Th e long s earch f or a "t oxi n" produced by plant path og ens met with dis appoi nt­ ment unti l att enti on was cent ered on a h ost-s pecifi c t oxi n (HST). Th e dis­ appoi nt ment th at s panned almost h alf a cent ury res ult ed most ly f rom th e st udy of t oxi ns th at f uncti on i n vari ous t ypes of s ympt om development, but are not th e i niti al i nciti ng ag ents of dis eas e. "Mi cro org anis m X (but not oth ers) produces s ubst ance Y whi ch damag es plant or plant g roup A but not oth ers , and only A is parasiti zed." This st at ement by Wood (174) at th e 1971 L ong Asht on Symposi um on F ung al P ath og eni city and th e P lant's Res pons e sh ows th e s eri ous need f or t oxi n st udy . Th e fi ndi ng of a g roup of high ly h ost -s electi ve HSTs , valua ble both as t ools f or academi c res earch on plant h ostparasit e i nt eracti ons and as markers f or epi demi ologi cal s urv ey of path og ens i n fi elds, confi rms th at th e s earch f or t oxi ns is an i mport ant part of modem plant path olog y . Th e pres ent knowledg e of HSTs h as come almost enti rely f rom th e s o-called "s aproph ytic path og ens." This g roup i ncludes f ami li ar f ungi , s uch as Alternar­ ia and Helminthosporium, and oth ers less well known. It is just withi n th e last 15 years that we h ave really beg un t o work with HSTs i n Alternaria s peci es . Th eref ore, th e pres ent st at us of our kno wl edg e is sti ll pri miti ve and much work remai ns to be do ne. Unti l recent ly, o ur att entio n fo r th e to xi ns was bi as ed t oward th e ph ysi ologi cal or bi och emi cal mech anis ms of th ei r s electi vit y, and

Host-specific toxins and chemical structures from alternaria species

The vegetative and reproductive anatomy of the grapevine is discussed with emphasis on recent interpretations based on scanning electron microscopy. The terminology of flowering in Vitis is defined and a developmental code, comprising Stages 0 to 11, is proposed for the events leading to formation of flowers. In brief, flowering in the grapevine involves three main steps: 1) Formation of Anlagen or uncommitted primordia (Stages 0 to 1); 2) Differentiation of Anlagen to form inflorescence primordia (Stages 2 to 7); and 3) Differentiation of flowers (Stages 8 to 11). The literature on the factors that influence flowering in grapes is reviewed under three major headings: 1) Biochemical changes in apices during inflorescence primordia formation; 2) Effects of environmental factors, including temperature, light intensity, photoperiod, water stress and mineral nutrition and 3) Role of phytohormones.

Anlagen develop into inflorescences, tendrils or shoots depending on the environment and hormonal factors. A hypothetical scheme for the hormonal control of Anlagen, tendril and inflorescence formation is proposed. It is suggested that flowering in grapes is controlled by the gibberellin:cytokinin balance. Formation of the inflorescence axis (the Anlage) is gibberellin controlled, but subsequent differentiation into flowers is regulated by cytokinin.

Physiology of Flowering in the Grapevine — a Review

Many pathogenic microorganisms have highly specific host ranges; only certain species, cultivars, or genotypes of plants are affected. In general, the chemical or physical bases of such host-specificity are unknown. In some cases, however, specificity or selectivity is related to production and release by the pathogen of toxic substances with remarkable characteristics. These are the so-called “hostspecific toxins” (Pringle and Scheffer, 1964), which damage or destroy plant tissues that are susceptible to the toxin-producing microorganism, but have little or no effect on other plants, microorganisms, or animals.

