Interaction of Apple Cultivars with Populations of Cedar-Apple Rust

Five physiological populations of Gymnosporangium juniperi-virginianae Schw. were identified on the basis of pycnial and aecial lesion formation when seven apple cultivars grown in a glasshouse were inoculated with basidiospores of rust populations collected from six locations in the U.S.A. The relationship between cultivars and rust populations was explored quantitatively using the parameters N, D, and DR, where N was the highest number of pycnial lesions on a leaf/plant; D was the largestdiameter measurement of pycnial lesions on a leaf/plant; and DR, the disease rating, was proportional to the diseased area of the leaf and calculated as ND². Statistically significant differences among cultivars over all rust populations for variables N, D, and DR were obtained, indicating the possible existence of race non-specific resistance in apple to cedar-apple rust. Moreover, significant differences among the rust populations over all cultivars for variable N and DR were obtained, confirming the existence of physiologically different rust populations of the pathogen. A change in the pathogenicities of these physiological populations must have occurred over time (10-year period). A significant interaction between cultivars and rust populations was observed for lesion size (D) only, indicating a probable existence of race specific resistance in apple as well.     

Effects of Leaf Age, Inoculum Dose and Freezing on Development of Chocolate Spot (Botrytis fabae) Lesions on Field Bean (Vicia faba) Leaves

Botrytis fabae spore suspensions containing c. 1, 10, 10², 10³, 10⁴, 10⁵, or 10⁶ spores/ml were used to inoculate 5, 17 or 30-day-old field bean leaves. The percentages of the leaf areas covered by, chocolate spot lesions and the percentages of the leaf areas bearing conidiophores were assessed 1, 6, 12, 14, and 19 days after inoculation. The percentage of the area covered by lesions and the percentage of the area bearing conidiophores (logit-transformed) increased linearly with increasing spore concentration (log₁₀-transformed). The proportions of leaf areas covered by lesions and bearing conidiophores were both greater on 17 and 30-day-old leaves than on 5-day-old leaves. The rate of lesion growth increased with both increasing inoculum dose and increasing leaf age. Generally there was no interaction between the effects of leaf age and the effects of inoculum dose on either lesion growth or sporulation. Two days after inoculation with suspensions of either 10⁴ or 10⁶ spores/ml, 7-day-old leaves grown at 15°C were transferred to –16°C or 2.5°C or kept at 15°C for 4 days. Two days later more spores had been produced on leaves which had been frozen (–16°C) than on, leaves kept at 2.5°C.     

Phylogenetic studies in <Emphasis Type="Italic">Ravenelia esculenta</Emphasis> and related rust fungi

Ravenelia esculenta Naras. and Thium. is a rust fungus, which infects mostly thorns, inflorescences, flowers and fruits of Acacia eburnea Willd. Aecial stages of the rust produce hypertrophy in infected parts. DNA of the rust fungus was isolated from aeciospores by ‘freeze thaw’ method. 18S rDNA was amplified and sequenced by automated DNA sequencer. BLAST of the sequence at NCBI retrieved 96 sequences producing significant alignments. Multiple sequence alignment of these sequences was done by ClustalW. Phylogenetic analysis was done by using MEGA 3.1. UPGMA Minimum Evolution tree with bootstrap value of 1000 replicates was constructed using these sequences. From phylogenetic tree it is observed that Ravenelia esculenta and the genus Gymnosporangium share a common ancestry, though Ravenelia esculenta is autoecious on angiosperm and the genus Gymnosporangium is heteroecious with pycnia, aecia on angiosperm and uredia, telia on gymnosperm. Two major clades are recognized which are based on the nature of aecial host (gymnosperm or angiosperm). These clades were also showing shift from pteridophytes to angiosperms as telial hosts. The tree can be interpreted in the other way also where there is separation of 14 families of Uredinales depending upon nature of teliospores, nature of aeciospores and structure of pycnia. These studies determine the phylogenetic position of Ravenelia esculenta among other rust fungi besides broad separation of Uredinales into two clades. These studies also show that there is phylogenetic correlation between molecular and morphological data. This is first report of DNA sequencing and phylogenetic positioning in genus Ravenelia from India.     

