Susceptible Clones Research Articles

Quantitative inheritance of Fiji disease resistance in sugarcane

The inheritance of Fiji disease resistance in sugarcane was studied, so that strategies for breeding for resistance could be developed. Resistance was highly heritable and most of the genetic variance was additive when infection pressure was low to moderate. Infection pressure was very heavy in one experiment and this reduced discrimination between parent clones and families. The data were skewed and this affected statistical and genetical analyses which showed that non-additive genetic variance was high. In general, however, it was concluded that selection of resistant parents would produce families with resistant progeny. Some moderately susceptible families produced a small number of resistant progeny and, if these families have agronomic merit, the breeding strategy should enable such families to be planted. The computerised strategy adopted rejects crosses if the average susceptibility of the two parents is too high, and emphasises the use of more resistant parent clones. As some susceptible clones will be selected, clones are subjected to a field screening trial as soon as practicable. These strategies have reduced the percentage of susceptible clones in the population from 70–80% to 20–30%.

Effects of Soil Moisture and Vapour Pressure Deficits on Shoot Growth and the Yield of Tea in the Kenya Highlands

SUMMARYProlonged moisture stress and high vapour pressure deficits reduced the shoot water potential, shoot population density, rate of shoot extension and yield of clonal tea. The more drought susceptible Clone 6/8 had a lower shoot water potential, rate of shoot extension, number of shoots per unit area, rate of shoot regeneration and yield than the more tolerant Clones 31/8, 57/15 and 15/10 during the periods of low soil moisture, which coincided with high vapour pressure deficits. The changes in the shoot growth components could be used as an index of the suitability of different clones for different regimes of soil moisture and vapour pressure deficits.Factores ambientales que afectan el rendimiento del té

Differential Tolerance of Sweet Potato (Ipomoea batatas) Clones to Metribuzin

Sweet potato clones were evaluated for metribuzin tolerance in field and greenhouse studies. ‘Tinian’ was the most tolerant and ‘SC-1149-19’ and ‘J-2’ were the most susceptible clones. ‘Jewel’, a clone widely grown commercially, was sensitive to metribuzin in the field and greenhouse. ‘Sumor’ and ‘White Triumph’ exhibited intermediate metribuzin tolerance. All metribuzin application-by-rate treatments reduced plant stands, caused season-long crop injury, and reduced yields. Metribuzin applied 3 wk posttransplant at 1.1 kg ha−1did not reduce total yield of Tinian. Total yield of all the clones except Tinian were reduced by metribuzin regardless of timing or rate.

In vitro activity of chloroquine and quinine in combination with desferrioxamine against Plasmodium falciparum.

The activity of chloroquine and quinine, alone and in combination with desferrioxamine (7 mumol/liter), was evaluated in vitro against susceptible and resistant clones of Plasmodium falciparum by a semimicroassay system. The addition of desferrioxamine had no effect on the activity of chloroquine against both clones. Desferrioxamine had no effect on the activity of quinine against the susceptible clone but had slightly enhanced quinine action against the resistant clone. Further development of desferrioxamine as an antimalarial drug may be of limited interest.

SCREENING FOR STREPTOMYCES SOIL ROT RESISTANCE IN SWEETPOTATO

Streptomyces soil rot or pox, caused by the actinomycete Streptomyces ipomoea, is a destructive root disease of sweetpotato. Evaluation for resistance to S. ipomoea in naturally infested fields, requires much space and results may vary from year to year. In this study a greenhouse method for evaluating the response of sweetpotato clones to infection with S. ipomoea was developed. The greenhouse method used fibrous roots, developed on terminal vine cuttings. Experiments showed no time by clone interaction, indicating that this method gave consistent results when repeated. A study to determine corrrelation between field resistance of clones and resistance as found by the greenhouse method was done. Thirty-nine clones were screened for resistance using the greenhouse method and were also planted in a field naturally infested with S. ipomoea. Severity of disease on fibrous roots (greenhouse method) and on storage roots (field method) was evaluated visually using a scale of 0 to 5 (0: no symptoms. 5: severe symptoms). Although correlations between data from the greenhouse and field methods were low lo moderate (r=0.17 to 0.49). extremely susceptible or resistant clones were identified as such by both methods. These results suggest that it is possible to select clones with high resistance to S. ipomoea using the greenhouse method, which provides a better controlled environment, and requires less space than field evaluations.

