Leaf Diffusates Research Articles

Evaluation of Pongamia pinnata Products against the Sclerotium rolfsii Extracted from Chickpea

This study was conducted to investigate antifungal properties of Pongamia pinnata products. Pongamia pinnata seed oils and leaf diffusates contain products that show fungi-static effect against Scelotium rolfssi on Chickpea. This study shows comparison between antifungal effects of Pongame seed oils and Leaves, as both of these potentially inhibit Sclerotial production and germination of S. rolfsii. It was noticed that ingredients of leaves were changed when autoclaved. It also showed that there were some ingredients that were altered in terms of composition when heated. These agents were thought to be proteins and carbohydrates. Similarly, ingredients of seed oil also undergo change in composition when autoclaved. Extract showed insignificant difference about 20% (v/v) in inhibiting concentrations when used before autoclaving, while there was a significant difference among various concentrations after autoclaving. This significantly increased inhibition was present in Sclerotial production, germination and growth of mycelia. Overall, leaf extract was more effective than seed oil extract.

Pre-illumination of rice blast conidia induces tolerance to subsequent oxidative stress

Many environmental factors, alone or combined, affect organisms by changing a pro-/antioxidant balance. Here we tested rice blast fungus (Magnaporthe oryzae) for possible cross-adaptations caused by relatively intense light and protecting from artificially formed reactive oxygen species (ROS) and ROS-dependent fungitoxic response of the host plant. Spore germination was found to be suppressed under 4-h and, to larger extent, 5-h illumination. The effect was diminished by antioxidants and, therefore, suggests involvement of ROS. One-hour of light did not affect spore germination, but stimulated their chemically assayed superoxide production. The illuminated spores were more tolerant (than non-illuminated ones) to artificially generated H2O2, O2−, or OH or to toxic diffusate of rice leaf. They also caused more severe disease symptoms if applied to leaves of the susceptible rice cultivar at low concentration. Spore diffusates decomposed hydrogen peroxide. They detoxified exogenous H2O2 and superoxide radical as well as leaf diffusates. Spore illumination increased some of these protective effects. It is suggested that short-term light led to mild oxidative stress, which induced spore antioxidant capacity, enhancing spore tolerance to subsequent stronger oxidative stress and its aggressiveness in planta. Such tolerance depends partly on the antidotal action of spore extracellular compounds, which may also be light-stimulated. Therefore, a certain ROS-related environmental factor may adapt a fungus to other factors and so modulate its pathogenic properties.

Exogenous superoxide dismutase may lose its antidotal ability on rice leaves

Leaf diffusates of the resistant rice (Oryza sativa L.) cultivars suppressed spore germination of blast fungus (Magnaporthe grisea (Hebert) Barr). Bovine Cu-Zn superoxide dismutase (SOD) added to the diffusate abolished its toxicity. However, the enzyme added to the inoculum did not affect the toxicity of the diffusate. Even the second SOD portion added to the diffusate was ineffective. As well, the enzyme exposed to leaves could not protect the fungus from artificially-generated superoxide. Presumably, SOD contacting with leaves induced an efflux of compound(s) inhibiting both portions of the enzyme. Evidence was obtained suggesting that neither enzymatic protein nor zinc of coenzyme but copper might be the inducer. A comparison of rice leaves and callus culture together with the effects of exogenous salicylic acid suggests that this compound may be the inhibitor liberating from leaves. It is not excluded that rice plants are capable of inactivation of antioxidant enzymes of pathogens and that this ability favors disease resistance.

HORMONAL CHANGES IN VARIOUS TISSUES OF MANGO TREES DURING FLOWER INDUCTION FOLLOWING COLD TEMPERATURE

Cold temperature (around 15°C) plays a major role in flower induction of mango trees. But so far hardly anything is known whether plant hormones mediate this temperature effect. To investigate this question, 16 potted 2-year-old 'Tommy Atkins' mango trees were subjected to either 13 or 25°C for 3 months, which led to almost 100 and 0% flowering trees, respectively. After changing the temperature the main plant hormones, viz. IAA, ABA, GA 3 and CK s were analyzed in terminal buds, bark and wood of the trees. IAA in leaf diffusates was also measured. In general, Z/ZR concentrations in all tissues, ABA in wood and IAA in leaf diffusates were higher, whereas GA 3 and IAA (wood and bark) were lower under cold temperature.

