled by a single recessive gene were induced in garden pea (Pisum sativum) after EMS, DES and gamma-ray-mutagen treatments singly and in combination. These mutants differ in the time and type of tapetal development due to differential action of male-sterile (ms) genes over the sporogenous and non-sporogenous anther tissue. In the msg1 mutant, the sporogenous tissue breaks down during premeiosis, followed by tapetal degeneration. In msg2, sporogenous tissue and tapetal tissue exhibit anomalies at early and late prophase 1, respectively. Although in msg3 and msg5 the ms gene action over sporogenous tissue initiates during early and late prophase, respectively, the tapetal tissue breaks down during post-meiosis. In msg6, anomalies in the sporogenous tissue appear during prophase II, but the tapetum degenerates during the mononucleate stage. Although both the tapetal and sporogenous tissue anomalies appear simultaneously at pachytene in msg4, the tapetal breakdown is delayed until the microspore stage. In msg7 and msg8, anomalies in both these tissues occur simultaneously during the tetrad and post-meiotic stages, respectively. Despite differences in the timing of tapetal and sporogenous tissue breakdown, tapetal development is normal in msg1, msg5, msg6, msg7 and nisg8 but abnormal in msg2, msg3 and msg4. The ms gene action is dual in msg2, msg3 and msg4 but single in msg1, msg5, msg6, msg7 and msg8. In all these mutants, the time of tapetal anomaly exhibits no correlation with the time of ms gene action. The gene for open flower found in one male-sterile mutant needs to be introduced into fertile peas for commercial hybrid-pea breeding.     

Testing for pea leafroll virus and inheritance of resistance in peas

Summary Different aspects of pea leafroll, the most important virus disease of peas and Vicia-beans in The Netherlands, are discussed. These aspects include the spread of the virus, the damage done by the disease, the symptoms, the nature of the virus, the vectors and the host plants. Pea leafroll virus (PLRV) is a persistent virus which is invariably transmitted by aphids. The most important vector is the pea aphid, Acyrthosiphon pisum Harris. Lucerne actas as a winter host for the virus and the pea aphid. The pea aphids are reared on diseased lucerne plants and are used in a glass-house experiment to test cross populations for resistance. In view of its importance for that test it is necessary to discuss the biology of the pea aphid in some detail. Besides the glasshouse test some field test methods are mentioned.Crosses between Cobri (resistant) and Gloire de Quimper (susceptible) as well as between Wyola (resistant) and Joserva (susceptible) served to study the resistance to the virus in peas. The results of testing well over 3600 plants justified the conclusion that the resistance is inherited as a single recessive character. It is suggested to refer to the gene for susceptibility to PLRV as Lr.     

Heritability and gene effects for root characteristics in peas measured at flowering

Summary Heritability and gene effects for root weight, root volume and root to shoot weight ratio were determined in peas (Pisum sativum L.) at flowering. The populations used were developed from four crosses between lines and cultivars differing in size of the root systems. Broad-sense heritability was between 0.41 and 0.81 for root weight, and between 0.44 and 0.77 for root volume. Additive and dominance effects were important in the genetic control of root weight and volume in all populations, while epistatic effects were important only in two populations. The importance of the genetic parameters in the control of root to shoot weight ratio was unclear. Assuming high correlations between root growth in soil-filled pots in the greenhouse and growth in the field, with the presence of large additive effects and high heritability estimates for root weight and volume, selection for superior pure lines with large root systems should be effective.     

Plant Mutation

The FAO/IAEA Joint Program is planning to publish an international journal of basic and applied research in plant mutation, Plant Mutation. It publishes research articles and short communications in the following fi elds:     

Variation in the storage proteins of peas in relation to sulphur amino-acid content

Summary A cellulose acetate electrophoretic technique has been used to characterise the storage proteins present in pea seeds in order to try and determine the proportions of proteins present which are enriched in sulphur amino-acids. Some of the eight varieties examined were shown to differ in their proportions of the various storage proteins. When the proteins were separated and estimated quantitatively and also characterised by their sub-unit composition, it was shown that cellulose acetate electrophoresis of crude protein extracts or of whole globulins did not give the degree of resolution required. The procedures which have to be undertaken in order to obtain this information are considered, and the difficulties of incorporating them into a plant breeding programme discussed.     