Response of Siberian Elm to Inoculations withSphaeropsis ulmicola

Eighty-one clones of Siberian elm (Ulmus pumila) were screened for resistance to Sphaeropsis ulmicola (=Borryodiplodia hypadermia) to determine if different levels of disease reaction or canker development could be detected. In 1989, inoculations with S. ulmicola resulted in significant differences among clones for branch dieback and canker length. In 1990, three clones with some resistance (small cankers) and three susceptible clones (large cankers) were inoculated with six isolates of S. ulmicola. On the basis of branch dieback and canker length, these clones were significantly different and responded similarly to inoculations performed in 1989. No significant differences in canker development among the six isolates were detected, and the isolate X clone interactions were not significant

Dry matter accumulation in potato clones under seasonal high temperature conditions in Pakistan

The effects of seasonal high temperatures on potatoes were investigated under field conditions near Peshawar, Pakistan. Five potato clones (A79196-1, Desiree, DTO-28, LT-1, Russet Burbank) were grown during the spring season at two locations. Canopy development, vine dry weight and tuber dry weight were determined at 13-day intervals, starting 68 days after planting (DAP). Tuber yield was higher in heat tolerant clones compared to heat susceptible clones. Location significantly affected tuber dry weights. Tuber dry weights of Russet Burbank were consistently lower than those of DTO-28. Ground canopy cover of DTO-28 occurred earlier and reached maximum at 75 DAP, compared to 90 DAP for Desiree. DTO-28, because of its high tuber yield under cool as well as hot temperatures, and its relatively early bulking, should be a promising clone for a short duration crop in hotter regions.

Oviposition choice and larval survival of Dasineura marginemtorquens (Diptera: Cecidomyiidae) on resistant and susceptible Salix viminalis

Abstract. Substantial intraspecific variation exists in Salix viminalis resistance to the gall midge Dasineura marginemtorquens. Earlier work has found this variation to have a large genetic component. Willow clones are stable in their resistances between midge generations and different nutrient levels in both field and laboratory culture. This study reports the results of laboratory experiments on female oviposition choice and larval survival on potted plants from clones that are very different in resistance as determined in field studies. In choice experiments using pairs of plants, the average female midge did not prefer susceptible willow clones over resistant ones for oviposition. In about one third of the replicates, midges actually laid more eggs on the resistant clone. Further work is necessary to examine the nature of variation among midges in discrimination of these plant types. Resistance is manifested as great differences in larval survival. Six days after oviposition survival was 92% on susceptible plants but only 6% on resistant ones. Galls developed on all of the susceptible plants, while in 73% of the resistant plants galls were not even initiated. The plant traits causing resistance are enigmatic. Larval behaviour suggests that resistant plants interfere with feeding behaviour. On resistant plants, most larvae wander for more than 24 h without initiating any galls before dying. On susceptible plants many first instar larvae begin feeding and initiate galls within this period.

Effekt und Risiko des Knöllchentests auf Braunfäuleresistenz bei Kartoffelsämlingen im System der Auslese in der Phytophthora-Resistenzzüchtung

The effects and risks involved with the small tuber assay in plant breeding programmes with potato seedlings for resistance to Phytophthora infestans In an assay which involved 838 potato seedlings, the relative resistance to leaf-Phytophthora (KRG) was tested at the 4–6 leaf growth stage, and the relative tuber resistance to infection was determined on small pot-grown tubers (BK) and, in the following 2 years, in slices from field-grown potatoes (Bs). The small tuber assay is described and its value as a measure of disease resistance, compared with the potato slice assay, discussed. Among 357 leaf-Phytophthora susceptible clones (KRG≤ 5) were 10 clones with a good to very good tuber resistance. 18 of 204 leaf-Phytophthora highly resistant idiotypes were extremely susceptible to tuber rot. After discarding those seedlings which showed KRG-values ≤ 5 and BX-values ≤ 5, 208 of the remaining 241 (= 86 %) tuber rot resistance carrying seedlings were selected. 14 % of the clones which showed adequate resistance in the potato slice assay were falsely discarded according to the small tuber assay. 80 clones remained as ballast in the field trials (BK≤ 5, Bs≤ 6.4), 160 (33 % of the idiotypes tested) had been correctly eliminated. The work-intensive small tuber assay presents a possibility by which breeding material can already be reduced in the seedling stage. In this respect there must be a pronounced genetic differentiation present in the potato population and the selection procedure carried out must not be too harsh.

