Compatibility of cherries in the Netherlands

Summary Results of pollination trials, carried out between 1908 and 1963 in The Netherlands and adjacent parts of Belgium, were compiled to detect groups of inter-incompatible cherry varieties.In sweet cherry (Prunus avium L.) there appeared to be at least six groups of inter-incompatible varieties; in sour cherry (P. cerasus L.) only one group of inter-incompatible varieties was found. Moreover two groups of inter-compatible sour and hybrid cherries (P. avium x P. cerasus) were encountered.A weak relation was found between fruit set of a variety and the capacity of its pollen to induce fruit set.     

Morphological variation within a sour cherry collection

Summary Morphological traits of 28 full-sib sour cherry (Prunus cerasus L.) families developed with pollen from European sour cherry selections were evaluated with principal component (PC) analysis. The traits which loaded on the first PC were size characters such as lateral length, leaf area, fruit weight, and trunk diameter increase. These character loading on the first PC could be interpreted as representing gradations between morphologies characteristic of the 2 presumed progenitor species, sweet cherry (P. avium L.) and ground cherry (P. fruticosa Pall.). Mean family differences in trunk diameter increase, lateral length, leaf area, and fruit weight varied approximately 12, 3.7, 2.5, and 2 fold, respectively. These results suggest that it may be possible to select sour cherry hybrids approaching the tree and fruit size of either progenitor species. The results are discussed in reference to germplasm collection and the potential of certain cultivars and hybrids as parents.     

Strawberry breeding for red core resistance in the Netherlands

Summary The appearance, a few years ago, of red core disease (Phytophthora fragariae Hickman) in strawberry crops in the Netherlands, has made it desirable to grow resistant varieties and to include red core resistance in our breeding programme.An account is given of the results of some field trials in 1968–1970 on a very wet, sandy soil, infected with P. fragariae, involving varieties, selections and seedling progenies.In both years distinct differences in resistance and susceptibility occurred between varieties and selections. The seedling progenies gave significant differences in percentages of surviving, healthy plants.Samenvatting Het optreden van rood wortelrot (Phytophthora fragariae Hickman) enkele jaren geleden in de aardbeiteelt in Nederland, heeft het gewenst gemaakt resistente rassen te telen en resistentie in ons veredelingsprogramma op te nemen.In dit artikel worden de resultaten vermeld van enkele veldproeven met rassen, selecties en zaailingpopulaties in de jaren 1968–69 en 1969–70 op een zeer natte, met P. fragariae besmette zandgrond.In beide jaren traden duidelijke verschillen in vatbaarheid op tussen de rassen en selecties. De zaailingpopulaties vertoonden eveneens duidelijke verschillen in de percentages overlevende, gezonde planten.     

Inheritance of resistance to Pyrenochaeta lycopersici in tomato

Summary Tomato accessions (Lycopersicon sp.), along with commercial cultivars and breeding lines were grown in a field infested with the brown root rot (BRR) organism, Pyrenochaeta lycopersici and evaluated for resistance. Three L. esculentum Mill. accessions, P.I. 260397, P.I. 262906 and P.I. 203231, were resistant and were used as male parents in crosses designed to transfer resistance to tomatoes of fresh market type. Through analysis of parental generations and F₁ and F₂ progenies from three crosses the heritability of resistance in the broad sense was estimated to range from 25 to 43 percent. The minimum number of genes influencing resistance was estimated to be from 4 to 8.Florida Agricultural Experiment Stations Journal Series Paper no. 317.     

Genetics of resistance to ascochyta blight in chickpea (Cicer arietinum L.)

Summary Six chickpea lines resistant to Ascochyta rabiei (Pass.) Lab. were crossed to four susceptible cultivars. The hybrids were resistant in all the crosses except the crosses where resistant line BRG 8 was involved. Segregation pattern for diseases reaction in F₂, BCP₁, BCP₂ and F₃ generations in field and glasshouse conditions revealed that resistance to Ascochyta blight is under the control of a single dominant gene in EC 26446, PG 82-1, P 919, P 1252-1 and NEC 2451 while a recessive gene is responsible in BRG 8. Allelic tests indicated the presence of three independently segregating genes for resistance; one dominant gene in P 1215-1 and one in EC 26446 and PG 82-1, and a recessive one in BRG 8.Research paper No. 3600     

