Effects of environmental factors on growth of lesions on field bean leaves infected by Botrytis fabae

Chocolate spot lesions increased in size only slowly when the relative humidity of the air was below 66%. Following a lag phase immediately after infection the rate of increase was linear and proportional to humidity between c. 70% and 100% r.h. Lesions on leaflets kept at 70% r.h. for 8 h and at 100% r.h. for 16 h/day increased in size at only 27% of the rate of those at continuous 100% r.h. The optimum temperature for lesion growth was between 15 and 22 °C, the minimum <4 °C and the maximum c. 30 °C. Humidity did not interact with temperature between 10 and 20 °C. Neither light intensity nor a film of water over the leaves affected lesion growth. These findings are discussed in relation to meteorological data and field observations. The possible mechanisms whereby humidity affects lesion growth did not appear to be related to CO₂ and O₂ concentrations nor to the overall water potential of the leaf. Preliminary evidence is presented for the production of phytotoxins within lesions.     

Integrated management of faba bean chocolate spot caused by Botrytis fabae in Gondar,Ethiopia

Abstract

Integrated management of faba bean chocolate spot (Botrytis fabae Sard.) was studied using moderately tolerant variety, “Hachalu” and the local cultivar at Chilga district during 2016 main cropping season. The objective was to evaluate effect of host resistance, intercropping and fungicide applications on epidemics of faba bean chocolate spot, yield and yield components of faba bean, and sole and intercrop systems productivity. The experiment was randomised complete block design in a factorial combination of two faba bean cultivars, two cropping systems (Hachalu- and local-barley intercropping in 2:1 ratio) and four levels of fungicide (Chlorothalonil) spray and integration in three replications of faba bean and barley, respectively. Cultivars and spray intervals significantly (p?<?.01) affected the seed yield while cultivars alone had significant variation (p?<?.01) on 100-seed weight as a main effect. Therefore, 21-days fungicide spray intervals integrated with Hachalu sole and Hachalu-barley intercropping may be considered for chocolate spot management.     

The rates of fungal development and lesion formation in leaves of Vicia faba during infection by Botrytis cinerea and Botrytis fabae

Loss of the water droplet above inoculation sites during the first day after inoculation inhibited lesion formation by Botrytis cinerea and prevented the development of spreading lesions of B. fabae. With droplets present two general patterns of infection by B. cinerea were determined; in one, few or no symptoms were produced and in the other, limited lesions developed with marked browning of the inoculation site. Where few or no symptoms were produced, germination and germ-tube growth were inhibited on the leaf surface. B. cinerea was inhibited within the leaf at sites bearing limited lesions; invading hyphae were restricted to brown epidermal cells. Fungal growth on the leaf surface was greatest at sites with most browning beneath the droplet area. Variation in lesion development by B. cinerea could not be related to droplet position or leaf damage during normal preparation for inoculation. Plants differed in their susceptibility to lesion formation by B. cinerea. B. fabae, with droplet present, was not inhibited on the leaf surface and spread inter- and intra-cellularly beneath the inoculum drop and then into surrounding tissues. Delay in spread until the inoculation site was completely necrotic and colonized suggested that B. fabae is partially inhibited during the initial phase of infection. The rate of lesion spread varied in different plants and was most rapid in the youngest leaves.     

Factors influencing the infestation of a bean field by Aphis fabae Scop

The infestation pattern in a bean field is related to the effects of shelter on the activity of the migrants and developing apterous colonies.

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Zusammemfassung Frühlingsmigranten von Aphis fabae, die ein Bohnenfeld befielen, waren hauptsächlich auf die Bestandsränder beschränkt, wo die von ihnen begründeten Kolonien Randbefall bildeten. Der Initialbefall nahm in der auf die primäre Migration folgenden Zeit an Dichte und Ausmaß zu, wobei die Befallsverteilung im wesentlichen die gleiche blieb wie die von den primären Zufliegern erzeugte. Der Innenteil des Feldes wurde allgemeiner befallen, als ein kleiner Teil der im Felde herangewachsenen Geflügelten in den Bestand eindrang und diesen Teil des Feldes besiedelte; jedoch faßte der Befall nicht Fuß.Auf der geschützten Leeseite des Feldes entwickelte sich ein viel schwererer Befall, obwohl die Anzahl der hier festgestellten Migranten nicht größer war als an jeder anderen Seite des Feldes. Es wird daraus geschlossen, daß die verhältnismäßig ruhigen Bedingungen auf dieser geschützten Seite eine größere Flugaktivität der einfallenden Frühjahrszuwanderer gestattete und daher jeder von ihnen eine größere Anzahl von Pflanzen infizierte als die Migranten in anderen Teilen des Feldes. Es wird angenommen, daß physikalische Wirkungen des Windschutzes, z.B. höhere Temperaturen, Ursache dafür waren, daß an dieser Seite größere Kolonien beobachtet wurden.