The restricted distribution of potato leafroll luteovirus antigen in potato plants with transgenic resistance resembles that in clones with one type of host genemediated resistance

SummaryThe distribution of virus‐infected cells was examined, by fluorescence microscopy, within plants of a range of potato clones infected with potato leafroll luteovirus (PLRV). This range included nine PLRV‐resistant clones, of which four were transgenic lines carrying the PLRV coat protein gene and five were conventionally bred. Plants of these clones were resistant to PLRV multiplication and accumulated less virus antigen in leaf tissue than did susceptible clones. Indirect fluorescent antibody staining of thin sections from carbodiimide‐fixed petiole tissue revealed that in plants of PLRV‐susceptible clones, virus‐infected cells were abundant within both external (abaxial) and internal (adaxial) phloem bundles. In plants of the PLRV‐resistant conventionally bred clones and in resistant transgenic lines of cv. Pentland Squire, virus‐infected cells were much fewer in number and largely restricted to internal phloem bundles. In resistant transgenic lines of cv. Désirée, this restricted distribution of PLRV antigen was only detected in petioles of young leaves. The results suggest that the transgenic and a host‐mediated type of resistance that restricts virtis multiplication have underlying similarities.

Spermatogonial apoptosis has three morphologically recognizable phases and shows no circadian rhythm during normal spermatogenesis in the rat.

In this study we examined the possibility that regular or circadian fluctuations occur in the frequency of spontaneous spermatogonial apoptosis. Apoptosis of A2, A3 and A4 type spermatogonia occurring spontaneously in the normal rat testis was studied by light and electron microscopy. Normal and apoptotic A3 spermatogonia were quantified in 36 animals killed at two-hourly intervals over a 24 h period. Three sequential phases of spermatogonial apoptosis were defined and quantified separately: (i) an early phase in which cells showed margination of nuclear chromatin, (ii) an intermediate phase in which phagocytosed apoptotic bodies were partly degraded and (iii) a late phase in which only debris of degraded apoptotic bodies was evident. Groups of spermatogonia linked by intercellular bridges underwent apoptosis synchronously. Normal and apoptotic A3 spermatogonia occurred at a mean frequency of 33.4 and 9.6 per 10 seminiferous tubule profiles respectively; there was a large variation in these frequencies between animals, but no peaks or circadian periodicity were detected. Progressive degradation of apoptotic bodies was evident, the average ratios of intermediate and late bodies to early bodies being 1.5 and 3.5, respectively. Absence of a circadian rhythm in these data does not exclude the possibility that initiation of apoptosis in susceptible spermatogonial clones is synchronous, and that affected clones undergo lag periods of differing duration before expressing morphological apoptosis.

Honeydew production, survival and reproduction by Chaetosiphon fragaefolii (Cockerell) (Homoptera: Aphididae) on susceptible and resistant clones of Fragaria spp.

Honeydew production, survival, and production of nymphs were tested as indicators of resistance of strawberry clones to the strawberry aphid, Chaetosiphon fragaefolii (Cockerell). All correlated with resistance but survival was the simplest to measure and was very consistent from plant to plant within clones. The results showed that field screening of strawberry seedlings for resistance to the aphid often falsely identifies seedlings as being resistant when, in reality, they have escaped infestation. The laboratory procedures permit quick confirmation of refutation of field results.