Selection of a mutant from adventitious shoots formed in X ray treated cherry leaves and differentiation of standard and mutant with RAPDs

Summary An obstacle when using scions orin vitro shoots for mutation induction is the occurrence of chimeras. When adventitious shoots are formed from irradiated material these usually are derived from single cells, this leading to homohistont mutants. SincePrunus avium regenerates adventitious shoots from leaves at a low rate only (Yang & Schmidt, 1992), leaves of the interspecific cherry rootstock ‘209/1’ (P. cerasus ×P. canescens) were irradiated. ‘209/1’ regenerates adventitious shoots readily. Dosages applied were 5, 10, 20 and 40 Gy. Shoot production following 5 Gy irradiation was similar to the control. The application of 40 Gy resulted in strong damage with only few leaves regenerating. Among the adventitious shoots from leaves irradiated with 20 Gy one shoot was evident alreadyin vitro with thicker and smaller leaves having a serrate margin. It was cloned as ‘209/1-20m’. The clone stayed stable since 1990in vitro, in the greenhouse and the field. Compared with standard ‘209/1’ the mutant is very dwarf. Research to differentiate between standard ‘209/1’ and ‘209/1-20m’ was done using RAPDs. Among the decamer primer kits D, J, and T from Operon Technologies, Calif. Only primer OPJ05 (5‘CTCCATGGGG3’) differentiated between ‘209/1’ and ‘209/1-20m’. Rootstock ‘209/1’ showed one band of 2 kb additionally. This band is missing in the mutant.     

Correlated resistance of cassava to mosaic and bacterial blight diseases

Summary The two most serious diseases of cassava (Manihot esculenta Crantz) are cassava mosaic disease (CMD) and cassava bacterial blight (CBB) (Xanthomonas manihotis Starr). Clone 58308, derived from the third backcross of the interspecific cross of cassava (M. esculenta) x ceara rubber (M. glaziovii), showed a high level of resistance to both diseases. Crosses of 58308 with several other clones which varied from susceptible to moderately susceptible to both diseases gave progenies with a significant genotypic correlation between resistance to both diseases (r=0.90), apparently due to linkage. The heritabilities of resistance to the diseases were estimated at 50–70% for CMD and 25–65% for CBB. Resistance to both diseases is assumed to be polygenic. The correlated response to selection for CMD and for CBB was estimated.     

Crossability values within the slash-caribbeanPinus species complex

Summary Crossability values were calculated for (a) eight individual tree crosses betweenPinus elliottii Engelm. var.elliottii L. & D. andP. caribaea Mor. var.caribaea B. & G., (b) ten crosses betweenP. caribaea var.caribaea andP. caribaea var.hondurensis B. & G., and (c) twelve crosses betweenP. elliottii var.elliottii andP. caribaea var.hondurensis. Individual trees showed differences in ability to hybridize. Despite wide variation for each combination, the compatibility of the various combinations could be defined. It was high for (a), moderate for (b) and poor for (c). These results indicate the need for taxonomic review of theP. elliottii — P. caribaea species complex and suggest that hybridization within the complex might have economic value in Queensland forests.     

S‐locus diversity and cross‐compatibility of wild Prunus avium for timber breeding

Prunus avium is primarily cultivated for its fruit, sweet cherries. However, it is also used to produce high‐quality timber. In a P. avium seed orchard, gametophytic self‐incompatibility is a restriction for free pollen flow and should be considered when establishing basic forest materials. In this study, S‐locus diversity and cross‐incompatibility of wild cherry individuals in clonal banks established for breeding for timber production were investigated. Wild cherry trees (140) with outstanding forest growth habit, collected in northern Spain, grafted and planted in two clonal banks, were genotyped at the S‐locus. The self‐incompatibility S‐locus genes, S‐RNase and SFB, were analysed by PCR. Twenty‐two S‐haplotypes, resulting in 72 different S‐genotypes, were identified. The genotypes were grouped into 33 incompatibility groups and 39 unique genotypes. This initial S‐locus analysis revealed large genetic diversity of wild cherry trees from the Spanish northern deciduous forest, and provides useful information for seed orchard design. Wild P. avium displays significantly more genetic diversity than what is detected in local cultivars, revealing a narrowing of genetic diversity during local domestication.     

