Resistant Diploids Research Articles

Realization of the genetic potential of frost hardiness in apple hybrids of different ploidy

The results of a study of resistance to unfavorable winter conditions of new selection seedlings of apple developed in the Institute as part of priority directions of apple breeding are presented. The goal of the work is to estimate winter hardiness of apple genotypes developed by combining scab resistance in a triploid genotype (RVi6+3х). Methods of a winter hardiness study in the field and laboratory conditions were used by modelling damage factors in a “ESPEC” PSL-2 KPN deep-freezer . It was determined that by early December the genotypes gained a good hardening and displayed the resistance of vitally important tissues to early winter frosts up to 30 °C (frost resistance component I). The genotypes were revealed that under artificial freezing bore critical temperatures –38 and –40 °C as well as –42 °C with damages of vitally important tissues at the level of Antonovka Obyknovennaya (component II). The modelling of a three-day artificial thaw (+2 °C) with the following temperature lowering to –30 °C showed that in all studied apple seedlings the damages of bark, cambium and wood were reversible and did not exceed 2.0 points while in immune, triploid forms 31-2-130 and ELS 31-36-149, the damages did not exceed 1.2 points. The winter hardiness study of selection apple seedlings allowed revealing the most winter hardy and promising genotypes: scab resistant and triploid forms 31-2-15, 31-2-115, 31-2-130 (Afrodita×13-6-106) and 31-36-149 [Veniaminovskoye×25-35-144 (Wealthy tetraploid× Papirovka tetraploid)] as well as scab resistant diploids 32-35-58 (Yubiley Moskvy×Krasa Sverdlovska) and 31-15-126 [23-16-96 (seedling 814 – open pollination)×Gulliver)]. Those genotypes displayed the resistance of vitally important tissues to early winter frosts, frosts in the middle of winter up to –40 °C at the level of Antonovka Obyknovennaya as well as to the frosts after thaws and retained the ability to restore resistance during repeated hardening after thaws.

Breeding and evaluation ofMusahybrids resistant toFusarium oxysporumf. sp.cubenserace 1

Introduction . Wilt caused by Fusarium oxysporum f. sp. cubense (Foc ) is the most important disease of banana worldwide, causing severe yield losses in commercial and local consumption cultivars. Chemical control is currently the most used method to manage the Fusarium wilt of banana, although it is toxic, expensive and dangerous. Therefore, control through genetic improvement is widely encouraged. Hence, breeding was carried out to develop banana hybrids with putative resistance. Materials and methods . Hybridization of identified resistant diploids with commercial triploids and tetraploids was carried out; it resulted in development of 22 hybrids with improved agronomic characters. In a second step, screening of these hybrids for resistance to Foc race 1 was attempted using the double cup method of challenge inoculation with the pathogen in the roots of the hybrids at optimum level. Host responses of the susceptible and resistant hybrids were examined under greenhouse conditions through biochemical and isozyme analysis. Results . Six hybrids among the 22 hybrids with improved agronomic characters were selected based on their yield and they were evaluated for resistance. Three of them were resistant to Foc and the others were susceptible. The resistance mechanism involving the relation of enzymes such as peroxidase (PO), polyphenol oxidase (PPO) and phenylalanine lyase (PAL), and biochemicals such as phenols, proline and lignin showed relatively higher activity in resistant hybrids and parents than susceptible ones. Isozyme analysis of PO and PPO carried out using selected resistant and susceptible hybrids revealed the induction of specific isoforms in the resistant hybrids upon challenge inoculation. Conclusion . Three hybrids were identified as potential hybrids with good yield and resistance to Foc race 1.

The inheritance of resistance to soft rot (Erwinia carotovora subsp.atroseptica) in diploid potato families

Soft rot of potato tubers, caused byErwinia (Pectobacterium), is a serious disease affecting potato crops during storage. Studies on the inheritance of resistance to tuber soft rot were undertaken on diploid potato hybrids. A total of 480 clones, derived from 12 families, were examined for resistance to soft rot in laboratory tests over 3 years and for basic agronomic traits in field experiments over 2 years. General (GCA) and specific (SCA) combining abilities were significant in the inheritance of resistance to soft rot; however, GCA for female parents were significant in 1 or 2 years during 3 years of evaluation and SCA was significant for eight, two, and six families out of 10 tested in 1994, 1995, and 1996, respectively. There were also significant differences between years. Moreover, marked interactions for GCAfemales × year and SCA × year in the variation of soft rot resistance were found. Broad-sense and narrowsense heritability of resistance, measured as diameter of rotten tissue, was estimated as 0.92 and 0.89, respectively. The maternal effect, evaluated in two sets of reciprocal crosses, was not significant for the genetic determination of resistance to soft rot. No significant relationships were found between resistance to soft rot and the main agronomic traits in the tested diploid families. These results suggest that diploid potato clones with resistance to soft rot can be selected after being evaluated over a few seasons. It is also possible to select clones combining good resistance to soft rot with high yield, superior tuber characteristics, and acceptable starch content. These resistant diploids can be used as male parents in 4x-2x crosses in breeding tetraploid potato resistant to soft rot.