Inhibition of pre-penetration development of blast fungus during the infection of resistant rice cultivars

Spore germination and appressorium formation of the rice blast fungus, Magnaporthe grisea, were compared during infection of rice cultivars differing for their resistance to strain H5-3. On leaves of the susceptible cv. Sha-tiao-tsao neither spore germination nor appressorium formation were inhibited, in comparison to a control germination test in water on polystyrene. On the resistant cv. Tadukan, both spore germination and appressorium development were strongly inhibited whereas on the partially resistant cv. Shimokita a slight inhibition of germination and significant delay of appressorium formation was observed. Inhibitors of germination were not produced in leaf diffusates of the susceptible cultivar Sha-tiao-tsao. On the contrary, such compounds were excreted by leaves of the two resistant cultivars. The fungitoxicity of diffusate of cv. Tadukan was strong from 5 to 24 h after inoculation. The diffusate of cv. Shimokita was less toxic at 5 h but at 24 h it reached the same level of toxicity as diffusate of cv. Tadukan. Such antifungal plant metabolites accumulating in drops of inoculum may inhibit the pre-penetration development of the rice blast fungus and presumably contribute to disease resistance, including the partial resistance. Plant resistance to fungal diseases might be associated with the inhibition of pathogen development in host tissues during early stages of the infection. The rice blast fungus Magnaporthe grisea does not penetrate readily into leaves of some resistant rice cultivars (Heath et al., 1990; Koga and Kobayashi, 1982) or cannot spread over the first invaded cells (Arase et al., 1983; Peng et al., 1988; Kaur et al., 1984). Inhibition of spore germination and appressoria formation were observed during inoculation of leaf fragments from completely resistant rice cultivars (Lapikova and Dzhavakhiya, 1987). This may be due to plant defence responses (syntheses of lignin, phytoalexins and pathogenesis-related proteins etc.) which may liberate fungitoxic products into the extracellular space. Previously, we found that the partially resistant cultivar Shimokita in combination with strain H53 manifests a reduced infection frequency, smaller lesions and a reduced rate of spore production per lesion (Pasechnik et al., 1995), phenomena typical for partial resistance (Roumen et al., 1993). The prepenetration development of the rice blast fungus on such rice cultivars is not well documented. The aim of the present work was to assess whether fungal development is affected on the leaf surface of cv. Shimokita. The susceptible cv. Sha-tiao-tsao and the completely resistant cv.Tadukan were taken as controls and intact plants rather than leaf fragments were used for the assessment. We used strain H5-3 (race 007) of the rice blast fungus, Magnaporthe grisea (Herbert) Barr. The rice (Oryza sativa L.) cultivars differ in their resistance to race 007: the susceptible cv. Sha-tiao-tsao develops numerous lesions, on the completely resistant cv. Tadukan no visible symptoms are produced and cv. Shimokita exhibits partial resistance with the rare occurrence of compatible-type lesions. Plants were grown in a climatic chamber up to the fourth fully expanded leaf stage (Lapikova et al., 1994). The fourth leaf was used for the analyses. The central part of the leaf was fixed horizontally in an inoculation chamber (Lapikova et al., 1995) and a plastic ring (ID 3 mm, height 1 mm) was placed on the leaf. One drop (10 l)

Possible Involvement of Reactive Oxygen Species in Action of Some Anti-Blast Fungicides

A mode of action of three commercial fungicides against rice blast disease was studied using susceptible cultivar. Tricyclazole or fthalide when added to fungal nutrient medium altered melanin pigmentation of spores. The spores from treated cultures lost their pathogenicity. Simultaneously they acquired an enhanced sensitivity to inhibition of germination by leaf diffusates, intensive light, and superoxide-generating model system, perhaps due to decreased tolerance to active oxygen mediating these damages. Probenazole had no such action on fungus. In soil application of tricyclazole this substance (or its derivatives) liberated from leaf into infective drop in quantities sufficient, to alter pigmentation of a fungal mycelium and to prevent the disease. Treatment of rice plants with each of three fungicides also stimulated oxygen activation in leaf excretions. It was expressed in an overproduction of chemically detected superoxide and in correlative enhancement of the fungitoxicity mediated with O2- and H2O2. In infected plants these effects were observed only with kinds of fungicide application prevented the disease. It is concluded that the antioxidative capacity of a parasite is one of the conditions of its pathogenicity. Inhibition of this capacity and/or stimulation of oxygen activation in host may be additional causes of disease-controlling action of fungicides tested.