Components of resistance to Cercospora arachidicola and Cercosporidium personatum in groundnuts*

The reactions of four groundnut cultivars to inoculation with two leaf spot pathogens (Cercospora arachidicola and Cercospodirium personatum) were investigated. Resistant cultivars showed longer latent periods, reduced sporulation and less defoliation; however, none of the cultivars was resistant to both pathogens. Numbers of lesions, time to leaflet loss and the percentage of spores which produced lesions were influenced by the concentration of C. personatum inoculum applied to the leaves and there were significant cultivar differences in lesion numbers at the lowest inoculum level. Only the first two characters were affected by applied spore concentration in the study with C. arachidicola. Generally it was found that lower inoculum levels gave a better separation of cultivars. The level of resistance was similar to that found in the slow resting reaction of cereal crops and should be useful in a groundnut breeding programme.     

Screening for fire blight resistance in apple (Malus pumila) using excised leaf assays from in vitro and in vivo grown material

The apple cultivars Greensleeves and Novole and somaclones derived from Greensleeves were tested for resistance to fire blight (Erwinia amylovora) using excised leaf bioassays. Cv. Greensleeves was consistently susceptible to fire blight in in vitro, and in glasshouse and excised leaf bioassays whilst cv. Novole was resistant. Greensleeves somaclones, identified as having intermediate levels of fire blight resistance in glasshouse and in vitro screening tests, also showed intermediate levels of resistance in excised leaf bioassays. The length of leaves and the inoculum concentration employed affected the severity of symptoms observed. Excised leaf bioassays were unsuitable as tests for fire blight resistance using field grown material.     

Alternaria alternata f.sp. cucurbitae, the cause of a new leaf spot disease of melon (Cucumis melo)

A leaf spot disease of melon caused by Alternaria alternata f.sp. cucurbitae was recorded for the first time in Crete. Necrotic flecks surrounded by chlorotic halos developed on the cotyledons and the leaves of the middle and the upper part of the plants; the flecks enlarged and coalesced to form lesions of 2 cm or more in diameter with brown fructifications of the pathogen on their surface. Severely affected cotyledons and leaves became chlorotic and died. Of 16 species from eight botanical families that were inoculated, only those of the Cucurbitaceae were susceptible. Of four isolates of A. alternata from tomato, sunflower, pear and cucumber, only the cucumber isolate was pathogenic to melon foliage.     

Effects of temperature, cultivar and isolate on the incubation period of white leaf spot (Mycosphaerella capsellae) on oilseed rape {Brassica napus)

When leaves of oilseed rape (cv. Cobra) were inoculated with conidial suspensions of Mycosphaerella capsellae (white leaf spot) and incubated in controlled environments, the lag period from inoculation to the appearance of the first lesions decreased, and the total number of lesions produced increased, as temperature increased from 5^oC to 20^oC, although differences between 15^oC and 20^oC were small. With incubation period estimated as the time from inoculation until 5%, 50% or 95% of the lesions were produced, there was a linear relationship between l/(incubation period in days) and temperature over the range 5^oC to 20^oC, from which values at intermediate temperatures could be estimated. Summed mean daily temperatures from inoculation to the production of 5% of the lesions were estimated as 115–130 degree-days in the controlled environment experiments at 5^oC to 20^oC. When pods or leaves of plants in oilseed rape crops (cv. Cobra or cv. Libravo) were inoculated with conidial suspensions of M. capsellae on five occasions from January to October, with variable temperatures during the incubation period, degree-days until the first appearance of lesions were in the range 115–230. The numbers of white leaf spot lesions cm^-2 which developed on inoculated leaves differed greatly between nine oilseed rape cultivars, with most on cv. Tapidor and fewest on cv. Libravo, but the incubation period differed little between cultivars. Similarly, the number of lesions which developed differed between four M. capsellae isolates from different regions but the incubation period did not.     

In vitro evaluation of sugarcane resistance to gumming disease and of Xanthomonas campestris pv. vasculorum aggressiveness

Sugarcane plantlets were sectioned halfway between the base and the youngest ligule and then inoculated by soaking the wound in a suspension of Xanthomonas campestris pv. vasculorum. The infection caused rapid necrosis of the inoculated leaves, chlorosis of uninoculated leaves, or death of the inoculated plantlet. New tillers sometimes showed chlorosis or white streaks. The effects of the inoculum concentration, the cultivar, and the bacterial strain on symptom severity were determined. The ranking of cultivars depended on the inoculum concentration, and strains were found to differ with regard to aggressiveness. However, cultivars and strains were more effectively classified in greenhouse trials. The poor expression of leaf resistance appeared to limit the use of the in vitro test.     