Pollen germination in pyrus species and species hybrids

Pollen germination in most Pyrus species was moderately high, usually averaging above 50 per cent. Five species were completely or nearly pollen sterile: P. nivalis Jacq., P. ovoideae Rehd., P. Decaisne, P. salicifolia, var. pendula and P. variolosa Wall. Microspores appear plump and normal following microsporogenesis. Degeneration of pollen grains occurred in the post-meiotic phase of pollen maturation.     

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.     

Pollen germination,pollen tube growth and fertilization following self and interspecific pollination of Paspalum species

Summary Crossability between most Paspalum species is very low. This study was undertaken to identify the impediments to hybridization. Accessions of P. intermedium Munro. ex Morong, P. jurgensii Hackel and P. dilatatum Poir were self-pollinated and crossed with one anther. Paspalum intermedium is essentially self-sterile but P. jurgensii and P. dilatatum are highly self-fertile. Following pollination, pollen germination and tube growth were studied by observing the pollinated pistils with fluorescent microscopy. Examination of self-pollinated pistils revealed that the pollen germinated shortly after contacting the stigmas. Germination was over 80% for the P. intermedium and P. dilatatum accessions but only 57% for P. jurgensii. Pollen tubes grew to the micropyle within 45 minutes after pollination in P. dilatatum and 1 hour and 15 minutes in P. jurgensii. However, in the P. intermedium accessions most tubes did not grow beyond the stigma and very few penetrated the style and ovary. Apparently stylar-incompatibility is the reason for the low selfed seed set. In the cross-pollinations, pollen germinated shortly after pollination and germination ranged from 57 to 88% for the different crosses. In all crosses the pollen tubes grew to the micropyle within 30 minutes to 2 hours after pollination indicating that a cross-incompatibility system is not the cause for low crossability among these species. By examining embryo sacs from P. intermedium × P. dilatatum, its reciprocal and P. intermedium × P. urvillei crosses, it was determined that gametes failed to unite in some crosses and this is a major reason for low crossability.     

Breeding alfalfa cultivars resistant to the alfalfa weevil

A ten-year study consisting of nine field experiments was conducted to evaluate alfalfa (Medicago sativa L.) for resistance to larval feeding by the alfalfa weevil (Hypera postica Gyllenhal). The results were consistent over years and experiments. Only one source of alfalfa germplasm, designated Starnes, showed resistance to larval feeding in the field under natural infestations of the weevil. The cultivars Team, Arc, and Liberty have been developed from this germplasm source. The only effective method of selection for field resistance to the weevil was field selection under natural weevil infestations. Selection was based on low larval feeding on spaced plants. After six generations of such selection the Starnes germplasm showed only one-third as much defoliation as did the check cultivars. The heritability of the weevil resistance was moderately high. Field resistance was transferred to other strains through hybridization; hybrids were intermediate to the resistant and susceptible parents. Resistance was stable.Laboratory and greenhouse efforts to breed alfalfa weevil resistant alfalfa-using such techniques as adult cotyledon-nonpreference tests, adult leaf-feeding tests, larval-growth and survival tests, oviposition-stimulus tests, and oviposition-nonpreference tests-have failed to produce field resistance.Paper No. 5308 of the Journal series of North Carolina Agricultural Experiment Station, Raleigh, N. C., in cooperation wich ARS, USDA. Received 15 June 1977.     

Cytology and leafspot resistance in Arachis hypogaea x wild species hybrids

Summary Introgression of germplasm from diploid wild Arachis species to A. hypogaea has great potential for improving pest resistance in cultivated peanuts. This investigation evaluated methods for incorporating exotic germplasm into cultivated peanuts, especially for Cercospora arachidicola Hori resistance. Interspecific hybrids between A. hypogaea (cvs. NC 2 and NC 5) and the wild species A. cardenasii Krap. et Greg. nom. nud. and A. chacoense Krap. et Greg. nom. nud. were analyzed cytologically and for leafspot resistance. All F₁ hybrids were sterile, had irregular meiosis, and very few multivalents. They were highly resistant to C. arachidicola in field tests and had a 10-fold reduction of conidia per lesion in the greenhouse as compared to A. hypogaea cultivars. After colchicine treatments of F₁ hybrids, hexaploids (2n=60) and aneuploids (2n=54, 56, 63) were observed. The hexaploids had up to 18 univalents per pollen mother cell and very few multivalents, indicating a low frequency of intergenomic chromosome pairing. For C. arachidicola resistance, significant differences were not found among wild species parents, F₁ hybrids and two generations of hexaploids. Most hexaploids were stable at 2n=60 and embryos aborted when backcrosses with the respective wild species were attempted. However, when hexaploids were backcrossed to A. hypogaea, several fertile pentaploid (2n=50) offspring were obtained. Use of self-pollinating pentaploids is believed to be the quickest method to recover 40-chromosome hybrid derivatives in these hybrids.     