Tyrosine synthesis in potato tuber tissue from blackspot-susceptible and resistant genotypes

Radioactively-labeled shikimic acid (14C) was incubated with potato tuber tissue disks to determine the relative rate of tyrosine synthesis in blackspot-resistant and susceptible cultivars. Tyrosine synthesis was 55% higher in the susceptible cultivar, Lemhi Russet, than the resistant clone TXA 763-5. The susceptible clone also partitioned a lower percentage of14C tyrosine into soluble protein than did the resistant genotype. The percentage of labeled free tyrosine which would be available for oxidation by polyphenyloxidase was therefore much higher in the susceptible cultivar.

Trypanosoma congolense: the in vitro akinetoplastic induction sensitivity assay

Incubation of Trypanosoma congolense in diminazene aceturate (Berenil) or isometamidium chloride (Samorin) induced akinetoplastic (AK) forms in vitro. The AK values (expressed in percent) obtained were found to be useful for rapid assessment of relative drug sensitivities. In susceptible clones, AK forms were induced at all drug concentrations tested, whereas in resistant clones they were induced only at higher concentrations. The Berenil-resistant clone exhibited AK values of 0.9% +/- 0.6%--8.9 +/- 2% at concentrations of 1-100 micrograms/ml at 4-10 h post-inoculation (p.i.), whereas the Berenil-susceptible clone displayed values of 9.3% +/- 13%--19.2% +/- 5% at 0.1-50 micrograms/ml. Motile trypanosomes were not seen at 100 micrograms/ml at 4 h p.i. or at 10 or 50 micrograms/ml at 10 h p.i. The Samorin-resistant clone showed AK values of 0.5% +/- 0.1%--43% +/- 3% at concentrations of 0.1-100 micrograms/ml at 4 and 10 h p.i., whereas the Samorin-susceptible clone exhibited values of 5.3% +/- 2%--45% +/- 4% at 0.0005-100 micrograms/ml. These results were supported by the findings obtained using a mouse infectivity test.

The role of phenolics in goldenrod ball gall resistance and formation

Some genotypes of Solidago altissima have been shown to exhibit a hypersensitive response to the tephritid ball gallmaker Eurosta solidaginis. When the gallmaker attempts to stimulate gall formation in these genotypes, necrotic tissue surrounds the larva and apparently causes larval death [Anderson, S. S., et al. (1989) Ecology 70, 1048]. Other genotypes have varying degrees of resistance or susceptibility [McCrea, K. D. and Abrahamson, W. G. (1987) Ecology 68, 822]. Studies of other host plants have shown that phenolic compounds can play an important role in this defensive reaction. To determine the role of phenolics in the resistance of S. altissima to ball gallmakers, weekly tissue samples were collected from two resistant and two susceptible clones, both with and without Eurosta attack. These samples were analysed for total phenolics using the Folin-Ciocalteau procedure. Phenolic content increased over time in all clones. In unattacked ramets, phenolic levels were higher in susceptible clones than in resistant clones. No evidence of an increase in phenolics was seen with a hypersensitive response, but a significantly higher concentration was found in plants that had initiated normal gall development. A second study of rapidly growing galls in three additional susceptible clones confirmed this increase in phenolics, demontrated that the higher phenolic concentrations were restricted to gall tissue, and showed that phenolic levels increase as much as five-fold in galls near their peak growth period. Increases in total phenolic levels were clearly not responsible for the hypersensitive reaction for resistance, but phenols could potentially play a role in gall formation by influencing the hormonal control of growth and/or in protection of the gallmaker from its natural enemies.

The effect of diminazene aceturate and isometamidium chloride on cultured procyclic forms of susceptible and drug-resistant Trypanosoma congolense

Cultures of insect forms of Trypanosoma congolense stocks and clones with different susceptibilities to trypanocidal drugs in vivo were initiated from bloodstream trypomastigotes harvested from mammalian hosts and maintained axenically in vitro at 27°C. Growth inhibition of procyclic forms of susceptible and drug-resistant T. congolense occurred after incubation for 48 h with 0.1 ng isometamidium chloride/ml or 500 ng diminazene aceturate/ml. Procyclic forms were propagated in vitro in the presence of 10 or 100 ng diminazene aceturate/ml for 20 days without or with only minor loss of growth. In the presence of 0.1 or 1 ng isometamidium chloride/ml the trypanocidal effect was detectable after 6–8 days and the cultures died after 10–12 days. Concentrations of 1 or 10 ng isometamidium chloride/ml had an irreversible effect when the trypanosomes were exposed to the drug for 24 h. Both drugs used in this study thus showed antitrypanosomal activity on T. congolense procyclic forms but it was not possible to distinguish between drug-resistant and susceptible stocks or clones employing the criteria of growth inhibition or death of trypanosomes in culture.