Selection of mutants resistant to Alternaria blotch from in vitro -cultured apple shoots irradiated with X- and γ-rays

We produced mutants resistant to Alternaria blotch disease in several cultivars of apple (Malus × domestica Borkh.) by irradiation with X- or γ-rays. An efficient in vitro assay method was established using chemically-synthesized AM-toxin I of Alternaria alternata (Fr.) Keissler to screen for mutants resistant to Alternaria blotch disease. The frequency of necrotic lesions was investigated by applying various concentrations of AM-toxin I to leaf discs of the first, third, and fifth leaves from the shoot apex of several apple cultivars, including Jonathan, Fuji, Oorin, and Indo. In vitro-grown apple shoots of susceptible cultivars were then treated with various doses of X- or γ-ray irradiation. Several mutants resistant to AM-toxin I were obtained by combining the techniques for tissue culture of apple shoots with the AM-toxin I screening method. Following a repeat second screening test with AM-toxin I, mutant plants were sprayed with a spore suspension of A. alternata and found resistant to be the fungal pathogen. These mutants showed normal phenotypic appearance, and so far, no difference has been observed between the original plants and mutants except for the susceptibility to Alternaria blotch.     

Effects of inoculum concentration, leaf age and wetness period on the development of dark leaf and pod spot (Alternaria brassicae) on oilseed rape (Brassica napus)

Experiments were done under controlled environment and glasshouse conditions to study the effects of inoculum concentration, leaf age and wetness period on the development of dark leaf and pod spot (Alternaria brussicae) on oilseed rape (Brassica napus). On leaves of potted oilseed rape plants (cv. Bienvenu) inoculated with A. brassicae conidial suspensions, the severity (number of lesions cm^-2) of dark leaf spot increased as inoculum concentration increased from 80 to 660 spores ml^-1and as leaf age increased from 4 to 14 days. On pods on detached racemes of spring oilseed rape (cv. Starlight), the incidence of dark pod spot (% of pods diseased) increased as inoculum concentration increased from 80 to 10⁴spores ml^-1. Increasing inoculum concentration above 10⁴spores ml^-1did not increase the incidence but did increase the severity of dark pod spot. A minimum wetness period of 4 h was needed for infection of oilseed rape leaves (cv. Envol) by A. brussicue at 18°C and disease severity increased with increasing wetness period up to 12 h. The length of dry interruptions after 3–8 h of initial wetness affected the severity of dark leaf spot. A second wetness period increased the severity of dark leaf spot if the dry interruption was ≤ 6 h and if the first wetness period was ≤ 8 h. The incubation period of A. brassicae decreased from 3.5 to 2.5 days as inoculum concentration increased from 80 to 660 spores ml^-on leaves (cv. Bienvenu) at 17–25°C and from 3.8 to 1.0 day as inoculum concentration increased from 80 to ≥2 ≥ 10³spores ml^-1on pods (cv. Starlight) at 18°C.     

The timing of sprays for the protection of terminal buds on apple shoots from powdery mildew

Post-blossom sprays of fungicides, repeated at 10-day intervals until leader (syn. extension) shoots had stopped producing new leaves, provided the best protection of terminal buds against Podosphaera leucotricha on the apple cv. Lane's Prince Albert. Spraying was most effective in early summer, although many of these buds were not invaded until later, when the rate of shoot growth declined; applications from July to September did not compensate for the enhanced infection which followed interruptions of the post-blossom programme between late May and early July. This early period was critical because most leaf infections occurred then, and because this phase of the epidemic on foliage determined the eventual intensity of mildew on terminal leaves, and hence the inoculum available for infecting terminal buds. Also, many lateral shoots ceased growth early and their apices were directly protected by sprays applied in June. Applications after early June were too late to protect newly formed fruit buds on spur branches.     

