Varietal Differences In Susceptibility Research Articles

Variations in Pathogenicity of Three Different Forms of Rhizoctonia Inoculum and Assessment of Cultivar Resistance of Sugar Beet

Rhizoctonia solani causes pre-emergence and post-emergence damping-off, as well as crown and root rot of sugar beet (Beta vulgaris L.), which significantly affects the yield returns in the USA and Europe. The pathogen overwinters as sclerotia or melanized mycelium. Traditionally, the resistance of cultivars to R. solani is evaluated by scoring disease reactions at the crowns and roots of older seedlings, thus resistance is not evaluated during seed germination. Moreover, earlier studies evaluated cultivars resistance to R. solani using colonized whole barley or wheat grains which, unlike sclerotia, are artificial inocula of the pathogen that require time, space and technical know-how to produce. Moreover, colonized grains are prone to contamination with other pathogens, consumed by rodents/birds while applied in the field, and are often uneconomic. Considering those limitations, a study was undertaken (1) to develop in vitro methods to generate large-scale sclerotia, (2) to compare pathogenic potentials of sclerotia, mycelia, and colonized barley grains for optimization of dampingoff assays, and (3) to evaluate Rhizoctonia resistance of selected commercial cultivars during the seed germination phase. Comparing six different culture media, we found that R. solani had the highest radial growth (8.9 ± 0.04, cm³) at 8-days and the maximum number of sclerotia produced (203 ± 4.6) at 28-days in CV8 medium. We demonstrated significant differences in pathogenicity of the three different forms of R. solani inocula and susceptibility of cultivars to preand post-emergence damping-off. The highest pre-emergence damping-off and root rot were observed with sclerotia, and the highest post-emergence dampingoff was recorded with both sclerotial and colonized barley inocula. In addition, varietal differences in susceptibility to pre- and post-emergence damping-off were noted. The highest pre-emergence damping-off was recorded on cv Crystal 101RR and lowest in Maribo MA 504. The highest post-emergence damping-off was recorded on BTS 8500 and the lowest in Crystal 467. The maximum mean root rot was observed in BTS 8500, BTS 8606, and Crystal 101R. Our studies demonstrated that sclerotia serve as efficient natural inocula, reemphasized that host-pathogen interactions differ at the early vs. late stages of sugar beet growth, and highlighted the need to reevaluate commercial sugar beet cultivars for resistance at the seed germination stage.

The Phenology of Infestations and the Impacts of Different Varieties of Cold Hardy Red Raspberries on <i>Drosophila suzukii</i>

Spotted wing drosophila, Drosophila suzukii (Matsumura) (SWD), is emerging as the most significant pest of berries and stone fruits worldwide. With a broad host range, thin-skinned berries are particularly susceptible to infestation, and fruit producers are desperate for methods to control this pest. One of the keys to developing an integrated management program for SWD is to understand host preference and varietal susceptibility of highly susceptible crop hosts. Working in replicated small plots, experiments were conducted to evaluate differences in varietal susceptibility on cold hardy red primocane fruiting raspberries. Significant differences were observed in both the level of infestation and in the average number of larvae per berry by variety. In addition, it appears that there is a significant negative correlation between the level of infestation and the number of larvae per fruit with the time of sampling, but only an interaction of variety and time for the number of larvae per berry. These data provide a better understanding of the biology and ecology of this pest which is critical in refining current management practices. Knowledge of these interactions can aid in optimizing control strategies such as fine-tuning spatial and temporal control measures, which may be particularly important for early season infestations.

Occurrence of Stem Rot of Sweet Potato in Hokkaido and Differences in Varietal Susceptibility

Occurrence of Stem Rot of Sweet Potato in Hokkaido and Differences in Varietal Susceptibility

The effects of storage duration, temperature and cultivar on the severity of garlic clove rot caused by Fusarium proliferatum

Diseases that affect garlic during storage can lead to severe economic losses for farmers worldwide. One causal agent of clove rot is Fusarium proliferatum. Here, the progress of clove rot caused by F. proliferatum and its dependence on different storage conditions and cultivar type were studied. The effect of temperature on mycelial growth, conidial viability, and fungal survival during garlic commercial storage was documented. Samples of 50 bulbs from a randomized field trial with three different clonal generations for purple garlic (F3, F4 and F5) and the F4 clonal generation for white garlic were labeled and stored for two months (short-term storage). In addition, another sample of the F5 clonal generation of purple garlic was stored for 6 months after harvest (long-term storage). The presence of the pathogen and the percentage of symptomatic cloves were evaluated. A notable difference in the rot severity index (RSI) of different garlic varieties was observed. In all studied cases, clove rot increased with storage time at 20°C, and the white garlic variety had a higher index of rot severity after two months of storage. Additionally, there were clear differences between the growth rates of F. proliferatum isolates.Studies conducted on the temperature responses of the pathogen propagules showed that exposure for at least 20min at 50°C was highly effective in significantly reducing the viability of fungal conidia.Pathogenicity studies showed that the fungus is pathogenic in all commercial varieties. However, there were significant differences in varietal susceptibility between Chinese and white garlic type cultivars (81.84±16.44% and 87.5±23.19% symptomatic cloves, respectively) and purple cultivars (49.06±13.42% symptomatic cloves).