Production of Sori and Dispersal of Teliospores ofUstilago scitamineain Louisiana

Production of sori by Ustilago scitaminea was monitored during two growing seasons in smut-inoculated sugarcane clones in Louisiana. The production of sori began during May, increased sharply during June, and continued at a lower rate through October. Smaller peaks in sorus production occurred in highly susceptible clones during August and October. Secondary infection cycles were detected in many highly and moderately susceptible clones and a few resistant clones. Sorus production began later and fewer sori were produced by resistant clones. Teliospore concentrations per cubic meter of air per day above the canopy increased with sorus production during June (...)

Electron microscopical studies of poplar clones inoculated with Xanthomonas populi subsp. populi

AbstractDistribution of Xanthomonas populi subs, populi was studied 21 days postinoculation in highly susceptible, susceptible and tolerant poplar clones (Populus trichocarpa): Heimburger, Muhle‐Larsen and Columbia River. Bacteria were observed in the intercellular spaces of leaf trace of both clones Heimburger and Muhle‐Larsen. No bacteria were detected 21 days after inoculation (dpi) in ultrathin sections of the clone Columbia River. The direct effect of bacteria on the host cells was the expanding intercellular space of leaf traces by dissolution of the middle lamellae and cell walls, and collapse of the surrounding cells.Sixteen weeks following the inoculation a tumour developed only at the inoculation site of the clone Muhle‐Larsen; Heimburger showed longitudinal cracks.

Expression of hollow heart in segregating tetraploid potato families

Expression of hollow heart, a physiological disorder in potato, is controlled by both genotype and environment. Development of high levels of resistance in cultivars would reduce economic yield losses that occur under conditions that promote hollow heart. This experiment was conducted to study hollow heart in segregating populations from parents in a breeding program. Nine families were planted in a replicated trial under dryland conditions and five of those families were also grown at an irrigated location under conditions favoring the expression of hollow heart. As expected, positive correlations between hollow heart and both mean yield and tuber weight were detected; correlations between hollow heart and tuber number were negative. Hierarchical regression analysis was performed on these yield traits to determine the independent contribution of each to the overall results. The highest levels of hollow heart were found in families with susceptible parents, but susceptible clones were obtained in families with two resistant parents. Regardless of the type of cross, selection of clones with large tubers increased the probability of selecting for susceptibility to hollow heart.

USE OF PROTOPLAST, CELL, AND SHOOT TIP CULTURE IN AN ELM GERMPLASM IMPROVEMENT PROGRAM

An elm germplasm improvement program was established using three distinct approaches: (1) development of protoplast regeneration protocols with the goal of attempting somatic hybridization between Ulmus americana and disease resistant hybrids; (2) evaluation of the extent of somaclonal variation in plants regenerated from protoplasts; and (3) selection in vitro of variants from Ulmus americana callus lines exposed to toxin and culture filtrates of Ceratocystis ulmi. Plants were regenerated from protoplasts of the Dutch elm disease resistant hybrid Ulmus x 'Pioneer', but repeated attempts to regenerate Ulmus x 'Homestead' failed. Somaclonal variation has been described in a population of plants regenerated from 'Pioneer' elm protoplasts and this variation can be fixed in clones through asexual propagation. Ulmus americana selections with field level resistance to Dutch elm disease demonstrate resistance in vitro, as evidenced by callus growth on media containing culture filtrates of Ceratocystis ulmi. Attempts to select variants of previously susceptible Ulmus americana clones have been frustrated by the inability to regenerate plants from callus of adult phase Ulmus americana.