     

Production of Conidia by Botrytis fabae grown in vitro

Conidiation in Botrytis fabae was stimulated by irradiating 1 to 3 day old, but not 4 to 5 day old mycelium. Three cycles of 12 h irradiation + 12 h darkness stimulated the production of about twice as many spores compared with only 12 h irradiation. At 18°C all the spores had been produced within 3 days but not within 2 days from the start of irradiation. Near-u.v. irradiation at wavelengths of 375–400 nm induced most sporulation. Red light at 600–650 nm also stimulated conidiation but irradiation at other wavelengths from 300 to 700 nm was ineffective. Fewer conidia were produced when the fungus was kept in darkness at 4°C between periods of irradiaton at 18°C compared with continuous 18°C. The optimum osmotic potential of the culture, medium for conidiation was about-27 bar although more mycelium grew at even lower osmotic potentials. Abundant spore production occurred when the fungus was grown in media with a wide range of pH values.     

Effects of Bean Leaf Age on Pathogenicity by Botrytis fabae

Leaves from field bean plants grown out of doors were inoculated with conidia of B. fabae immediately after detaching from stems. The oldest leaves developed more lesions than youngest ones, although they were not chlorotic. On intact plants at high humidities, established lesions on young leaves increased in size at only half the rate of those on old. but still green leaves. Seven days after inoculation a higher proportion of lesions on old leaves bore conidia than those on young leaves, but leaf age had no significant effect on numbers of conidia per mm² of lesion area. Young leaflets from bean plants grown in a controlled environment or in the field challenged with β. cinerea accumulated more phytoalexins than did old ones.     

Tunisian isolates of Trichoderma spp. and Bacillus subtilis can control Botrytis fabae on faba bean

Faba bean crops worldwide are often attacked by different diseases, particularly chocolate spot caused by Botrytis fabae Sard. Fungal and bacterial isolates collected from faba bean and barley leaves in Tunisia were evaluated for their antagonistic potential against B. fabae. In a test on detached leaves, the highest rate of decrease in disease severity was scored by Trichoderma viride, followed by T. harzianum, the fungicide Carbendazim then Bacillus subtilis. Under glasshouse conditions, all tested fungi resulted in significant disease severity reduction. T. viride reduced the rate of chocolate spot infestation on leaves and stems by 35% and 31.5%, respectively, when the rate on the control was 100%. For T. harzianum, Carbendazim and B. Subtilis, the rates of infestation on the leaves were 41.7%, 43.1% and 59.7%, respectively. On the stems, T. harzianum scored the lowest rate of 54.2% followed by B. subtilis with 79.2% then Carbendazim with 87.5%. Two consecutive seasons of field trials using the Trichoderma species, B. subtilis and Carbendazim showed significant and consistent reduction in the severity of chocolate spot infestation rates. The highest protection against the disease was obtained from T. viride. Based on these results, Tunisian isolates of Trichoderma spp. can be recommended for developing commercial bio-fungicides for integrated management of chocolate spot.     

Changes in wyerone acid concentrations in leaves of Vicia faba after infection by Botrytis cinerea or B.fabae

Wyerone acid was produced by leaves of Vicia faba in response to infection by both Botrytis cinerea and B.fabae. Host cell death caused by either fungus appeared to be the trigger for rapid wyerone acid synthesis, although the phytoalexin was not confined to brown cells. At B. cinerea inoculation sites wyerone acid concentration increased rapidly, at the time of fungal invasion of the epidermis, to levels greater than that completely inhibitory to mycelial growth. Wyerone acid is therefore probably the primary cause of the inhibition of B. cinerea within infected tissue. The partial blackening of B.fabae inoculation sites and surrounding peripheral tissues was accompanied by an increase in wyerone acid. There followed a striking decrease as tissues became completely blackened and invaded by B.fabae. B.fabae appeared to metabolize wyerone acid and prevent its accumulation in invaded tissues. Mycelial growth of B. fabae was less sensitive to wyerone acid than was B. cinerea. The differing abilities of B.fabae and B. cinerea to spread from lesions after both have induced wyerone acid production probably depend on both their differing sensitivities to the phytoalexin and their abilities to metabolize it to less toxic products.     