Accumulation of Free Proline at Low Temperatures

The accumulation of free proline in the first leaves of barley, Hordeum distichum L., and wheat, Triticum aestivum L., in response to a range of low temperatures was examined with 10-day-old plants. In barley (cv. Prior) no proline accumulated at 8°C or above, but in wheat (cv. Gabo) proline accumulated at 12°C and lower temperatures. In barley, the first leaf survived for 29 days following transfer to 5°C and continued to accumulate proline throughout this period. In contrast, the first leaves of plants maintained at 20°C survived for 13 days only and accumulated no proline. Proline accumulation at low temperature was shown to be light-dependent, both in intact plants and excised leaf sections, and the light requirement could not be replaced by supplying leaf segments with precursors of proline. Proline accumulation in response to water stress was not light-dependent at 20°C but was at 5°C. Inter-specific and intra-specific variation in the extent of accumulation in response to low temperature was also examined. Considerable variation was encountered but there was no clear relationship with geographical distribution or chilling sensitivity for the species and no correlation with accumulation in response to water stress in the cultivars of barley examined.     

Local and systemic changes in glucosinolates in Chinese and European cultivars of oilseed rape (Brassica nap us L.) after inoculation with Sclerotinia sclerotiorum (stem rot)

Four Chinese Brassica napus lines, generated through a breeding programme to identify Sclerotinia sclerotiorum tolerant and susceptible lines, and three European varieties were analysed for changes in glucosinolates (qualitative and quantitative), and general host reactions, after localised inoculation with a UK S. sclerotiorum isolate. Plants at the fifth leaf stage were either singly inoculated (third leaf) or were inoculated once (third leaf) and then challenged a second time (seventh leaf) 7 days after the first inoculation. The results showed very distinct reactions in the different lines and cultivars to the fungus, both locally and systemically. Of the European lines B. napus cv. Bienvenu showed good resistance (small lesions and less host damage) both 3 and 7 days post-inoculation. Capricorn was the most susceptible followed by Cobra; the third leaves of these cultivars were showing strong chlorotic and necrotic reactions by day 3 and lesions were well developed. By day 7 the third leaves of Capricorn were completely rotten whilst Cobra still had a little healthy tissue. Inoculation of the four Chinese lines showed that two had moderate resistance (014 and 020 — slightly less resistant than Bienvenu) and two were very susceptible (016 and 024 — similar reactions to Capricorn and Cobra), based on lesion size and host tissue damage. Glucosinolate induction in line 014 was good both locally and systemically, with clear local and systemic induction of indolylglucosinolates and 2-phenylethylglucosinolate both 3 and 7 days post-inoculation. Line 020 did not show no particular increases in glucosinolates after inoculation either locally or systemically. In line 016 there was a small local increase and a large systemic reduction in total glucosinolates. Inoculation of line 024 caused no major local changes in glucosinolates and again a big reduction in glucosinolates systemically. The dual inoculation system, with lines 014 and 016, produced comparable results, with line 014 showing good local and systemic induction of glucosinolates (after the first inoculation) and a further local and systemic induction after the second inoculation. This induction in pre-inoculated line 014 plants was associated with a reduction in lesion size of the second inoculum. Line 016 responded poorly both locally and systemically, and there were no real decrease in the lesion size of the second inoculum. It appears that in line 014 glucosinolate induction may be an important part of resistance, whereas in line 020 there are clearly other non-glucosinolate factors involved. The poor local and systemic induction of glucosinolates in lines 016 and 024, and subsequent susceptibility, implies that glucosinolate induction may be an important marker of resistance to S. sclerotiorum in oilseed rape.     

Life history ofAphis gossypii on cucumber: influence of temperature, host plant and parasitism