Varietal Differences in Susceptibility to Bacterial Spot (Xanthomonas arboricola pv. pruni) among 69 Peach Cultivars and Selections as Evaluated by Artificial Inoculation to Shoots

Varietal Differences in Susceptibility to Bacterial Spot (Xanthomonas arboricola pv. pruni) among 69 Peach Cultivars and Selections as Evaluated by Artificial Inoculation to Shoots

<p><strong>Coconut destiny after the invasion of </strong><strong><em>Aceria guerreronis </em></strong><strong>(Acari: Eriophyidae) in India*</strong></p>

The coconut mite, Aceria guerreronis Keifer, has emerged as a common menace to most of the coconut plantations in India. After its first upsurge in Kerala at the end of the 1990´s, the mite has spread to many states in southern and northern India, causing considerable damage. Coconut provides one third of the agricultural income in the regions in which it is grown and more than 10 million people are dependent on this cash crop directly or indirectly through coconut-based industries like coir, copra, oil, honey, furniture, handicrafts, beverages, bakery products and so on. The economic instability of the coconut farming community and the people employed in coconut-based industries rank the highest order. A critical assessment of the various problems created by A. guerreronis in the agricultural economy of India is presented in order to supplement data on crop loss through nut malformation, nut fall, loss in fibre and copra. Varietal differences in susceptibility of the plant and future strategies in terms of management practices for an early control of the mite are discussed, and suggestions for future activities to alleviate mite damage are presented.

Mango diseases in Egypt

Mango diseases in Egypt

Varietal Differences in Susceptibility to Early or High Temperature-induced Watercore in Apples

To determine the susceptibility to early or high temperature-induced watercore, seasonal changes in the incidence and intensity of watercore, ethylene evolution, and sorbitol content in 4 apple (Malus pumila Mill. var. domestica Schneid.) cultivars grown at Matsuyama were investigated. Mean air temperature was above 25°C from early July to mid-September. ‘Himekami’ and ‘Shinsekai’ apples started to develop watercore from mid- and early August, respectively, before the onset of ethylene production. The incidence and intensity of watercore in ‘Orin’ apples increased from mid-July to early September, followed by a decrease through late October, whereas no watercore was observed until early November in ‘Fuji’. In conclusion, ‘Himekami’ and ‘Shinsekai’ are regarded as moderately, and ‘Orin’ as highly susceptible to early or high temperature-induced watercore, whereas ‘Fuji’ is considered as being resistant. Significant correlations between sorbitol and early or high temperature-induced watercore were observed.

Fungi and decay associated with wild mango fruits (Irvingia gabonensis) under different postharvest conditions

AbstractFungi and percentage decay associated with wild mango fruits during storage at different postharvest conditions were monitored. In addition the effect of chemical treatments (hot water, solutions of benomyl, sodium acetate and sodium metabisulphite) and film packaging on percentage rate of decay was investigated.The characteristic brownish black rot, brownish discolouration and rotting of tissue, and greenish‐black soft rot common in wild mango fruits during storage are associated with fungi of the genera Aspergillus, Botrytis and Penicillium. The use of hot water, hot benomyl, hot sodium dehydroacetate and hot sodium metabisulphite (55 °C each) dips alone, or in combination with film packaging helped in reducing postharvest decay of wild mango fruits. Varietal differences in susceptibility of wild mango fruits to decay was also observed.

Xylem, Phloem and Transpiration Flows in Developing Apple Fruits

Xylem, phloem and transpiration flows were measured in developing fruits of the apples Royal Gala and Cox's Orange Pippin at early, mid and late stages during their development. Fruit volume growth was first computed from measurements of diameter made using a system of sensitive displacement transducers. Xylem, phloem and transpiration flow components (of which fruit volume growth is the integral) were then separated using a scheme of treatments which disabled one or other flow at a time. Changes observed during development in the patterns of the three flows are in general agreement with expectations based on less direct observations (loc. cit. Ferguson and Watkins, 1989). Recognizing the distinctive mineral compositions of xylem and phloem streams, the changes also accommodate, and seem to explain, published observations of mineral accumulation in apple. Significant differences in the pattern of xylem and phloem flow were observed between the varieties examined. These may explain varietal differences in susceptibility to the mineral imbalance disorder bitter-pit. Xylem flows were shown to reverse at times; that is they flowed from fruit to tree. This occurred particularly during periods of high evaporative demand. Xylem reversal is of importance to the overall water economy of a tree but may also have special importance to the mineral composition of the fruit.