Genetic studies of selection criteria for productive and stable peas

In this study we investigated the genetic determinism of criteria suitable for breeding for seed yield and yield stability in dry pea (Pisum sativumL.) using a diallel cross involving eight genotypes. Seven criteria related to plant and seed development were evaluated including: onset of flowering, node of first flower, leaf appearance rate, rate of progression of flowering, number of podded nodes on the main stem, mean dry seed weight per podded node and number of basal branches per plant. Most of these traits measured are related to timing of seed set and are thought to be critical in determining yield stability. We combined different diallel analyses (Hayman,1954; Griffing, 1956) with a Principal Component Analysis, to divide the parental lines into groups sharing similar genetic control for the traits studied. We found that the two main groups, defined according to their genetic control of node of first flower, also differed for all the others characters and, in particular, did not reach the same levels of productivity. These results indicated that crosses within the group with the highest productivity, but between lines with differing development and architectural features, could be a good starting point for breeding high-yield pure lines. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mutation breeding in bulbous iris

Summary To make the sterile iris cultivar Wedgwood accessible to selection, bulbs were irradiated with X-rays. The aim is to induce flower colour mutations in this early flowering cultivar which is specially suitable for early forcing.The optimal dose turned out to be 1000 rad X-rays; the best moment for irradiation is immediately after lifting the bulbs in August when the growing points, which will form the new bulbs, are in the youngest possible ontogenetic stage. The size of the bulb does not seem to be an important factor.Since 1964 almost 6000 bulbs, representing approximately 25,000 growing points. have been irradiated. So far over 160 flower colour mutants, ranging from paler to darker blue with or without purple, have been obtained. Moreover, a number of other mutants — more flowers per stalk, other form of the flower or different flowering dates — have been observed.These results are discussed as well as other possible ways to reach the goal.     

On the differences between smooth and three types of wrinkled peas

In white-flowering peas two seed types could be distinguished until recently: smooth and wrinkled peas. They differ not only in the appearance of the seed surface but also in appearance of the starch grains and in chemical composition. Thus far the factor pair R-r has been held responsible for these differences.Now two new types of wrinkled peas are described. One has already existed for some time although unrecognized. It resembles the wrinkled pea in seed surface, the smooth pea in appearance of the starch grains. Crosses between these and the old-established type of wrinkled pea resulted in a third type of wrinkled pea. The smooth and the three types of wrinkled peas were found to differ in chemical composition.Two factors, R _a and R _b, could be shown to be responsible for the observed differences (R _a replaces the symbol R used so far). It was suggested that R _a and R _b primarily have a different effect on starch synthesis, and that the differences in starch synthesis underlie the other differences, also the morphological ones like those of the seed surface and the starch grains.The difference in appearance of the starch grains, often used as the criterion to distinguish between smooth and wrinkled peas, can no longer be used as such.Institute of Horticultural Plant Breeding With 3 Figures     

Selection for partial resistance to downy mildew in peas by means of greenhouse tests

Summary A partially downy mildew resistant pea line was back-crossed to a susceptible cultivar with more pods per node and lower seed weight. Breeding lines with different degrees of infection in a greenhouse test were selected. These lines and the two parental lines were investigated in field trials and tested in the greenhouse for four generations. Significant genetic variation among lines was found for infection of seedlings in greenhouse tests, and infection of pods, pod set and seed weight in field-trials. Infection of seedlings in the greenhouse was correlated with infection of pods in the field. In greenhouse tests, the non-genetic variance component was large in comparison with the genetic component and a significant genotype trial interaction was found. Significant repeatability was obtained for downy mildew on seedlings and pods, number of pods per node and seed weight. An unfavourable correlation between susceptibility to downy mildew and number of pods per node was found. No single breeding line showed the ideal combination of good resistance, high number of pods per node and small seeds. However, one line showing better resistance than the susceptible parent, with smaller seeds and more pods per node than the resistant parent was found. The susceptible parent also carries some resistance factor that is not present in the resistant parent.