An association between resistance to root aphid (Pemphigus bursarius L.) and downy mildew (Bremia lactucae Regel) in lettuce

Summary Many lettuce cultivars (Lactuca sativa L.) with high resistance to lettuce root aphid (Pemphigus bursarius L.) also carried the gene Dm-6 for specific resistance to downy mildew (Bremia lactucae Regel). This suggests the possibility of linkage between this gene and root aphid resistance. The origin of this association is discussed.     

Turkish barley varieties as a source of resistance to net blotch

Summary From the world collection, 875 barley varieties of Turkish origin have been screened for resistance to local races of net blotch caused by Drechslera teres (Sacc.) Shoem. Six of these exhibited a high degree of resistance, which varied in expressivity when tested under a wider range of environmental conditions. In this respect these varieties rank between the consistency of resistance expressed by varieties from Ehtiopia, and the inconsistency with which resistance is expressed by varieties from Manchuria. The implications are discussed.     

Field screening ofPisum accessions to evaluate their susceptibility to the pea weevil (Coleoptera: Bruchidae)

Summary Seventeen unreplicated field trials over nine sites and four years were used to classifyPisum germplasm (P. sativum L. &P. fulvum Sibth. & Sm) as potential sources of resistance to the pea weevil,Bruchus pisorum (L.). The emergence of adult weevils from <10% of harvested seed was used as the selection criterion to indicate possible resistance. A total of 1900Pisum accessions were assessed using the field trials and 1754 of theP. sativum accessions were eliminated. However in the 18P. fulvum accessions screened, the level of infestation by pea weevil was always below the arbitrary resistance threshold selected. This suggests thatP. fulvum accessions could be a valuable source of resistance to the pea weevil.     

Reactions of poplar clones to physiologic races of Melampsora larici-populina Kleb.

Summary Four mono-uredospore isolates of Melampsora larici-populina Kleb. produced qualitatively distinct reactions on four half-sib clones of Populus deltoides Marsh. and thus were recognisable as races. Two of the races could be distinguished equally readily by the distinctness of their reactions (three quantitative parameters) on four compatible clones of Populus spp. The pronounced race specific reactions of the clones of P. deltoides, allied to the less distinct, but nevertheless race specific reactions, of the compatible clones are consistent with an integrated rather than a disjunctive concept of resistance in Populus spp. to M. larici-populina.     

Identification of self-incompatibility (S) alleles in Latvian and Swedish sweet cherry genetic resources collections by PCR based typing

The Latvian and the Swedish sweet cherry (Prunus avium L.) genetic resources collections comprise valuable material for breeding. The collections represent local Latvian and Scandinavian genetic resources: semi-wild samples, landraces, and cultivars developed in local breeding programmes, as well as diverse germplasm from the northern temperate zone. The objective of this investigation was to determine which S ₁ –S ₆ alleles are most important in the sweet cherry genetic resources collections and to compare the identified allelic and genotypic frequencies in material of different origin. Accessions in the two collections were screened for the presence of the self-incompatibility (S) S ₁ to S ₆ alleles, using PCR based typing. Significant differences (P < 0.05) between screened collections were found in frequencies of S ₄ and S ₅ alleles. Analysis of allele combinations identified the high occurrence of selections with the S-genotype S ₃ S ₆ in both collections. Compared to the S-allele frequencies published for over 250 sweet cherry cultivars from Western and Southern Europe, the Latvian and Swedish germplasm appeared to have a high frequency of the S ₆ allele in both collections, and a relatively high frequency of the S ₅ allele in Latvian germplasm. This study represents the first comprehensive S-allele screening for the sweet cherry genetic resources collections in Latvia and Sweden. Both sweet cherry collections contain high proportion of accessions adapted to north central European growing conditions, not typical for the majority of the documented sweet cherry genetic resources, which explains differences in certain S-allele occurrence.