Host-specific Toxins in Relation to Pathogenesis and Disease Resistance

The relationship of assimilate supply to grape (Vitis vinifera L.) berry growth and development was studied with a seeded ('Kyohoʼ) and a seedless ('Seedless Wuhehongʼ) cultivar. A single shoot girdling between the second and third nodes below the basal cluster at the end of Stage I of berry growth shortened Stage II (the lag phase) of 'Kyohoʼ grape berries by 10 days, and eliminated Stage II in 'Seedless Wuhehongʼ grape berries. Double shoot girdling between the second and third nodes below the basal cluster and above the upper cluster, respectively, at the same time at the end of Stage I, advanced Stage II by 3 days in both cultivars. Normal accumulation of dry weight in the 'Kyohoʼ grape berry is in a double sigmoidal pattern, but it became a single sigmoidal pattern in response to a single basal girdling. The highest percent moisture in berries was at 20 days after full bloom. Rapid changes in berry pectin substances lagged behind those of soluble solids and titratable acidity, and behind the onset of berry softening at veraison in 'Kyohoʼ, but not in 'Seedless Wuhehongʼ, for which the three processes were con cur rent. It is suggested that the slow growth of the berries during Stage II is a result of a decrease in the rate of water accumulation on a whole berry basis and a decrease in accumulation of dry matter in the skin and fl esh (pericarp) due to assimilate com pe ti tion within grapevines and within berries. The relationships between levels of endogenous hormones (IAA, GA3, zeatin, zeatin riboside, and ABA) and berry growth were also studied with 'Kyohoʼ grapes. The results showed that the slow growth of grape berries during Stage II was associated with assimilate com pe ti tion between the skin-fl esh (pericarp) and seeds, and with peak shifts of concentrations of IAA, GA3, zeatin and zeatin riboside. Changes in ABA levels were closely associated with ripening and senescence during late Stage III. has been paid to the ripening process with the suggestion that the auxin-ABA relationship might be involved in the hormonal regulation of veraison and ripening of grape berries.

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Growth and Developmental Responses of Seeded and Seedless Grape Berries to Shoot Girdling

The Japanese pear (Pyrus pyrifolia Nakai) is one of the most widely grown fruit trees in Japan, and it has been used throughout Japan's history. The commercial production of pears increased rapidly with the successive discoveries of the chance seedling cultivars 'Chojuro' and 'Nijisseiki' around 1890, and the development of new cultivars has continued since 1915. The late-maturing, leading cultivars 'Niitaka' and 'Shinko' were released during the initial breeding stage. Furthermore, systematic breeding by the Horticultural Research Station (currently, NARO Institute of Fruit Tree Science, National Agriculture and Food Research Organization (NIFTS)) began in 1935, which mainly aimed to improve fruit quality by focusing on flesh texture and black spot disease resistance. To date, 22 cultivars have been released, including 'Kosui', 'Hosui', and 'Akizuki', which are current leading cultivars from the breeding program. Four induced mutant cultivars induced by gamma irradiation, which exhibit some resistance to black spot disease, were released from the Institute of Radiation Breeding. Among these cultivars, 'Gold Nijisseiki' has become a leading cultivar. Moreover, 'Nansui' from the Nagano prefectural institute breeding program was released, and it has also become a leading cultivar. Current breeding objectives at NIFTS mainly combine superior fruit quality with traits related to labor and cost reduction, multiple disease resistance, or self-compatibility. Regarding future breeding, marker-assisted selection for each trait, QTL analyses, genome-wide association studies, and genomic selection analyses are currently in progress.

http://www.jstage.jst.go.jp/article/jsbbs/66/1/66_46/_pdf

Advances in Japanese pear breeding in Japan.

The relationship between seeded berry growth and endogenous auxin and abscisic acid-like activities in Delaware grape was studied.1. The growth of seeded grape berry showed a typical double sigmoid curve, and was greater than that of GA-induced seedless grape berry.2. There was a close relationship between high activity of endogenous auxin in berries and the rapid growth rate in early stage (Stage-I).3. The concentration of endogenous abscisic acid-like inhibitors in the grape berries was low during rapid growth of the berries in stage-I and increased rapidly thereafter until veraison.4. The application of naphthaleneacetic acid retarded ripening of the seeded grape berries. On the contrary, the applications of abscisic acid, gibberellin (GA3) and benzyladenine did not affect ripening of such berries.