Sugar beets homozygous for resistance to beet cyst nematode (Heterodera schachtii Schm.), developed from monosomic additions of Beta procumbens to B. vulgaris

Monosomic additions of Beta vulgaris x B. procumbens with resistance to beet cyst nematode (Heterodera schachtii Schm.) were used for the production of resistant diploids through incorporation of the B. procumbens chromosome fragment bearing the resistance gene(s) into one of the sugar beet chromosomes. The heterozygotes obtained accordingly were selfed for producing homozygotes. These homozygotes differed morphologically from commercial sugar beet varieties, but produced reasonable amounts of pollen. Female transmission of resistance was 100%, whereas male transmission, apart from some exceptions, was more than 90%. The number of hypersensitivity reactions to penetrated larvae was related to the degree of susceptibility. Larval development was severely retarded in the resistant plants, preventing most of them to produce cysts. If cysts were formed, their content was considerably less as compared to those in the susceptible plants.

Nematode Resistance and Meiotic Abnormality in Diploid Sugar Beet Selected from Interspecific Beta vulgaris×B. procumbens Hybrids*

AbstractTwo nematode‐resistant trisomic lines which were derived from interspecific Beta, vulgaris × B. procumbens hybrids were intercrossed or backcrossed with susceptible diploid sugar beer and their progenies were screened for nematode resistance. The transmission rate of resistance varied from 1.5 % to 47.6 % with an average of 20.4 % in the progenies of individual insomics derived from the two trisomic lines. Eleven resistant diploads were selected with a frequency of 0.2 %. These resistant diploids were classified into two groups, i.e., one group showed relatively high transmission rates of resistance with an average of 25.4 % and the other extremely low with an average of 1.2 % in their backcrossed and s el fed progenies., Meiotic chromosome behavior in a resistant diploid group with high transmission rates was considerably normal as compared to that in a resistant diploid group with low transmission rates. Chromatid bridges and acertric fragments were detected in 93 % of resistant diploids and in 46 % of susceptible diploids. Two different sized fragments occurred in resistant diploids, while only a smaller fragment was present in susceptible diploids. A frequency of sporocytes with bridges‐fragments was 17.4% at anaphase I and 13.9 % at anaphase II in resistant diploids, while in susceptible diploids a frequency was 2.9 % and 5.3 % at the respective stages. These results suggest that at least two paracentric inversions are present in resistant diploids, one of which is linked to nernatode resistance and may be responsible for the low transmission rate of resistance.

MODIFICATION AND INHERITANCE OF PLEIOTROPIC CROSS RESISTANCE AND COLLATERAL SENSITIVITY IN SACCHAROMYCES CEREVISIAE

A meiotic segregant (oliPR1) was isolated with a phenotype of multiple cross resistance and collateral sensitivity. Strain oliPR1 has increased sensitivity to ethidium bromide, dequalinium chloride, acriflavin, paromomycin and neomycin, and increased resistance to oligomycin, rutamycin, venturicidin, triethyltin bromide, antimycin, carbonylcynamide-m-chlorophenylhydrazone, tetra-N-butylammonium bromide, dibenzyldimethylammonium chloride, triphenylmethlphosphonium bromide, chloramphenicol, carbomycin, tetracycline, triton X-165 and cycloheximide. Single gene inheritance of the cross resistance and collateral sensitivity was shown by 2:2 parental ditype segregation and reversion of the complete phenotype by a spontaneous revertant. The locus conferring the oliPR1 phenotype was mapped 11.7 units from an unspecified centromere. Antibiotic resistance showed incomplete dominance, with the level of hybrid resistance dependent upon the inhibitor tested. Resistant diploids that produced four resistant ascospores were the result of mitotic recombination prior to meiosis. A partial revertant phenotype (sensitive to all inhibitors except oligomycin, antimycin and carbonylcyanide-m-chlorophenylhydrazone) was shown to be due to a single nuclear gene causing partial suppression of oliPR1. Anaerobic pretreatment, 37degrees and 0.5 MKC1 were observed to reduce the growth of oliPR1 when challenged with seven diverse inhibitors (antimycin, carbonylcyanide-m-chlorophenylhydrazone,-chloramphenicol, cycloheximide, oligomycin, triethyltin bromide, and triphenylmethylphosphonium bromide). Resistance to cycloheximide was not altered by the [rho--] state. A revertant of oliPR1 (sensitive to the above inhibitors but resistant to ethidium bromide, paromycin and neomycin) showed anaerobic and temperature sensitization to ethidium bromide, paromomycin and neomycin. Continuous monitoring of oxygen uptake by the revertant afteranaerobic pretreatment revealed that anaerbiosis sensitized respiratory adaptation of the revertant to neomycin. It is proposed that oliPR1 is a mutation resulting in the alteration of plasma membrane permeability to many diverse inhibitors.

Parasexual genetics in Dictyostelium discoideum: mitotic analysis of acriflavin resistance and growth in axenic medium.

SUMMARY: Drug resistant mutants of the slime mould Dictyostelium discoideum useful for mitotic genetic analysis have been studied. Mutations to acriflavin resistance are recessive and have been assigned to two genes (acrA, acrB) located in different linkage groups. One of these (acrA) confers resistance to the unrelated compounds methanol and thiabendazole. Ability to grow axenically (in the absence of bacteria) is determined by genes on two linkage groups, one carrying acrA and the other an established temperature sensitive mutation. Preliminary results for two linkage groups show that the sequence of genes on a linkage group can be determined by analysis of homozygous drug resistant diploids, obtained by drug selection from diploids heterozygous for recessive drug resistance markers.