M. A. B. Morandi

Biotic and abiotic factors associated with soil suppressiveness to Rhizoctonia solani

Crop management may modify soil characteristics, and as a consequence, alter incidence of diseases caused by soilborne pathogens. This study evaluated the suppressiveness to R. solani in 59 soil samples from a microbasin. Soil sampling areas included undisturbed forest, pasture and fallow ground areas, annual crops, perennial crops, and ploughed soil. The soil samples were characterized according to abiotic variables (pH; electrical conductivity; organic matter content; N total; P; K; Ca; Mg; Al; H; S; Na; Fe; Mn; Cu; Zn; B; cation exchange capacity; sum of bases and base saturation) and biotic variables (total microbial activity evaluated by the CO 2 evolution and fluorescein diacetate hydrolysis; culturable bacterial, fungal, actinomycetes, protozoa, fluorescent Pseudomonas and Fusarium spp. communities). The contribution and relationships of these variables to suppression to R. solani were assessed by path analysis. When all samples were analyzed together, only abiotic variables correlated with suppression of R. solani, but the entire set of variables explained only 51% of the total variation. However, when samples were grouped and analyzed by vegetation cover, the set of evaluated variables in all cases accounted for more than 90% of the variation in suppression of the pathogen. In highly suppressive soils of forest and pasture/ fallow ground areas, several abiotic variables and fluorescein diacetate hydrolysis correlated with suppression of R. solani and the set of variables explained more than 98% of suppressiveness.

Biological control of Pythium aphanidermatum root rot and growth promotion of hydroponic lettuce by Clonostachys rosea

Clonostachys rosea was evaluated for growth promotion and control of root rot (Pythium aphanidermatum) in hydroponic lettuce in NFT and floating systems. For growth promotion, Clonostachys (0, 103, 104, 105, 106 and 107 conidia/mL) was added in nutrient solution (NS) and the mass of the plants was measured. To evaluate the control of the disease in NFT, Clonostachys was applied to the NS (106 conidia/mL) i. one day after transplanting in the absence of Pythium; ii. three days before and simultaneously with Pythium infestation; and, iii. three days before, simultaneously and three days after Pythium infestation. To evaluate the control of root rot in floating system, Clonostachys was added in NS (106 conidia/mL) i. four days before, and at the moment of pathogen infestation, and, ii. four days before, simultaneously, and four days after pathogen infestation. Plant mass and the recovery of pathogen and antagonist from the roots were evaluated. Clonostachys did not improve plant growth in the absence of Pythium. In the NFT system Clonostachys protected the plants from yield losses caused by Pythium, but not in the floating system. Pythium recovery from the roots was reduced by 28,6% and 42,8% when Clonostachys was applied two or three times, respectively.

Limitations in controlling white mold on common beans with Trichoderma spp. at the fall-winter season

We studied the effectiveness of application of Trichoderma spp. in controlling white mold on common beans at the fall-winter crop in the Zona da Mata region of the State of Minas Gerais, Brazil. There was no effect of the antagonist in reducing the disease severity, which could be explained by the low temperatures and the high inoculum pressure in the field. We concluded that Trichoderma applications are not recommended for control of white mold on common beans at the fall-winter season in regions with average temperature bellow 20 °C, since this condition favor more the pathogen than the antagonist.

Efeito de hidrolisado de peixe sobre o crescimento micelial e controle de Cylindrocladium spathiphylli em espatifilo

Fish hydrolyzed (HP), poultry manure (CF), shrimp skin (CC), cattle manure (EB), sewage sludge (LE) and castorbean presscake (TM) were evaluated for their effect of aqueous extracts with and without autoclaving, on mycelial growth and conidial germination of Cylindrocladium spathiphylli. The effect of mixtures of residues with potting mixes and their volatile compounds were also evaluated on the mycelial growth of the pathogen. To evaluate the effect of HP in the suppressiveness to Cylindrocladium spathiphylli, HP was added in potting mix artificially infested, at concentrations of 0, 10, 20, 30, 40 and 50% of the volume of water required to reach the water retention capacity of the potting mix. The mixtures were incubated for 10 days and transferred to pots containing one plug of Spathiphyllum Opal per pot. In the experiments in vitro, aqueous extracts and mixtures containing HP showed the highest suppressiveness against the pathogen. In the Spathiphyllum growing, the suppressiveness occurred at concentrations higher than 20% of fish hidrolyzed.