Changes in Auxin and Abscisic Acid-Like Activities in Grape Berries

Phenoic compounds were separated with chromatographical and chemical techniques from extracts of Japanese pear tissue. And they were identified as arbutin, chlorogenic acid, chlorogenic acid isomers, caffeic acid, quinic acid, catechin and its isomer.The young leaf contained more amount of arbutin, caffeic acid and quinic acid than old one, but did not contain catechins. Much amount of chlorogenic acids were contained in the leaf without any distinction of its age.Infecting with host-specific toxin produce dby the fungus, the young leaf of susceptible variety (Nijusseiki) has been browned at a short time and decreased the content of arbutin and chlorogenic acid. On the other hand, the young leaf of resistant variety (Chojuro) remained green upon the same product treatment and no effect on the content of those phenolic compounds.Reacting the phenolic compounds with polyphenol oxidase extracted from the young leaf of susceptable variety, arbutin and chlorogenic acid were oxidized and browned immediately.So from above results, authors believed that arbutin and chlorogenic acid may have close contact with brown of the leaf infected with that metabolic product.

Studies on Resistance of Japanese Pear to Black Spot Disease Fungus (Alternaria kikuchiana TANAKA)

Endogenous cytokinins in Delaware grape berries were separated and partially purified for, their identification and the relationship between seeded berry growth and free cytokinins in the berries were studied.1. Cytokinin activities in the cluster just before anthesis and in the pericarp during flowering were markedly high. This activity in the pericarp decreased gradually thereafter and almost disappeared 50 days after anthesis.2. There was a close relationship between cytokinin activity in seed and growth of seed. High activity of cytokinin was observed during the rapid growth stage of seed.3. At least two free cytokinins were present in the seeded grape berries. Zeatin and zeatin riboside were supposed to be responsible for the activities in the ammonia eluated fraction (AE).4. In addition to these free cytokinins, at least two unknown cytokinin-like substances were present in the grape seed.

Cytokinin Activities in Grape Berries

The isolation of host-specific toxin from natural lesions attacked the young leaves of Nijisseiki, susceptible variety, by black spot disease fungus of Japanese pear (Alternaria kikuchiana TANAKA) and decrease in toxicity of that toxin with various chemicals was described.The isolation of K-III fraction (host-specific toxin) from culture filtrate and mycelium of causal fungus was previously reported. The toxin isolated from natural lesions was identified that fraction with thin layer chromatography and plant test, so that the fraction was regarded as vivotoxin.Toxicity of that fraction was decreased with tannic acid, pyrogallol, hydroxyhydroquinone, pcresol and dimethyl sulfoxide. Effect of tannic acid on toxicity of that fraction was excelled. Toxicity of that fraction (200ppm) was completely inhibited with tannic acid of 10, 000ppm and moderately inhibited with the same substance 1, 000 and 100ppm. The consequent decrease in necrosis on the young leaves was depened upon the relative concentration of both that fraction and tannic acid.

Studies on resistance of black spot disease fungus of Japanese pear (Alternaria kikuchiana TANAKA). VII

Immature fruits of Japanese pear, Pyrus serotina, were picked and homogenized with 70% ethanol. The homogenate was extracted with 70% ethanol three times and filtrated. The filtrate was concentrated, the residue adjusted to pH 8.4 with 1N NaOH and then extracted with n-butanol. The butanol phase was evaporated and aqueous extract of the residue was added to a Dowex-50(H+ form) column and eluted with water, 1N NH4OH and 5N NH4OH successively. Cytokinin activities in the three fractions were tested by tobacco(Wisconsin No. 38) pith callus assay. Cytokinin activities were detected in both 1N and 5N NH4OH fractions, but not in the water. Based on these results, the NH4OH fractions (Am-fraction) were combined and analysed by microcrystalline cellulose thin layer and gas liquid chromatographies. The fraction separated by TLC for the bioassay of cytokinin revealed activities at Rf values 0.5 and 0.7. Analyses of TMS derivative of Am-fraction by GLC gave four peaks. Mixture of the TMS derivative with that of authentic zeatin analyzed on GLC revealed that peak 2 coincides with zeatin, and peak 1 was considered to be dihydrozeatin.

Masanori Ohkawa

Papers

Changes in Auxin and Abscisic Acid-Like Activities in Grape Berries

Studies on Resistance of Japanese Pear to Black Spot Disease Fungus (Alternaria kikuchiana TANAKA)

Cytokinin Activities in Grape Berries

Studies on resistance of black spot disease fungus of Japanese pear (Alternaria kikuchiana TANAKA). VII

Studies on Growth of Japanese Pear Fruits