Influence of Cultivar and Plant Age on European Corn Borer (Lepidoptera: Pyralidae) Infestation in Snap Bean

Nineteen cultivars of snap bean and wax bean, Phaseolus vulgaris L., were uniformly infested with egg masses of European corn borer, Ostrinia nubilalis (Huibner). A 5-fold difference in number of tunnels was found on the various cultivars. Cultivars differed in whether pod injuries or stem injuries predominated. Pod tunneling was most common on ‘Gold Crop’ and ‘Pillsbury 516’ and least common on ‘Sungold.’ Varietal differences in susceptibility to stem tunneling varied with plant age at time of infestation. Larval survival appeared to increase with age of the host plant at the time of egg hatch. Adult moths confined on four cultivars showed no ovipositional preferences. Newly hatched larvae bored into stems within 4 days, but were not found in the pods in the first 10 days.

Susceptibility of strawberry varieties to breakdown in sulphite by endopolygalacturonase from zygomycete spoilage fungi

AbstractDifferences were observed in the texture and susceptibility to enzymic breakdown of sulphited fruit of eight strawberry varieties. Cambridge Favourite was the softest variety in sulphite and was also the most susceptible to breakdown by pectolytic enzymes of Rhizopus and Mucor spp. Endopolygalacturonases (endo‐PG) from these species were more rapidly inactivated in sulphite liquor in the presence of fruit of the variety Harvester, which consequently showed the greatest resistance to breakdown. Isoelectric focusing indicated that a single major isoenzyme from each strain of R. sexualis, R. stolonifer and M. piriformis persisted in sulphite liquor and was, therefore, responsible for breakdown, although the major form of M. piriformis was less acid‐stable than those of the Rhizopus spp. Other minor isoenzymes produced by the fungi were inactivated within 24 h of sulphiting. Each species produced its major acid‐stable endo‐PG in the three varieties tested; thus varietal differences in susceptibility to breakdown may be related to the occurrence of natural enzyme inhibitors and/or fruit structure.

The susceptibility of potato varieties to internal rust spot

SummaryIn tubers of ten potato varieties the incidence of internal rust spot lesions increased and the calcium concentration decreased when the concentration of calcium chloride supplied to the plants fell from 9 to 1 mM. A simple linear model relating the probit transformation of internal rust spot incidence to tuber calcium concentration for each variety showed that there were substantial differences in varietal susceptibility to internal rust spot which were not related to tuber calcium concentration.

The influence of photoperiod on growth patterns of Erysiphe graminis f. sp. hordei

SUMMARYDetached seedling leaf segments of five spring barley genotypes were inoculated with an isolate of barley mildew to which they possessed different levels of resistance. Segments of each host genotype were then incubated under either continuous light or treatments with 2, 4, 8 or 16 h darkness per 24 h cycle. Macroscopic observation showed that the latent period of infection was reduced slightly in treatments with at least 4 h darkness/24 h. Yellowing of detached segments occurred fastest under continuous light and slowest under a 16 h dark/8 h light cycle. Microscope observation of segments fixed 4·5 days after inoculation showed that as the length of the dark period increased, so the number of haustoria formed per colony also increased. This increase in haustorial production appeared to be associated with an accentuation in the synchrony of production of the secondary and tertiary haustorial generations. Varietal differences in susceptibility were also more marked in segments incubated under short days. It is concluded that under the conditions of temperature and light intensity used, a 16 h dark/8 h light system is most desirable for quantifying mildew resistance because it allows confident identification of distinct haustorial generations, accentuates differences in varietal susceptibility and delays chlorophyll degradation in detached barley leaves infected with mildew.