Induction of suppressiveness to Fusarium wilt of chrysanthemum with composted sewage sludge

The effectiveness of composted sewage sludge incorporated into Pinus bark-based substrate with or without biofertilizer, fish hydrolyzate, chitosan and Trichoderma asperellum was evaluated for the control of Fusarium wilt in chrysanthemum. The substrate was obtained from pots containing chrysanthemum plants killed by the pathogen. Half of the substrate was sterilized prior to the incorporation of sewage sludge (0, 10%, 20% and 30% v/v). These substrates were or were not supplemented with the following: biofertilizer, fish hydrolyzate and Trichoderma. The mixtures were transferred to pots, and the chrysanthemum was transplanted. For all treatments, half of the plants were sprayed weekly with chitosan. Assessment of severity was performed on the 8th, 12th, 15th and 20th week after transplanting. In the 12th week, microbiological and chemical analysis of the substrate was performed. The incorporation of composted sewage sludge into the Pinus bark-based substrate significantly reduced Fusarium wilt, which was progressively decreased as the concentration of sewage sludge increased. The addition of biofertilizer, fish hydrolyzate, chitosan and Trichoderma had no effect on the disease. The microbial community was greater in non-disinfested substrates. The results indicate that suppressiveness is related to the interaction of chemical and microbiological factors.

Efeito de casca de camarão, hidrolisado de peixe e quitosana no controle da murcha de Fusarium oxysporum f.sp. chrysanthemi em crisântemo

The incorporation of shrimp peelings and fish hydrolyzate into a pine-bark container medium and an aerial spray of chitosan were investigated for the control of Fusarium wilt of chrysanthemum. Disease severity was evaluated by means of a six-category scale (0 - healthy plant to 5 - dead plant) at 8, 12, 15 and 20 weeks after planting in experiments with shrimp peelings and fish hydrolyzate, and after 18 weeks in the chitosan experiment. The total microbial activity of the container media was evaluated (by fluorescein diacetate hydrolysis), physicochemical attributes of the media were assessed, and plant growth components were measured. Incorporation of shrimp peelings into the pine-bark medium at 4% (v/v) suppressed wilt, but at 5% the plants exhibited symptoms of phytotoxicity and died. The suppression of Fusarium wilt was possibly due to physicochemical and biological changes in container medium induced by the shrimp peel. Given that the concentration which was phytotoxic was only slightly higher than the concentration which suppressed wilt and promoted plant growth, caution is needed in any use of shrimp peelings for wilt control. The fish hydrolyzate increased wilt severity as the concentration was increased. No consistent effects were found of chitosan applied to the aerial parts of the plant.

UV-B radiation reduces biocontrol ability of Clonostachys rosea against Botrytis cinerea

ABSTRACT There is a lack of information comparing UV-B radiation conidial sensitivity of the biocontrol agent Clonostachys rosea (Cr) and its target pathogen, Botrytis cinerea (Bc). We investigated the interactions in vitro and on strawberry leaf discs between previously selected Cr and Bc strains tolerant to UV-B radiation. Strawberry leaf discs inoculated with Bc, Cr, or combinations of both fungi were exposed to UV-B doses (2.9, 5.9, and 8.9 kJ m−2). Incidence and sporulation of both fungi were evaluated, and the Area Under Incidence Progress Curve (AUIPC) and Area Under Sporulation Progress Curve (AUSPC) were calculated. AUIPC and AUSPC of Cr on leaf discs were negatively correlated to increased UV-B. When inoculated alone on leaf discs, Bc was not affected by UV-B, but when inoculated with Cr the incidence and sporulation of Bc were positively correlated to UV-B radiation dose. In the absence of UV-B, Cr reduced incidence and sporulation of Bc. However, the ability of Cr to control Bc was reduced by 20% to 50% with increasing UV-B radiation. Increasing the applied concentration of Cr conidia 10-fold partially overcame the deleterious effects of UV-B on the ability of the biocontrol agent to reduce Bc sporulation in strawberry leaves. The selection of antagonists must fulfil many requirements; besides being active against the specific targeted plant pathogens, they must be cost-effective and have ecological characteristics suitable for the desired use conditions. We suggest that UV-B exposure must be taken into account during the development of bio-fungicides based on Cr.