Accumulation of antifungal compounds in tea leaf tissue infected with Bipolaris carbonum.

Varietal resistance of tea towards Bipolaris carbonum was tested following detached leaf inoculation technique. Among the fourteen varieties tested, three were found to be highly susceptible, while other three were resistant. Leaf exudates and diffusates collected from the resistant varieties were more fungitoxic than those from the susceptible ones. Two antifungal compounds isolated from healthy and B. carbonum-infected tea leaves exhibited clear inhibition zones at RF 0.8 and 0.65, respectively, in a chromatographic bioassay. On the basis of their color reaction on TLC and UV-spectra these were identified to be catechin and pyrocatechol. Resistant and susceptible varieties accumulated 439-510 and 187-212 micrograms/g fresh mass tissue of pyrocatechol, respectively, 2 d after inoculation with B. carbonum, while a low concentration (45-58 micrograms/g) of this compound was detected in healthy leaf tissue.

Identification, quantitation and distribution of gibberellins in fruits of Pisum sativum L. cv. Alaska during pod development

In addition to the previously-reported gibberellins: GA1; GA8, GA20 and GA29 (García-Martínez et al., 1987, Planta 170, 130-137), GA3 and GA19 were identified by combined gas chromatography-mass spectrometry in pods and ovules of 4-d-old pollinated pea (Pisum sativum cv. Alaska) ovaries. Pods contained additionally GA17, GA81 (2α-hydroxy GA20) and GA29-catabolite. The concentrations of GA1, GA3, GA8, GA19, GA20 and GA29 were higher in the ovules than in the pod, although, with the exception of GA3, the total content of these GAs in the pod exceeded that in the seeds. About 80% of the GA3 content of the ovary was present in the seeds. The concentrations of GA19 and GA20 in pollinated ovaries remained fairly constant for the first 12 ds after an thesis, after which they increased sharply. In contrast, GA1 and GA3 concentrations were maximal at 7 d and 4-6 d, respectively, after anthesis, at about the time of maximum pod growth rate, and declined thereafter. Emasculated ovaries at anthesis contained GA8, GA19 and GA20 at concentrations comparable with pollinated fruit, but they decreased rapidly. Gibberellins a1 and A3 were present in only trace amounts in emasculated ovaries at any stage. Parthenocarpic fruit, produced by decapitating plants immediately above an emasculated flower, or by treating such flowers with 2,4-dichlorophenoxyacetic acid or GA7, contained GA19 and GA20 at similar concentrations to seeded fruit, but very low amounts of GA1 and GA3 Thus, it appears that the presence of fertilised ovules is necessary for the synthesis of these last two GAs. Mature leaves and leaf diffusates contained GA1, GA8, GA19 and GA20 as determined by combined gas chromatography-mass spectrometry using selected ion monitoring. This provides further evidence that vegetative tissues are a possible alternative source of GAs for fruit-set, particularly in decapitated plants.

Leaf spot disease of soybean caused by Drechslera rostrata

Summary Drechslera rostrata causes a distinctive circular leaf spot on Glycine max that usually develops through lamina. Leaf penetration is direct through the epidermal cells. Leaf exudates stimulated conidial germination of the fungal pathogen. On the other hand leaf diffusates inhibited conidial germination of the fungal pathogen.