Life table data forAphis gossypii Glover (Homoptera: Aphididae), an important pest in glasshouse cucumber crops, were studied at 20, 25 and 30°C on two cucumber cultivars (Cucumis sativus L.) in controlled climate cabinets. The development time on the cucumber cv. ‘Sporu’ ranged from 4.8 days at 20°C to 3.2 days at 30°C. Immature mortality was approximately 20% and did not differ between temperatures. Most mortality occurred during the first instar. Reproduction periods did not differ among temperatures, but at 25 and 30°C more nymphs were produced (65.9 and 69.8 nymphs/♀, respectively) than at 20°C (59,9 nymphs/♀) because of a higher daily reproduction. Intrinsic rate of increase was greatest at 25°C (r _m =0.556 day⁻¹). At 20 and 30°C the intrinsic rate of increase was 0.426 and 0.510, respectively. On cv. ‘Aramon’, the development time ofA. gossypii was approximately 20% longer at all temperatures. Immature mortality did not differ between the two cultivars. The intrinsic rate of increase on cv. ‘Aramon’ was 15% smaller than on cv. ‘Sporu’. The use of cucumber cultivars partially resistant to aphids is discussed in relation to biological control of cotton aphid in glasshouses. Development time and immature mortality on leaves of the middle and upper leaf layer of glasshouse grown cucumber plants (cv. ‘Aramon’) were comparable to development in the controlled climate cabinets. On the lower leaves immature mortality was much higher (approximately 82%) than on leaves of the middle (24.0%) and upper leaf layer (24.5%). Reproduction was less on the lower leaf layer (45.9, 70.5 and 70.1 nymphs/♀ on leaves of the lower, middle and upper leaf layer, respectively). Aphids, successfully parasitized byAphidius colemani Viereck (Hymenoptera: Braconidae) only reproduced when they were parasitized after the third instar. Fecundity was 0.1 to 0.9 and 10.5 to 13.3 nymphs/♀ for aphids parasitized in the fourth instar or as adults, respectively. Reproduction of aphids that were stung but survived the attack was lower than for aphids not stung. Average longevity of these aphids was equal to the longevity of aphids not stung byA. colemani.     

Resistance of Hibiscus esculentus L. and Vigna sinensis (L.) Endl. to Pseudocercospora and plant peroxidase activity in relation to infection

Five cultivars of Hibiscus esculentus L. and six cultivars of Vigna sinensis (L.) Endl. were tested for their relative resistance to Pseudocercospora spp. Differences in susceptibility to the leaf spot pathogen were observed in both host and non-host interactions. The H. esculentus cv. South Sea and V. sinensis cv. Purple Mart were most susceptible to Pseudocercospora abelmoschi and P. cruenta, respectively. The H. esculentus cv. Pure Luck was most tolerant to P. abelmoschi while the V. sinensis cv. KY Bush was highly resistant to P. cruenta. A distinct host-specific interaction was observed among the different species of Pseudocercospora. Cultivar specific interactions were most pronounced between V. sinensis and P. cruenta. A direct correlation was observed between the variation in peroxidase activity in the soluble fraction of inoculated leaves and resistance to infection in H. esculentus and V. sinensis cultivars. The soluble fraction of inoculated leaves had higher peroxidase activity than either mitochondrial or chloroplast extracts.     

Species composition and distribution of Coleosporium species on the needles of Pinus densiflora at a semi-natural vegetation succession site in central Japan

Coleosporium species cause pine needle rust. Most species have heteromacrocyclic life cycles, and 12 species use Pinus densiflora as aecial hosts. To understand the biology of rust fungi and develop better methods for controlling rust diseases, it is necessary to clarify that which Coleosporium species affect pine trees. However, Coleosporium on pine trees have rarely been identified at the species level because of their morphological similarities. We used polymerase chain reaction - restriction fragment length polymorphism (PCR-RFLP) to clarify the species composition, abundance, and distribution of Coleosporium in a P. densiflora forest. We surveyed a site where several Coleosporium species might complete their life cycles. PCR-RFLP revealed four species on the pines: C. asterum, C. clematidis-apiifoliae, C. lycopodis, and C. phellodendri. Coleosporium phellodendri was distributed throughout the forest and was the most abundant. Aecia of C. phellodendri formed mainly on 2-y-old needles. The abundance and distribution of C. phellodendri appeared to be affected by the longer effective dispersal range of basidiospores and the existence of abundant inoculum sources. The age of leaves where C. phellodendri form aecia mainly was thought to be influenced by the characteristic life cycle, with aecial formation requiring 2?y after basidiospore infection.     