Effect of excess Cu on the photosynthetic apparatus of runner bean leaves treated at two different growth stages

Variations in water binding strength, water relations and the accumulation of solutes during water stress of three durum wheat ( Triticum durum Desf.) cultivars are reported and discussed. Water binding strength was determined by constructing adsorption isotherms at 5 and 20°C and by calculating the differential enthalpy (ΔH) after van't Hoff.
Reducing sugars, proline, K⁺ and Cl⁻ were the major contributors to osmotic adjustment. Solutes, such as quaternary ammonium compounds, and non-reducing sugars contributed to osmotic potential at full turgor, but did not increase in proportion to water stress. Genotypic differences have been observed for K⁺ accumulation capability, the water-stressed leaves of cv. Capeiti 8 showing the largest increase. The same cultivar demonstrated the most negative ΔH values, indicative of strongly bound water, and the highest integrated enthalpy (ΔH_inf) values for leaf moisture below 0.1 g H₂O per g dry weight, i.e. in the isotherm region where water was presumably chemisorbed to the charged groups of macromolecules. The accumulation of ions (Cl⁻, K⁺) and proline was concurrent with an increase in the binding-strength of tightly and weakly bound water, respectively.     

Mould deterioration of feeding-stuffs in relation to humidity of storage: Part I. The growth of moulds at low humidities

The literature relating to the growth of moulds at different humidities is surveyed.
Observations were made on the development of mould growth on six widely different types of feeding-stuffs for storage periods extending over some 3 1/2 years. The main factors controlling mould growth were found to be:
1. The relative humidity rather than the moisture content of the food.
2. The length of the storage period. Mould growth took place relatively quickly on all feeding-stuffs stored at 100-75% R-H. Below 75% R.H. mould growth, while not prevented, only developed after a very prolonged latent period. Mould development was observed on locust beans exposed to a humidity as low as 65 % after a latent period of over 2 years.
3. The balance and type of nutrients provided by the various feeding-stuffs was shown to influence the latent period as well as the extent of mould deterioration. This was confirmed by experiments on artificially dried grass fractions and by experiments on starch, protein and fibre mixtures.
4. The temperature of storage was found to affect the rate of mould development; mould growth developed sooner on samples stored at 22C. than at 15.5C.
5. The type of mould species present. At high humidities all mould species grew rapidly: at low humidities, only a few types were capable of growth.     

Phytoalexin production by leaves of Pisum sativum in relation to senescence

A sterile culture nitrate of Penicillium expansum was shown to induce pisatin synthesis in pea leaf discs. The amount of pisatin produced by pea leaves was shown to decrease as they underwent senescence. N⁶-benzyladenine delayed senescence, and at the same time maintained the production of pisatin at a high level. In darkness, leaf discs maintained on either benzyl-adenine solution or distilled water produced greater amounts of pisatin than leaf discs which were not treated in this way. Benzyladenine also increased pisatin production by leaf discs kept in the light. The relevance of these results to disease resistance and possible mechanisms involved are discussed.     

Acid-soluble nucleotides of pinto bean leaves at different stages of development

Acid-soluble nucleotides of unifoliate leaves of Pinto bean plants (Phaseolus vulgaris L.) were determined at young, mature, and senescent stages of development. At least 25 components could be distinguished on the basis of inorganic phosphorus determinations and 37 or more fractions on the basis of ³²P labeling, with adenosine di- and triphosphates accounting for 60% of the total moles of nucleotide. The total nucleotide P and inorganic P, on a fresh weight basis, decreased about 44% between each stage of leaf development, but decrements in the levels of individual nucleotides varied from this over-all pattern.     

Mould deterioration of feeding-stuffs in relation to humidity of storage: Part II. The water uptake of feeding-stuffs at different humidities

The water uptake of a wide variety of feeding-stuffs was determined over a range of fixed humidities. It was shown that the level and shape of the water uptake curves are closely related to the amounts of soluble carbohydrate and protein present. Fibre exerts a depressing effect on the water uptake, while the value is also lowered by the presence of inert fats and non-hygroscopic ash constituents. These conclusions were confirmed by direct experiments on the water uptake of samples of pure starch, protein and fibre.
The results of the investigations have enabled safe limits of moisture content to be laid down, for both short- and long-period storage, below which mould growth will not normally take place. These limits vary for each individual feed, representative figures being included in the paper in tabular form.     