Some biophysical principles underlying the controlled atmosphere storage of plant material

SUMMARYControlled atmosphere (CA) storage is of use for commodities which potentially can undergo rapid and unacceptable biochemical change. In air, the oxygen status of most plant material, including fleshy storage organs and fruits, suffices, even in the centre, for cytochrome oxidase to be fully saturated. Conflict of evidence exists as to possible O2 and CO2 gradients in fruit which, though physiologically unimportant in air, could be important under CA conditions. CA storage gives possible control of internal O2 from o to about 80–95%; internal CO2 from about 3–4 to 100%; and both simultaneously to intermediate values. Calculated molarities of dissolved O2, CO2 and ethylene are given for various atmospheres.The differences in the O2 concentrations recommended for different varieties of apple are not readily explicable. Varietal differences in susceptibility to CO2 injury could possibly result from anatomical, rather than biochemical, differences. This could be determined partly by resolving the conflict of evidence mentioned above. Variability of plant material prevents precise control of intercellular atmosphere; recommended atmospheres can be designed only to avoid completely anaerobic conditions and a harmful level of CO2 in the centre of the least permeable individual fruit or vegetable. Effects of low O2 and high CO2 are briefly described.

Effects of flower removal on the development of theSclerotinia/Botrytiscomplex of tobacco

Abstract Removal of flower heads markedly decreased infection of tobacco by Sclerotinia and Botrytis. Infection was correlated with the density of corollas falling on to the leaves; a greater proportion of those falling from axillary shoots than of those falling from apical shoots incited the diseases. It was not possible to determine whether differences in varietal susceptibility arose from differences in leaf susceptibility or from differences in the ability of the corollas to carry the diseases. Any change in agronomic practice which tended to extend the life of corollas on the plant could lead to increased incidence of these diseases.

Varietal resistance to Verticillium wilt of cotton in Queensland

Varietal differences in susceptibility (as assessed by the proportion of affected plants) to wilt of cotton caused by Verticillium dahliae Kleb., were observed in south-eastern Queensland. The progression of the disease within individual plants, however, was similar in all varieties. Deltapine Smoothleaf, the most widely grown variety in Queensland was one of the most susceptible varieties. Derivatives of Rex or Dixie King were less affected. The disease caused a difference in yield between healthy and diseased plants which could be as high as 30 per cent.

Correlation of ectodesmata number with nonspecific resistance to initial virus infection

The resistance of T.I. 245 tobacco to initial infection by necrotic strains of cucumber mosaic or tobacco mosaic viruses was markedly decreased by darkening plants before inoculation, by immersing leaves in water at 45° for 2 minutes, or by keeping plants at 16° for 3 days before inoculation. There was more chlorogenic acid oxidase and peroxidase in the resistant T.I. 245 tobacco than in the susceptible T.I. 787 tobacco. Treatments decreasing resistance, however, did not significantly alter the content of these two enzymes. In each variety virus became resistant at about the same rate, after inoculation, to external application of infection-inhibiting Phytolacca extract. Bentonite stimulated infectivity of TMV-RNA to about the same extent on each variety, indicating that resistance was not due to destruction of virus by leaf ribonuclease. Varietal differences in susceptibility and alterations in susceptibility due to age were correlated with numbers of ectodesmata demonstrable in the outer walls of epidermal cells. Similarly, darkening and temperature treatments that increased susceptibility of T.I. 245 tobacco also increased numbers of ectodesmata. These treatments had little effect on ectodesmata numbers or susceptibility of T.I. 787 tobacco. It was concluded that ectodesmata function as infection sites, and their number or condition determine relative susceptibility.

Differential Reaction of Lolium perenne Genotypes to Certain Herbicides

THE rapid progress in weed destruction made possible simply by introducing new chemicals has resulted in a concentration on obvious and gross effects. Examples of the selective toxicity of various chemicals between different plant genera and between different species of the same genus1 have been widely reported. Much less frequently cited are differential responses between varieties of one species. In potatoes, variation in varietal reaction to pre-planting application of trichloroacetic acid (TCA) has been noted2 and large differences in varietal susceptibility to 2 : 4-dichlorophenoxyacetic acid (2,4D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA)3 have been found. Hayes4 has demonstrated the differential response of barley to DDT, susceptible varieties being killed by DDT application. Commercial varieties of sugar-cane differ in physiological tolerance to dalapon5. Fiddian6 gave evidence of differential susceptibility of cereal varieties to some commonly used herbicides, variation occurring in amount of leaf scorch, growth deformity, ripening retardation, ear malformation and spikelet sterility.

Variation Among Tomato Lines with Respect to Ammonium Tolerance1

Abstract Variation within a particular species has resulted in the development of large numbers of cultivars in important horticultural and agronomic crops. A great number of characters are important in the determination of the merit of any cultivar. Variation among characters relating to plant nutrition have not been as well studied as some other characters. Nevertheless, sizeable reviews on this topic have been prepared by Millikan (4) and Vose (5). Stem lesions (Fig. 1) resulting from excess ammonium have recently been described (2, 3). Differences in varietal susceptibility were indicated. The purpose of this investigation was to ascertain if further varietal differences among commercial and experimental lines could be demonstrated.