Aphanocladiutn album, a fungus inducing teliospore production in rusts

The hyphomycetous fungus Aphanocladiutn album can grow over and around uredia of the rusts Puccinia coronata, P. hordei, P. graminis f.sp. avenae and P. recondita f.sp. triticina when host plants are kept under very humid conditions, but not on such plants not infected with rusts; uredia are adversely affected and telia develop in their vicinity. Plants inoculated with these rusts and with five isolates of A. album (one from a dead insect) showed: (1) much earlier development of telia on detached and non-detached rusted leaves inoculated with A. album than on corresponding leaves not thus inoculated; (2) telial induction by A. album in some isolates of rust species which hitherto had rarely or never produced telia; (3) precocious telial formation, in comparison with controls, when A. album spores were sprayed on leaves as much as 3 days before and 9 days after rust inoculation, and occasionally after uredia had already matured. As affected leaves remained green until the whole leaf became moribund, senescence is apparently not the factor inducing telia formation. The normal-appearing teliospores of some isolates were induced to germinate, whereas others did not. Rhamnus palaestina inoculated with basidiospores of one isolate of A. album-treated P. coronata f.sp. avenae produced pycnia and fertile aecia. The importance of A. album as a working tool in rust research and as a possible means for biological control of rust epiphytotics is discussed.     

Oviposition preference of Anthocoris nemorum and A. nemoralis for apple and pear

Anthocoris nemorum L. and Anthocoris nemoralis Fabricius (Heteroptera: Anthocoridae) are important predators of insect pests in pome fruit. Females insert their eggs in leaf tissue. The females’ choice of oviposition site is important for the subsequent distribution of nymphs on host plants. Oviposition preference for apple and pear leaves was tested in the laboratory in four experiments (experiments 1–4). In three experiments it was tested whether simulated insect damage to leaves (experiments 5 and 6) or the presence of prey (experiment 7) influenced oviposition preference. The effect of the presence of prey was only tested for A. nemorum on apple leaves. There was a highly significant anthocorid species × plant interaction for the number of eggs laid on apple and pear leaves. Anthocoris nemorum laid more eggs on apple than on pear leaves, while A. nemoralis preferred pear. Anthocoris nemorum's preference for apple increased over the 6‐week period in which experiments 1–4 were performed, from 66% to 91% eggs laid on apple leaves. No change over time in preference was found for A. nemoralis. Across experiments 1–4, the majority of A. nemorum eggs were laid near leaf margins, whereas eggs of A. nemoralis were more commonly found in the leaf centre, 5 mm or more from the margin, with a highly significant leaf region × species interaction. There was no significant difference in preference for leaf side between A. nemorum and A. nemoralis, but there was a highly significant plant × leaf side × experiment interaction. Thus, more eggs were laid on the ventral than on the dorsal side of pear leaves in experiment 4, while significantly more eggs were laid on the dorsal side of apple leaves in experiments 3 and 4. Choice tests between damaged and healthy leaves showed that A. nemorum laid significantly more eggs on the damaged leaves, while A. nemoralis preferred healthy leaves. Anthocoris nemorum showed a near‐significant preference for ovipositing on leaves with eggs of Operophtera brumata (Lepidoptera: Geometridae). The oviposition preferences found correspond to the natural distribution of these predators in apple and pear orchards. The preference of A. nemorum for leaf margins, and of A. nemoralis for the leaf centre as an oviposition site, supports earlier observations. A preference for leaf side for oviposition site has not been reported earlier. Preference for damaged leaves could help A. nemorum to locate prey in a field situation.     

Accelerated leaf senescence takes part in enhanced resistance in cucumber mosaic virus inoculated pepper leaves

Altered photosynthetic reactions in cucumber mosaic virus (CMV) inoculated leaves of virus resistant lines L113 and L57 and susceptible pepper (Capsicum annuum L.) plants cv. Albena grown in controlled environment and in the field were investigated. The CMV inoculated leaves of virus resistant lines developed different symptoms—necrotic local lesions on L113 and chlorotic spots on L57 while the same leaves of susceptible cv. Albena were symptomless. The changes in Photosystem II (PSII) and PSI electron transport were evaluated by chlorophyll fluorescence, and far-red (FR) light induced leaf absorbance A _810–860. CMV infection caused a decrease in maximal PSII quantum yield, F _v/F _m, in susceptible leaves. Increased non-photochemical fluorescence quenching in CMV-inoculated leaves of both resistant lines were observed. In CMV-inoculated leaves of all tested plants FR light induced P700 oxidation was decreased. In the present study, the viral-infected pepper plants grown in controlled environment to avoid the effects of abiotic factors were used as model system that allow us to investigate the differences in leaf senescence in CMV-inoculated leaves of susceptible and resistant pepper lines expressing different symptoms. Earlier leaf falls of inoculated leaves as a result of accelerated leaf senescence is important for building successful secondary virus resistance strategy following fast responses such as hypersensitive reaction.