Radiation Effects on Cellular Metabolism and Disease Resistance of Jute

AbstractAir dried seeds of seven jute (Corchorus capsularis L.) cultivars were irradiated with different doses of X‐rays. JRC 1108 and JRC 412 were most and least sensitive to X‐rays, respectively. JRC 412 was susceptible to Colletotrichum corchorum both before and after X‐irradiation while JRC1108 became more resistant after treatment. Leaf diffusates but not leaf exudates of both non‐irradiated and X‐irradiated (40,000 r) cvs. exhibited antifungal activity which was more pronounced in case of irradiated JRC 1108. JRC 412 contained greater amounts of amino acids than JRC 1108 both before and after X‐irradiation. Signifinon‐irradiated, infected ones. The physiological implications of the results are discussed in relation to greater resistance of X‐irradiated JRC 1108.

Effects of heavy metal salts on susceptibility of rice seedlings to brown spot disease

SUMMARYHeavy metal salts, known to induce phytoalexin production in different plant species, were used at dilute concentrations (10‐3 to 10‐5 M) in different treatments to control brown spot infection in rice seedlings caused by Drechslera oryzae. Foliage sprays, root‐dips for 24 h at the time of transplanting, or seed soaking for 24 h provided moderate to substantial protection to rice seedlings, at different stages after treatment, against artificial inoculation with the pathogen or natural infection under field conditions and mostly caused significant reductions in symptoms. Of the three methods, greatest and most durable protection was achieved with the wet seed treatment. The number of successful infections was appreciably reduced in most treatments and some also inhibited lesion expansion. Ferric chloride and nickel nitrate were the most effective and mercuric chloride the least effective of the chemicals tested. There was no fungitoxicity in leaf diffusates from 3‐ and 5‐wk‐old seedlings that had been treated with heavy metal salts and only mild toxicity in that from untreated, inoculated seedlings. However, treated seedlings inoculated at the 3‐and 5‐wk stages produced leaf diffusates with significantly greater toxicities which were in proportion to their abilities to resist attack.

Phytoalexin production and the resistance of lucerne ( Medicago sativa L.) to Verticillium albo-atrum

The production of phytoalexins (determined as sativan and medicarpin) in leaf diffusates, leaf tissue and stem segments of lucerne cultivars resistant and susceptible to infection by Verticillium albo-atrum has been determined. No relationship between resistance and the formation of the antifungal compounds by leaves was observed. With stem segments, however, both the rates and amounts of phytoalexin synthesis were directly related to host resistance.

Relationship between a phytoalexin-like response in coffee leaves ( Coffea arabica L.) and compatibility with Hemileia vastatrix Berk. & Br

In a range of Coffea genotypes, resistance at the S H1 and S H2 loci was associated with accumulation of antifungal substances in leaf diffusates in response to incompatible races of Hemileia vastatrix. Spore germination and germ-tube extension were suppressed. However, with compatible combinations of host and pathogen, the diffusates did not suppress germination and stimulated germ-tube extension. Inoculation of leaves with an incompatible race of the fungus decreased the subsequent proportion of each leaf infected by a compatible one.

Inhibition of Conidial Germination and Germ Tube Growth of Cercospora canescens by Cowpea Leaf Diffusates

Inhibition of Conidial Germination and Germ Tube Growth of Cercospora canescens by Cowpea Leaf Diffusates

Inhibition of Helminthosporium turcicum Spore Germination by Leaf Diffusates from Northern Leaf Blight-Susceptible or -Resistant Corn

Inhibition of Helminthosporium turcicum Spore Germination by Leaf Diffusates from Northern Leaf Blight-Susceptible or -Resistant Corn

Effects of Amino Acids on Bean Leaf Abscission

Stimulatory and inhibitory effects of auxin on leaf abscission were reported by Addicott and Lynch (1) using an abscission test with bean petiole explants. This test was modified by Gaur and Leopold (4), and then more extensively by Biggs and Leopold (2) in describing the range of auxin effects. Osborne (7) reported that besides auxins, diffusates from senescing leaves of various species were able to accelerate abscission of bean explants, while green leaf diffusates showed smaller effects. Since then, other workers (3, 5) have shown that compounds which are not auxins are produced by senescent leaves and are capable of stimulating abscission. It would seem worthwhile, therefore, to attempt to investigate substances other than auxins which could not only affect the abscission of bean explants, but might also be related to the natural abscission processes associated with leaf senescence.