Stimulation of ethylene production in asparagus bean leaves by cupric ion

Asparagus bean (Vigna sesquipedalis Fruhw.) cuttings responded to Cu²⁺ treatments by a rapid and marked increase in ethylene production. This response showed a transient nature but was only partially reversed by returning cuttings to water after prolonged Cu²⁺ treatments suggesting that relative stable links between Cu²⁺ and the ethylene forming system may occur. Cu²⁺ treatments did not induce any visible necrosis nor affect ethane release from cuttings. The Cu²⁺-stimulated ethylene production was not attributable to a light-driven peroxidation of membrane lipids, because it was not affected by a quencher of singlet oxygen nor by a free radical scavenger, whereas it was strongly depressed by light and entirely suppressed by aminoethoxy-vinylglycine. These results support previous finding on the so-called “stress ethylene” and suggest that the Cu²⁺-stimulated ethylene production may be attributable to an enhanced conversion of S-adenosylmethionine to l-aminocyclopropane-l-carboxylie acid. Research work supported by CNR, Italy. Special grant IPRA-Subproject 1. Paper No. 1614.     

The gum tree thrips Isoneurothrips australis Bagnall. Survival at different temperatures and humidities and its relation to capacity for dispersal

Thrips are carried long distances on the wind. Their ability to survive periods of fasting may determine their chance of completing such journeys alive. Thrips’survival was measured at various temperatures and humidities. Survival is best related to saturation deficit. This relation can be combined with meteorological data to calculate the survival time of thrips migrating at various times of year. From May to September inclusive a thrips can probably survive over 24 h in the air and runs little risk of death from desiccation. From December to March survival times average about 6h but can be as low as 3h on hot summer days.     

The energetics and growth efficiency of Aphis fabae Scop. Reared on different parts of the broad bean plant (Vicia faba)

Apterous virginoparae of A. fabae were reared on four different parts of broad bean seedlings. The energy channeled into larval growth, exuvia, adult reproduction and excretion was measured throughout the aphid's life. The greatest differences in the energy budgets were during reproductive life when aphids living on young stems fed at a much greater rate and were more fecund than those living on mature stems. There were also considerable differences in energy utilization of aphids reared on young plant growth and mature plant growth but there were few differences between stem and leaf dwellers.

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Résumé Le puceron noir de la fève A. fabae, bien que vivant normalement sur les extrêmités des tiges en croissance des plantes herbacées, peut en fait vivre et se reproduire sur d'autres parties de la plante. Le budget énergétique de cet insecte a été établi comparativement pour des pucerons vivant sur de jeunes tiges sur de jeunes feuilles, sur des tiges et des feuilles pleinement développées de pieds issus de semis. On a mesuré pour des aphides élevés sur chacun de ces sites: l'énergie utilisée pour la croissance pondérale au cours de la croissance larvaire, Pg, l'énergie correspondant aux exuvies larvaires Pe, l'énergie utilisée pour la reproduction de l'adulte Pr, celle correspondant aux excrétions de la larve et de l'adulte. Pour des pucerons vivant sur des feuilles pleinement développées on trouvé: Pg=10% de l'énergie totale consommée, Pr=45%; Pe 1%; R 7% et F+U 37%. Pour des pucerons vivant sur des jeunes feuilles: Pg=7%; Pr 34%; Pe 1%, R 5% et F+U 53%. Pour des pucerons vivant sur des tiges âgées: Pr=18%, Pr 36%; Pe 1%, R 8% et F+U 37%. Pour des pucerons élevés sur jeunes tiges: Pg 9%, Pr 42%; Pe 1%, R 6% et F+U 43%. Les différences les plus significatives s'observent pour des pucerons adultes dont l'énergie utilisée pour la reproduction est sérieusement réduite pour les individus s'alimentant sur des tiges âgées.

     

The Accumulation of Amino-acids by Fungi, with particular reference to the Plant Parasitic Fungus Botrytis fabae

A method is described for the assay of the uptake of amino-acidsfrom aqueous solution by fungus mycelia. The rate of uptakein Botrytis fabae was found to vary with the age of the fungus,the pH, and the concentration of the amino-acid. Both L- andD-isomers were accumulated, but the system had a greater affinityfor the L-isomer. Unsubstituted —NH₂, and —COOHgroups were necessary for the process, which was constitutiveand inhibited by uncouplers of oxidative phosphorylation. Competitionexperiments with several amino-acids suggest that one uptakeprocess is common to all. Although both peptides and amineswere accumulated they did not compete effectively with amino-acidsfor uptake.